Table of Contents provided as an aid to reviewers.  It will not be
included in the formal package.  Each heading is hyperlinked to the text
of this preamble; hold down the Control key and right click any heading
to go to that point in the text.

  TOC \o "1-4" \h \z \u    HYPERLINK \l "_Toc244324206"  I.	General
Information	  PAGEREF _Toc244324206 \h  5  

  HYPERLINK \l "_Toc244324207"  A.	Does This Action Apply to Me?	 
PAGEREF _Toc244324207 \h  5  

  HYPERLINK \l "_Toc244324208"  B.	Where Can I Get a Copy of this
Document and Other Related Information?	  PAGEREF _Toc244324208 \h  6  

  HYPERLINK \l "_Toc244324209"  II.	Purpose	  PAGEREF _Toc244324209 \h 
6  

  HYPERLINK \l "_Toc244324210"  III.	Overview of Final PM2.5 PSD
Regulations	  PAGEREF _Toc244324210 \h  7  

  HYPERLINK \l "_Toc244324211"  A.	Increments	  PAGEREF _Toc244324211 \h
 7  

  HYPERLINK \l "_Toc244324212"  B.	SILs	  PAGEREF _Toc244324212 \h  8  

  HYPERLINK \l "_Toc244324213"  C.	SMC	  PAGEREF _Toc244324213 \h  9  

  HYPERLINK \l "_Toc244324214"  IV.	Background	  PAGEREF _Toc244324214
\h  10  

  HYPERLINK \l "_Toc244324215"  A.	PSD Program	  PAGEREF _Toc244324215
\h  10  

  HYPERLINK \l "_Toc244324216"  B.	History of Particulate Matter (PM)
NAAQS	  PAGEREF _Toc244324216 \h  14  

  HYPERLINK \l "_Toc244324217"  1.	Total Suspended Particulate (TSP) and
PM10 NAAQS	  PAGEREF _Toc244324217 \h  14  

  HYPERLINK \l "_Toc244324218"  2.	PM2.5 NAAQS	  PAGEREF _Toc244324218
\h  15  

  HYPERLINK \l "_Toc244324219"  3.	Revised PM2.5 and PM10 NAAQS	 
PAGEREF _Toc244324219 \h  15  

  HYPERLINK \l "_Toc244324220"  C.	Implementation of NSR for PM2.5	 
PAGEREF _Toc244324220 \h  16  

  HYPERLINK \l "_Toc244324221"  D.	Increments Under the PSD Program	 
PAGEREF _Toc244324221 \h  18  

  HYPERLINK \l "_Toc244324222"  E.	Historical Approaches for Developing
Increments	  PAGEREF _Toc244324222 \h  27  

  HYPERLINK \l "_Toc244324223"  1.	Congressional Enactment of Increments
for PM and SO2	  PAGEREF _Toc244324223 \h  27  

  HYPERLINK \l "_Toc244324224"  2.	EPA’s Promulgation of Increments
for NO2 and PM10	  PAGEREF _Toc244324224 \h  28  

  HYPERLINK \l "_Toc244324225"  a.	Increments for NO2 Using the
“Contingent Safe Harbor” Approach Under Section 166(a) of the Act	 
PAGEREF _Toc244324225 \h  29  

  HYPERLINK \l "_Toc244324226"  b.	Increments for PM10 Using
“Equivalent Substitution” Approach Under Section 166(f) of the Act	 
PAGEREF _Toc244324226 \h  31  

  HYPERLINK \l "_Toc244324227"  V.	Final Action on PM2.5 Increments	 
PAGEREF _Toc244324227 \h  33  

  HYPERLINK \l "_Toc244324228"  A.	Decision to Establish PM2.5
Increments Using “Contingent Safe Harbor Approach” Under Section
166(a)	  PAGEREF _Toc244324228 \h  33  

  HYPERLINK \l "_Toc244324229"  B.	Rationale for the Applicability of
Section 166(a)	  PAGEREF _Toc244324229 \h  35  

  HYPERLINK \l "_Toc244324230"  C.	EPA’s Interpretation of the
Requirements under Sections 166(a)-(d) of the Act	  PAGEREF
_Toc244324230 \h  44  

  HYPERLINK \l "_Toc244324231"  1.	Regulations as a Whole Should Fulfill
Statutory Requirements	  PAGEREF _Toc244324231 \h  45  

  HYPERLINK \l "_Toc244324232"  2.	Contingent Safe Harbor Approach	 
PAGEREF _Toc244324232 \h  46  

  HYPERLINK \l "_Toc244324233"  3.	The Statutory Factors Applicable
under Section 166(c)	  PAGEREF _Toc244324233 \h  48  

  HYPERLINK \l "_Toc244324234"  4.	Balancing the Factors Applicable
under Section 166(c)	  PAGEREF _Toc244324234 \h  51  

  HYPERLINK \l "_Toc244324235"  5.	Authority for States to Adopt
Alternatives to Increments	  PAGEREF _Toc244324235 \h  52  

  HYPERLINK \l "_Toc244324236"  D.	Framework for Pollutant-Specific PSD
Regulations for PM2.5	  PAGEREF _Toc244324236 \h  56  

  HYPERLINK \l "_Toc244324237"  1.	Increment System	  PAGEREF
_Toc244324237 \h  57  

  HYPERLINK \l "_Toc244324238"  2.	Area Classifications	  PAGEREF
_Toc244324238 \h  60  

  HYPERLINK \l "_Toc244324239"  3.	Permitting Procedures	  PAGEREF
_Toc244324239 \h  64  

  HYPERLINK \l "_Toc244324240"  4.	AQRV Review by Federal Land Manager
(FLM) and Reviewing Authority	  PAGEREF _Toc244324240 \h  65  

  HYPERLINK \l "_Toc244324241"  5.	Additional Impacts Analysis	  PAGEREF
_Toc244324241 \h  73  

  HYPERLINK \l "_Toc244324242"  6.	Installation of BACT	  PAGEREF
_Toc244324242 \h  75  

  HYPERLINK \l "_Toc244324243"  E.	Final PM2.5 Increments	  PAGEREF
_Toc244324243 \h  76  

  HYPERLINK \l "_Toc244324244"  1.	Identification of Safe Harbor
Increments	  PAGEREF _Toc244324244 \h  78  

  HYPERLINK \l "_Toc244324245"  2.	Data Used by EPA for the Evaluation
of the Safe Harbor Increments for PM2.5.	  PAGEREF _Toc244324245 \h  81 


  HYPERLINK \l "_Toc244324246"  3.	Scope of Effects Considered	  PAGEREF
_Toc244324246 \h  84  

  HYPERLINK \l "_Toc244324247"  4.	Evaluation of the Health and Welfare
Effects of PM2.5	  PAGEREF _Toc244324247 \h  85  

  HYPERLINK \l "_Toc244324248"  a.	Health Effects	  PAGEREF
_Toc244324248 \h  86  

  HYPERLINK \l "_Toc244324249"  b.	Welfare Effects	  PAGEREF
_Toc244324249 \h  87  

  HYPERLINK \l "_Toc244324250"  5.	Fundamental Elements of Increments	 
PAGEREF _Toc244324250 \h  89  

  HYPERLINK \l "_Toc244324251"  6.	Evaluation of the Safe Harbor
Increments	  PAGEREF _Toc244324251 \h  90  

  HYPERLINK \l "_Toc244324252"  7.	Compliance Determinations for the
PM2.5 Increments	  PAGEREF _Toc244324252 \h  112  

  HYPERLINK \l "_Toc244324253"  a.	Modeling Compliance with PM2.5
Increments	  PAGEREF _Toc244324253 \h  112  

  HYPERLINK \l "_Toc244324254"  b.	Condensable PM	  PAGEREF
_Toc244324254 \h  114  

  HYPERLINK \l "_Toc244324255"  c.	PM2.5 Precursors	  PAGEREF
_Toc244324255 \h  115  

  HYPERLINK \l "_Toc244324256"  F.	Final Action on Trigger and Baseline
Dates for PM2.5 Increments	  PAGEREF _Toc244324256 \h  117  

  HYPERLINK \l "_Toc244324257"  G.	Definition of “Baseline Area” for
PM2.5	  PAGEREF _Toc244324257 \h  124  

  HYPERLINK \l "_Toc244324258"  H.	No Final Action with Respect to the
Proposed Revocation of PM10 Annual Increments	  PAGEREF _Toc244324258 \h
 126  

  HYPERLINK \l "_Toc244324259"  I.	Other Comments on Increments	 
PAGEREF _Toc244324259 \h  133  

  HYPERLINK \l "_Toc244324260"  VI.	Final Action on PM2.5 SILs	  PAGEREF
_Toc244324260 \h  137  

  HYPERLINK \l "_Toc244324261"  A.	EPA’s Determination on SILs for
PM2.5	  PAGEREF _Toc244324261 \h  137  

  HYPERLINK \l "_Toc244324262"  B.	Response to Comments Concerning the
SILs	  PAGEREF _Toc244324262 \h  139  

  HYPERLINK \l "_Toc244324263"  1.	Legal Basis for SILs	  PAGEREF
_Toc244324263 \h  141  

  HYPERLINK \l "_Toc244324264"  2.	Levels of the SILs	  PAGEREF
_Toc244324264 \h  142  

  HYPERLINK \l "_Toc244324265"  a.	Class I SILs	  PAGEREF _Toc244324265
\h  146145  

  HYPERLINK \l "_Toc244324266"  b.	Class II and III SILs	  PAGEREF
_Toc244324266 \h  151  

  HYPERLINK \l "_Toc244324267"  3.	Relationship Between SILs and AQRVs	 
PAGEREF _Toc244324267 \h  156156  

  HYPERLINK \l "_Toc244324268"  4.	Form of the SILs	  PAGEREF
_Toc244324268 \h  158  

  HYPERLINK \l "_Toc244324269"  5.	SILs for Other Pollutants	  PAGEREF
_Toc244324269 \h  160159  

  HYPERLINK \l "_Toc244324270"  VII.	Final Action on the PM2.5 SMC	 
PAGEREF _Toc244324270 \h  163162  

  HYPERLINK \l "_Toc244324271"  A.	EPA’s Determination on the PM2.5
SMC	  PAGEREF _Toc244324271 \h  163162  

  HYPERLINK \l "_Toc244324272"  B.	Response to Comments Concerning the
SMC	  PAGEREF _Toc244324272 \h  164  

  HYPERLINK \l "_Toc244324273"  1.	Legal Issues	  PAGEREF _Toc244324273
\h  164  

  HYPERLINK \l "_Toc244324274"  2.	Level of the SMC	  PAGEREF
_Toc244324274 \h  167  

  HYPERLINK \l "_Toc244324276"  C.	Correction of Cross Reference in PSD
Ambient Monitoring Requirements	  PAGEREF _Toc244324276 \h  172171  

  HYPERLINK \l "_Toc244324277"  VIII.	Dates Associated With
Implementation of the Final Rule	  PAGEREF _Toc244324277 \h  172  

  HYPERLINK \l "_Toc244324278"  A.	Effective Date of the Final Rule	 
PAGEREF _Toc244324278 \h  173  

  HYPERLINK \l "_Toc244324279"  1.	State PSD Programs	  PAGEREF
_Toc244324279 \h  177  

  HYPERLINK \l "_Toc244324280"  2.	Federal PSD Program	  PAGEREF
_Toc244324280 \h  179  

  HYPERLINK \l "_Toc244324281"  B.	Transition Period	  PAGEREF
_Toc244324281 \h  183  

  HYPERLINK \l "_Toc244324282"  C.	SILs and SMC for PM2.5	  PAGEREF
_Toc244324282 \h  186  

  HYPERLINK \l "_Toc244324283"  IX.	Other Regulatory Changes	  PAGEREF
_Toc244324283 \h  189  

  HYPERLINK \l "_Toc244324284"  X.	Statutory and Executive Order Reviews
  PAGEREF _Toc244324284 \h  190  

  HYPERLINK \l "_Toc244324285"  A.	Executive Order 12866 - Regulatory
Planning and Review	  PAGEREF _Toc244324285 \h  190  

  HYPERLINK \l "_Toc244324286"  B.	Paperwork Reduction Act	  PAGEREF
_Toc244324286 \h  191190  

  HYPERLINK \l "_Toc244324287"  C.	Regulatory Flexibility Act	  PAGEREF
_Toc244324287 \h  193192  

  HYPERLINK \l "_Toc244324288"  D.	Unfunded Mandates Reform Act	 
PAGEREF _Toc244324288 \h  194193  

  HYPERLINK \l "_Toc244324289"  E.	Executive Order 13132 - Federalism	 
PAGEREF _Toc244324289 \h  194  

  HYPERLINK \l "_Toc244324290"  F.	Executive Order 13175 - Consultation
and Coordination with Indian Tribal Governments	  PAGEREF _Toc244324290
\h  195  

  HYPERLINK \l "_Toc244324291"  G.	Executive Order 13045 - Protection of
Children from Environmental Health and Safety Risks	  PAGEREF
_Toc244324291 \h  196  

  HYPERLINK \l "_Toc244324292"  H.	Executive Order 13211 - Actions That
Significantly Affect Energy Supply, Distribution, or Use	  PAGEREF
_Toc244324292 \h  196  

  HYPERLINK \l "_Toc244324293"  I.	National Technology Transfer and
Advancement Act	  PAGEREF _Toc244324293 \h  197196  

  HYPERLINK \l "_Toc244324294"  J.	Executive Order 12898 – Federal
Actions to Address Environmental Justice in Minority Populations and
Low-Income Populations	  PAGEREF _Toc244324294 \h  197  

  HYPERLINK \l "_Toc244324295"  K.	Congressional Review Act	  PAGEREF
_Toc244324295 \h  198  

  HYPERLINK \l "_Toc244324296"  XI.	Judicial Review	  PAGEREF
_Toc244324296 \h  199  

  HYPERLINK \l "_Toc244324297"  XII.	Statutory Authority	  PAGEREF
_Toc244324297 \h  200199  

 

6560-50-P

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 51 and 52

[EPA-HQ-OAR-2006-0605; FRL-       ]

RIN 2060-AO24 

Prevention of Significant Deterioration (PSD) for Particulate Matter
Less Than 2.5 Micrometers (PM2.5) – Increments, Significant Impact
Levels (SILs) and Significant Monitoring Concentration (SMC)

AGENCY:  Environmental Protection Agency (EPA).

ACTION:  Final rule.

SUMMARY:  The EPA is amending the requirements for particulate matter
less than 2.5 micrometers (PM2.5) under the Prevention of Significant
Deterioration (PSD) program by adding maximum allowable increases in
ambient pollutant concentrations (“increments”) and two screening
tools, known as the Significant Impact Levels (SILs) and a Significant
Monitoring Concentration (SMC) for PM2.5.  The SILs for PM2.5 are also
being added to two other New Source Review (NSR) rules that regulate the
construction and modification of any major stationary source locating in
an attainment or unclassifiable area, where the source’s emissions may
cause or contribute to a violation of the national ambient air quality
standards (NAAQS).

DATES:  This final rule is effective on [INSERT DATE 60 DAYS AFTER DATE
OF PUBLICATION IN THE FEDERAL REGISTER].  

ADDRESSES:  The EPA has established a docket for this action under
Docket ID No. EPA-HQ-OAR-2006-0605.  All documents in the docket are
listed on the   HYPERLINK "http://www.regulations.gov" 
www.regulations.gov  Web Site.  Although listed in the index, some
information may not be publicly available, e.g., Confidential Business
Information (CBI) or other information whose disclosure is restricted by
statute.  Certain other material, such as copyrighted material, is not
placed on the Internet and will be publicly available only in hard copy
form.  Publicly available docket materials are available either
electronically through   HYPERLINK "http://www.regulations.gov" 
www.regulations.gov  or in hard copy at the Air Docket, EPA/DC, EPA
West, Room 3334, 1301 Constitution Avenue, Northwest, Washington, DC. 
The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday
through Friday, excluding legal holidays.  The telephone number for the
Public Reading Room is (202) 566-1744, and the telephone number for the
Air Docket is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT:  Mr. Dan deRoeck, Air Quality Policy
Division, Office of Air Quality Planning and Standards (C504-03), U.S.
Environmental Protection Agency, Research Triangle Park, North Carolina
27711, telephone number: (919) 541-5593, facsimile number: (919)
541-5509, e-mail address:   HYPERLINK "mailto:rao.raj@epa.gov" 
deroeck.dan@epa.gov . 

SUPPLEMENTARY INFORMATION:

	The information in this Supplementary Information section of this
preamble is organized as follows:

  TOC \o "1-4" \n \h \z \u    HYPERLINK \l "_Toc244324114"  I.	General
Information 

  HYPERLINK \l "_Toc244324115"  A.	Does This Action Apply to Me? 

  HYPERLINK \l "_Toc244324116"  B.	Where Can I Get a Copy of this
Document and Other Related Information? 

  HYPERLINK \l "_Toc244324117"  II.	Purpose 

  HYPERLINK \l "_Toc244324118"  III.	Overview of Final PM2.5 PSD
Regulations 

  HYPERLINK \l "_Toc244324119"  A.	Increments 

  HYPERLINK \l "_Toc244324120"  B.	SILs 

  HYPERLINK \l "_Toc244324121"  C.	SMC 

  HYPERLINK \l "_Toc244324122"  IV.	Background 

  HYPERLINK \l "_Toc244324123"  A.	PSD Program 

  HYPERLINK \l "_Toc244324124"  B.	History of Particulate Matter (PM)
NAAQS 

  HYPERLINK \l "_Toc244324125"  1.	Total Suspended Particulate (TSP) and
PM10 NAAQS 

  HYPERLINK \l "_Toc244324126"  2.	PM2.5 NAAQS 

  HYPERLINK \l "_Toc244324127"  3.	Revised PM2.5 and PM10 NAAQS 

  HYPERLINK \l "_Toc244324128"  C.	Implementation of NSR for PM2.5 

  HYPERLINK \l "_Toc244324129"  D.	Increments Under the PSD Program 

  HYPERLINK \l "_Toc244324130"  E.	Historical Approaches for Developing
Increments 

  HYPERLINK \l "_Toc244324131"  1.	Congressional Enactment of Increments
for PM and SO2 

  HYPERLINK \l "_Toc244324132"  2.	EPA’s Promulgation of Increments
for NO2 and PM10 

  HYPERLINK \l "_Toc244324133"  a.	Increments for NO2 Using the
“Contingent Safe Harbor” Approach Under Section 166(a) of the Act 

  HYPERLINK \l "_Toc244324134"  b.	Increments for PM10 Using
“Equivalent Substitution” Approach Under Section 166(f) of the Act 

  HYPERLINK \l "_Toc244324135"  V.	Final Action on PM2.5 Increments 

  HYPERLINK \l "_Toc244324136"  A.	Decision to Establish PM2.5
Increments Using “Contingent Safe Harbor Approach” Under Section
166(a) 

  HYPERLINK \l "_Toc244324137"  B.	Rationale for the Applicability of
Section 166(a) 

  HYPERLINK \l "_Toc244324138"  C.	EPA’s Interpretation of the
Requirements under Sections 166(a)-(d) of the Act 

  HYPERLINK \l "_Toc244324139"  1.	Regulations as a Whole Should Fulfill
Statutory Requirements 

  HYPERLINK \l "_Toc244324140"  2.	Contingent Safe Harbor Approach 

  HYPERLINK \l "_Toc244324141"  3.	The Statutory Factors Applicable
under Section 166(c) 

  HYPERLINK \l "_Toc244324142"  4.	Balancing the Factors Applicable
under Section 166(c) 

  HYPERLINK \l "_Toc244324143"  5.	Authority for States to Adopt
Alternatives to Increments 

  HYPERLINK \l "_Toc244324144"  D.	Framework for Pollutant-Specific PSD
Regulations for PM2.5 

  HYPERLINK \l "_Toc244324145"  1.	Increment System 

  HYPERLINK \l "_Toc244324146"  2.	Area Classifications 

  HYPERLINK \l "_Toc244324147"  3.	Permitting Procedures 

  HYPERLINK \l "_Toc244324148"  4.	AQRV Review by Federal Land Manager
(FLM) and Reviewing Authority 

  HYPERLINK \l "_Toc244324149"  5.	Additional Impacts Analysis 

  HYPERLINK \l "_Toc244324150"  6.	Installation of BACT 

  HYPERLINK \l "_Toc244324151"  E.	Final PM2.5 Increments 

  HYPERLINK \l "_Toc244324152"  1.	Identification of Safe Harbor
Increments 

  HYPERLINK \l "_Toc244324153"  2.	Data Used by EPA for the Evaluation
of the Safe Harbor Increments for PM2.5 

  HYPERLINK \l "_Toc244324154"  3.	Scope of Effects Considered 

  HYPERLINK \l "_Toc244324155"  4.	Evaluation of the Health and Welfare
Effects of PM2.5 

  HYPERLINK \l "_Toc244324156"  a.	Health Effects 

  HYPERLINK \l "_Toc244324157"  b.	Welfare Effects 

  HYPERLINK \l "_Toc244324158"  5.	Fundamental Elements of Increments 

  HYPERLINK \l "_Toc244324159"  6.	Evaluation of the Safe Harbor
Increments 

  HYPERLINK \l "_Toc244324160"  7.	Compliance Determinations for the
PM2.5 Increments 

  HYPERLINK \l "_Toc244324161"  a.	Modeling Compliance with PM2.5
Increments 

  HYPERLINK \l "_Toc244324162"  b.	Condensable PM 

  HYPERLINK \l "_Toc244324163"  c.	PM2.5 Precursors 

  HYPERLINK \l "_Toc244324164"  F.	Final Action on Trigger and Baseline
Dates for PM2.5 Increments 

  HYPERLINK \l "_Toc244324165"  G.	Definition of “Baseline Area” for
PM2.5 

  HYPERLINK \l "_Toc244324166"  H.	No Final Action with Respect to the
Proposed Revocation of PM10 Annual Increments 

  HYPERLINK \l "_Toc244324167"  I.	Other Comments on Increments 

  HYPERLINK \l "_Toc244324168"  VI.	Final Action on PM2.5 SILs 

  HYPERLINK \l "_Toc244324169"  A.	EPA’s Determination on SILs for
PM2.5 

  HYPERLINK \l "_Toc244324170"  B.	Response to Comments Concerning the
SILs 

  HYPERLINK \l "_Toc244324171"  1.	Legal Basis for SILs 

  HYPERLINK \l "_Toc244324172"  2.	Levels of the SILs 

  HYPERLINK \l "_Toc244324173"  a.	Class I SILs 

  HYPERLINK \l "_Toc244324174"  b.	Class II and III SILs 

  HYPERLINK \l "_Toc244324175"  3.	Relationship Between SILs and AQRVs 

  HYPERLINK \l "_Toc244324176"  4.	Form of the SILs 

  HYPERLINK \l "_Toc244324177"  5.	SILs for Other Pollutants 

  HYPERLINK \l "_Toc244324178"  VII.	Final Action on the PM2.5 SMC 

  HYPERLINK \l "_Toc244324179"  A.	EPA’s Determination on the PM2.5
SMC 

  HYPERLINK \l "_Toc244324180"  B.	Response to Comments Concerning the
SMC 

  HYPERLINK \l "_Toc244324181"  1.	Legal Issues 

  HYPERLINK \l "_Toc244324182"  2.	Level of the SMC 

  HYPERLINK \l "_Toc244324184"  C.	Correction of Cross Reference in PSD
Ambient Monitoring Requirements 

  HYPERLINK \l "_Toc244324185"  VIII.	Dates Associated With
Implementation of the Final Rule 

  HYPERLINK \l "_Toc244324186"  A.	Effective Date of the Final Rule 

  HYPERLINK \l "_Toc244324187"  1.	State PSD Programs 

  HYPERLINK \l "_Toc244324188"  2.	Federal PSD Program 

  HYPERLINK \l "_Toc244324189"  B.	Transition Period 

  HYPERLINK \l "_Toc244324190"  C.	SILs and SMC for PM2.5 

  HYPERLINK \l "_Toc244324191"  IX.	Other Regulatory Changes 

  HYPERLINK \l "_Toc244324192"  X.	Statutory and Executive Order Reviews


  HYPERLINK \l "_Toc244324193"  A.	Executive Order 12866 - Regulatory
Planning and Review 

  HYPERLINK \l "_Toc244324194"  B.	Paperwork Reduction Act 

  HYPERLINK \l "_Toc244324195"  C.	Regulatory Flexibility Act 

  HYPERLINK \l "_Toc244324196"  D.	Unfunded Mandates Reform Act 

  HYPERLINK \l "_Toc244324197"  E.	Executive Order 13132 - Federalism 

  HYPERLINK \l "_Toc244324198"  F.	Executive Order 13175 - Consultation
and Coordination with Indian Tribal Governments 

  HYPERLINK \l "_Toc244324199"  G.	Executive Order 13045 - Protection of
Children from Environmental Health and Safety Risks 

  HYPERLINK \l "_Toc244324200"  H.	Executive Order 13211 - Actions That
Significantly Affect Energy Supply, Distribution, or Use 

  HYPERLINK \l "_Toc244324201"  I.	National Technology Transfer and
Advancement Act 

  HYPERLINK \l "_Toc244324202"  J.	Executive Order 12898 – Federal
Actions to Address Environmental Justice in Minority Populations and
Low-Income Populations 

  HYPERLINK \l "_Toc244324203"  K.	Congressional Review Act 

  HYPERLINK \l "_Toc244324204"  XI.	Judicial Review 

  HYPERLINK \l "_Toc244324205"  XII.	Statutory Authority 

 

General Information

Does This Action Apply to Me?

Entities affected by this rule include sources in all industry groups. 
The majority of sources potentially affected are expected to be in the
following groups:  

Industry group	

	NAICSa



Electric services		

221111, 221112, 221113, 221119, 221121, 221122



Petroleum refining		

32411



Industrial inorganic chemicals		

325181, 32512, 325131, 325182, 211112, 325998, 331311, 325188



Industrial organic chemicals		

32511, 325132, 325192, 325188, 325193, 32512, 325199



Miscellaneous chemical products		

32552, 32592, 32591, 325182, 32551



Natural gas liquids		

211112



Natural gas transport		

48621, 22121



Pulp and paper mills		

32211, 322121, 322122, 32213



Paper mills		

322121, 322122



Automobile manufacturing		

336111, 336112, 336712, 336211, 336992, 336322, 336312, 33633, 33634,
33635, 336399, 336212, 336213



Pharmaceuticals		

325411, 325412, 325413, 325414

a North American Industry Classification System.

Entities affected by this rule also include states, local reviewing
authorities, and Indian country where affected new and modified major
stationary sources will locate.

Where Can I Get a Copy of this Document and Other Related Information?

In addition to being available in the docket, an electronic copy of this
final rule will also be available on the World Wide Web.  Following
signature by the EPA Administrator, a copy of this final rule will be
posted in the regulations and standards section of our NSR home page
located at   HYPERLINK "http://www.epa.gov/nsr"  http://www.epa.gov/nsr
.

Purpose 

	The purpose of this rulemaking is to finalize certain program
provisions under the regulations to prevent significant deterioration of
air quality due to emissions of PM2.5 (i.e., under the PM2.5 PSD
regulations).  This final rule supplements the final implementation rule
for PM2.5, known as the Clean Air Fine Particle Implementation Rule
(CAFPIR) that we promulgated on April 25, 2007 (72 FR 20586), and the
PM2.5 NSR Implementation Rule that we promulgated on May 16, 2008 (73 FR
28321).  Together, these three rules encompass the elements necessary
for implementation of a PM2.5 program in any area.  This final rule is
important because it establishes new increments, SILs, and an SMC for
PM2.5 to facilitate ambient air quality monitoring and modeling under
the PSD regulations for areas designated attainment or unclassifiable
for PM2.5. 

Overview of Final PM2.5 PSD Regulations

Increments

This rulemaking establishes new increments for PM2.5 pursuant to the
legal authority contained in section 166(a) of the Clean Air Act (CAA or
Act) for pollutants for which NAAQS are promulgated after 1977.  The
final PM2.5 increments were identified as Option 1 in the 2007 Notice of
Proposed Rulemaking (NPRM) for this action, and are as follows: 

Averaging Period	NAAQS

(µg/m3)	Increments (µg/m3)



Class I	Class II	Class III

Annual	15	1	4	8

24-hour	35	2	9	18



As discussed in more detail in sections V.F and VIII, the new increments
for PM2.5 will become effective 1 year from the date of promulgation of
this final rule, that is, on [INSERT DATE 1 YEAR AFTER DATE OF
PUBLICATION IN THE FEDERAL REGISTER].

This final rule does not revoke the annual increments for particulate
matter less than 10 micrometers (PM10) as proposed under Option 1 in the
2007 NPRM, but instead retains, in addition to the PM2.5 increments,
both the annual and 24-hour increments for PM10.  This outcome is
discussed in greater detail in section V.H of this preamble.

SILs 

	This rule establishes new SILs for PM2.5 for evaluating the impact a
proposed new source or modification may have on the NAAQS and PSD
increments for PM2.5.  The SILs for PM2.5 were developed by scaling the
existing PM10 SILs using a PM2.5-to-PM10 NAAQS ratio.  The final SILs
were identified as Option 3 in the 2007 NPRM, and are as follows:

Averaging Period	SILs (µg/m3)

	Class I	Class II	Class III

Annual	0.06	0.3	0.3

24-hour	0.07	1.2	1.2



These values will be added to the state implementation plan (SIP)
requirements for PSD at 40 CFR 51.166 (as an optional screening tool)
and the federal PSD program at 40 CFR 52.21, as well as under the
preconstruction review permit requirements at 40 CFR 51.165(b) and part
51, Appendix S.  See a more detailed discussion of the SILs, as well as
the relevant comments and our responses to them, in section VI of this
preamble.  The SILs for PM2.5 are incorporated into the federal PSD
program as well as into the regulations for state-implemented PSD
programs, although they are regarded as optional for state programs. 
The effective date for implementing the new SILs under the federal PSD
program is the effective date of this final rule.  See section VIII of
this preamble for further discussion of the effective date.

SMC

 μg/m3 PM2.5 (24-hour average).  This value has been developed pursuant
to proposed Option 1; however, it should be noted that the value being
established in this final rule is lower than the proposed value of 10
μg/m3 that was originally developed under Option 1.  A more detailed
discussion of the proposed SMC is presented in section VII of this
preamble, describing the rationale for altering the proposed SMC, and
the relevant comments on the proposed SMC and our responses to them. 
The SMC for PM2.5 is incorporated into the federal PSD program as well
as into the regulations for state-implemented PSD programs, although
they are regarded as optional for state programs.  As with the SILs for
PM2.5, the effective date for implementing the new SMC under the federal
PSD program is the effective date of this final rule.  See section VIII
of this preamble for further discussion of the effective date.

Background

PSD Program

The NSR provisions of the Act are a combination of air quality planning
and air pollution control technology program requirements for new and
modified stationary sources of air pollution.  In brief, section 109 of
the Act requires us to promulgate primary NAAQS to protect public health
and secondary NAAQS to protect public welfare.  Once we have set these
standards, states must develop, adopt, and submit to us for approval
SIPs that contain emission limitations and other control measures to
attain and maintain the NAAQS and to meet the other requirements of
section 110(a) of the Act.    SEQ CHAPTER \h \r 1 Part C of title I of
the Act contains the requirements for a component of the major NSR
program known as the PSD program.  This program sets forth procedures
for the preconstruction review and permitting of new and modified major
stationary sources of air pollution locating in areas meeting the NAAQS
(“attainment” areas) and areas for which there is insufficient
information to classify an area as either attainment or nonattainment
(“unclassifiable” areas).  Most states have SIP-approved
preconstruction permit (major NSR) programs.  The federal PSD program at
40 CFR 52.21 applies in some states that lack a SIP-approved permit
program, and in Indian country.  The applicability of the PSD program to
a major stationary source must be determined in advance of construction
and is a pollutant specific determination.  Once a major source is
determined to be subject to the PSD program (PSD source), among other
requirements, it must undertake a series of analyses to demonstrate that
it will use the best available control technology (BACT) and will not
cause or contribute to a violation of any NAAQS or increment.  For the
latter demonstration, the PSD regulations generally require sources to
submit for review and approval a source impact analysis and an air
quality analysis.  

The source impact analysis is primarily a modeling analysis designed to
show that the allowable emissions increase from the proposed project, in
conjunction with other emissions increases from existing sources, will
not result in a violation of either the NAAQS or increments.  In cases
where the source’s emissions may adversely affect an area classified
as a Class I area, additional review is conducted to protect the
increments and special attributes of such an area defined as “air
quality related values” (AQRVs).

The air quality analysis must assess the ambient air quality in the area
that the proposed project would affect.  For this analysis, the owner or
operator of the proposed project must submit as part of a complete
permit application air quality monitoring data that represent the air
quality in the area affected by the proposed source for the 1-year
period preceding receipt of the application.  Where data may already
exist to represent existing air quality, it may be used by the
applicant; otherwise, the source owner or operator must be responsible
for the installation and operation of monitors to collect the necessary
data.   

Historically, EPA has allowed the use of several types of screening
tools to help facilitate implementation of the preconstruction review
process to reduce the permit applicant’s burden and streamline the
permitting process for de minimis circumstances.  These tools include a
significant emissions rate (SER), SILs, and a SMC.  The SER, defined in
tons per year (tpy) for each regulated pollutant, is used to determine
whether the emissions increase from any proposed source or modification
can be excluded from review on the grounds that the increase of any
particular pollutant is de minimis. 

The SIL, expressed as an ambient pollutant concentration (micrograms per
cubic meter (µg/m3)), is used to determine whether the ambient impact
of a particular pollutant (once it is determined to be emitted in
significant amounts) is significant so as to warrant a complete source
impact analysis involving modeling the collective impacts of the
proposed project and emissions from other existing sources. 

The PSD regulations generally require each PSD applicant to collect 1
year of continuous air quality monitoring data for any pollutant
determined to be subject to preconstruction review as part of complete
PSD permit application.  Using the SMC as a screening tool, expressed as
an ambient pollutant concentration (µg/m3), sources may be able to
demonstrate that the modeled air quality impact of emissions from the
new source or modification, or the existing air quality level in the
area where the source would construct, are less than the SMC, i.e., de
minimis, and may be allowed to forego the preconstruction monitoring
requirement for a particular pollutant at the discretion of the
reviewing authority.  See 40 CFR 51.166(i)(5) and 52.21(i)(5). 

  SEQ CHAPTER \h \r 1 When the reviewing authority reaches a preliminary
decision to authorize construction of a proposed major new source or
major modification, it must provide notice of the preliminary decision
and an opportunity for comment by the general public, industry, and
other persons that may be affected by the emissions of the proposed
major source or major modification.  After considering these comments,
the reviewing authority may issue a final determination on the
construction permit in accordance with the PSD regulations.  

History of Particulate Matter (PM) NAAQS

Total Suspended Particulate (TSP) and PM10 NAAQS

	The EPA initially established NAAQS for PM in 1971, measured by the TSP
indicator.  Based on the size of the particles collected by the
“high-volume sampler,” which at that time was the reference method
for determining ambient concentrations, TSP included all PM up to a
nominal size of 25 to 45 micrometers.  We established both annual and
24-hour NAAQS for TSP.

	On July 1, 1987, we revised the NAAQS for PM and changed the indicator
from TSP to PM10; the latter indicator includes particles with a mean
aerodynamic diameter less than or equal to 10 micrometers.  The PM10
particles are the subset of inhalable particles small enough to
penetrate to the thoracic region (including the tracheobronchial and
alveolar regions) of the respiratory tract (referred to as thoracic
particles).  We established annual and 24-hour NAAQS for PM10, and
revoked the NAAQS for TSP.  (52 FR 24634). 

PM2.5 NAAQS

	On July 18, 1997, we again revised the NAAQS for PM in several
respects.  While we determined that the NAAQS should continue to focus
on particles less than or equal to 10 micrometers in diameter, we also
determined that the fine and coarse fractions of PM10 should be
considered separately.  We established new annual and 24-hour NAAQS
using PM2.5 (referring to particles with a nominal mean aerodynamic
diameter less than or equal to 2.5 micrometers) as the indicator for
fine particles.  The 1997 NAAQS rule also modified the PM10 NAAQS for
the purpose of regulating the coarse fraction of PM10 (referred to as
thoracic coarse particles or coarse-fraction particles; generally
including particles with a nominal mean aerodynamic diameter greater
than 2.5 micrometers and less than or equal to 10 micrometers, or
PM10-2.5); however, this part of the rulemaking was vacated during
subsequent litigation, leaving the pre-existing 1987 PM10 NAAQS in place
(62 FR 38652).  

Revised PM2.5 and PM10 NAAQS   

	On October 17, 2006, we promulgated revisions to the NAAQS for PM2.5
and PM10 with an effective date of December 18, 2006 (71 FR 61144).  We
lowered the 24-hour NAAQS for PM2.5 from 65 µg/m3 to 35 µg/m3, and
retained the existing annual PM2.5 NAAQS of 15 µg/m3.  In addition, we
retained the existing PM10 24-hour NAAQS of 150 µg/m3, and revoked the
annual PM10 NAAQS (set at 50 µg/m3). 

Implementation of NSR for PM2.5

	After we established new annual and 24-hour NAAQS based on  PM2.5 as
the indicator for fine particles in July 1997, we issued a guidance
document “Interim Implementation for the New Source Review
Requirements for PM2.5,” John S. Seitz, Director, Office of Air
Quality Planning and Standards, EPA, October 23, 1997.  As noted in that
guidance, section 165 of the Act implies that certain PSD requirements
become effective for a new NAAQS upon the effective date of the NAAQS. 
Section 165(a)(1) of the Act provides that no new or modified major
source may be constructed without a PSD permit that meets all of the
section 165(a) requirements with respect to the regulated pollutant. 
Moreover, section 165(a)(3) provides that the emissions from any such
source may not cause or contribute to a violation of any increment or
NAAQS.  Also, section 165(a)(4) requires BACT for each pollutant subject
to PSD regulation.  The 1997 guidance stated that sources would be
allowed to use implementation of a PM10 program as a surrogate for
meeting PM2.5 NSR requirements until certain difficulties were resolved.
 These difficulties included the lack of necessary tools to calculate
the emissions of PM2.5 and related precursors, the lack of adequate
modeling techniques to project ambient impacts, and the lack of PM2.5
monitoring sites.  

	On April 5, 2005, we issued a guidance document entitled
“Implementation of New Source Review Requirements in PM-2.5
Nonattainment Areas,” Stephen D. Page, Director, Office of Air Quality
Planning and Standards, EPA.  This memorandum provided guidance on the
implementation of the nonattainment major NSR provisions in PM2.5
nonattainment areas in the interim period between the effective date of
the PM2.5 NAAQS designations 

(April 5, 2005) and when we promulgate regulations to implement
nonattainment major NSR for the PM2.5 NAAQS.  In addition to affirming
the continued use of the John S. Seitz guidance memo in PM2.5 attainment
areas, this memo recommended that, until we promulgate the PM2.5 major
NSR regulations, states should use a PM10 nonattainment major NSR
program as a surrogate to address the requirements of nonattainment
major NSR for the PM2.5 NAAQS.

	On November 1, 2005, we proposed a rule to implement the PM2.5 NAAQS,
including proposed revisions to the NSR program.  For those states with
EPA-approved PSD programs, we proposed to continue the 1997 NSR guidance
to use PM10 as a surrogate for PM2.5, but only during the SIP
development period.  We also indicated in that proposal that we would be
developing increments, SILs, and an SMC in a separate rulemaking, i.e.,
this final rule.  Since there was an interim surrogate NSR program in
place, i.e., the PM10 Surrogate Policy, EPA decided to first promulgate
the non-NSR part of the implementation rule (including attainment
demonstrations, designations, control measures, etc.) – which was
promulgated as the CAFPIR on    April 25, 2007 (72 FR 20586).  

	The NSR part of the implementation rule was issued separately as a
final rule on May 16, 2008 (73 FR 28321), and included sets of NSR
regulations for both attainment (PSD) and nonattainment areas
(nonattainment NSR) for PM2.5.  In the May 16, 2008 rule we added one of
the important screening tools — the SER — for PM2.5.  The SER for
PM2.5 is defined as an emissions rate of 10 tpy for direct PM2.5
emissions.  We also listed sulfur dioxide (SO2) and nitrogen oxides
(NOx) as precursors of ambient PM2.5 and defined “significant” as 40
tpy or more of either precursor pollutant.  States were allowed up to 3
years from the date of publication in the Federal Register to revise
their SIPs and submit their revised NSR programs to EPA for approval.

Increments Under the PSD Program

	Under section 165(a)(3) of the Act, a PSD permit applicant must
demonstrate that emissions from the proposed construction and operation
of a facility “will not cause, or contribute to, air pollution in
excess of any (A) maximum allowable increase or maximum allowable
concentration for any pollutant ….” 42 U.S.C. 7475(a)(3).  The
“maximum allowable increase” of an air pollutant that is allowed to
occur above the applicable baseline concentration for that pollutant is
known as the PSD increment.  By establishing the maximum allowable level
of ambient pollutant concentration increase in a particular area, an
increment defines “significant deterioration” of air quality in that
area.

iable area in which the source’s emissions of that pollutant are
projected (by air quality modeling) to result in an ambient pollutant
increase of at least 1 μg/m3 (annual average).  See, e.g., 40 CFR
52.21(b)(15)(i).  Once the baseline area is established, subsequent PSD
sources locating in that area need to consider that a portion of the
available increment may have already been consumed by previous emissions
increases. 

	In general, the submittal date of the first complete PSD permit
application in a particular area is the operative “baseline date.” 
On or before the date of the first complete PSD application, emissions
generally are considered to be part of the baseline concentration,
except for certain emissions from major stationary sources, as explained
in the following discussion of baseline dates.  Most emissions increases
that occur after the baseline date will be counted toward the amount of
increment consumed.  Similarly, emissions decreases after the baseline
date restore or expand the amount of increment that is available.  

	In practice, three dates related to the PSD baseline concept are
important in understanding how to calculate the amount of increment
consumed — (1) trigger date; (2) major source baseline date; and (3)
minor source baseline date.  The first relevant date is the trigger
date.  The trigger date, as the name implies, triggers the overall
increment consumption process nationwide.  Specifically, this is a fixed
date, which must occur before the minor source baseline date can be
established for the pollutant-specific increment in a particular
attainment area.  See, e.g., 40 CFR 52.21(b)(14)(ii).  For PM (regulated
as TSP) and SO2, Congress defined the applicable trigger date as August
7, 1977 – the date of the 1977 amendments to the Act when the original
statutory increments were established by Congress.  For nitrogen dioxide
(NO2), we selected the trigger date as February 8, 1988 – the date on
which we proposed increments for NO2.  See 53 FR 40656, 40658; October
17, 1988.  In this final rule, as described later, we are establishing a
separate trigger date for purposes of implementing the PM2.5 increments.
 See section V.F of this preamble for additional discussion of the
trigger date for PM2.5.

	The two remaining dates – “minor source baseline date” and
“major source baseline date” – as described later, are necessary
to properly account for the emissions that are to be counted toward the
amount of increment consumed following the national trigger date, in
accordance with the statutory definition of “baseline concentration”
in section 169(4) of the Act.  The statutory definition provides that
the baseline concentration of a pollutant for a particular baseline area
is generally the air quality at the time of the first application for a
PSD permit in the area.  Consequently, any increases in actual emissions
occurring after that date (with some possible exceptions that we will
discuss later) would be considered to consume the applicable PSD
increment.  However, the statutory definition in section 169(4) also
provides that “[e]missions of sulfur oxides and particulate matter
from any major emitting facility on which construction commenced after
January 6, 1975, shall not be included in the baseline and shall be
counted in pollutant concentrations established under this part.”  

	To make this distinction between the date when emissions resulting from
the construction at a major stationary source consume the increment and
the date when emissions changes in general (i.e., from both major and
minor sources) begin to consume the increment, we established the terms
“major source baseline date” and “minor source baseline date,”
respectively.  See 40 CFR 51.166(b)(14) and 52.21(b)(14).  Accordingly,
the “major source baseline date,” which precedes the trigger date,
is the date after which actual emissions increases associated with
construction at any major stationary source consume the PSD increment. 
In accordance with the statutory definition of “baseline
concentration,” the PSD regulations define a fixed date to represent
the major source baseline date for each pollutant for which an increment
exists.  Congress defined the major source baseline date for the
statutory increments for PM and SO2 as January 6, 1975.  For the NO2
increments, which we promulgated in 1988 under our authority to
establish an increment system under section 166(a) of the Act, the major
source baseline date we selected was February 8, 1988 – the date on
which we proposed increments for NO2.  53 FR 40656.  In both instances,
the major source baseline date for the individual increments was set as
a date which preceded the date on which the regulations pertaining to
those increments were issued.  In this final rule, as described later,
we are establishing a separate major source baseline date for
implementing the PM2.5 increments.  See section V.F of this preamble for
further discussion of the major source baseline date for PM2.5.  

	The “minor source baseline date” is the earliest date after the
trigger date on which a source or modification submits the first
complete application for a PSD permit in a particular area.  After the
minor source baseline date, any increase in actual emissions (from both
major and minor sources) consumes the PSD increment for that area.	

	The PSD regulations set out the third date – the “trigger date” -
that is relevant to the PSD baseline concept.  These regulations provide
that the earliest date on which the minor source baseline date can be
established is the date immediately following the “trigger date” for
the pollutant-specific increment.  See, e.g., 40 CFR 52.21(b)(14)(ii). 
For PM and SO2, Congress defined the applicable trigger date as August
7, 1977 – the date of the 1977 amendments to the Act when the original
statutory increments were established by Congress.  For NO2, we selected
the trigger date as February 8, 1988 – the date on which we proposed
increments for NO2.  See 53 FR 40656, 40658; October 17, 1988.

Once the minor source baseline is established, the new emissions
increase from that major source consumes a portion of the increment in
that area, as do any subsequent actual emissions increases that occur
from any new or existing source in the area.  When the maximum pollutant
concentration increase defined by the increment has been reached,
additional PSD permits cannot be issued until sufficient amounts of the
increment are “freed up” via emissions reductions that may occur
voluntarily, e.g., via either source shutdowns or control requirements
imposed by the reviewing authority.  Moreover, the air quality in a
region cannot deteriorate to a level in excess of the applicable NAAQS,
even if all the increment in the area has not been consumed.  Therefore,
new or modified sources located in areas where the air pollutant
concentrations are near the level allowed by the NAAQS may not have full
use of the amount of pollutant concentration increase allowed by the
increment.	

Under EPA guidance, the actual increment analysis that a proposed new or
modified source undergoing PSD review must complete depends on the area
impacted by the source’s new emissions.  We have also provided
approved air quality models and guidelines for sources to use to project
the air quality impact of each pollutant (over each averaging period)
for which an increment analysis must be done.  In addition, we
established SILs for each pollutant under the permit requirements
applicable to new and modified major stationary sources locating in
attainment areas that would cause or contribute to a violation of any
NAAQS.  These SILs have also been used for implementing the PSD program
to identify levels below which the source’s modeled impact of a
particular pollutant is regarded as de minimis.  See 40 CFR 51.165(b)
and part 51, Appendix S, section III.A.  In this final rule, we are
establishing SILs (24-hour and annual) for PM2.5 that are being added to
the aforementioned regulations containing SILs for other pollutants, as
well as to the PSD regulations in 40 CFR 51.166 and 52.21.  See further
discussion of the SILs for PM2.5 in section VI of this preamble.  

In the event that a source’s modeled impacts of a particular pollutant
are below the applicable SIL at all ambient air locations modeled, i.e.,
de minimis everywhere, EPA’s policy for PSD provides that no further
modeling analysis is required for that pollutant.  Our longstanding
policy under the PSD program is that when a preliminary screening
analysis based on the SIL is sufficient to demonstrate that the
source’s emissions throughout the area modeled will not cause or
contribute to a violation of the increment, there is no need for a
comprehensive source impact analysis involving a cumulative evaluation
of the emissions from the proposed source and other sources affecting
the area. 

Within the impact area of a source subject to PSD, that is, the area
within which the proposed project’s emissions increase does have a
significant impact, increment consumption is calculated using the
source’s proposed emissions increase, along with other actual
emissions increases or decreases of the particular pollutant from any
sources in the area, which have occurred since the minor source baseline
date established for that area.  In addition, the emissions increases or
decreases from any major source that has commenced construction since
the major source baseline date (which precedes the minor source baseline
date) will consume or expand increment.  Thus, an emissions inventory of
sources whose emissions, in whole or in part, of a particular pollutant
consume or expand the available increment in the area must be compiled. 
The inventory of increment-consuming emissions includes not only sources
located directly in the impact area, but sources outside the impact area
that affect the air quality for the particular pollutant within the
impact area.  

The inventory of increment-consuming emissions includes emissions from
increment-affecting sources at two separate time periods – the
baseline date and the current period of time.  For each source that was
in existence on the relevant baseline date (major source or minor
source), the inventory includes the source’s actual emissions on the
baseline date and its current actual emissions.  The change in emissions
over these time periods represents the emissions that consume increment
(or, if emissions have gone down, expand the available increment).  For
sources constructed since the relevant baseline date, all their current
actual emissions consume increment and are included in the inventory.  

When the inventory of increment-consuming emissions has been compiled,
computer modeling is used to determine the change in ambient
concentration that will result from these emissions when combined with
the proposed emissions increase from the new major source or major
modification that is undergoing PSD review.  The modeling has generally
been guided by the “Guideline on Air Quality Models” (40 CFR part
51, Appendix W), which includes provisions on air quality models and the
meteorological data input into these models.  The model output
(expressed as a change in concentration) for each relevant averaging
period is then compared to the corresponding allowable PSD increment.  

Historical Approaches for Developing Increments

Congressional Enactment of Increments for PM and SO2

	Congress established the first increments defining significant
deterioration of air quality in the 1977 Amendments to the Act.  These
amendments, among other things, added part C to title I, setting out the
requirements for PSD.  In section 163, Congress included numerical
increments for PM and SO2 for Class I, II, and III areas. 

	The three area classes are part of the increment system originally
established by Congress.  Congress designated Class I areas (including
certain national parks and wilderness areas) as areas of special
national concern, where the need to prevent deterioration of air quality
is the greatest.  Consequently, the allowable level of incremental
change is the smallest relative to the other area classes, i.e., most
stringent, in Class I areas.  The increments of Class II areas are
larger than those of Class I areas and allow for a moderate degree of
emissions growth.  For future redesignation purposes, Congress defined a
“Class III” classification to allow the redesignation of any
existing Class II area for which a state may desire to promote a higher
level of industrial development (and emissions growth).  Thus, Class III
areas are allowed to have the greatest amount of pollutant increase of
the three area classes while still achieving the NAAQS.  To date, there
have been no redesignations made to establish a Class III area.	

	In establishing these PSD increments, Congress used the then-existing
NAAQS for those pollutants as the benchmark for determining what
constitutes “significant deterioration.”  Congress established the
increments for PM as a percentage of the then-existing PM NAAQS.  At the
time the Act was amended in 1977, the NAAQS for PM were expressed in
terms of ambient concentrations of TSP.  Thus, EPA interpreted the
statutory increments for PM using the same ambient TSP “indicator.” 
 

EPA’s Promulgation of Increments for NO2 and PM10

	Congress also provided authority for EPA to promulgate additional
increments and to update the original PM increments created by statute. 
The EPA has promulgated two regulations pursuant to this authority. 

Increments for NO2 Using the “Contingent Safe Harbor” Approach Under
Section 166(a) of the Act

	Based on section 166(a) of the Act, on October 17, 1988, EPA
promulgated increments for NO2 to prevent significant deterioration of
air quality due to emissions of NOx (53 FR 40656).  The EPA based these
increments on percentages of the NAAQS in the same way that Congress
derived the statutory increments for PM and SO2.  Those NO2 increments
were challenged in 1988 by the Environmental Defense Fund (EDF) when EDF
filed suit in the U.S. Court of Appeals for the District of Columbia
Circuit against the Administrator (Environmental Defense Fund, Inc. v.
Reilly, No. 88–1882).  The EDF successfully argued that we failed to
sufficiently consider certain provisions in section 166 of the Act.  The
court remanded the case to EPA “to develop an interpretation of
section 166 that considers both subsections (c) and (d), and if
necessary to take new evidence and modify the regulations.”  See
Environmental Defense Fund v. EPA, 898 F.2d 183, 190 (D.C. Cir. 1990). 
Section 166(c) of the Act requires the PSD regulations to, among other
things, meet the goals and purposes set forth in sections 101 and 160 of
the Act.  Section 166(d) requires these regulations be at least as
effective as the increments established for PM (in the form of TSP) and
SO2 in section 163 of the Act.  The court considered the NO2 increment
values determined using the percentage-of-NAAQS approach as “safe
harbor” increments which met the requirements of section 166(d) of the
Act.  However, the court also determined that EPA’s reliance on such
increment levels was contingent upon our completing the analyses
required under section 166(c), which provided that the final increment
values must address the goals of sections 101 and 160 of the Act to
protect public health and welfare, parks, and AQRVs and to insure
economic growth. 

	In response to the court’s decision, we proposed rulemaking on
increments for NO2 on February 23, 2005 (70 FR 8880) and finalized the
rule on October 12, 2005 (70 FR 59582).  In the final rule, we
established our policy on how to interpret and apply the requirements of
sections 166(c) and (d) of the Act.  In accordance with the court
ruling, we conducted further analyses (considering the health and
welfare effects of NOx) and concluded that the existing NO2 increments
were adequate to fulfill the requirements of section 166(c).  See 70 FR
59586 for our detailed analysis of how pollutant regulations satisfy the
requirements of section 166 of the Act.  Hence, we retained the existing
NO2 increments along with other parts of the existing framework of
pollutant-specific NO2 increment regulations.  We also amended the PSD
regulations under 40 CFR 51.166 to make it clear that states may seek
EPA approval of SIPs that utilize a different approach than EPA used to
establish these NO2 increments.  To receive our approval of an
alternative program, a state must demonstrate that its program satisfies
the requirements of sections 166(c) and 166(d) of the Act and prevents
significant deterioration of air quality from emissions of NOx.

Increments for PM10 Using “Equivalent Substitution” Approach Under
Section 166(f) of the Act

	On October 5, 1989, we proposed PM10 increments.  See 54 FR 41218. 
Although section 163 did not expressly define the existing statutory
increments for PM in terms of a specific indicator, EPA reasoned that
Congress’ knowledge that TSP was the indicator for the PM NAAQS, and
that the TSP standards were the starting point for the increments levels
when the increments were established in 1977, meant that TSP was also
the appropriate measure for the PM increments in section 163.  As a
consequence, EPA believed that the statutory PM increments could not
simply be administratively redefined as PM10 increments, retaining the
same numerical values, following the revision of the PM NAAQS.  Rather,
we stated our belief that with the promulgation of the PM10 NAAQS, EPA
had both the responsibility and the authority under sections 166 and 301
of the Act to promulgate new increments for PM to be measured in terms
of PM10.  We further concluded that promulgating PM10 increments to
replace, rather than supplement, the statutory TSP increments under
section 163 represented the most sensible approach for preventing
significant deterioration with respect to PM.  See 54 FR 41220 - 41221.

	We promulgated PM10 increments to replace the then-existing TSP
increments on June 3, 1993 (58 FR 31622).  In the interim between
proposal and promulgation, Congress enacted the 1990 Act Amendments.  As
part of these Act Amendments, Congress amended section 166 to add a new
section 166(f).  This section specifically authorized EPA to substitute
PM10 increments for the existing section 163 PM increments based on TSP,
provided that the substituted increments are “of equal stringency in
effect” as the section 163 increments.

	Thus, we were able to replace the TSP increments under section 163 of
the Act using PM10 increments based directly on the newly enacted
authority under section 166(f) of the Act.  In the PM10 rule, we
maintained the existing baseline dates and baseline areas for PM that
had been previously established using the TSP indicator.  Also, as
proposed, we promulgated PM10 increments based on an approach we called
the “equivalent to statutory increments” approach.  Under this
approach, we used the original TSP increments as a benchmark for
calculating the PM10 increments, thereby retaining roughly the same
limitations on future deterioration of air quality as was allowed under
the TSP increments.  

	In using this approach, we considered the historical consumption of TSP
increment by a sample population of permitted PSD sources, and then
determined the PM10 increments for each area classification and
averaging time that would provide approximately the same percentage of
PM10 increment consumption, on average, by the same population of
sources.  Then, all future calculations of increment consumption after
the PM10 implementation date would be based on PM10 emissions.  See 58
FR 31622 and 31625.

Final Action on PM2.5 Increments

Decision to Establish PM2.5 Increments Using “Contingent Safe Harbor
Approach” Under Section 166(a)

	The EPA’s 2007 NPRM contained three options for developing numerical
PM2.5 increments.  Option 1 used the authority of section 166(a) of the
Act to establish increments for PM2.5 as a new pollutant for which NAAQS
were established after August 7, 1977, and established 24-hour and
annual PM2.5 increments (Class I, II, and III) based on the
“contingent safe harbor” approach.  Options 2 and 3 used the
contingent safe harbor approach under section 166(a) to develop 24-hour
PM2.5 increments (Class I, II, and III), while using the “equivalent
substitution” approach under section 166(f) of the Act to develop
annual PM2.5 increments.  Each of these options is discussed in detail
in the 2007 NPRM.  72 FR 54123 - 54138.  In addition, significant
comments on each of the three options, and our responses to them, are
provided in this section.

	In this final rule, after considering the available information and
comments from interested parties, EPA has decided to select Option 1 and
establish increments for PM2.5 using the “contingent safe harbor”
approach in accordance with the authority provided in section 166(a) of
the Act.  In this section of the preamble, we will summarize the
considerations that went into our proposed action and describe the final
action being taken regarding new regulations for preventing significant
deterioration of PM2.5 air quality — including PM2.5 increments,
baseline dates and other permit requirements for PM2.5 (see preamble
section V.F), and PM10 increments (section V.H). 	

	This final rule establishes increments for PM2.5 at the following
levels:

Averaging Period	NAAQS

(µg/m3)	Increments (µg/m3)



Class I	Class II	Class III

Annual	15	1	4	8

24-hour	35	2	9	18



Rationale for the Applicability of Section 166(a) 

In the 2007 NPRM, we expressed our belief that it is permissible to
interpret section 166(a) to apply to PM2.5.  Section 166(a) requires EPA
to develop regulations to prevent the significant deterioration of air
quality due to emissions of certain named pollutants, and to develop
such regulations for any pollutants for which NAAQS are subsequently
promulgated.  Although EPA has generally characterized the NAAQS for
PM2.5 as a NAAQS for a new indicator of PM, EPA did not replace the PM10
NAAQS with the NAAQS for PM2.5 when the latter NAAQS were promulgated in
1997.  Rather, EPA retained the annual and 24-hour PM10 NAAQS (retaining
PM10 as an indicator of coarse particulate matter), and established new
annual and 24-hour NAAQS for PM2.5 as if PM2.5 was a new pollutant, even
though EPA had already developed air quality criteria for PM generally. 
Thus, for purposes of section 166(a), the promulgation of a NAAQS for
PM2.5 established a NAAQS for an additional pollutant after 1977.

Nine commenters supported our proposed Option 1, although only one of
these explicitly expressed support for the use of section 166(a)
authority to promulgate PM2.5 increments.  Ten other commenters
specifically opposed the use of section 166(a) authority and/or
supported the use of section 166(f) authority (on which the annual
increments under Options 2A and 2B were based).  

The commenter (0040) who explicitly agreed with our proposed use of
section 166(a) authority stated that it is the only option that is
legally available.  This commenter asserted that section 166(a) plainly
applies to PM2.5 because PM2.5 is a pollutant for which NAAQS were
promulgated after August 7, 1977.  This commenter held that EPA’s
rulemaking duty under section 166(a) is not confined to “new
pollutants,” but is triggered by post-1977 NAAQS promulgations,
regardless of whether for new or previously regulated pollutants.  On
the other hand, this commenter noted that by its terms, section 166(f)
is limited to authorizing the adoption of PM10 increments as a
substitute for the statutory TSP increments and does not provide for
substitution of PM2.5 increments for TSP or PM10 increments.  Another
commenter (0029) who favors Option 1 stated simply that EPA's analysis
backing Option 1 was correct, without specifically mentioning section
166(a).

The opposing commenters did not believe that section 166(a) provides a
legal basis for EPA to promulgate PM2.5 increments.  One of these
commenters (0033) stated that section 166(a) can only be used for a new
pollutant, and PM2.5 is not a new pollutant.

Another commenter (0019) who opposed the use of section 166(a) authority
argued that nothing in section 166(a) of the Act can be interpreted to
allow it to be used as the basis of increments when EPA revises an
existing NAAQS.  The commenter explained that, on its face, section
166(a) can only be interpreted to apply to pollutants other than PM and
SO2 since increments for these pollutants were enacted by Congress in
section 163 of the Act.  The commenter added that it can be argued that
Congress intended to have section 166(a) apply to the four other
pollutants specifically listed there.

This commenter (0019) found unpersuasive our argument that we are not
“substituting” increments (as section 166(f) requires for PM10) but
rather adding PM2.5 increments to the existing PM10 increments, and that
only section 166(a) allows such an approach (72 FR 54121).  The
commenter asserted that if EPA had defined a coarse fraction to the
particulate matter standards, then that fraction, together with the
PM2.5 standards, would form the set of “substituted” new standards
for the existing PM10 standards, and, thus, the increments.

The commenter (0019) also disagreed with EPA’s argument that it can
treat PM2.5 as a new pollutant under section 166(a) of the Act since it
has been demonstrated that sub-PM2.5 particles have distinctly different
health and welfare effects than the other forms of PM (i.e., coarse or
PM10).  The commenter (0019) indicated that just as EPA replaced the TSP
standards by PM10 as a better indicator of health effects, ongoing
research has lead to establishment of the PM2.5 standards as a better
indicator of certain health effects, and it is the natural outcome of
such research that has enabled EPA to separate the effect of total
particulate matter into two fractions with distinct effects.  The
commenter (0019) added that given that the definition of particulate
matter includes a vast conglomeration of solids and liquids, the finding
of differing effects should not come as a surprise.  The commenter
(0019) explained that as is the case of different pollutants having
similar effects and are, nonetheless, treated as separate pollutants,
the same concept should apply to a range or fraction of particulate
matter found to have different effects in establishing it as another
indicator and not a different pollutant.

The commenter (0019) did not disagree with the specific numerical
increments proposed by EPA under Option 1, but did have concerns with
the potential consequences of the section 166(a) approach.  The
commenter’s primary concern was the proposal to allow states to
substitute other measures in the place of uniform national increments
for PM2.5.  (This is discussed further in section V.C.5 of this
preamble.)  Another commenter (0018) also expressed this concern.

Another commenter (0034) who opposed the section 166(a) approach
believes that the legal and Congressional history regarding the
establishment of PM increments shows that Congress added section 166(f)
to the Act based on the conviction that without it, EPA had no authority
to revise the PM increments for PM10 (citing and quoting from S. Rep.
No. 228, 101st Cong., 2nd Sess. 75 (1990), reprinted in 1990
U.S.C.C.A.N. 3385, 3461).  The commenter (0034) concluded that EPA did
not have authority in 1987 under section 166(a) to adopt PM10
increments, and does not have authority now under section 166(a) to
adopt PM2.5 increments.

We read section 166(a) to authorize EPA to promulgate pollutant-specific
PSD regulations meeting the requirements of sections 166(c) and 166(d)
for any pollutant for which EPA promulgates a NAAQS after 1977.  Most of
the pollutants identified in section 166(a) (NOx, photochemical
oxidants, carbon monoxide) are pollutants for which EPA had established
NAAQS in 1977 when Congress adopted section 166 of the Act.  There was
no need for Congress to list other criteria pollutants, SO2 and PM, in
section 166(a) because Congress had already established increments for
these pollutants in section 163 of the Act.  In addition to requiring
regulations for the enumerated pollutants, Congress clearly intended to
authorize EPA to establish additional pollutant-specific PSD
regulations, potentially containing increments, for any additional
pollutants for which EPA promulgated a NAAQS under section 109 of the
Act.  Furthermore, because the Act refers to pollutants for which EPA
promulgates NAAQS after 1977, and does not use the phrase “additional
pollutants,” section 166(a) provides authority for EPA to promulgate
new increments after revising an existing NAAQS (including one first
promulgated before 1977), when we find that such action is appropriate. 


Moreover, any new increments developed pursuant to section 166(a) have
no effect on existing increments, as there is no indication therein that
an existing increment should be revoked or replaced when additional
increments are promulgated.  This was the situation following the
promulgation of new NAAQS for PM in 1987 when EPA replaced the old NAAQS
based on TSP with new ones based on PM10.  Had Congress not added new
section 166(f) in 1990, increments for PM10 could have been developed
pursuant to section 166(a) of the Act, but such increments would have
had no effect on the original statutory increments for PM (based on
TSP).  Consequently, seeing no basis for retaining the original
increments, Congress added section 166(f) which explicitly provides for
the replacement of the existing increments with PM10 increments.

One commenter (0031) asserted that if EPA establishes increments for
PM2.5 under the authority of section 166(a) on the basis that PM2.5 is a
new pollutant, then it must also establish PM10 increments under section
166(a) because (according to the commenter’s analysis) PM10 is also a
new pollutant.  In the same analysis, the commenter concluded that EPA
must adopt new measures to prevent significant deterioration from coarse
PM based on section 166(a). 

In this final rule, EPA is not setting or amending any increments for
PM10 or otherwise taking action with respect to PM10 increments.  The
preexisting annual and 24-hour increments for PM10 are being retained. 
See section V.H.  Similarly, EPA is not taking any action with respect
to coarse PM in this rule.  For these reasons, the commenter’s
arguments on what authority must be used to set increments for PM10
and/or coarse PM, and that EPA has some obligation to take action with
respect to coarse PM, are not on point for this rule.  Thus, no
substantive response to this comment is needed.  Nevertheless, as
mentioned earlier, it is clear that Congress provided explicit authority
under section 166(f) of the Act to address increments for PM10, because
it intended for such increments to be substitute increments for the
original statutory increments for PM measured as TSP.  Thus, the PM10
increments legally supersede the original statutory increments for PM. 
Had the PM10 increments been developed under section 166(a), which prior
to the 1990 Act Amendments was the only authority available for
developing new increments, then the original statutory PM increments
would have remained in effect in addition to the PM10 increments.

One commenter (0016) expressed general objections to EPA's legal
rationale for the PM2.5 increments proposal, asserting that we failed to
expressly state and support our legal authority for the PM2.5
increments, offering two possible sources of authority (“contingent
safe harbor,” “equivalent substitution,” or possibly a combination
of the two) but never stating our legal position with clarity.  The
commenter agreed with EPA’s assessment that the PM2.5 increments
should and must fulfill the legal requirements of the Act (72 FR 54121),
and added that it is the government’s burden of proof to establish its
legal authority for action.  The commenter stated that it would be
arbitrary and capricious to promulgate these regulations for which EPA
has not stated legal authority.

We do not disagree that the 2007 NPRM described two different legal
authorities for the two different options for establishing increments,
but we disagree that these discussions did not clearly present the
alternative legal bases that the Agency was considering for taking
action in this rule.  In particular, we clearly described our legal
authority for developing the 24-hour increments under section 166(a) of
the Act, which is the basis on which we are taking final action in this
rule.  First, we expressly stated that Option 1 was based on the
statutory authority of section 166(a) of the Act.  See 72 FR 54123
(Under the first option, “we would use the authority of section 166(a)
of the Act to develop new increments for PM2.5”).  Second, we provided
a discussion of this authority both in general (see 72 FR 54118 - 54119
and 54120 - 54123), and how it would be applied to establish increments
for PM2.5 (see 72 FR 54119-120 and 54123 - 54136).

We now believe that section 166(a) provides the clearest reading of the
Act, as well as the most straightforward approach for developing
increments for a pollutant or pollutant indicator for which no
increments have yet been established.  Our position also relies, to some
extent, on the comments we received which supported the delay in
implementation of the new increments, opposed the potential for two sets
of definitions for “major source baseline date” and “trigger
date” for the PM2.5 increment system, and highlighted the complexities
involved with having to establish and maintain two sets of emissions
inventories for the 24-hour and annual PM2.5 increments.  (See further
description of relevant comments in section VIII of this section.)

 EPA’s Interpretation of the Requirements under Sections 166(a)-(d) of
the Act

	In   SEQ CHAPTER \h \r 1 section 166(a) of the Act, Congress directed
EPA to develop pollutant-specific regulations to prevent significant
deterioration of air quality.  Congress further specified that such
regulations meet specific requirements set forth in sections 166(c) and
166(d) of the Act.  We stated in the 2007 NPRM that because we believed
that section 166(a) could be applied to the development of increments
for PM2.5, we would follow the interpretation of sections 166(a)-(d)
that the Agency adopted in its most recent NO2 increments rule.  70 FR
59582, October 12, 2005.  That particular interpretation and application
was upheld in   SEQ CHAPTER \h \r 1 Environmental Defense v. EPA, 489
F.3d 1320 (D.C. Cir. 2007).  

	The   SEQ CHAPTER \h \r 1 EPA’s interpretation of these provisions is
grounded on five principles and conclusions.  First, we read section 166
of the Act to direct EPA to conduct a holistic analysis that considers
how a complete system of regulations will collectively satisfy the
applicable criteria, rather than evaluating one individual part of a
regulatory scheme in isolation.  Second, we use a “contingent safe
harbor” approach which calls for EPA to first determine an increment
with the minimum level of effectiveness necessary to satisfy section
166(d) and then to conduct further analysis to determine if additional
measures are necessary to fulfill the requirements of section 166(c). 
Third, we interpret section 166(c) of the Act to identify eight
statutory factors that EPA must apply when promulgating
pollutant-specific regulations to prevent significant deterioration of
air quality.  Fourth, where these factors are at odds with each other,
we interpret the statute to require EPA to use its judgment to balance
the conflicting factors.  Fifth, we recognize that the requirements of
section 166 may be satisfied by adopting other measures besides an
increment and that EPA may allow states to demonstrate that alternatives
to increments contained in a SIP meet the requirements of sections
166(c) and 166(d).  Below is a brief discussion of each of these five
principles and conclusions.  A more detailed description of each of
these is contained in the 2007 NPRM at pages 54121 - 54123.

  SEQ CHAPTER \h \r 1 Regulations as a Whole Should Fulfill Statutory
Requirements

Section 166(a) directs EPA to develop pollutant-specific regulations to
prevent the significant deterioration of air quality.  Sections 166(c)
and 166(d) provide detail on the contents of those regulations, but do
not necessarily require the same type of increment system Congress
created in section 163 of the Act.  The EPA interprets section 166 to
require that the entire system of PSD regulations (the framework and
details, as described in section V.D of this preamble) for a particular
pollutant must, as a whole, satisfy the criteria in sections 166(c) and
166(d) of the Act.

Contingent Safe Harbor Approach

Section 166(c) of the Act describes the kinds of measures to be
contained in the regulations to prevent significant deterioration of air
quality called for in section 166(a) and specifies that these
regulations are to “fulfill the goals and purposes” set forth in
sections 160 and 101 of the Act.  Subsection (d) directs EPA to
“fulfill such goals and purposes” by providing “specific measures
at least as effective as the increments established in section 7473 of
this title [section 163 of the Act].”  42 U.S.C. 7476.  Thus, EPA
reads subsection (d) to require that the Agency identify a minimum level
of effectiveness, or “safe harbor,” for the body of
pollutant-specific PSD regulations adopted under section 166.  The EPA
reads subsection (c) to require that the Agency conduct further review
to determine whether, based on the criteria in subsection (c), EPA’s
pollutant-specific PSD regulations under section 166 should contain
measures that are different from the minimum “safe harbor”
identified under subsection (d).  The EPA construes subsection (d) to
require that the measures be “at least as effective” as the
statutory increments set forth in section 163.

	To apply the “contingent safe harbor” approach for PM2.5, we first
identified “safe harbor” increments for each area classification
(Class I, II, or III), using: (1) equivalent percentages of the NAAQS as
the percentages used for developing the statutory increments; (2) the
same pollutant as the NAAQS, i.e., PM2.5, and (3) the same time
(averaging) periods as were used for the PM2.5 NAAQS.  We interpreted
that this approach would ensure that the increments would be “at least
as effective as the increments established in [section 163],” as
required by section 166(d).  Second, EPA conducted further review to
determine whether the “safe harbor” increments, in conjunction with
existing elements of the PSD program or additional measures proposed
under section 166 to augment the increments, sufficiently fulfill the
criteria in subsection (c) of section 166.  In this review, we weighed
and balanced the criteria set forth in subsection (c) (and the
incorporated goals and purposes of the Act in section 101 and the PSD
program in section 160) to determine whether additional measures might
be needed to satisfy the criteria in subsection (c).  See section V.E.6
of this preamble for further discussion of our evaluation, comments on
the evaluation, and our response to them.

The Statutory Factors Applicable under Section 166(c) tc "3.  The
Statutory Factors Applicable Under Section 166(c) " \l 3 

The EPA interprets section 166(c) of the Act to establish eight factors
to be considered in the development of PSD regulations for the
pollutants covered by this provision.  These eight factors included the
three criteria stated in section 166(c) and the five goals and purposes
identified in section 160 of the Act (which, as noted below, also cover
the goals and purposes set forth in section 101).  The three stated
criteria in section 166(c) indicate that PSD regulations for specific
pollutants should provide: (1) specific numerical measures for
evaluating permit applications; (2) a framework for stimulating improved
control technology, and (3) protection of air quality values.  42 U.S.C.
7476(c).  The five goals and purposes in section 160 are incorporated
into the analysis by virtue of the fourth criterion in section 166(c),
which directs that EPA’s pollutant-specific PSD regulations “fulfill
the goals and purposes” set forth in sections 160 and 101 of the Act. 
We construed the term “fulfill the goals and purposes,” as used in
section 166(c), to mean that EPA should apply the goals and purposes
listed in section 160 as factors applicable to pollutant-specific PSD
regulations established under section 166.  The Agency’s view is that
PSD measures that satisfy the specific goals and purposes of section 160
also satisfy the more general purposes and goals identified in section
101 of the Act.  See 72 FR 54122.

One commenter (0040) disagreed with our interpretation that the goals
and purposes of section 160 also satisfy all of those in section 101. 
This commenter asserted that although there is some overlap between the
two sections, they are not identical.  As an example, the commenter
noted that section 101 expressly states that a primary goal of the Act
is to promote pollution prevention — a goal not stated in section 160.
 The commenter asserted that, although the proposed increments would
limit some pollution increases, there was no provision in the proposal
that would require or promote pollution prevention.

	We disagree with the commenter and continue to believe that measures
that satisfy the specific goals and purposes of section 160 also satisfy
the more general purposes and goals identified in section 101 of the
Act.  As we stated in the 2005 NO2 increment rulemaking, the overall
goals and purposes of the Act listed in sections 101(b) and 101(c) are
general goals regarding protecting and enhancing the nation’s air
resources and controlling and preventing pollution.  Because these broad
goals are given more specific meaning in section 160, EPA does not
believe it is necessary to consider them in detail when evaluating
whether PSD regulations satisfy the criteria in section 166(c).  70 FR
59587 FN 3, October 12, 2005.

	Regarding pollution prevention specifically, we believe that this
general goal is encompassed in, and given more specific meaning by,
sections 160(1), 160(2), and 160(4) of the Act.  These sections spell
out the specific purposes under the PSD program for the general section
101 goals of controlling and preventing pollution.  We believe that any
requirement to limit or reduce emissions serves to promote pollution
prevention, which is often the most cost effective means of lowering
pollutant emissions.

	In addition to citing the purposes set out in section 160, section
166(c) includes the criterion that pollutant-specific PSD regulations
should provide a framework for stimulating improved control technology. 
As discussed subsequently in sections V.D.1 and V.D.6 of this preamble,
we believe that this criterion is fulfilled by the system of increments
for PM2.5 and by the requirement for PSD permittees to apply BACT to
minimize PM2.5 emissions.  In stimulating improved control technology
generally, these elements of the PSD program also promote pollution
prevention.  As noted previously, pollution prevention is often the most
cost effective means of control, particularly for new sources and new
process lines at existing sources.  In addition, because BACT is a
case-by-case determination that considers cost and collateral
environmental impacts, pollution prevention, where technically feasible,
often fairs well in BACT analyses because it is typically free from the
negative environmental impacts that result from the use of add-on air
pollution control devices.

Balancing the Factors Applicable under Section 166(c)

	While the eight factors in section 166(c) are generally complementary,
there are circumstances where some of the objectives may be in conflict
with each other.  In these situations, some degree of balance or
accommodation is inherent in the requirement to establish regulations
that satisfy all of these factors.  As first discussed in our 2005 NO2
increments rulemaking (70 FR 59582, at 59587), we believe this balancing
test derives primarily from the third goal and purpose set forth in
section 160: to insure economic growth consistent with the preservation
of existing clean air resources.  42 U.S.C. 7406(3).  A more detailed
discussion of how the balancing of factors should be interpreted is
contained in the 2007 NPRM at 72 FR 54122 – 54123. 

	One commenter (0040) claimed that EPA “incorrectly and repeatedly
asserts” that a goal of section 160 of the Act is to insure economic
growth.  The commenter claimed that neither section 160 nor section 101
of the Act uses language to support a goal of promoting or maximizing
opportunities for economic growth.  Instead, the commenter asserted that
both sections state only that any growth that does occur must be
consistent with protection of air quality.  The commenter concluded that
“EPA’s notion that the need to satisfy the other requirements of
Section 166 and other goals and purposes in Sections 101 and 160 can
never preclude additional emissions from economic growth unlawfully
elevates such growth over all other statutory factors.”

	The language in section 160(c) provides that one of the purposes of the
PSD program is “to insure that economic growth will occur in a manner
consistent with the preservation of existing clean air resources.” 
The commenter suggests that this language can only be read as if the
words were “to insure that any economic growth that does occur will
occur in a manner consistent with the preservation of existing clean air
resources.”  We disagree; the phrasing used by Congress is “to
insure that economic growth will occur.”  Thus, we believe the plain
language of the statute supports EPA’s reading that section 160(3)
requires a balancing of the goals of (1) economic growth and (2)
preservation of existing clean air resources.  At a minimum, if the
language were to be considered ambiguous enough to allow the
commenter’s reading, then the Agency’s interpretation is also a
reasonable reading of the statutory language.  

Authority for States to Adopt Alternatives to Increments

While section 166 of the Act authorizes EPA to promulgate increments for
pollutants listed under section 166(a), we have also interpreted the
section to allow states to employ approaches other than increments to
prevent significant deterioration of air quality, so long as such an
approach otherwise meets the requirements of sections 166(c) and 166(d).
 This interpretation was explained in the 2005 NO2 increment rulemaking
(70 FR 59582, October 12, 2005), in which we amended the PSD regulations
at 40 CFR 51.166 by adding new paragraph (c)(2) to codify this statutory
authority.  Under the existing provision in 40 CFR 51.166(c)(2), states
may seek EPA approval of SIPs that use an alternative approach to
increments if the state can demonstrate that the alternative program
satisfies the requirements of sections 166(c) and 166(d).  However, the
current language at paragraph (c)(2) stated the authority for states to
adopt alternative measures only with respect to increments for NO2.  To
clarify our interpretation that the authority to adopt alternative
measures covers any pollutant listed in section 166(a), we are revising
40 CFR 51.166(c)(2) to make it inclusive to all applicable pollutants
rather than just NO2.  

Two commenters supported our proposal to revise paragraph (c)(2) to
include PM2.5, while four state/local agency commenters expressed
opposition.  An environmental commenter (0040) agreed that the Act
allows for other approaches, but believes that such approaches must be
in addition to the national increments.  Specifically, this commenter
stated that “although EPA can provide for states to adopt approaches
in addition to increments in order to fulfill the statutory purposes,
the agency must make clear that states cannot adopt approaches that are
less protective that the national increments.”  This commenter further
stated that “to the extent that EPA is suggesting that it can allow
states to adopt PSD programs that do not include the minimum federal
increments, that position is contrary to the statute.”  

	As in the 2005 NO2 increment rulemaking, we are codifying the basic
principle that states can seek to use alternative measures without
defining any specific type of alternative program that would be approved
or otherwise creating standards beyond the requirements of sections
166(c) and 166(d).  Instead, we plan to make determinations on a
case-by-case basis when a state submits a specific alternative approach
for EPA to approve as part of a SIP.  In making those determinations, we
will address the specific alternative measures as states propose them to
the Agency in light of the requirements of sections 166(c) and 166(d),
including whether the alternative program is “at least as effective as
the increments established in section 163,” as required in section
166(d).

The four state/local agency commenters opposing the revision to 40 CFR
51.166(c)(2) expressed the importance of using uniform national
increments for PM2.5.  One commenter (0021) argued that a nationally
inconsistent approach to PM2.5 in attainment areas could result in a
patchwork of state PSD regulations — and the exact kinds of economic
repercussions that Congress wished to avoid.  The same commenter argued
that varying increment-equivalent measures could also result in an
uneven playing field for industry and could exacerbate difficulties
between states experiencing transport problems.  

Another opposing commenter (0033) was concerned that allowing states to
adopt alternatives to increments will likely lead to a “mish-mash”
of state approaches which defeats the intention of Congress that there
be uniformity in PSD rules to avoid economic dissimilarities from state
to state that could allow interstate competition for industry based upon
which state offers the best (least expensive) environmental compliance
regulations.  Another commenter (0019) objected to allowing the use of
alternatives to increments by stating that such alternative allowances
undermine the desired national consistency, and EPA has failed to even
identify any Act programs which would benefit from this approach.

While we acknowledge the potential problems identified by the commenters
associated with allowing states to adopt alternative approaches to the
numerical increments that we are establishing, we also note that section
166(d) expressly gives EPA some latitude in promulgating regulations
that will be at least as effective as the increments in section 163, by
stating that such regulations “may contain air quality increments,
emission density requirements, or other measures.”  Thus, EPA is
authorized to provide that states may consider alternatives to the
increments established in this rule.  That said, the statutory authority
is not a blank check for states to do as they please, but enables states
to consider options that may provide a meaningful way for them to manage
their air resources within the framework allowed by the statutory PSD
requirements.

Framework for Pollutant-Specific PSD Regulations for PM2.5

In the 2007 NPRM, we proposed to apply the same basic framework for
pollutant-specific PSD regulations for PM2.5 that we used in our 2005
NO2 increments regulations.  Specifically, we proposed adopting an
increment and area classification system for PM2.5 and applying the
statutory AQRV review process to PM2.5 as well.  We also indicated that
while some of the factors applicable under section 166(c) are fulfilled
by using this type of framework for pollutant-specific PSD regulations
under section 166(a) of the Act, this framework of regulations may not
fully satisfy the other applicable factors.  In these instances, the
details of our regulations (such as the characteristics of the
increments themselves) are also important, and we evaluated the
effectiveness of the framework in conjunction with more detailed
elements of our regulations.  As discussed in the following subsections,
we believe our obligations under section 166(c) of the Act are satisfied
when the PSD regulations collectively satisfy the factors applicable
under 166(c) of the Act.

Increment System

An increment-based program satisfies the requirements under 166(c) to
provide “specific numerical measures against which permit applications
may be evaluated.”  An increment is the maximum allowable level of
ambient pollutant concentration increase that is allowed to occur above
the applicable baseline concentration in a particular area.  As such, an
increment defines “significant deterioration.”  Establishing an
increment system for PM2.5 will fulfill two of the factors applicable
under section 166(c): (1) providing specific numerical measures to
evaluate permit applications, and (2) stimulating improved control
technology.  

First, under section 165(a)(3) of the Act, a permit applicant must
demonstrate that emissions from the proposed construction and operation
of a facility “will not cause, or contribute to, air pollution in
excess of any (A) maximum allowable increase or maximum allowable
concentration for any pollutant ….”  42 U.S.C. 7475(a)(3).  Once the
baseline date associated with the application for the first new major
stationary source or major modification in an area is established, the
new emissions from that source consume a portion of the increment in
that area, as do any subsequent emissions increases that occur from any
source in the area.  When the maximum pollutant concentration increase
defined by the increment has been reached, additional PSD permits cannot
be issued until sufficient amounts of the increment are “freed up”
via emissions reductions that may be required by the reviewing
authority.  Thus, an increment is a quantitative value that establishes
a “maximum allowable increase” for a particular pollutant.  It
functions, therefore, as a specific numerical measure that can be used
to evaluate whether an applicant’s proposed project will cause or
contribute to air pollution in excess of allowable levels.

Increments also satisfy the second factor in section 166(c) by providing
“a framework for stimulating improved control technology.” 
Increments establish an incentive to apply improved control technologies
in order to avoid violating the increment and to “free-up” available
increment to promote continued economic growth.  These control
technologies may become the basis of BACT determinations elsewhere, as
the technologies become more commonplace and the costs tend to decline. 


One commenter (0040) stated that, although increments may encourage the
use of existing control technologies, EPA has not cited any evidence
that increments actually stimulate the development of improved
technologies.  Moreover, the commenter asserted that even if increments
provide the incentive asserted by EPA, any encouragement of improved
control technology is wholly incidental and hardly amounts to a
“framework” whose purpose is to stimulate such technology.

We continue to believe that the total program, encompassing increments
and BACT, does provide an appropriate framework to stimulate BACT in
such a way that it is not simply “wholly incidental,” as the
commenter claims.  The fact that economic growth in an area must occur
within a defined amount of allowable air quality deterioration should
logically lead to the application of improved pollution control
technology as the amount of deterioration increases, and should not be
regarded as an incidental consequence.  As stated in the 2007 NPRM,
Congress envisioned that the increments they originally established
would serve as an incentive: “the incremental ceiling should serve as
an incentive to technology, as a potential source may wish to push the
frontiers of technology in a particular case to obtain greater
productive capacity with the limits of the increments.”  S. Rep.
95-127 at 18, 30 (3 LH at 1392, 1404).  We, too, believe that as the
available increment in an area becomes smaller, and as states try to
preserve some of the remaining increments for future growth, it will be
necessary to require sources to install more stringent controls in that
area.  Such levels of control ultimately must be considered in
subsequent BACT evaluations in other PSD areas throughout the country. 
Admittedly, the increasing stringency of control technologies over time,
as observed in EPA’s BACT/Lowest Achievable Emission Rate (LAER)
Clearinghouse, cannot in itself serve as the indicator of how the PSD
program has already stimulated development of improved control
technology; there are undoubtedly a number of factors that could cause
such trends.  Nevertheless, even the need to require a more stringent
BACT determination in only a few PSD areas (due to dwindling increment
availability) necessitates consideration of that level of control for
all other PSD sources wherever they may decide to locate.  In any event,
while the commenter generally questions the effectiveness of the
increments as an incentive for tightening BACT, they provided no
evidence that more stringent BACT is not related to the increment system
established as an integral part of the PSD program. 

Area Classifications

In this final rule, EPA is establishing the same three-tiered area
classification system for PM2.5 that is applicable to the increments for
NO2 and other pollutants under the PSD program and the Act. 
Accordingly, areas that are currently Class I for other pollutants will
also be Class I for PM2.5 and all other areas will be Class II for PM2.5
unless we redesignate the area based on a request by a state or tribe
pursuant to the process in section 164 of the Act and EPA’s
regulations at 40 CFR 51.166(g) and 52.21(g).  

As explained earlier in section IV.E.1, Class I areas are areas where
very clean air is most desirable.  In contrast, Class III areas are
designed as those areas in which a state wishes to permit the highest
relative level of industrial development, and thus allow the largest
incremental increase in pollution.  Areas that are not especially
sensitive and where states have not provided for a higher level of
industrial growth are classified as Class II.  When Congress established
this three-tiered scheme for SO2 and PM, it intended that Class II areas
be subject to an increment that allows “moderately large increases
over existing pollution.”  H.R. Rep. 95-294, 4 LH at 2609.  

Establishing increments at different levels for each of the three area
classifications helps to fulfill two of the factors applicable under
section 166(c) of the Act.  First, establishing the smallest increments
in Class I areas helps fulfill EPA’s obligation to establish
regulations that “preserve, protect, and enhance the air quality” in
parks and special areas.  Class I areas are primarily the kinds of parks
and special areas covered by section 160(2) of the Act.  Second, by
providing for two additional area classifications with increment levels
that are higher but still protective, the area classification system
helps satisfy the goal in section 160(3) of the Act that EPA “insure
that economic growth will occur in a manner consistent with preservation
of clean air resources.”  In those areas where clean air resources may
not require as much protection, more growth is allowed.  By employing an
intermediate level (Class II areas) and higher level (Class III areas),
this classification scheme helps ensure that growth can occur where it
is needed (Class III areas) without putting as much pressure on existing
clean air resources in other areas where some growth is still desired
(Class II areas).

By requesting that EPA redesignate an existing Class II area to Class
III, states may accommodate economic growth and air quality in areas
where the Class II increment is too small to allow the siting of new or
modified sources.  The procedures specified by the Act for such a
redesignation require a commitment by the state government to create
such an area, extensive public review, local government participation in
the SIP area redesignation process, and a finding that the redesignation
will not result in the applicable increment being exceeded in a nearby
Class I or Class II area.  See 42 U.S.C. 7474(a) and (b) (sections
164(a) and (b) of the Act).  (No state has yet requested a Class III
redesignation.)  The EPA believes that the three-tiered classification
system has allowed for economic growth, consistent with the preservation
of clean air resources.

However, an area classification system alone may not completely satisfy
the factors applicable under section 166(c) of the Act.  The increment
that is employed for each class of area is also relevant to an
evaluation of whether the area classification system achieves the goals
of the PSD program.  We briefly discuss the characteristics of
increments in section V.E.5.

One commenter (0040) took issue with our assessment of the two factors
that we believe a classification system helps to fulfill.  As discussed
previously in section V.C.4, the commenter (0040) asserted that EPA has
unlawfully interpreted section 160(3) of the Act to elevate economic
growth over all other statutory factors.  As explained in greater detail
in section V.C.4, we disagree that our interpretation elevates economic
growth over other factors, and believe that the plain language of the
statute supports EPA’s reading that section 160(3) requires a
balancing of the goals of (1) economic growth and (2) preservation of
existing clean air resources.

The commenter (0040) also stated that EPA has failed to demonstrate that
the classification system and safe harbor increments, in combination
with the other elements of the regulatory framework, will “preserve,
protect, and enhance the air quality” in parks and special areas as
required under section 160(2) of the Act.  These comments and our
response to them are found in section V.E.6 of this preamble where we
discuss our evaluation of the safe harbor increments.

Permitting Procedures

Two of the factors applicable under section 166(c) are fulfilled by the
case-by-case permit review procedures that are built into our existing
PSD regulations.  The framework of our existing PSD regulations employs
the preconstruction permitting system and procedures required under
section 165 of the Act.  42 U.S.C. 7475.  These requirements are
generally reflected in 40 CFR 51.166 and 52.21 of EPA’s PSD
regulations.  These permitting and review procedures, which apply to
construction of new major sources and to major modifications, fulfill
the goals set forth in sections 160(4) and 160(5) of the Act.  These
goals require that PSD programs in one state not interfere with the PSD
programs in other states and that PSD programs assure that any decision
to permit increased air pollution is made after careful evaluation and
public participation in the decision-making process.  For the same
reasons discussed in our proposal for the pollutant-specific NO2
increments regulations (70 FR 8896, February 23, 2005), we believe these
factors are also fulfilled for PM2.5 by employing the permit review
procedures.

AQRV Review by Federal Land Manager (FLM) and Reviewing Authority

In this final rule, we apply the existing requirements to evaluate
impacts on AQRVs in Class I areas (see existing 40 CFR 51.166(p) and
52.21(p)) to PM2.5.  These existing requirements for an AQRV review
provide FLMs with the responsibility to review source impacts on
site-specific AQRVs in Class I areas and to bring any alleged adverse
impacts to the attention of the reviewing authority.  Under an increment
approach, we consider this review to be an additional measure that helps
satisfy the factors in sections 166(c) and 160(2) which require EPA’s
pollutant-specific PSD regulations to protect (1) air quality values,
and (2) parks and other special areas, respectively.

Two state/local agency commenters supported our proposal to apply the
requirements to evaluate impacts on AQRV in Class I areas to PM2.5
review.  However, one commenter (0040) indicated that FLM review does
not and cannot assure the prevention of all significant PM2.5-related
deterioration because it applies only to the construction or
modification of very large stationary sources (e.g., factories and power
plants) affecting Class I areas.  This commenter pointed out that Class
I areas do not include Bureau of Land Management wilderness and
wilderness study areas (encompassing more than 15 million acres), 341 of
the nation’s 390 national park units (only 49 national parks are Class
I), and many U.S. Forest Service lands (including a number of wilderness
areas).  The commenter added that FLM review does not help to fulfill
section 160(2)’s goal of preserving and protecting air quality in
“other areas of special national or regional natural, recreational,
scenic, or historic value,” such as state and local parks, wildlife
refuges, recreation areas, lakes, and historic areas, none of which are
Class I areas.  In addition, the commenter noted that FLM review does
not apply to emissions increases from sources of PM2.5 and precursor
pollution other than major stationary sources, such as motor vehicles
and non-major industrial sources (which are sources that emit
substantial amounts of PM2.5 and precursors).  Alabama Power v. Costle,
636 F.2d 323, 362 (D.C. Cir. 1979) (expressly recognizing that
“[s]ignificant deterioration may occur due to increased emissions from
unregulated minor sources.”).

The commenter (0040) also asserted that FLM review is of limited reach
even where it does apply.  Under the current PSD regulations, a state
must consider an FLM’s objections and must justify its decision in
writing when it disagrees with those objections, but the state can still
issue a PSD permit over those objections unless emissions are predicted
to cause an exceedance of the applicable increment.  The commenter
believes that, given these limitations, EPA cannot plausibly claim that
the existing provision for FLM review ensures the preservation,
protection, and enhancement of air quality for parks and natural areas
throughout the nation as required by section 160(2) of the Act.

In our rulemakings addressing PSD for NOx, EPA extended the AQRV review
procedures set forth in 40 CFR 51.166(p) and 52.21(p) to cover NO2. 
These AQRV review procedures were established based on section 165(d) of
the Act, and they were originally applied only in the context of the
statutory increments for PM and SO2.  However, because they also address
many of the factors applicable under section 166(c) of the Act, EPA also
applied them to NOx through regulation.  In this final rule, we are
amending the existing PSD regulations to extend, as proposed, the AQRV
review procedures to include PM2.5 by explicitly including PM2.5 in the
regulatory text that now simply references “particulate matter.” 
See new 40 CFR 51.166(p)(4) and 52.21(p)(5).

Section 165(d) creates a scheme in which the FLM and reviewing authority
must review the impacts of a proposed new or modified source’s
emissions on AQRVs.  The Act assigns to the FLM an “affirmative
responsibility” to protect the AQRVs in Class I areas.  This is in
notable contrast to the reviewing authority’s responsibility for
protecting the increments — including Class I increments.  The FLM may
object to or concur in the issuance of a PSD permit based on the impact,
or lack thereof, that new emissions may have on any affected AQRV that
the FLM has identified and for which information is available to the
general public.  If the proposed source’s emissions are shown not to
cause or contribute to a violation of a Class I increment, the FLM may
still prevent issuance of the permit by demonstrating to the
satisfaction of the reviewing authority that the source or modification
will have an adverse impact on AQRVs.  Section 165(d)(2)(C).  On the
other hand, if the proposed source is shown to cause or contribute to a
violation of a Class I increment, the reviewing authority (state or EPA)
shall not issue the permit unless the owner or operator demonstrates to
the satisfaction of the FLM that there will be no adverse impact on
AQRVs.  Thus, the showing of compliance with the increment determines
whether the FLM or the permit applicant has the burden of satisfactorily
demonstrating whether or not the proposed source’s emissions would
have an adverse impact on AQRVs.  In any event, the FLM plays an
important and material role by raising these issues for consideration by
the reviewing authority, which in the majority of cases will be the
state.

Extending the AQRV review procedures of the PSD regulations to PM2.5
helps to provide protection with respect to potential adverse effects
from PM2.5 for parks and special areas (which are generally the Class I
areas subject to this review) not afforded by the increment system
alone.  As discussed later, we believe the factors applicable under
section 166(c) of the Act can be fulfilled when the review of AQRVs is
applied in conjunction with increments and other aspects of our PSD
regulations.  In those cases where the increment is not violated and the
reviewing authority agrees that a proposed project will adversely affect
AQRVs, the parks and other special areas will be protected by denying
issuance of the permit or by requiring the applicant to modify the
project to alleviate the adverse impact.  

We read the legislative history to show that Congress intended the AQRV
review provisions of section 165(d) to provide a special layer of
protection, beyond that provided by increments.  The Senate committee
report stated the following:  “A second test of protection is provided
in specified federal land areas (Class I areas), such as national parks
and wilderness areas; these areas are also subjected to a review process
based on the effect of pollution on the area’s air quality related
values.”  S. Rep. 95-127, at 17, 4 LH at 1401.  As we stated in the
NO2 increment rule, we believe the term “air quality values” should
be given the same meaning as “air quality related values.” 
Legislative history indicates that the term “air quality value” was
used interchangeably with the term “air quality related value”
(AQRV) regarding Class I lands.

The commenter is correct that the FLM (or AQRV) review applies only to
Class I areas, and not to other “special” areas such as the numerous
state and local parks and some other areas that could be seen as being
covered by the protective purposes of section 160(2) of the Act.  This
level of coverage by FLM review to protect AQRVs was established by
Congress when it enacted the PSD program, including the purposes set out
in section 160(2).  Thus, we conclude that Congress believed that the
special areas not designated as Class I areas were properly addressed by
the other elements of the PSD program.  As discussed further in the next
section, one such element is the requirement for sources to conduct an
“additional impacts analysis,” which includes an analysis of the
impacts on visibility, soils, and vegetation of the proposed source and
associated growth, regardless of the classification of the area impacted
by the source.  Note also that states have the option under the Act of
designating additional areas as Class I areas and providing for AQRV
review for these state Class I areas if they believe that there are
areas within their borders that merit such protection.

The commenter is not correct in saying that the review to protect AQRVs
does not apply to emissions increases from sources other than major
stationary sources.  While it is generally true that a major stationary
source may trigger the analysis as part of the required PSD review for
new major stationary sources and major modifications where such
source’s emissions increase may affect a Class I area, the review
itself may include the impacts on an AQRV of other emissions in the
area, including emissions from non-major sources.  In addition, states
may adopt requirements in their state implementation plans to require
certain minor sources seeking a permit to undergo an AQRV analysis if
they choose to do so.  

We agree with the commenter that the AQRV review has certain limitations
in that a state can, under some circumstances, issue a PSD permit over
the objection of the FLM.  Here again, Congress enabled this outcome
when it provided that a permit would not be issued when the FLM
demonstrates “to the satisfaction of the State” that the source will
have an adverse impact on AQRVs in a Class I area.  Section
165(d)(2)(C)(ii).  We read this provision to reflect Congress’s
judgment on the appropriate balance between state and FLM discretion in
the reach of AQRV review.  That said, when a reviewing authority
declines to follow a determination of adverse impact by the FLM, the
reviewing authority is expected to provide a rational basis for doing
so, and a reviewing authority’s rejection of an FLM’s finding may
not be arbitrary and capricious.  As stated by EPA’s Environmental
Appeals Board in In the Matter of: Hadson Power 14 – Buena Vista, 4
E.A.D. 258, 1992 WL 345661 (October 5, 1992)(in Section II.A): 

States do not have unfettered discretion to reject an FLM's adverse
impact determination.  If a state determines that an FLM has not
satisfactorily demonstrated an adverse impact on AQRVs from the proposed
facility, the state must provide a “rational basis” for such a
conclusion, “given the FLMS' affirmative responsibility and expertise
regarding the Class I areas within their jurisdiction.”  50 FR 28549,
July 12, 1985.  Arbitrary and capricious rejections of adverse impact
determinations are not sustainable.  (citations omitted).

  

In sum, the commenter correctly enumerated some of the limitations of
the AQRV review under the Act.  However, such review is only one element
of the full PSD program, which must be evaluated against the statutory
requirements in their entirety.  We continue to believe, as previously
stated, that under an increment approach, FLM review for AQRV impacts is
an additional measure that helps satisfy the factors in sections 166(c)
and 160(2) of the Act (which require EPA’s pollutant-specific PSD
regulations to protect (1) air quality values, and (2) parks and other
special areas, respectively) in balance with the other statutory
factors.  We add that the AQRV review requirements of the existing
regulations mirror these requirements in the Act, which reflect
Congress’ judgment of how AQRV review should properly be used to
promote the purposes of the program as set out in section 160 of the
Act.

Additional Impacts Analysis

	The “additional impacts analysis” requirements set forth in our
part 51 and 52 PSD regulations also help fulfill the criteria and goals
and purposes in sections 166(c) and 160.  The additional impacts
analysis involves a case-by-case review of potential harm to visibility,
soils, and vegetation in Class II and III areas that could occur from
the construction or modification of a PSD source.

	Sections 51.166(o)(1) and 52.21(o)(1) of the PSD regulations require
that a permit provide the following analysis:

an analysis of the impairment to visibility, soils and vegetation that
would occur as a result of the source or modification, and general
commercial, residential, industrial and other growth associated with the
source or modification.  The owner or operator need not provide an
analysis of the impact on vegetation having no significant commercial or
recreational value.

This requirement was based on section 165(e)(3)(B) of the Act, which
provides that EPA establish regulations that require “an analysis of
the ambient air quality, climate and meteorology, terrain, soils and
vegetation, and visibility at the site of the proposed major emitting
facility and in the area potentially affected by emissions from such
facility ....”  42 U.S.C. 7475(e)(3)(B).

	As mentioned in the previous section, one commenter (0040) argued that
the provisions for protection of Class I areas are of no help in
fulfilling the goal set forth in section 160(2) of the Act to preserve
and protect air quality in the countless “other areas of special
national or regional natural, recreational, scenic, or historic value”
such as state and local parks, wildlife refuges, recreation areas, lakes
and historic areas, none of which were originally defined by Congress as
Class I areas.

	We acknowledge that the special provisions for protecting Class I areas
are not applicable for protecting areas that are not designated as
“Class I.”  However, we believe that the “additional impacts
analysis” provisions are especially helpful for satisfying the
requirements of section 166(c) in Class II and Class III areas,
including the types of areas described by the commenter, that are not
Class I areas but are worthy of special protection beyond what might be
provided by the NAAQS and increments.  See, e.g., 40 CFR 52.21(o). 
These areas are not subject to the special AQRV review that applies only
in Class I areas.  While the additional impacts analysis is not as
intensive a review as the AQRV analysis required in Class I areas, the
requirement to consider impairments to visibility, soils, and vegetation
through the additional impacts analysis contributes to satisfying the
factors applicable under section 166(c) of the Act in all areas,
including Class II and Class III areas.

Installation of BACT

The requirement that new sources and modified sources subject to PSD
apply BACT is an additional measure that helps to satisfy the factors in
sections 166(c), 160(1), and 160(2) of the Act.  This requirement, based
on section 165(a)(4) of the Act, is already included in EPA’s PSD
regulations for all pollutants generally and thus, in the 2007 NPRM we
considered it to be a part of the regulatory framework for the
Agency’s pollutant-specific regulations for PM2.5.  40 CFR 52.21(j);
40 CFR 51.166(j).  Our existing regulations define “best available
control technology” as “an emission limitation ... based on the
maximum degree of reduction for each pollutant subject to regulation
under the Act ... which the Administrator, on a case-by-case basis,
taking into account energy, environmental, and economic impacts and
other costs, determines is achievable for such source through
application of production processes or available methods, systems, and
techniques ….”  40 CFR 52.21(b)(12); 40 CFR 52.166(b)(12).  This
pollutant control technology requirement, in practice, has required
significant reductions in the pollutant emissions increases from new and
modified sources while also stimulating the on-going improvement of
control technology.  The control of PM2.5 emissions through the
application of BACT helps to protect air quality values, public health
and welfare, and parks and other special areas.

Final PM2.5 Increments

Based on our evaluation of the effects of PM2.5 and a balancing of the
criteria in section 166(c) of the Act (and the incorporated goals and
purposes of the Act contained in section 101 and the statutory PSD
program in section 160 of the Act), EPA has concluded that the “safe
harbor” increments for PM2.5 (which satisfy section 166(d) of the Act)
are sufficient to fulfill the criteria in section 166(c) when combined
with the other measures described earlier that we apply to PM2.5.  Since
several of the eight factors applicable under section 166(c) are
satisfied by adopting the framework and other measures described
earlier, our development of these increments for PM2.5 was guided by the
four remaining factors that may not be fully satisfied by the framework
and other measures: (1) protecting AQRVs; (2) protecting the public
health and welfare from reasonably-anticipated adverse effects; (3)
protecting the air quality in parks and special areas, and (4) insuring
economic growth.  In accordance with the “contingent safe harbor”
approach, to determine the specific characteristics of the proposed
increments, we first established safe harbor increments representing the
level of effectiveness necessary to satisfy the “at least as effective
as” requirement in section 166(d) of the Act and then conducted
further analysis to determine if additional measures are necessary to
fulfill the requirements of section 166(c).  

Identification of Safe Harbor Increments 

	Using the percentage-of-NAAQS approach under proposed Option 1, as
explained in section V.C.2 of this preamble, we derived the following
safe harbor increments for PM2.5:

Averaging Period	NAAQS

(µg/m3)	Increments (µg/m3)



Class I	Class II	Class III

Annual	15	1	4	8

24-hour	35	2	9	18



	The table shows PM2.5 NAAQS levels (primary and secondary NAAQS) at 15
µg/m3 for the annual averaging time and 35 µg/m3 for the 24-hour
averaging time.  See 40 CFR 50.7.  From these NAAQS levels, we
calculated the safe harbor increments based on the same percentages that
were used by Congress to establish the original PM increments (measured
as TSP) in section 163 of the Act, i.e., 6.6 percent of the NAAQS for
Class I areas, 25 percent of the NAAQS for Class II areas, and 50
percent of the NAAQS for Class III areas.  We have concluded that
increments with these characteristics are sufficient to satisfy the
requirement in section 166(d) that we adopt increments (or other PSD
regulations) that are “at least as effective as” the increments
established in section 163 of the Act.  42 U.S.C. 7476(d); See EDF v.
EPA, 898 F.2d at 188, 190. 

	Nine commenters supported proposed Option 1, either explicitly or
implicitly supporting our method of calculating the safe harbor
increments used to develop increments for PM2.5.  One of these
commenters (0040), while agreeing with the safe harbor increment
approach under Option 1, disagreed with our analysis of the adequacy of
the safe harbor increments, as discussed in other sections of this
preamble.  One commenter (0019) who opposed Option 1 (based on the
belief that section 166(a) of the Act is not the appropriate basis for
PM2.5 increments) nevertheless supported the percentage-of-NAAQS
approach for developing PM2.5 increments under the statutory authority
at section 166(f).  

	A commenter who opposed our proposal to calculate increments using
percentages of the NAAQS argued that this approach for setting the PM2.5
increments is not scientifically supported.  This commenter indicated
that basing the PM2.5 increments on the same percentage of the NAAQS
that were used to set PM10 increments based on the TSP NAAQS ignores the
relationship between PM10 and PM2.5 emissions, which may be much
different than the relationship between TSP and PM10 emissions.  The
commenter argued that, because the ratio of PM2.5 to PM10 emissions is
0.8, it appears that using the percentages proposed by EPA would
indirectly restrict PM10/TSP emissions and air quality impacts to
proportionally lower levels than the PM10 increments in order to avoid
exceeding the PM2.5 increments.  The commenter conceded that using the
0.8 factor to set PM2.5 increments may seem too high, but asserted that
using the safe harbor approach would set increments for PM2.5 that are
too low.

	We conclude that the commenter is mistaken in saying that the PM2.5
increments use the same percentage of the NAAQS that were used to set
the PM10 NAAQS.  We adopted the PM10 increments using the “equivalent
substitution” approach set forth under section 166(f) of the Act. 
Under that approach, rather than calculating the PM10 increments as
specific percentages of the PM10 NAAQS (using the same percentages that
Congress used for setting the statutory increments for PM and SO2), EPA
determined the levels of the PM10 increments that could represent an
equivalent amount of increment consumed, as if the TSP increments were
still in effect.  See 58 FR 31622, June 3, 1993, at pages 31626 - 31627.
 Nevertheless, the commenter is correct that, in cases where the ratio
of PM2.5 to PM10 emissions is 0.8 for an individual source, the source
may have to reduce its PM10 emissions more than would otherwise be
necessary to meet the PM10 increments in order to control its PM2.5
emissions sufficiently to meet the safe harbor PM2.5 increments.  This
is because the safe harbor PM2.5 increments are less than 80 percent of
the PM10 increments.  For example, the Class II 24-hour PM2.5 safe
harbor increment (9 µg/m3) is only 30 percent of the corresponding PM10
increment (30 µg/m3).

	The underlying reason that the safe harbor PM2.5 increments are so much
less than the PM10 increments is that the PM2.5 NAAQS are much less than
the PM10 NAAQS.  This is the result of the evolution in our knowledge
about the health and welfare effects of PM, in particular the effects of
the fine PM represented by PM2.5.  We believe that it is fitting for
PM2.5 increments to reflect our greater knowledge about PM2.5 effects
(as embodied in the NAAQS), rather than to simply maintain the control
level required by the PM10 increments as suggested by the commenter.  If
this results in PM2.5 increments that are more limiting than PM10
increments, we believe that this outcome is appropriate in light of our
statutory requirement to prevent significant deterioration of air
quality as it relates to PM2.5.

Data Used by EPA for the Evaluation of the Safe Harbor Increments for
PM2.5. 

	We evaluated whether measures other than the safe harbor increments are
necessary by analyzing primarily the scientific and technical
information on the health and welfare effects of PM2.5 contained in the
June 2005 OAQPS Staff Paper which accompanied the last full review of
the PM NAAQS completed in 2006. 

	Section 166 of the Act provides that EPA establish pollutant-specific
PSD regulations, such as increments, after the establishment of a NAAQS
for the applicable pollutants.  42 U.S.C. 7476(a).  The Act provides
that EPA will promulgate new PSD regulations under section 166,
including new increments if appropriate, within 2 years from the
promulgation of any NAAQS after 1977.  42 U.S.C. 7476(a).  Within that
time frame, the health and welfare information used for the setting of
the NAAQS would also be “current” for purposes of establishing
pollutant-specific PSD regulations.  We believe this timing reflects
Congressional intent that EPA consider the same body of information
concerning a pollutant’s health and welfare effects when it
promulgates the NAAQS and subsequent PSD increments (or other measures)
defining significant air quality deterioration for the same pollutant. 
However, when we used that same information as the basis for our
proposed pollutant-specific PSD regulations, we evaluated that
information under the legal criteria in section 166 of the Act rather
than the criteria in section 109 applicable to the promulgation of
NAAQS.  See EDF v. EPA, 898 F.2d at 190. 

retaining the level of the annual standard and tightening the level of
the 24-hour standard from 65 to 35 μg/m3 while retaining the 24-hour
PM10 NAAQS and revoking the annual PM10 NAAQS.  The information
contained in both the 2004 Criteria Document and 2005 Staff Paper that
was used for the latest review of the PM NAAQS was also considered for
the purpose of evaluating the PM2.5 increments that we have established
in this final rule.  

	The 2004 Criteria Document and 2005 Staff Paper are the products of a
rigorous process that is followed to validate and interpret the
available scientific and technical information, and provided the basis
for recommending the PM2.5 NAAQS.  In accordance with the Act, the NAAQS
process begins with the development of “air quality criteria” under
section 108 for air pollutants that “may reasonably be anticipated to
endanger public health or welfare” and that come from “numerous or
diverse” sources.  42 U.S.C. 7408(a)(1).  For each NAAQS review, the
Administrator must appoint “an independent scientific review committee
composed of seven members of the National Academy of Sciences, one
physician, and one person representing state air pollution control
agencies,” known as the Clean Air Scientific Advisory Committee
(CASAC).  42 U.S.C. 7409(d)(2)(A).  The CASAC is charged with
recommending revisions to the criteria document and NAAQS, and advising
the Administrator on several issues, including areas in which additional
knowledge is required to appraise the adequacy and basis of existing,
new, or revised NAAQS.  42 U.S.C. 7409(d)(2)(B),(C). 

	“Air quality criteria” must reflect the latest scientific knowledge
on “all identifiable effects on public health or welfare” that may
result from a pollutant(s presence in the ambient air.  42 U.S.C.
7408(a)(2).  The scientific assessments constituting air quality
criteria generally take the form of a “criteria document,” a
rigorous review of all pertinent scientific studies and related
information.  The EPA also develops a “staff paper” to “bridge the
gap” between the scientific review and the judgments the Administrator
must make to set standards.  See Natural Resources Defense Council v.
EPA (“NRDC”), 902 F.2d 962, 967 (D.C. Cir. 1990).  Both documents
undergo extensive scientific peer review as well as public notice and
comment.  See, e.g., 62 FR 386542. 

Scope of Effects Considered 

	The effects of ambient PM2.5 concentrations may include effects from
secondarily-formed PM2.5.  Thus, when we analyzed the data in this
rulemaking, we evaluated the health and welfare effects of both direct
PM2.5 and secondarily-formed PM2.5 that may result from the
transformation of other pollutants such as SO2 and NOx.  This was
consistent with the approach we described for addressing these effects
in the review of our pollutant-specific NO2 increments regulations.  70
FR 59590. 

Evaluation of the Health and Welfare Effects of PM2.5 

	Airborne PM is not a specific chemical entity, but rather is a mixture
of liquid and solid particles from different sources and of different
sizes, compositions, and properties.  Particle size distributions show
that atmospheric particles exist in two classes: fine particles and
coarse particles.  The indicator for fine particles is PM2.5, which
represents that population of particles that is mostly less than 2.5
micrometers in size.  The indicator for thoracic coarse particles is
“PM10-2.5,” which represents particles sized between 2.5 and 10
micrometers.  In the last two reviews of the PM NAAQS, EPA concluded
that these two indicators, because of their different sources,
composition, and formation processes, should be treated as separate
subclasses of PM pollution for purposes of setting ambient air quality
standards.

Fine PM is derived directly from combustion material that has
volatilized and then condensed to form primary PM or from precursor
gases, such as SO2 and NOx, reacting in the atmosphere to form secondary
PM.  Major components of fine particles are sulfates, strong acid,
ammonium nitrate, organic compounds, trace elements (including metals),
elemental carbon, and water.  Primary and secondary fine particles have
long lifetimes in the atmosphere (days to weeks) and travel long
distances (hundreds to thousands of kilometers).  They tend to be
uniformly distributed over urban areas and larger regions, especially in
the eastern United States.  As a result, they are not easily traced back
to their individual sources.  

Health Effects  

The EPA reported important progress since the last PM NAAQS review in
advancing our understanding of potential mechanisms by which ambient
PM2.5, alone and in combination with other pollutants, is causally
linked to a number of key health effects.  The more extensive and
stronger body of evidence used by EPA to study the health effects of
PM2.5 in our latest review identified a broader range of effects than
those previously documented, involving premature mortality and indices
of morbidity (including respiratory hospital admissions and emergency
room visits, school absences, work loss days, restricted activity days,
effects on lung function and symptoms, morphological changes, and
altered host defense mechanisms) associated with both long-term and
short-term exposure to PM2.5.  A more detailed discussion of the health
effects associated with PM2.5 is contained in the 2007 NPRM.  72 FR
54127 – 54128.  In addition, an overview of the scientific and
technical evidence considered in the 2004 Criteria Document and 2005
Staff Paper can be found in our proposed rule for revising the NAAQS for
PM (71 FR 2619, January 17, 2006). 

Welfare Effects

	Ambient PM alone, and in combination with other pollutants, can have a
variety of effects on public welfare.  While visibility impairment is
the most noticeable effect of fine particles present in the atmosphere,
both fine and coarse particles can have other significant
welfare-related effects, including effects on vegetation and ecosystems,
materials (e.g., soiling and corrosion), and climate change processes.  


	In reaching our decision in 2006 to revise the suite of PM secondary
standards, EPA factored in several key conclusions from the scientific
and technical information contained in the 2004 Criteria Document and
2005 Staff Paper.  These conclusions included the following: (1)
PM-related visibility impairment is principally related to fine particle
levels, and most directly related to instantaneous levels of visual air
quality associated with short-term averaging periods; (2) PM2.5
concentrations can be used as a general surrogate for visibility
impairment in urban areas; (3) any secondary NAAQS for visibility
protection should be considered in conjunction with the regional haze
program as a means of achieving appropriate levels of protection against
PM-related visibility impairment in urban, non-urban, and Class I areas
nationwide; (4) the available evidence is not sufficient to support
distinct secondary standards for fine or coarse particles for any
non-visibility related welfare effects; and (5) the secondary standards
should be considered in conjunction with protection afforded by other
programs intended to address various aspects of air pollution effects on
ecosystems and vegetation, such as the acid deposition program and other
regional approaches to reducing pollutants linked to nitrate or acidic
deposition.  

	In this rulemaking, EPA has reviewed the scientific and technical
information concerning welfare related effects considered in the 2004
Criteria Document and 2005 Staff Paper to determine whether there is any
basis for modifying the safe harbor increments developed for PM2.5 to
satisfy the criteria under sections 166(c) and 160 of the Act.  Our
review included information on visibility impairment, and effects on
vegetation and other ecosystem components, materials and soiling, and
climate changes.  A detailed discussion of the various welfare effects
we considered for evaluating the safe harbor increments for PM2.5 is
contained in the 2007 NPRM.  72 FR 54128 – 54133.

Fundamental Elements of Increments

As we have previously noted, under the model established in the Act and
prior EPA regulations, the function of an increment is not like that of
the NAAQS in that an increment is not intended to set a uniform ambient
pollutant concentration “ceiling” across the United States.  See 70
FR 59600.  Instead, while both increments and NAAQS generally serve to
limit ambient air pollution levels, increments are designed to allow a
uniform amount of pollutant concentration increase for each area in the
United States having a particular classification, i.e., Class I, II, or
III.  The amount of the allowable increase is measured against a
baseline air quality level that is typically different for each
particular area.  Because the baseline air quality level varies from one
location to another, and is not established for a particular area until
a source proposing to construct in that area submits a complete PSD
permit application, it is not possible to determine what the maximum
ambient pollutant concentration attainable will be for a given area (to
be used to determine the protection afforded by an increment against
potential adverse environmental effects) until the specific baseline air
quality level is known.

	For the reasons described in our NO2 increments rule, our objective is
to establish uniform increments, consistent with the increments for SO2
and PM originally established by Congress, that allow the same level of
deterioration for each area of the country having the same
classification.  70 FR 59601, October 12, 2005.  It is important to
understand that increments are not intended to reduce ambient
concentrations of an air pollutant below existing baseline levels in
each area, but rather to define a level of allowable increase in
pollutant concentrations above baseline levels, and to identify the
level at which “significant” deterioration occurs for each area, in
accordance with its specific classification.  70 FR 59600.

Evaluation of the Safe Harbor Increments

	As indicated earlier (in section V.E.2 of this preamble), mindful of
the considerations made about the fundamental characteristics of the
increments, we reviewed the scientific and technical evidence available
for the 2005 review of the NAAQS for PM in order to determine whether,
and to what extent, the “safe harbor” increments might need to be
modified in order to protect air quality values, health and welfare, and
parks while insuring economic growth consistent with the preservation of
clean air resources in accordance with sections 166(c) and 160 of the
Act.  As we did in our evaluation of the safe harbor NO2 increments (70
FR 59603 – 59606, October 12, 2005), we relied on an approach that
evaluates how protective the safe harbor PM2.5 increments are by
comparing the marginal pollutant concentration increases allowed by the
safe harbor increment levels against the pollutant concentrations at
which various environmental responses occur.  

	We analyzed the available evidence from both a quantitative and
qualitative perspective to reach a decision about whether we should
modify the contingent safe harbor PM2.5 increments and whether we have
sufficient information to select a specific alternative level, averaging
time, or pollutant indicator for the increments.  As a result of our
analysis, we proposed to conclude that it was not necessary to modify
the safe harbor increments to protect human health, address
non-visibility welfare effects, or further protect visibility.  This
analysis is described in detail in the 2007 NPRM.

	After considering the comments on our evaluation of the safe harbor
increments and the conclusions we reached in the NPRM (summarized in the
following paragraphs), we continue to believe that the safe harbor
increments for PM2.5 (which satisfy section 166(d) of the Act) are
sufficient to fulfill the criteria in section 166(c) of the Act (and the
incorporated goals and purposes of the Act in section 101 and the PSD
program in section 160) when combined with the other measures described
earlier that we apply to PM2.5.  Consequently, this final rule
establishes the PM2.5 increments at the level of the proposed safe
harbor increments.

	An environmental group submitted extensive comments arguing that the
PM2.5 safe harbor increments are not sufficient to meet the Act’s
requirements for PSD and that our analysis was inadequate, and two other
commenters submitted more narrowly targeted comments in this area.  A
summary of the major comments, along with our responses, follows.  A
more detailed treatment of the comments can be found in the Response to
Comments document for this rulemaking, which is available in the
rulemaking docket.

	The environmental group commenter stated that EPA has not complied with
section 166(c) of the Act because the Agency has not made a finding or
demonstrated that the PM2.5 PSD rules will (as required by section
160(2) of the Act) preserve, protect, and enhance the air quality in
parks and special areas.  The commenter asserted that EPA offered only
vague assertions that the proposed increments would “satisfy” the
statutory factors and that they, along with other programs, would
“help” to fulfill the statutory purposes.  The commenter went on to
argue that EPA sought to excuse its failure to show fulfillment of the
statutory purposes by asserting that it cannot develop a uniform,
quantitative, dose-response relationship between fine particle levels
and certain ecosystem impacts (citing 72 FR 54134), but that, even if
true, such a claim does not excuse the agency from satisfying its
statutory duty under section 166(c).

	We conclude that the 2007 NPRM demonstrated that the safe harbor
increments, in combination with the other aspects of the regulatory
framework, fulfill the statutory requirements despite the scientific
uncertainties.  We reiterate that finding today.  The fact that we did
not, in the NPRM, explicitly state this as a finding does not diminish
the demonstration made there and reiterated in this preamble.  

	The environmental group commenter believes that the relationship
between PM2.5 and adverse effects can be quantified to a greater extent
than stated by EPA.  Regarding acid rain and other adverse ecological
impacts, the commenter asserted that critical loads can be established
as a way of quantifying and limiting the PM2.5 contribution to
degradation, and noted that critical loads are now used by authorities
in Europe, have been endorsed by leading North American scientists, and
have been used by federal land management agencies.  To comply with
section 166(c), the commenter believes that EPA must establish a
mechanism to supplement the nationally uniform increments with
additional measures, including a requirement to establish area-specific
critical loads or equally protective limits, where necessary to protect
and enhance air quality in specific parks and natural areas.

	With regard to the critical load concept, we agree conceptually with
the commenter that critical loads could be used to supplement the
existing increments, especially as a means of protecting the known
sensitive ecosystems within Class I areas.  While we disagree that the
critical loads concept can be used as an effective replacement to
increments for limiting air quality degradation, we believe that the
concept offers considerable promise in helping to protect sensitive
receptors in specific Class I areas.  However, we do not believe that it
would be appropriate at this time to establish a requirement for
area-specific critical loads under the PSD program.  In our 2005 PSD
rule for NO2 increments, we indicated that states could propose using
information on critical loads as part of their approach for managing air
quality in their individual SIP-approved PSD programs, but sufficient
information was not yet available for EPA to incorporate the use of
critical loads into the national PSD program.  See 70 FR 59582, October
12, 2005, at page 59613.

	The concept of critical loads is useful for estimating how much
pollution a particular ecosystem can experience on a prolonged basis
without showing adverse effects.  In addition to addressing the
opportunity for using critical loads under its NO2 increment rule, EPA
has addressed the concept of critical loads in the last review of the PM
NAAQS and currently in the secondary NO2/SO2 NAAQS review.  To date in
the United States, critical loads have had their primary application in
the area of atmospheric deposition of sulfur (S) and nitrogen (N).  In
the last review of the PM NAAQS, EPA found that ambient PM was
contributing to the total load of pollutants entering the U.S. ecosystem
annually.  However, the review also concluded that there was
“insufficient data for the vast majority of U.S. ecosystems that
differentiate the PM contribution to total N [nitrate] or S [sulfate]
deposition to allow for practical application of this approach as a
basis for developing national standards to protect sensitive U.S.
ecosystems from adverse effects related to PM deposition.”  The 2005
Staff Paper for the PM NAAQS, in reaching this conclusion, addressed
various important factors, including (1) the lack of a long-term,
historic database of annual speciated PM deposition rates to establish
relationships between PM deposition and ecosystem responses; (2)
uncertainty in predicting the amount of PM deposited to sensitive
receptors from measured concentrations of PM in the ambient air; and (3)
the vast majority of ecosystems and the current inability to extrapolate
with confidence any effect from one ecosystem to another.  The 2005
Staff Paper recommended that EPA give serious attention to the critical
load concept and recommended the collection of data from a “greater
variety of ecosystems over longer time scales to determine how
ecosystems respond to different loading rates over time.”  2005 Staff
Paper at page 7-19. 

	The secondary NO2/SO2 NAAQS review, which is currently underway, is
evaluating ecological effects due to the atmospheric deposition of NOx
and SOx.  The two main targeted effects are acidification and nutrient
enrichment in both aquatic and terrestrial ecosystems.  This review has
used critical loads to evaluate the impact of current depositional loads
and alternative loads in several case study areas.  However, as
mentioned earlier, the estimation of ecosystem critical loads expressed
in terms of PM requires long-term ecosystem-level data on speciated PM
deposition rates for which an adequate database is currently lacking for
most sites in the United States. 

35 μg/m3 (24-hour average) were protective of public health (citing 72
FR 54128).

	The environmental group commenter’s analysis showed similar results
for the proposed annual PM2.5 increments.  The commenter asserted that
PM2.5 concentrations would be allowed to increase up to the level of the
annual NAAQS in 55 percent of the locations that are currently in
attainment, and that 87 percent of these sites would be allowed PM2.5
concentrations of 12 μg/m3 or higher.  Again, the commenter believes
that allowing annual concentrations at or above 12 μg/m3 would not be
protective of public health, based on our statement in the NPRM that we
had previously found that PM2.5 concentrations less than a range of 12 -
15 μg/m3 (annual average) were protective of public health (citing 72
FR 54128).

	We do not believe that increments must be set at levels that ensure
that the full amount of increment will be available in all locations. 
The statutory provisions in the PSD program have always been clear that
a source must demonstrate that it will comply with both the NAAQS and
increments for any pollutant.  Consistent with Congressional intent, the
PSD program does not allow a source to violate the NAAQS just because
its emissions will not cause the increments to be exceeded.  If the
increments were to be developed in such a way that all areas, taking
into account current ambient air quality status, would be able to
utilize the full amount of increment, then the increment levels would
have to be unnecessarily stringent in areas that are substantially
cleaner than levels allowed by the NAAQS.  

	Congress recognized that all areas of the country might not be able to
utilize the full amount of increment when they provided provisions
within the Act requiring that both the NAAQS and increments must
continue to be met at all times.  In areas where the full amount of
increment is not available due to levels of pollution approaching the
NAAQS, emissions reductions may be required to allow for economic growth
to occur within the limits allowed by the increments.  Hence, we do not
believe it is reasonable to unduly restrict economic growth in cleaner
areas by setting more restrictive increments to help maintain air
quality levels below the NAAQS in areas which are currently only
marginally attainment.  

	In addition, we disagree with the commenter’s assertion that the
increments will not protect public health.  In setting the PM2.5 NAAQS
at 35 μg/m3 (24-hour) and 15 μg/m3 (annual), EPA concluded that these
levels protect public health with an adequate margin of safety. 
Regardless of the level at which the increments are set, no source is
permitted to cause the NAAQS to be exceeded.  That is, as noted
previously, the upper bound on the permissible concentration of PM2.5 is
determined by the increment or the NAAQS, whichever is more restrictive
in each particular case.  Thus, the entire framework of the PM2.5
regulations, including the safe harbor increments, is protective of
public health.  In asserting otherwise, the commenter has misconstrued
our statements in this regard.  

	In the NPRM section on the health effects of PM2.5 (72 FR 54127 –
54128), we discussed the fact that we considered setting the 24-hour
NAAQS in the range of 30 to 35 μg/m3 and the annual NAAQS in the range
of 12 to 15 μg/m3.  However, we concluded in setting the NAAQS that 35
μg/m3 (24-hour) and 15 μg/m3 (annual) are protective of public health
with an adequate margin of safety.  We did not say, nor do we believe,
that PM2.5 concentrations must be below 30 μg/m3 (24-hour average) or
12 μg/m3 (annual average) to protect public health.

	The environmental group commenter believes that there is a quantifiable
relationship between visibility impairment and PM2.5 levels, citing the
NPRM discussion (72 FR 54135) as well as the most recent Criteria
Document and Staff Paper for PM2.5.  The commenter pointed out that in
the 2007 NPRM (72 FR 54135), EPA observed that the proposed Class II
short-term safe harbor increment of 9 μg/m3, if combined with the
estimated daily background levels in most areas (i.e., 10 μg/m3), would
be below the minimum values recommended in the 2005 Staff Paper for the
secondary short-term standard for PM2.5 (which was 20 μg/m3).  Rather
than supporting the adequacy of 9 μg/m3 as an increment to protect
visibility, the commenter believes that this shows that the safe harbor
increment is inadequate because consumption of an increment of 9 μg/m3
combined with background levels alone would cause an area to reach
within 1 μg/m3 of the staff-recommended value of 20 μg/m3.  The
commenter added that most areas would have PM2.5 pollution from motor
vehicles and stationary sources in concentrations substantially greater
than background levels, easily placing these areas above 20 μg/m3
(citing the 2005 Staff Paper at 2-77).

	The environmental group commenter went on to assert that the safe
harbor PM2.5 increments will not be sufficient to protect visibility in
parks and other natural areas.  In the NPRM, we stated that a 24-hour
average PM2.5 concentration of 20 μg/m3 correlates to a visual range of
approximately 25 to 35 kilometers.  72 FR 54129.  The commenter asserted
that this visual range distance falls far short of what the National
Park Service considers to be good visibility for national parks, adding
that the National Park Service has stated that visibility used to be 90
miles (145 km) on average in eastern parks, and 140 miles (225 km), on
average in western parks.  The commenter stated that the safe harbor
increments would allow parks and other natural areas to experience PM2.5
pollution that is correlated with a 25 – 35 km visual range.

  	The visibility impairment issue is more complex than suggested by the
environmental group commenter.  In addition to predicting what the
maximum ambient change in air quality is for a particular area, a
visibility impairment assessment considers such things as the frequency,
magnitude, and duration of visibility impacts in order to conclude that
an adverse impact will occur.  

	In addition, the environmental group commenter misconstrued the
illustration we included in the NPRM.  We noted that the lowest level we
considered as a secondary PM2.5 NAAQS was 20 μg/m3, which was
considered to address visibility issues in urban areas.  We also noted
that in most areas, the estimated 98th percentile of daily background
concentrations is less than 10 μg/m3.  In adding the Class II safe
harbor increment (9 μg/m3) to the 98th percentile of background levels,
we were simply showing that even in the worst case, the combination of
the safe harbor increment and background PM2.5 would not exceed the most
stringent level we considered for the secondary Class II incrementPM2.5
NAAQS.  The commenter presented this rough, worst-case calculation as if
it represented the typical situation that would result from the safe
harbor increments.  In addition, the   environmental group commenter’s
statements do not apply to parks and special areas that are classified
as Class I areas because the safe harbor increments for such areas are
much lower.

	Another commenter stated that the proposed 24-hour Class I increment (2
μg/m3) would not be protective of AQRVs, particularly visibility.  This
commenter noted that the National Park Service uses a 5 percent change
in light extinction from estimated natural conditions as the threshold
for “adverse impacts” to Class I visibility.  The commenter
indicated that depending on the constituents of the ambient PM2.5 and
the humidity, a concentration of 2 μg/m3 in a typical Class I area
would result in a change in light extinction ranging from 13 to 80
percent in the Western United States and from 8 to 50 percent in the
Eastern United States and, therefore, would likely constitute "adverse
impacts" to Class I visibility.  While acknowledging that the FLM may
still determine that the visibility in the Class I area is adversely
affected by an increase in concentration that is less than the
increment, this commenter pointed out that we stated in the 2007 NPRM
that “generally speaking an increment should not be so large that it
routinely results in substantially more pollution in Class I areas than
is generally acceptable under the AQRV approach” (citing 72 FR 54135).
 The commenter concluded that the proposed 24-hour PM2.5 increment does
not meet this test and recommended that EPA set a lower PM2.5 24-hour
increment.

	This commenter appears to have identified a worst-case scenario in
terms of increment concentrations, and although we agree with the
visibility impacts related to those concentrations discussed in the
comment, we do not believe the proposed increment level compromises the
protection of visibility or other AQRVs.  Although the “AQRV test”
uses 5 percent light extinction as a screening threshold, the
determination of adverse impact is made on a case-by-case basis taking
into account the geographic extent, intensity, duration, frequency, and
time of visibility impairment and how these factors correlate with
visitation to the Class I area.  The suggestion that the 5 percent
threshold is routinely exceeded by PSD sources or that an absolute
worst-case scenario is occurring to the geographic extent, intensity,
duration, and frequency that would warrant an adverse impact
determination is unsupported, especially considering the relatively few
adverse impact determinations that have been made in the past.  It is,
however, important to note that the AQRV analysis is independent of the
PSD increment analysis; whether or not the increment is projected to be
exceeded does not eliminate the need for an AQRV analysis.  The
determination that a facility does or does not cause an adverse impact
on a Class I area is not solely contingent upon the PSD increment, so we
do not believe that lowering the proposed increment is necessarily more
protective of the AQRV.

	With respect to these two commenters’ concerns about visibility
protection, we continue to believe that the increments cannot be
expected to be the sole means of protecting various welfare concerns. 
In the NPRM, we stated that “visibility protection in Class I areas is
more adequately provided by the AQRV process.”  Congress defined AQRVs
to specifically include visibility and left it for the FLMs to define
other special attributes of Class I areas that warranted special
protection.  We also noted that Congress has established several
visibility programs that target emissions reductions to achieve desired
visibility benefits.  See 72 FR 54135.  Collectively, these protective
programs, along with the totality of the PSD program, offer an effective
means of addressing unique local problems that cannot be addressed
solely by uniform national increments.

	However, the environmental group commenter asserted that these other
programs will not fulfill the statutory purposes.  As discussed
previously in sections V.D.4 and 5, the commenter does not believe that
FLM review in the AQRV process and the air quality impacts analysis
required by section 165(a) of the Act are adequate.  We disagree; see
sections V.D.4 and 5 for more detail on the comments and our responses.

	The environmental group commenter also noted that we cited the regional
haze program as a justification for adopting less protective PSD rules
(referring to 72 FR 54135), but the commenter pointed out that the haze
program applies only to Class I areas and does not apply at all to the
majority of the nation, which is Class II.  The commenter further noted
that we stated in the NPRM that “some State and local governments have
also developed programs to improve visual air quality in specific urban
areas” (citing 72 FR 54135), and pointed out that we gave no specific
information on such programs, nor any information about the visibility
protection that they provide beyond that provided by the proposed
increments.  The commenter asked that we identify the specific state and
local programs, and that we specify how much visibility protection such
programs are providing.

	The commenter is correct that the regional haze program directly
addresses only Class I areas.  As we have discussed before, these are
the areas that Congress defined as deserving of the most protection
under PSD, including the visibility protection provisions in subpart 2
of title I, part C of the Act, which is the statutory basis for the
regional haze program.  While Class I areas are the target for the
regional haze program, we believe that many areas of the nation will
receive collateral visibility benefits from this program.  As emissions
of the pollutants that cause regional haze are reduced, many areas in
the paths of transport will benefit.  In addition, as discussed
previously in section V.D.5 of this preamble, PSD applicants must
prepare an analysis of “other impacts,” including visibility
impacts, in areas other than Class I areas. 

	Regarding state and local visibility programs, in the 2005 Staff Paper
EPA described several existing programs to improve visual air quality in
urban areas.  These programs were located in Denver, CO; Phoenix, AZ;
and Lake Tahoe, CA.  Also, the states of California and Vermont have
each established standards to protect visibility.  See the 2005 Staff
Paper, pages 6-17 through 6-23.

	The environmental group commenter cited the 2007 NPRM (72 FR 54135)
where we said that the use of “distinct PM increments for visibility
protection is not the most effective means of addressing the visibility
problem.”  The commenter believes that this claim is based on false
premises, including the idea (discussed previously) that other programs
effectively protect visibility nationwide, and the idea that the only
option is a “distinct” PM increment for visibility protection.  As
to the latter, the commenter stated that EPA can strengthen the safe
harbor increment to ensure visibility protection and need not adopt a
separate “visibility” increment.  In addition, the commenter
asserted that EPA has ignored the statutory mandate that the PSD rules
fulfill the statutory goals and purposes, and that we cannot shirk that
statutory duty merely because we claim some other type of action would
be “more effective.”  

	We continue to believe that Class I area visibility protection under
the PSD program is appropriately addressed via the AQRV process.  As
mentioned previously, Congress explicitly included “visibility” as
an AQRV for which FLMs would have an affirmative responsibility to
protect in Class I areas under their jurisdictions.  Where the FLM
successfully demonstrates that there would be an adverse impact on the
AQRV (e.g., visibility), a state cannot issue a PSD permit, even when
the source’s emissions do not violate the PM2.5 increments.  In
addition, we continue to believe that the analysis of other impacts,
including visibility, in non-Class I areas is the appropriate means of
addressing visibility protection in these areas, as envisioned by
Congress when it enacted the PSD provisions of the Act.

	As a result, we do not believe it is necessary to create a distinct
increment (e.g., with a different averaging period) or to lower the safe
harbor increments to protect visibility in urban, non-urban, or Class I
areas across the United States.  We reach this conclusion in proper
consideration of the other, more direct approaches being used to address
visibility problems in the United States.  The primary such approach,
the regional haze program, is within the PSD framework for PM2.5.  Note
that part C of title I of the Act, “Prevention of Significant
Deterioration of Air Quality,” includes subpart 2, which is the
statutory basis for the regional haze program.  In regards our
consideration of other state and local visibility protection measures
that are outside the PSD framework, we do not believe it is reasonable
to disregard these area-specific measures that focus on the preferences
of individual communities where a uniform national increment for
visibility protection generally cannot.

	The environmental group commenter also stated that the proposed PSD
rules fail to ensure fulfillment of “enhancement goal” set out in
the Act.  The commenter noted that section 101(a) states as the Act’s
first purpose: “to protect and enhance the quality of the Nation’s
air resources,” while section 160(2) states that the purpose of the
PSD program is to “preserve, protect, and enhance” air quality in
parks and other special areas.  The commenter asserted that the proposed
rule did not address these enhancement requirements or explain how the
proposed increments would fulfill those requirements.

	This same issue was raised in the 2005 PSD rule affirming the NO2
increments.  At that time we expressed our belief that the goal to
enhance air quality in national parks and wilderness areas is
implemented through the regional haze program while the PSD program
focuses on preserving and protecting air quality in these areas. 
However, when a PSD increment violation is identified, we agree that EPA
may require a state to revise its SIP to correct the violation.  See 40
CFR 51.166(a)(3).  Otherwise, we do not interpret these PSD provisions
to authorize us to direct states in their SIPs to achieve reductions in
emissions from existing sources for PSD purposes.  

	We recognized at that time, and continue to believe, that the growth
management goals of PSD may also be fulfilled when the states adopt
controls on existing sources that would reduce emissions and allow
growth from new sources and major modifications to existing sources
without causing significant deterioration.  Under the increment
approach, we have interpreted the PSD rules to allow states to require
reductions from existing sources in order to expand the allowable
increments and, thereby, allow for more growth under the PSD program. 
However, we have never required states to do so because, in the absence
of an increment violation, we do not believe section 166 and other
provisions in part C of title I of the Act give us the legal authority
to mandate such reductions for PSD purposes.	

	Another commenter stated that the PM2.5 increments should be twice the
recommended levels because scientific studies do not support the need
for such low levels for protection of health and welfare.  The commenter
believes that increments at the proposed levels would jeopardize the
goal of providing opportunities for economic growth.  The commenter
expressed concern over EPA’s use of epidemiologic studies and
questioned the ability of such studies to provide a reliable evaluation
of health risks.  The commenter claimed that epidemiologic studies are
capable of finding association between a substance or exposure and a
health effect but rarely capable of determining if there is causation,
while toxicological studies using randomized trials are specifically
designed to determine causation.  The commenter added that other factors
providing evidence for causation include dose-response relationships,
consistency, and repeatability of studies, which the commenter said are
not present in the studies cited by EPA.  The commenter specifically
referred to two studies, acknowledged by EPA to show no evidence of a
dose-response relationship gradient between PM2.5 and specific health
related effects.

	We disagree with the commenter’s recommendation that the increments
should be twice the proposed (and final) levels.  The scientific studies
to which the commenter referred pertain to studies that EPA used to
determine the health-based NAAQS for PM2.5, and we do not believe it is
relevant to this rule to respond to comments related to the setting of
the NAAQS.  The NAAQS are designed to protect public health and welfare;
increments then are intended to insure that air quality in clean areas
is not allowed to deteriorate significantly, and the PSD regulations
insure that any such deterioration does not lead to air pollution levels
that exceed the levels defined by the NAAQS.  As discussed previously,
we are finalizing this rulemaking using the safe harbor approach under
section 166(a) of the Act.  Using this approach, we calculated the
“safe harbor” increments as percentages of the NAAQS comparable to
the percentages that Congress used to establish the original statutory
increments for PM and SO2.  These values represent the minimum level of
effectiveness necessary to satisfy section 166(d) of the Act, and could
be tightened if necessary based on further analysis to determine if
additional measures are necessary to fulfill the requirements of section
166(c) of the Act.  Thus, under this approach and on this record, we do
not conclude that it is appropriate to finalize increments at levels any
less stringent than the safe harbor increments, as the commenter
recommends.

Compliance Determinations for the PM2.5 Increments

Modeling Compliance with PM2.5 Increments

	Section 163(a) of the Act provides that “In the case of any maximum
allowable increase … for a pollutant based on concentrations permitted
under the national ambient air quality standards for any period other
than an annual period, such regulations shall permit such maximum
allowable increase to be exceeded during one such period per year
[emphasis added].”  Accordingly, the existing PSD rules allow one
exceedance per year of each short-term increment defined by the rules. 
See, e.g., 40 CFR 51.166(c).  With the addition of the PM2.5 increments
to the list of maximum allowable concentrations in the PSD rules, the
existing provision allowing one exceedance per year applies equally to
the PM2.5 increments as well.  Thus, when modeling increment compliance,
the highest value of the second-highest modeled increase in estimated
PM2.5 concentrations at each model receptor for the 24-hour averaging
time should be less than or equal to the maximum allowable increase for
PM2.5.  For the annual increments, the modeled annual averages should
not exceed the annual maximum allowable increase for PM2.5.  

	We did not expressly state in the 2007 NPRM the implications of adding
PM2.5 increments to the existing list of increments in paragraphs
51.166(c) and 52.21(c) of the PSD regulations.  Nevertheless, it should
have been clear at the time that, in the absence of alternative language
for PM2.5, the existing provision allowing one exceedance for the
short-term increments would apply to the increments for PM2.5 along with
the increments already listed.  We did not receive any comments either
supporting or opposing these methods for determining compliance with the
PM2.5 increments.

	We recognize that the above approach for determining compliance with
the 24-hour PM2.5 increments differs from the approach used for the
24-hour PM2.5 NAAQS, which is based on compliance with the 98th
percentile value monitored concentration (or the highest eighth-highest
modeled concentration at a location).  A similar situation exists for
the 24-hour PM10 increments where compliance with the 24-hour PM10 NAAQS
is based on an expected exceedance form of the standard, resulting in
compliance based on impacts less than a modeled Highest (n+1) Highest
concentration at a receptor location, where n is equal to the number of
years of meteorological data that is used for modeling.  Often 5 years
of meteorological data are used, so that the Highest 6th Highest modeled
concentration is used to determine whether a violation is predicted. 
This inconsistency, however, should not cause complications in carrying
out the required compliance determinations for the NAAQS and increments
for the same pollutant because these determinations are typically
different anyway, based on separate, independent analyses resulting from
the inherently different emissions data bases from which ambient air
quality concentrations are predicted under the NAAQS and increments
analyses.

Condensable PM  

	Initially, the EPA will not require PSD applicants under the federal
PSD program to consider condensable PM in emissions calculations to
determine whether a proposed project is subject to the PSD requirements.
 In addition, we will not require the condensable portion to be
considered in the required PM2.5 air quality analyses either.  In our
May 2008 PM2.5 NSR Implementation Rule, we announced that we would not
require that states address condensable PM in establishing enforceable
emissions limits for either PM10 or PM2.5 in NSR permits until the
completion of a transition period.  Further, we indicated that the
transition period would end January 1, 2011 unless EPA advanced the date
through the rulemaking process.  We also indicated that such rulemaking
would involve the assessment and possible revision of test methods for
measuring condensable emissions and taking comment on an earlier closing
date for the transition period in the NSR program if we are on track to
meet our expectations to complete the test methods rule much earlier
than January 1, 2011.  In addition, states that have developed the
necessary tools are not precluded from acting to include condensable PM
emissions in NSR permit actions prior to the end of the transition
period, especially if it is required in an applicable SIP.  See 73 FR
28321 at 28334 – 28336.

PM2.5 Precursors  

	In the 2007 NPRM, we proposed to add SILs for PM2.5 to the PSD
regulations at 40 CFR 51.166 and 52.21.  (The SILs are described more
fully in section VI of this preamble.)  Accompanying these SILs, we
proposed to add a new paragraph to the regulations explaining that the
requirements for a source impact analysis for PM2.5 would be considered
to be satisfied, without further air quality modeling, if it were to be
shown that the increase in direct PM2.5 emissions from the source or
modification will cause air quality impacts less than the prescribed
SILs for PM2.5.  The reasoning at the time was that state-of-the-art
modeling would not be available to adequately account for secondary
PM2.5 impacts resulting from emissions of precursors of PM2.5, e.g., SO2
and NOx.  Nevertheless, the existing PSD rules currently define
potential precursors of PM2.5.  Based on the proposed language, the
required compliance demonstration for the PM2.5 NAAQS and the PM2.5
increments (when promulgated) would be limited by regulation to an
analysis of direct PM2.5 emissions, and would not include consideration
of emissions of PM2.5 precursors for comparing the modeled source
impacts to the prescribed SILs for PM2.5.

	The impacts of PM2.5 precursors on ambient concentrations of PM2.5
cannot be determined from the dispersion models that EPA has currently
approved for modeling individual PSD sources.  Such models are not
designed to consider chemical transformations that occur in the
atmosphere after the precursor emissions have been released from the
source.  Consideration of these transformations is necessary to be able
to add precursor impacts to the total impact that ambient PM2.5
concentrations have in order to compare the results to the SILs for
PM2.5.  

	The technical tools needed to complete a comprehensive analysis of all
emissions that contribute to ambient concentrations of PM2.5 are only in
the developmental stage; nevertheless, we believe that it would be
inappropriate to restrict the regulatory language in such a way that
future regulatory amendments would be required to enable the inclusion
of precursor impacts in the PM2.5 analysis as the necessary technical
tools become available.  Estimating techniques are being developed that
will be able to be applied to the PM2.5 analysis in the near future,
which could not be required if the regulatory language precluded them. 
We acknowledge the concerns that have been expressed by some commenters
about the shortcomings of not considering the impacts of PM2.5
precursors under the PM2.5 air quality analyses.  Accordingly, we
believe that the new provision for applying the SILs for PM2.5 to the
required analyses for the NAAQS and increments should not be
self-limiting by specifying the use of only direct PM2.5 emissions. 
Instead, the new provision contained in this final rule now enables the
test to be based on “the emissions increase...that would cause...air
quality impacts less than [the SILs].”  See, e.g., new 40 CFR
52.21(k)(2).  We believe that it would be more effective to rely on
interim policy and guidance as appropriate to help determine the best
methods available to make the required assessment of source impacts.    
 

Final Action on Trigger and Baseline Dates for PM2.5 Increments

	In the 2007 NPRM, we proposed as part of Option 1 to require the
implementation of the PM2.5 increment system (annual and 24-hour
increments) with new baseline areas, baseline dates, and trigger date. 
Specifically, we proposed that the major source baseline date and
trigger date, both fixed dates, would be defined as the effective date
of the final rule and would reflect a date 1 year from the date of
publication, in accordance with section 166(b) of the Act.  In contrast,
under Option 2 (both 2A and 2B), we proposed to establish new baseline
dates for the 24-hour PM2.5 increments, but to retain the existing
baseline areas and dates for the annual PM2.5 increments because the
annual increments would be equivalent substitutes for the existing
annual PM10 increments.

	In light of the then-current and expected trends in PM2.5
concentrations, our judgment was that starting with new baseline dates
on or after the effective date of this rule would make the new PSD
increments more protective.  We proposed that any emissions reductions
occurring prior to the effective date of this rule would be counted
toward the baseline concentration rather than be used for expanding the
PM2.5 increment.  If a retroactive baseline date were to apply,
emissions reductions occurring prior to the effective date of this rule
would serve to expand the available increments, enabling more new
pollution than would otherwise be allowed to occur.

	We also expressed our belief that starting with new baseline dates to
implement increments for PM2.5 would be appropriate because Option 1
treats PM2.5 essentially as a “new” pollutant for purposes of PSD
and section 166 of the Act.  We continue to believe that establishing a
new baseline also overcomes significant implementation concerns that
would otherwise exist if the existing PM baseline were maintained.  If
we were to require sources and reviewing authorities to conduct PM2.5
increment analyses based on the minor source baseline dates previously
established under the TSP or PM10 program, they would have to attempt to
recreate the PM2.5 emissions inventory as of the minor source baseline
date in order to determine the baseline PM2.5 concentration for the
area.  For early minor source baseline dates in particular (e.g., 1976
in some areas of the United States), establishing the emissions
inventory for PM2.5 would be extremely difficult, cumbersome, and
potentially inaccurate because historic emissions inventories did not
include PM2.5 emissions.  For all of these reasons, we proposed Option 1
as our preferred option and requested comment on this contingent safe
harbor approach for annual and 24-hour PM2.5 increments under Option 1.

	Under Option 1, we proposed that the PM2.5 increments would be
subjected to a 1-year delay consistent with the procedures under section
166(b) of the Act, which provides in general that these rules “shall
become effective 1 year after the date of promulgation.” 
Alternatively, we sought comment on a 60-day delay as part of our
proposal under Option 1.  In the proposal we requested comment on the
argument that, while the Act includes a 1-year implementation delay for
new increments, the same provision calls for EPA to promulgate new
increments within 2 years of the promulgation of the NAAQS, and given
that these new increments are being promulgated after the 2-year
interval, we expressed our belief that the overall Congressional intent
reflected in section 166 of the Act could possibly be met by advancing
the effective date of the PM2.5 increments. 

	Twelve commenters supported our proposal under Option 1 to establish
new trigger and baseline dates for PM2.5, regardless of the particular
increment option that they otherwise supported.  These commenters
generally saw new dates as being the best approach because of various
problems that would result from retaining existing trigger and baseline
dates.  Some commenters claimed that it would be technically difficult
to try to reconstruct old inventories to determine the amount of PM2.5
emitted by sources in the past.

	One commenter stated that establishing new PM2.5 increment inventories
using existing PM10 baseline dates would be “extremely difficult,
cumbersome, and necessarily inaccurate and unreliable as historic
emissions did not speciate PM2.5 emissions.”  A state/local agency
commenter said that it would be “virtually impossible for States to
calculate the PM2.5 component of previously consumed PM10 increments
because data on the fine and coarse fractions of source emissions are
largely unavailable.”  

	Yet another commenter claimed that “resurrecting PM2.5 inventories
based on the PM10 baseline dates would be insurmountable.”  Similar
comments were echoed by several commenters who supported the use of
legal authority set forth in section 166(f) (“equivalent
substitution” approach) for developing the numerical values for the
PM2.5 increments.  One of these commenters stated that he did not
“believe the establishment of new baseline dates for PM2.5 would
abandon past cases of increment consumption for PM10, because the
24-hour PM10 increments would still be in effect ….”

	One commenter suggested that “EPA establish the trigger date as of
the date when it officially established the non-attainment and
attainment areas for PM2.5; that is, April 5, 2005.”  The commenter
explained that this approach is consistent with the PSD regulations from
their inception and partially mitigates EPA’s delays in implementing
the PSD program for PM2.5.  The commenter believes “that States should
be required to use the baseline areas previously established for their
PSD program, unless the process for redefining these areas strictly
follow procedures in the PSD regulations and EPA policy.”  The
commenter claimed, “this will minimize any inconsistent applications
of the regulations for PM2.5.”  

	One commenter noted that our proposed PM2.5 increments were very low
and “facilities may find themselves immediately out of compliance with
the PM2.5 increments upon promulgation of the rule, based on a January
1975 or 1977 baseline date.”

	One commenter indicated that the historic TSP/PM10 baseline dates
should be retained.  This commenter favored the equivalent substitution
approach and, consistent with that approach, retention of the existing
baseline dates.

	Having considered all the comments, we believe that the most reasonable
approach for addressing the relevant dates associated with the PM2.5
increments is to start anew with the baseline date concept.  As
mentioned earlier, the commenters tended to support our proposed
approach under Option 1 to establish new dates for implementing the
PM2.5 increments even when not supporting the proposed Option 1 approach
for defining increment values, generally citing the difficulties that
would occur if the PM2.5 emissions inventory for increment analyses had
to be created for an earlier period of time.  Also, these new dates will
not undo increment already consumed under the existing increments for PM
because we are not revoking the 24-hour or annual PM10 increments under
this new rule.  Accordingly, this final rule establishes independent
PM2.5 increments using a “trigger date” and “major source baseline
date” that are separate from the dates defined for the PM10
increments.  Consequently, new minor source baseline dates and the
corresponding baseline areas will be used for the annual and 24-hour
PM2.5 increments and will be established when a source applies for a PSD
permit any time on or after the new trigger date for PM2.5.  (See also
the discussion about changes to the definition of “baseline area” in
section V.G., below. of this preamble)   

	The “major source baseline date” for PM2.5 is being set as [INSERT
DATE OF PUBLICATION IN THE FEDERAL REGISTER] — the date of publication
of this final rule.  The setting of this date differs from previous
major source baseline dates which were set as the date of publication of
the proposed rule, but is similar to the major source baseline date set
for the other increments in that the date precedes the effective date
for implementing the increments, and thereby requires that certain major
source emissions increases that occur before the trigger date
retroactively count toward the amount of increment consumed.  

The “trigger date” is being set at [INSERT DATE 1 YEAR AFTER DATE OF
PUBLICATION IN THE FEDERAL REGISTER], which is 1 year after the date of
publication of this final rule.  We are using this approach to define
the date on which the PM2.5 increments become effective as 1 year from
the date of publication, consistent with the 1-year delay required under
section 166(b) of the Act.  This date for the “trigger date”
separates the effective date of the new increments from the effective
date of this final rule in general, but also ensures that the “minor
source baseline date” for PM2.5 for any particular PM2.5 attainment or
unclassifiable area cannot be established until after the increments
become effective in this final rule.  The implementation of these dates
as part of the new PM2.5 increment system is discussed in greater detail
in section VIII of this preamble.  

	We recognize that some may still have a concern about our decision to
set the major source baseline date as the date of publication of this
final rule in light of the fact that the PM2.5 NAAQS have been in place
since 1997; however, we believe that the selection of possible earlier
dates would require states to retroactively establish PM2.5 emissions
inventories for increment analyses during a period when sources were
generally not required to conduct PM2.5 air quality analyses due to the
lack of adequate technical tools and emissions data for PM2.5.  Hence,
we do not believe that it would be appropriate to require states and
sources to retroactively account for PM2.5 increment consumption by
setting the major source baseline date at an earlier date than the date
we have selected.  

Definition of “Baseline Area” for PM2.5

No changes were proposed with respect to the definition of “baseline
area” for PM2.5 increments.  One commenter (0040), however, noted that
fact in claiming that we did not adequately account for significant
impacts of PM2.5 for purposes of defining the “baseline area” for
the PM2.5 increments.  Under the existing regulations, the establishment
of a baseline area for any PSD increment results from the submittal of
the first complete PSD application, and is based on both the location of
the proposed source and the impact of the source’s emissions on the
area.  In accordance with the definition, the attainment or
unclassifiable area in which the proposed source would construct is
always part of the baseline area in which the minor source baseline date
is established and the increment analysis is conducted.  In addition,
the definition provides that any surrounding attainment or
unclassifiable area in which the proposed source’s impact is greater
than 1 µg/m3, annual average, would also become part of the baseline
area, assuming the area had not already been established as a baseline
area by a previous application for a PSD permit.  See, e.g., 40 CFR
52.21(b)(15).  

	As explained in the preamble for the 1980 PSD regulations, EPA selected
an impact of 1 µg/m3, annual average, for the definition of “baseline
area” because that value was considered the level of significance for
both SO2 and PM when the definition was originally established.  There
was no mandate at that time that a 1 µg/m3 impact be used to determine
the baseline area for increments for other pollutants; however, the use
of a 1 µg/m3 impact in the definition of “baseline area” was not
changed when EPA developed increments for NO2 in 1988 because EPA also
defined “significant” for NO2 using the same annual average
concentration of 1 µg/m3.  The EPA has determined, however, that
“significant” for PM2.5 ambient impacts should be considered to
occur at a lower concentration than 1 µg/m3.  Elsewhere in this
preamble, we have indicated that the SIL for PM2.5 in this final rule is
0.3 µg/m3, annual average.  Consequently, although no change to the
definition of “baseline area” was proposed in this rule, we believe
it is necessary and appropriate to define in this final rule a level of
significance of 0.3 µg/m3, annual average, for establishing a new
baseline area for purposes of PM2.5 increments.  See e.g., revised 40
CFR 52.21(b)(15)(i).  Had we established the SIL at 1 µg/m3, annual
average, as proposed under Option 1 for SILs, then the definition of
“baseline area” would not need to be revised.  However, the revised
definition in this final rule is consistent with our decision to
establish a SIL of 0.3 µg/m3, annual average, for PM2.5.  We consider
this action to be a logical outgrowth of our decision to establish a SIL
for PM2.5 and the comment concerning the effect of that action on the
definition of “baseline area.”  Thus, we believe that our failure to
initially propose this change to the definition of “baseline area,”
based on the possibility of selecting Option 3 for defining the SIL for
PM2.5, does not warrant a reproposal.

No Final Action with Respect to the Proposed Revocation of PM10 Annual
Increments

	In the 2007 NPRM, we proposed to either revoke or replace the annual
increments (Class I, II, and III) for PM10 to conform to the earlier
revocation of the annual PM10 NAAQS.  We proposed to revoke the annual
increments, based on the same technical evidence that led us to revoke
the annual PM10 NAAQS, if we decided to use Option 1 for adopting PM2.5
increments, and discussed our authority and rationale for doing so.  72
FR 54136.  In comparison, we proposed to replace the existing annual
PM10 increments with equivalent substitute PM2.5 increments using the
authority under section 166(f) of the Act.  After further analysis and
consideration of the comments on this issue, we have decided not to take
final action on our proposal to revoke those increments for PM10 as part
of this rulemaking.  The effect of not taking final action with respect
to the PM10 annual increments is to leave those increments in place and
unchanged.

	Three commenters agreed with EPA’s proposal to “adopt the 24-hour
and annual PM2.5 increments and to revoke the annual PM10 increments.”
 One commenter stated, “counting and tracking increment is confusing
enough without adding the confusion of potentially overlapping PM
standards.”  The commenter noted that the “cleanest approach is to
establish a single new PM2.5 increment and work from there.”  The
commenter suggested that EPA first “develop a coarse fraction
increment, once EPA establishes coarse PM NAAQS.”  The commenter added
that the removal of the PM10 annual increment is supported by the
removal of the “health based standard for annual PM10.”

	One of the commenters agreed, “it makes no sense for EPA’s
regulations to contain an annual increment for PM10 even though an
annual PM10 NAAQS no longer exists.”  The commenter added, “EPA is
without authority under Section 166(f) to retain the PM10 annual
increment if it adopts a PM2.5 annual increment.  This commenter
explained, “EPA is compelled by law to eliminate the PM10 annual
increment.”

	We agree with this commenter that section 166(f) is a
“substitution” approach; however, as we stated in our 2007 NPRM, we
expressed some concern about using section 166(f) to substitute PM2.5
increments for PM10 increments.  In fact, some commenters challenged our
authority under section 166(f) to replace the PM10 increments.  In our
response to the following comments, we address the legal issues that we
believe prevent us from simply revoking the PM10 increments.    

   	One environmental commenter (0040) claimed, “the agency has no
authority to repeal an existing PM10 increment without at the same time
restoring the corresponding TSP increment.”  The commenter noted,
“Congress established the TSP increments by statute and gave EPA no
authority to revoke them,” and “instead, Congress gave EPA only
limited authority to substitute PM10 increments for TSP increments under
the conditions specified in Section 166(f).”  The commenter explained,
“EPA cannot revoke the annual PM10 increments, either by
“replacing” them with PM2.5 increments or otherwise, unless EPA at
the same time restores the annual TSP increment.”  The commenter
noted, “retention of the PM10 annual increment is also entirely
compatible with the statutory purposes, notwithstanding EPA’s
revocation of the annual PM10 NAAQS.”	The commenter further noted the
following examples/evidence “that retention of the annual PM10
increments is important to achieving the goals of the Act’s PSD
provisions.”  

“While EPA attributes the visibility impairing impacts of PM pollution
primarily to elevated short term fine particle concentrations, EPA
recognizes that PM10 plays a significant role in the other welfare
related impacts of PM pollution.”  72 FR 54136. 

“EPA also states that the most significant PM-related ecosystem-level
effects result from long term cumulative deposition . . . that exceeds
the natural buffering or storage capacity of the ecosystem and/or
affects the nutrient status of the ecosystem.”  72 FR 54131. 

	Five state/local agency commenters opposed the revocation of PM10
annual increments “until EPA makes a determination on a PM-coarse
NAAQS” and/or “establishes equivalent increments for PM-coarse.” 
One of these commenters added, “it is prudent to maintain the PM10
increments until EPA makes a determination on the health and
environmental effects of the coarse fraction of PM.”  The commenter
claimed that, “if EPA retains the annual PM10 increments” “then
the determination of PM2.5 increments can complement the continuation of
PM10 increment determinations without any discontinuities or unwanted
degradation concerns.” 

	Another one of these commenters stated, “the basis for dismissing the
annual PM10 NAAQS by the substitution of fine particle NAAQS to address
certain health and welfare effects does not provide a basis for
dismissing a PSD increment which is meant to stop significant
degradation of air quality.”  The commenter noted, “as refinements
are made to estimation of fine particle emissions or in instances where
these are deemed not to be a major component of particulate emissions,
the PM10 annual increment could prevent long term deterioration of air
quality associated with the coarse component.”  The commenter added,
“it is prudent for EPA to retain the PM10 increment until such time
that it makes a final determination on the coarse component of
particles.”  

	One state/local agency commenter (0019) noted, “EPA also proposes to
replace the PM10 annual increment with the corresponding PM2.5 increment
under the Section 166(f) options 2A and 2B as well, but does not provide
a substantive basis for such an action.”  The commenter (0019) does
“not see the tension noted by EPA between Sections 166(a) and (f) with
respect to reaching a holistic solution if EPA views PM2.5 as a new
indicator of PM, as we believe it can.”  The commenter (0019)
explained, “under this approach, if EPA determines that coarse
particle levels are necessary to protect the public from certain
exposures not addressed by PM2.5, then it will be appropriate for EPA to
define complementary increments for coarse particulates as another
indicator of PM.”  The commenter also asserted that the 24-hour
increments for PM2.5 must be based on section 166(f) authority, but
believes that the PM2.5 increment need not replace the PM10 increment
for this averaging period.

	One commenter (0028) requested that EPA “keep the PM10 PSD program
(especially the increments) in place until the full PM2.5 program is
adopted and in place.” 

	One commenter (0033) “does not support revoking the annual PM10
increments,” because the commenter feels that “there are too many
uncertainties regarding PM2.5.”  The commenter (0033) provided the
following example: “the program has been dragging for years,
analytical methods are not formulated, the NSR part of the
implementation rule has not issued, condensables are not yet included,
and the impact of precursors has not been definitively explored.”  The
commenter (0033) explained that “under these conditions, nothing
concerning PM10 should be revoked until the reasons for doing so are
clearly understood and the overall impact on ensuring clean air and the
public health and welfare have been fully explored.”  The commenter
suggested, “PM10 increments and NAAQS should remain in effect until
these issues have been resolved to the satisfaction of the
Administrator.”  This commenter believed that Options 2A and 2B must
be based entirely on section 166(f) of the Act, but that the presence of
increments for both PM10 and PM2.5 can be supported under this section
because the two sets of increments complement each other.  The commenter
indicated that the problem will be resolved when sufficient data are
available to revoke the PM10 NAAQS and increments and/or PM10 is
replaced by PM10-2.5.

	One state/local agency association commenter (0021) recommended that
“EPA can and should continue both the 24-hour and annual average PM10
PSD increment program until PM10-2.5 standards are promulgated.”  The
commenter (0021) explained that “EPA has the discretion to accomplish
this under CAA §166(f)” and “at a minimum, the agency should
continue the 24-hour PM10 increments in conjunction with the
continuation of the 24-hour PM10 NAAQS.”

	As stated previously, in this rule we are taking no final action on our
proposal to revoke the annual PM10 increments even though the annual
PM10 NAAQS has been revoked.  Based on comments and our own legal
analysis of the PM10 increments, we have concluded that there is a
strong legal basis for not revoking the annual increments at this time. 
The PM10 increments were promulgated on June 3, 1993 (58 FR 31622) as
replacement increments for the then existing statutory increments for PM
measured as TSP.  The fact that EPA promulgated the PM10 increments as
“equivalent” replacements for the TSP increments under the authority
of section 166(f) of the Act is important in that EPA does not have
authority to simply remove the TSP increments that were explicitly
defined within the PSD program requirements in the Act.  Accordingly, we
believe that the annual TSP increments would be restored by default
should we decide to revoke the annual PM10 increments as proposed. 
However, even if the original annual TSP increments were not restored,
there is no basis for automatically revoking the annual PM10 increments
simply because we have revoked the annual PM10 NAAQS, because annual
increments are not contingent upon the existence of annual NAAQS.  This
is clear from the court’s decision in the earlier NO2 increment
litigation stating that increments for a particular pollutant do not
necessarily need to match the averaging periods that have been
established for NAAQS for the same pollutant.  Environmental Defense
Fund, Inc. v. EPA, 898 F.2d 183, 189-190 (D.C. Cir. 1990)(“… the
‘goals and purposes’ of the PSD program, set forth in § 160, are
not identical to the criteria on which the ambient standards are
based.”)

Other Comments on Increments

	Ten commenters (four state/local agencies (0019, 0025, 0028, 0033), two
state/local agency associations (0018, 0021), two industry commenters
(0031, 0042), and two industry associations (0034, 0039)) supported
section 166(f) of the Act as the basis for PM2.5 increments.  These
commenters typically voiced the belief that when Congress enacted
section 166(f), it authorized EPA to update PM increments when another
indicator was defined, and that section 166(f) allows EPA to continue do
so as long as these increments are of equal stringency to the prior
increments.  Some of these commenters believe that section 166(f) is the
only legitimate approach under the Act, while others indicated simply
that it is preferable to section 166(a).  Some of the commenters believe
that section 166(f) authority can be used to add PM2.5 increments to the
existing PM10 increments.  Others believe that PM2.5 increments
finalized under section 166(f) must fully replace the existing PM10
increments, and recommended doing so.

	For the reasons discussed previously in this preamble, EPA has decided
to finalize the PM2.5 increments under the authority of section 166(a)
of the Act.  With respect to the potential creation of PM2.5 increments
under section 166(f) (as discussed in the 2007 NPRM at 72 FR 54120 –
54121), we have not reached any final conclusion as to whether that
approach is authorized by the statute, but believe that such an approach
raises significant legal issues.  Because the Agency is not relying on
section 166(f) in this rulemaking, we do not address these issues in
this preamble, though some additional discussion is included in the
Response to Comments document for this rule. 

	One industry association (0029) that supported the Option 1 approach
based on section 166(a) authority also acknowledged that EPA is
authorized to use the Option 2 approach based on section 166(f)
authority.  An industry commenter (0043) indicated that 2007 NPRM’s
arguments regarding the alternative legal authorities under section
166(a) and (f) were not compelling; the commenter recommended setting
the PM2.5 increments at the levels proposed as Option 2B because they
would have the lowest economic impact.

	As noted previously, we have decided to finalize Option 1 based on
section 166(a) authority because we believe that provision provides the
clearest statutory authority for purposes of developing the new
increments based on PM2.5.  We would point out, however, that any
conclusion as to which option would yield increments that “have the
lowest economic impact” must include a consideration of not only the
levels of the increments but also the associated baseline dates that
define when emissions changes must be considered to affect the amount of
increment consumed.  Under options 2 and 3, the PM2.5 increments would
be regarded as replacement increments for the PM10 increments and, as
such, would include amounts of increment (based upon the PM2.5
component) already consumed under the existing PM10 increment system. 
Thus, portions of the substitute PM2.5 increments could have already
been consumed by previous PSD sources that emit PM.  If, in fact, a
portion of the PM2.5 increments have already been consumed by the prior
PM10 increment consumption process, than there would be a basis to
conclude that less additional economic growth would be allowed under a
set of replacement PM2.5 increments as compared to PM2.5 increments
based on separate, independent baseline dates.  	

	One industry commenter (0016.1) suggested that EPA develop geographic
area-specific increments (and SILs and SMCs) that take local conditions
into account.  The commenter pointed out that PM2.5 levels in PSD areas
proximate to international borders may be elevated by sources outside
the legal and practical control of the United States and state
authorities.  The commenter also noted that PM2.5 levels may be elevated
by natural conditions, such as drought, fires, geologic formations
(sandy or fine-grained surface features), high winds, etc., leading to
excessively dusty ambient conditions over which the local area has no
control.  The commenter indicated that local area baselines must reflect
these PM emissions, though they are not reflected in the local area’s
emissions inventory.  The commenter urged EPA not to penalize such PSD
areas by imposing uniform national PSD increments (or SILs or SMCs)
where the conditions of concern are not capable of control.

	As previously discussed, this final rule establishes an area
classification system with prescribed, uniform PM2.5 increments for each
class.  We do not believe that it is necessary to develop different
increments (or SILs or SMC) for different areas of the country. 
Emissions from natural conditions such as those described by the
commenter would not consume increment, provided that they remain
constant from the baseline period onward due to their natural and
temporary nature (i.e., increased emission from such sources do not
result from changing land use after the minor source baseline date).  In
addition, if a state wishes to disregard new emissions from sources
outside the United States, the state’s PSD program may provide that
such emissions do not consume increment (see 40 CFR 51.166(f)(1)(iv)).

Final Action on PM2.5 SILs

EPA’s Determination on SILs for PM2.5

It is EPA’s longstanding policy to allow the use of the SILs as de
minimis thresholds under the NSR programs at 40 CFR 51.165(b) and part
51, Appendix S, to determine whether the predicted ambient impact
resulting from the emissions increase at a proposed major new stationary
source or modification is considered to cause or contribute to a
violation of the NAAQS.  As described in section IV.D of this preamble,
we have also allowed the SILs under the PSD program to determine: (1)
when a proposed source’s ambient impacts warrant a comprehensive
(cumulative) source impact analysis; (2) the size of the impact area
within which the air quality analysis is completed, and (3) whether the
emissions increase from a proposed new major stationary source or major
modification is considered to cause or contribute to a violation of any
NAAQS.  

We proposed three separate options for setting SILs for PM2.5.  The
first option relied upon the same approach we proposed for PM10 in the
1996 NSR Reform proposal.  This set included Class I SILs set at 4
percent of the Class I PM2.5 increments.  For class II and III areas, we
proposed to codify the SIL values that already existed for PM10, i.e.,
1.0 µg/m3 (annual) and 5.0 µg/m3 (24-hour).  Options 2 and 3 relied on
scaling the PM10 SILs, as codified in 40 CFR 51.165(b), by a particular
ratio.  Specifically, for Option 2, the multiplier was the emissions
ratio of PM2.5 to PM10 for point sources in the 1999 NEI; for Option 3
the multiplier was the ratio of the PM2.5 NAAQS to the PM10 NAAQS.  The
resulting SILs were proposed as follows:   

Option	Proposed SILs (µg/m3)

	Class I	Class II	Class III

	Annual	24-hr	Annual	24-hr	Annual	24-hr

1	0.04	0.08	1.0	5.0	1.0	5.0

2	0.16	0.24	0.8	4.0	0.8	4.0

3	0.06	0.07	0.3	1.2	0.3	1.2



	We have decided to finalize the PM2.5 SILs proposed under Option 3.  As
explained earlier, these values will be used in the federal PSD
preconstruction review process consistent with our proposal.  See 72 FR
54122 at pages 54138-41 and 54143.  

States are not required to adopt SILs in their NSR or PSD programs; the
analyses for PM2.5 required by each applicable regulation can be carried
out without using a SIL.  Therefore, we do not intend for any specific
deadlines to apply under the regulations at 40 CFR 51.165(b), 51.166, or
part 51, Appendix S for states to submit SILs for PM2.5, should they
choose to do so, as part of their revisions to incorporate the final
rules for PM2.5 into SIPs.  Nonetheless, we believe that the
availability of SILs as a screening tool greatly improves PSD program
implementation by streamlining the permit process and reducing labor
hours necessary to submit and review a complete permit application where
the projected impact of the proposed source is de minimis in the
relevant area.  For these reasons, we are including the PM2.5 SILs in
the federal PSD regulations at 40 CFR 52.21 to screen proposed projects
concerning the need for a cumulative source impact analysis for PM2.5.  

Response to Comments Concerning the SILs 

The primary purpose of the SILs is to identify a level of ambient impact
that is sufficiently low relative to the NAAQS or increments that such
impact can be considered trivial or de minimis.  Hence, the EPA
considers a source whose individual impact falls below a SIL to have a
de minimis impact on air quality concentrations that already exist. 
Accordingly, a source that demonstrates that the projected ambient
impact of its proposed emissions increase does not exceed the SIL for
that pollutant at a location where a NAAQS or increment violation occurs
is not considered to cause or contribute to that violation.  In the same
way, a source with a proposed emissions increase of a particular
pollutant that will have a significant impact at some locations is not
required to model at distances beyond the point where the impact of its
proposed emissions is below the SILs for that pollutant.  When a
proposed source’s impact by itself is not considered to be
“significant,” EPA has long maintained that any further effort on
the part of the applicant to complete a cumulative source impact
analysis involving other source impacts would only yield information of
trivial or no value with respect to the required evaluation of the
proposed source or modification. 

	While some commenters opposed all of the proposed options for PM2.5
SILs, most commenters generally supported the use of a SIL as a
screening tool for PM2.5 air quality analyses.  Commenters who supported
one of the proposed options for the SILs were divided as to their
support of a particular approach for selecting the SIL value, with each
option receiving some support.  Commenters also tended to agree that the
SILs should not be used for determining significant impacts on AQRVs in
Class I areas.  	

	Those commenters supporting the concept of the SILs, yet opposing all
proposed options, believed that all options yielded SILs that were too
low.  Another commenter, an environmental group, presented extensive
legal and policy arguments against the SILs concept in general.  Some of
the significant comments and our responses to them are addressed herein,
while others are covered in the Response to Comments document which we
have placed in the docket for this rulemaking.  

Legal Basis for SILs

	One commenter opposed all three proposed options on both legal and
policy grounds claiming that EPA has no legal authority to promulgate
SILs and that the de minimis doctrine endorsed by the court does not
apply to increment analyses, where Congress has expressly directed that
the letter of the law applies in all circumstances, as it has in this
case.  (The commenter’s policy concerns about SILs are discussed later
in this section of this preamble.)  The commenter stated that
“Congress codified increments in section 163 of the Act, directing
that SIPs contain measures assuring that the increments shall not be
exceeded.”  According to the commenter, “The Act plainly provides
that no major source may be constructed unless it meets this
requirement, and may not contribute to an exceedance ‘for any
pollutant in any area.’”  The commenter further stated that “the
de minimis doctrine is inapplicable because it applies only where the
regulations will yield a gain that is demonstrably trivial or zero.”  

We disagree with this commenter’s claim that there is no legal basis
for SILs.  As stated in the 2007 NPRM, the concept of a SIL is grounded
on the de minimis principles described by the court in Alabama Power Co.
v. Costle, 636 F.2d 323, 360 (D.C. Cir. 1980).  In this case reviewing
EPA’s 1978 PSD regulations, the court recognized that “there is
likely a basis for an implication of de minimis authority to provide
exemption when the burdens of regulation yield a gain of trivial or no
value.”  636 F.2d at 360.  See the 2007 NPRM preamble for more on how
we have applied the de minimis principle in the past.

Levels of the SILs

	Several commenters opposed all three proposed options on the grounds
that all yielded levels of SILs that are too low.  One of these
commenters argued that the proposed SILs “imply a level of monitoring
and modeling sophistication that is currently absent in our regulatory
scheme.”  This commenter recommended that EPA “rethink the level of
the proposed SILs and select concentrations less likely to be within the
level of error inherent in current monitoring and modeling methods.”  
We disagree with these commenters’ concerns about all the proposed
SILs being too low.  While we did not select the Option 1 levels, the
Class II and III SILs for PM2.5 are the same ambient concentration
levels that are used for the SILs for the other criteria pollutants
under 40 CFR 51.165(b), and those existing SILs values are associated
with NAAQS that are considerably higher than the NAAQS for PM2.5. 
Clearly, it would have been inappropriate to select Class II and III
SILs for PM2.5 that represent relatively higher values than the existing
SIL values for other pollutants in light of the more stringent NAAQS
levels that exist for PM2.5.  We also disagree that the SILs should be
consistent with current monitoring capabilities for PM2.5.  The SILs are
a screening tool used in comparison with modeled predictions — not
monitored concentrations — of PM2.5.  Monitoring accuracy is not a
relevant concern in predicting with air quality dispersion models the
concentrations of a pollutant that a source will cause if its
construction and operation are allowed to occur.

	Two commenters expressed concern about national de minimis values.  One
stated that “the idea that a single national number can define
‘trivial’ is flawed, given that even very small impact can be of
great significance in an area that is close to an increment or NAAQS.”
 The other commenter recommended that EPA “develop geographic
area-specific … levels that take local conditions into account.” 
This commenter reasoned that some PSD areas “should not be
‘penalized’ by a single, national PSD increment, significant impact
levels and significant monitoring level, where the conditions of concern
are not capable of control.” 

With regard to the first of these commenters, our longstanding policy
has been that when a source has a de minimis impact on an existing air
quality problem, that source should not necessarily be required to bear
the burden of addressing its small contribution to a problem caused
primarily by other sources.  However, notwithstanding the existence of a
SIL, permitting authorities should determine when it may be appropriate
to conclude that even a de minimis impact will “cause or contribute”
to an air quality problem and to seek remedial action from the proposed
new source or modification.  For example, where a proposed modification
to an existing major stationary source would have what is normally
considered to be a de minimis impact on air quality but would
nevertheless result in air quality concentrations exceeding the NAAQS or
increments, it might be appropriate to require the source to take
remedial action despite its “de minimis” contribution.  This could
be the case if the review authority finds that the source’s existing
(that is, pre-modification) emissions are not being sufficiently
controlled and the source is a primary contributor to the overall air
quality problem.

	We do not agree with the second of these comments concerning the
development of regional SILs based on a concern that some amounts of
PM2.5 in a particular area are “not capable of control.”  The PM2.5
SILs define a threshold level for determining whether a predicted
ambient impact by a proposed major stationary source or major
modification of PM2.5 needs to undergo a more thorough analysis of the
PM2.5 NAAQS or increments.  This value is not directly affected by the
total amounts of PM2.5 that may exist in an area or by what causes the
existing PM2.5 concentrations, rather by the impact of a single source
relative to the levels of the NAAQS and increments that must be
protected.  Therefore, we do not see why the SILs should be influenced
by the geographic area of concern, or how different levels of SILs for
the same pollutant and averaging period would be necessary.

	With regard to the commenters that supported at least one of the
proposed SILs options, they generally did not prefer the entire suite of
SILs (Class I, II, and III SILs) from a single option, but instead
supported parts of different options, primarily divided by drawing a
distinction between the Class I SILs and the SILs for Class II and III
areas.  Consistent with the way that commenters addressed the Class I,
II, and III SILs, we will address the comments separately herein as
well.

Class I SILs

	Support and opposition for the proposed PM2.5 SILs for Class I areas
was fairly evenly divided.  The PM2.5 SILs for Class I areas proposed
under Option 2 received the support of some commenters, but also
received an equal amount of opposition.  Option 1, which yielded the
lowest (most restrictive) values for the Class I area SILs for PM2.5
(annual and 24-hour averages), was supported by some commenters,
including a federal agency that serves as a FLM for federal Class I
areas under the PSD program, but was equally opposed.  Finally, comments
supporting the Class I SILs proposed under Option 3 (from which we
derived the values included in the final rules) were matched by comments
that opposed the Class I SILs under Option 3.

 	One commenter (0043) opposing the Option 3 SILs for Class I areas said
that the values “appear to be unrealistically low and, if selected,
would point to the need for EPA to conduct an economic impact
analysis.”  We disagree that adopting the Option 3 SILs for Class I
areas (and Class II and III areas) will result in economic impacts
significant enough to warrant an economic impact analysis.  Under the
Paperwork Reduction Act, EPA is required to analyze, and receive
approval from the Office of Management and Budget for, the recordkeeping
and reporting burden imposed by its regulations (referred to as the
“Information Collection Request” for the regulation).  For the PSD
program, this includes the burden associated with the entire permitting
process, including any required modeling analyses.  In our analysis for
this rulemaking, we have concluded that the number of PSD permits issued
annually will be unchanged (at an estimated 274 per year), while the
total burden across all PSD permit applicants of adding PM2.5 analyses
will increase by a total of approximately 29,000 hours per year at a
cost of approximately $2.8 million per year.  This total annual impact
on industry is a small fraction of the threshold ($100 million per year)
that is considered “significant” under Executive Order 12866
(Regulatory Planning and Review) and the Unfunded Mandates Reform Act. 
See sections X.B and X.D of this preamble for more on the Paperwork
Reduction Act and the Unfunded Mandates Reform Act, respectively.  Our
analysis of the recordkeeping and reporting burden of this rulemaking
can be found in the docket for this Information Collection Request.

	Another commenter (0037) stated that the use of a NAAQS-based ratio
under Option 3 for the proposed SILs does not “translate back to the
emissions point level when comparing PM10 and PM2.5.”  This commenter
continued, “this is an invalid method of proceeding because EPA has
not shown that there is a correlation between the NAAQS and direct PM2.5
since there is no accounting for precursors and EPA does not have a
quantifiable sense of the portion of PM2.5 that is condensable for
various industries.”

	We disagree with the commenter’s concern that the use of NAAQS-based
ratios is an invalid method for developing the PM2.5 SILs.  The purpose
of using the NAAQS ratio with the PM10 SILs to develop PM2.5 SILs is to
establish values that have a comparable relationship between ambient
concentrations of PM10 and PM2.5 and their respective NAAQS levels. 
Whether a particular ambient concentration of PM2.5 results from direct
PM2.5 emissions or from precursor emissions is not relevant to this
particular approach.  The PM2.5 SILs in this final rule are intended to
be compared to the ambient concentrations of PM2.5 that are predicted by
modeling the emissions of a proposed new project.  Ambient
concentrations of PM2.5 can be the result of direct PM2.5 emissions,
which may include condensable particulate matter, as well as precursor
emissions, e.g., SO2 and NOx.  

	We note that the 2007 NPRM included proposed regulatory language
providing that demonstrations of whether the air quality impact of a
major new source or modification would be less than the PM2.5 SILs be
based on direct PM2.5 emissions from the proposed project.  The intent
of this was to recognize the technical limitations associated with
modeling precursor emissions to predict ambient PM2.5 impacts.  However,
in this final rule we have removed that limitation by removing the
reference to “direct” PM2.5 emissions.

	One commenter (0029), who did not support any of the proposed SILs
options, was especially critical of the Class I SILs for PM2.5 under
Option 1, stating that multiplying the proposed PM2.5 increment by 4
percent is without legal or practical merit.  The commenter stated that
just because “4 percent may have been a reasonable multiplier to use
in establishing a significant emission rate threshold does not mean that
the multiplier should be used for a completely different regulatory
purpose.”  The commenter added that if the PM2.5 SILs for Class I
areas under Option 1 were codified, emissions from even the most
well-controlled coal-fired electric generating station located as far
away as 300 km from a Class I area could well exceed the threshold.

	In contrast, the federal agency commenter supporting the PM2.5 SILs for
Class I areas under Option 1 explained that they analyzed the
effectiveness of the three sets of proposed SILs by modeling four
different coal-fired power plant scenarios using an EPA-approved
long-range transport model.  The modeled plants included a large 1,500
MW facility, a moderate-sized 500 MW facility, and two medium 800 MW
facilities.  Based on this modeling analysis, the commenter concluded
that the proposed levels of the Class I 24-hour SILs based on Option 1
and Option 3 are “more appropriately protective of the proposed Class
I PM2.5 increment and impacts to visibility than the level obtained
under Option 2.”  This commenter supported the consistency of using 4
percent of the Class I increments that was used by EPA in proposing
Class I SILs for SO2, NOx, and PM10 in 1996.

	We chose the Class I SILs under Option 3 because we believe that this
option yields the most appropriate combination of SILs for all area
classifications.  Whether a particular source will have a significant
impact on an area is determined to some extent by the amount of its
emissions, but also by other factors such as the height of release,
pollutant transport distance, terrain features, and meteorological
factors.  Thus, we did not select SILs values to address a certain size
source or the degree of control of that source, but the ambient impact
of that source relative to the NAAQS and increments that will result
from the source’s emissions.  While the annual Class I SIL under
Option 3 represents a level that is somewhat greater than 4 percent of
the PM2.5 annual increment for Class I areas, it is sufficiently close
(as derived from a ratio of the PM2.5 NAAQS to the PM10 NAAQS) so as to
provide a reasonable threshold for defining de minimis for purposes of
conducting a Class I increment analysis.  We had proposed the use of 4
percent of the existing Class I increments to develop SILs for
pollutants in a 1996 NPR for a PSD rulemaking; however, that particular
component of the proposal was never finalized.  See 61 FR 38250
beginning at page 38291.  We will further discuss our rationale for
selecting the SILs under Option 3 in the discussion which follows for
the Class II and III SILs.

Class II and III SILs    

While many commenters tended to favor Option 2 with regard to the
proposed Class I increments, they tended clearly to support Option 1 for
defining Class II and III SILs for PM2.5.  These particular SILs for
PM2.5 were proposed so as to be equal to the existing Class II and III
SILs for the existing pollutants (e.g., SO2, PM10, NOx).  In all, six
commenters supported Option 1.  One of these commenters stated that
Option 1 SILs for Class II and III areas are “sufficiently stringent
and fully consistent with the de minimis justification for SILs.”  The
commenter added that “when conducting an air quality impact analysis
… most applicants assume all coarse PM10 to be PM2.5.”  The
commenter claimed that this assumption is conservative and
“overestimates the amount of fine particles being emitted and renders
the effective SIL thresholds for PM2.5 lower than those written into the
regulations.” 

We strongly disagree that the SILs proposed under Option 1 as applied to
PM2.5 are sufficiently stringent.  The application of such values as
SILs for PM2.5 would result in ambient concentrations of PM2.5 that
consume a much larger portion of both the PM2.5 NAAQS and increments
than either of the other two options proposed for PM2.5 in light of the
correspondingly more stringent levels of the PM2.5 NAAQS and increments
than those for the other pollutants.  We believe that of the 3 options
proposed, the PM2.5 SILs based on Option 3 represent values that are
more closely aligned percentage-wise with the SILs that have been or are
being used for other forms of PM when compared to their respective NAAQS
and increments.

We also disagree with the commenter’s suggestion that the development
of the SILs for PM2.5, or any other pollutant, should in any way be
influenced by the possibility that some sources may use conservative
techniques for estimating a source’s emissions rate.  Such
conservative techniques may be needed on an interim basis while
technical issues associated with the calculation of PM2.5 emissions
exist, and can certainly be used at any time as a simplified methodology
for estimating PM2.5 emissions.  But when such an overly conservative
approach fails to yield de miminis results, the source may find it
necessary to rely upon more accurate techniques for determining the
amount of PM2.5 that the source will emit.  

	Finally, one commenter, objecting to all of the proposed SILs, stated
that EPA must assure that SILs are truly de minimis and must also
include limitations on the use of SILs as necessary to prevent air
quality from significantly deteriorating.	 We acknowledge that we did
not conduct any new modeling or other types of analyses of the proposed
SILs in order to explicitly show that the final PM2.5 SILs values in
this final rule are de minimis.  Instead, we have relied on past actions
regarding the setting of de minimis levels to illustrate that the PM2.5
values selected via Option 3 represent values that are as stringent as
the previous levels that have been established to define de minimis for
PM10 and TSP.  See 45 FR 52676, 52706-708 (August 7, 1980)(using
modeling and representative data).  

Using the 24—hour and annual NAAQS ratios of PM2.5 to PM10, and
multiplying them by the corresponding existing PM10 SILs, we are assured
that the PM2.5 SILs define de mimimis for the PM2.5 NAAQS in the same
way as the PM10 SILs do for PM10 NAAQS.  With regard to the increments,
the annual and 24-hour PM2.5 SILs represent about 7.5 and 13 percent of
the annual and 24-hour PM2.5 increments, respectively.  By comparison,
the annual and 24-hour PM10 SILs represent about 5 and 17 percent of the
annual and 24-hour PM10 increments, respectively.  We believe the PM2.5
SILs fall into a comparable relative range with the PM10 SILs and can be
considered de minimis.

     In EPA’s 1980 final rule for PSD, EPA adopted significant
emissions rates for the pollutants then subject to regulation under the
PSD requirements.  The significant emissions rate adopted for PM (then
measured as TSP) was 25 tpy, which represented an emissions rate for
which EPA modeled impacts that represented about 4 percent of the TSP
24-hour NAAQS and about 28 percent of the 24-hour TSP increment.  Thus,
EPA considered it acceptable under the de minimis assessment for PM that
a source of particulate matter capable of consuming around 28 percent of
the applicable 24-hour TSP increment could be exempted from the
requirements to complete a comprehensive source impact analysis for the
PM NAAQS and increments.  45 FR at 52708.

	In looking at the amount of increment that could be consumed by a
source that is ultimately exempted from having to complete a
comprehensive modeling analysis, it should be pointed out that the
maximum modeled concentration typically occurs in a relatively limited
area, as compared to the entire modeling domain.  In particular, for the
short-term averaging periods, such as the 24-hour averaging period,
modeled concentrations across the modeled area generally drop off from
the peak value fairly rapidly, so that the peak modeled concentrations
represent the source’s impact at only a relatively few receptors
within the modeled area.  In addition, it is important to note that the
temporal and spatial conditions which lead to a maximum impact by one
source are seldom the same for other sources, such that maximum impacts
of individual sources do not typically occur at the same location.

Thus, in an area where several sources can demonstrate that their
modeled impacts are de minimis, it generally should not be assumed that
their individual maximum (albeit de minimis) impacts on the increment
are additive.  For example, four sources with de minimis PM2.5 impacts,
each consuming 12 percent of the 24-hour PM2.5 increment, would not
necessarily consume almost half of the 24-hour increment.  Increment
consumption is determined by the cumulative impact of source emissions
on each individual receptor or modeling point in the area of impact
within the baseline area defined for the affected PSD sources.  

	The preamble for the August 7, 1980 final rule for PSD included a
description of a modeling analysis that EPA conducted to illustrate that
a number of major sources each making only a de minimis emissions
increase for SO2 could locate in an area (in that case, the Dayton area)
and not cause a violation of either the applicable SO2 increment or
NAAQS.  In that particular case, the modeling indicated that the maximum
aggregate increment consumption for 37 sources emitting 40 tpy of SO2
(the de minimis emissions rate for SO2) would have a cumulative impact
at any location of less than 1.5 µg/m3 on a 24-hour basis—well below
the NAAQS and increments for SO2.  45 FR 52708.

	With regard to the commenter’s recommendation that we place
limitations on the use of SILs, we earlier provided an example of when
it might be appropriate to require a modified source to mitigate its
contribution to a violation of a NAAQS or increment even when the
predicted ambient impact of the proposed emissions increase would result
in what is normally considered to be de minimis.  In addition, we have
historically cautioned states that the use of a SIL may not be
appropriate when a substantial portion of any NAAQS or increment is
known to be consumed.  We have indicated elsewhere in this preamble that
States are not required to adopt the SILs for PM2.5 in this final rule. 
At their discretion they may choose not to rely on SILs to screen
applicants or they may establish more stringent values contingent upon a
demonstration that such values represent de minimis values for their
permitting purposes.

	Finally, it should be noted that while a source having only de miminis
impacts may not be required to complete a comprehensive source impact
analysis, the emissions from such sources are still considered to
consume increment and would be counted as part of the next increment
analysis required to be completed by a PSD applicant in that same area,
or by the state under a periodic increment review.

Relationship Between SILs and AQRVs  

	While commenters generally supported EPA’s position that the SILs
should not be used in any way to determine effects of emissions
increases on the AQRVs in a Class I area, two commenters urged that the
de minimis concentration be used for analyzing Class I area impacts
under certain circumstances.  That is, they believed that the SILs
should be used to determine the need for a Class I area air quality
analysis when an FLM has not identified a specific AQRV related to the
pollutant under evaluation or obtained ambient monitoring data to
confirm that predicted concentrations from air dispersion models are
representative of actual AQRV impacts in the Class I area.  The
commenters claimed that without this flexibility, applicants would be
required to conduct complex and extensive Class I air dispersion
modeling without any clear objective, and regulatory agencies would have
to review the modeling with limited information to determine if the
emissions could cause an “adverse” impact or if potentially costly
controls should be required.    

	These commenters appear to be suggesting that an FLM may needlessly
call for an analysis of a particular Class I area, involving “complex
and extensive Class I area dispersion modeling” despite the fact that
no AQRV has been identified for that Class I area.  We agree that a
Class I analysis in the absence of any known AQRVs would be unnecessary
because any demonstration of an adverse impact must be made with respect
to a pollutant adversely affecting an AQRV.  We believe, however, that
such analyses would be avoided under the procedures set forth in section
165(d)(2)(C) of the Act which require that a notice be filed alleging
that a proposed source may cause or contribute to adverse effects, and
identifying the adverse impact.  Insofar as the FLM must also
demonstrate “to the satisfaction of the State that emissions from such
facility will have an adverse impact on the air quality related
values,” it would be difficult to require the source to undertake any
kind of detailed analysis in the absence of an AQRV on which such
adverse impacts must be demonstrated.  Thus, we have concluded that it
is not necessary to use the SILs as a safeguard against unnecessary
Class I area analyses.  Instead, we believe that the need for a Class I
analysis, other than the required analysis of the NAAQS and Class I
increments (both for which the SILs were intended to be used), should be
based on the potential for adverse effects on an AQRV that the FLM has
identified and believes could be affected by a pollutant that would be
emitted by the proposed project.  

4.	Form of the SILs

	One commenter (0038) stated that “the Proposal does not indicate how
the proposed PM2.5 SILs are to be interpreted.”  This commenter
believed that “the form of the SILs should be consistent with the form
of the PM2.5 NAAQS” adding that “the current PM2.5 NAAQS requires
that compliance with the 24-hour and annual standards be determined
using 3-year averaging.”  Specifically, “The annual standard is
calculated based upon the 3-year average of annual mean PM2.5
concentrations, and the 24-hour standard is based on the 3-year average
of the 98th percentile (or highest-8th high value) of 24-hour
concentrations.”

	We agree that the form of the standard should be given consideration
and we will address this in forthcoming guidance on how the PM2.5 SILs
are to be interpreted.  The SILs are intended to be used as screening
tools that can readily be used with screening models to provide
conservative estimates of the air quality impact of a proposed project. 
They are especially useful because they can eliminate the need for more
detailed modeling for those sources that will not exceed a defined “de
minimis” impact.  As can be seen from the earlier explanation of how
the SILs were developed, the form of the standard was not considered;
thus, the SIL values should be used in a straightforward comparison with
modeled values.  Once the screening tool has been applied and no
potential problem has been identified, the reviewing authority generally
will conclude that a more refined modeling analysis is not needed.  In
the event that a significant impact is predicted, then it will be
necessary for the applicant to carry out additional analyses consistent
with the modeling compliance guidance set forth for both the increments
and the NAAQS.

5.	SILs for Other Pollutants

	In proposing Option 1, we noted that many who commented on the 1996 NSR
Reform proposal supported this approach and believed that the proposed
PM10 SIL values would serve as appropriate de minimis values.  In fact,
we are aware that many states have been using these proposed SILs for
PM10 as screening tools since 1996 or earlier.  

	Regarding the proposed Class I SILs under Option 1, we expressed our
belief that where a proposed source consumes less than 4 percent of the
Class I increment, the source’s impact is sufficiently low so as not
to warrant requiring the source to carry out a detailed analysis of the
combined effects of the proposed source and all other
increment-consuming emissions in the area.  72 FR 54112, September 21,
2007, at 54140.  We previously used a similar rationale to establish the
significant emissions rates for PSD applicability purposes, concluding
in part that emissions rates that resulted in ambient impacts less than
4 percent of the 24-hour standards for PM and SO2 were sufficiently
small so as to be considered de minimis.  45 FR 52676, August 7, 1980,
at 52707-8.  

	The original SIL values of 1.0 and 5.0 µg/m3 for TSP and PM10 were
interpreted by EPA as representing the minimum amount of ambient impact
that is significant.  This formed the basis of the proposed PM2.5 SIL
values of 1.0 and 5.0 µg/m3 for the annual and 24-hour averaging
periods for Class II and III areas. 

	The SILs currently appear in EPA’s regulations at 40 CFR 51.165(b). 
That particular NSR regulation provides that states must include a
preconstruction review permit program for any new major stationary
source or major modification that proposes to locate in an attainment or
unclassifiable area and would cause or contribute to a violation of the
NAAQS.  These values, added to 40 CFR 51.165(b) on July 1, 1987, have
previously been referred to as “significant ambient impact
concentrations” and are used to enable a source to determine whether
its emissions would cause or contribute to a NAAQS violation at “any
locality that does not or would not meet the applicable national
standard.”  52 FR 24672, April 2, 1985, at 24688.

	In 1985, when EPA proposed to add “significant ambient impact
levels” for PM10, we also indicated that for PSD purposes the
requirements under section 51.1565(b) “would be applied to all
applicable PSD requirements.”  The EPA has since applied these values
in other analogous circumstances under the PSD program.  Based on EPA
interpretations and guidance, SILs have also been widely used in the PSD
program as a screening tool for determining when a new major source or
major modification that wishes to locate in an attainment or
unclassifiable area must conduct a more extensive air quality analysis
to demonstrate that it will not cause or contribute to a violation of
the NAAQS or PSD increment in the attainment or unclassifiable area. 
The SILs are also used to define the extent of the Significant Impact
Area where, using air dispersion models and ambient monitoring data, a
cumulative source impact analysis accounting for emissions changes from
affected sources is performed.  See the 2007 NPRM preamble for
additional information on the history of EPA’s guidance related to
SILs (72 FR 54138-39).

	In the 1996 NSR Reform proposal, we proposed to add the SILs for PM10
and other pollutants already contained in 40 CFR 51.165(b)(2) directly
into the PSD regulations at 40 CFR 51.166 and 52.21.  Because the SILs
in 40 CFR 51.165(b) did not include thresholds for Class I areas, we
proposed to set Class I SILs at the level of 4 percent of the respective
Class I increments.  Thus, for PM10, the proposed Class I SILs were 0.2
µg/m3 (annual) and 0.3 µg/m3 (24-hour), and the proposed Class II and
III SILs were 1.0 µg/m3 (annual) and 5.0 µg/m3 (24-hour).  The EPA has
not yet taken final action on the 1996 proposal on SILs for pollutants
other than PM2.5; therefore, we rely upon our longstanding policy to use
those values, as codified in

40 CFR 51.165(b)(2), for PSD permitting.

Final Action on the PM2.5 SMC

EPA’s Determination on the PM2.5 SMC

	As with the increments and SILs for PM2.5, we proposed three different
options for establishing an SMC for PM2.5.  The first option, referred
to as the “lowest detectable concentration” approach, relied on the
method we used in 1980 to develop the SMCs for all the criteria
pollutants then subject to PSD.  This particular method focused on
development of the SMC value based on the current capability of
providing a meaningful measure of the pollutants.  See relevant
discussion later in this section and at 45 FR 52676, August 7, 1980 at
52710.  Options 2 and 3, called the “PM2.5 to PM10 emissions ratio”
and the PM2.5 to PM10 NAAQS ratio,” respectively, used the SMC for
PM10 as the base for multiplying the emissions and NAAQS ratios to
derive an SMC for PM2.5.  See 72 FR at 54141.  The three proposed
options yielded the following numerical levels for the SMC:

Option 1: 10 μg/m3, (24-hour average);

Option 2: 8.0 μg/m3 (24-hour average); and 

Option 3: 2.3 μg/m3 (24-hour average).

	We are taking final action on the SMC for PM2.5 using the “lowest
detectable concentration” approach (Option 1).  However, we have
determined that it is necessary to modify the methodology to reflect
“current capability” with respect to the measurement of ambient
PM2.5 concentrations.  The result of such modification is that the SMC
value in this final rule is different from (more stringent than) the
proposed level.  The revised value is 4 µg/m3 (24-hour average).  Our
basis for the modified approach and the resulting lower value is
described in greater detail later in this section.

	The EPA and its delegated reviewing authorities will use the PM2.5 SMC
to determine when it may be appropriate to exempt a proposed new major
stationary source or major modification from the ambient monitoring data
requirements under the PSD rules.  Similarly, states with EPA-approved
PSD programs that adopt the SMC for PM2.5 may use the SMC, once it is
part of an approved SIP, to determine when it may be appropriate to
exempt a particular major stationary source or major modification from
the monitoring requirements under their state PSD programs (see, e.g.,
40 CFR 51.166(m)(1)). 

Response to Comments Concerning the SMC

Legal Issues

	Under the Act and EPA regulations, an applicant for a PSD permit is
required to gather preconstruction monitoring data in certain
circumstances.  Section 165(a)(7) of the Act calls for “such
monitoring as may be necessary to determine the effect which emissions
from any such facility may have, or is having, on air quality in any
areas which may be affected by emissions from such source.”  42 U.S.C.
7475(a)(7).  In addition, section 165(e) of the Act requires an analysis
of the air quality in areas affected by a proposed major facility or
major modification and calls for gathering 1 year of monitoring data
unless the reviewing authority determines that a complete and adequate
analysis may be accomplished in a shorter period.  42 U.S.C. 7575(e)(3).
 These requirements are codified in EPA’s PSD regulations at 40 CFR
51.166(m) and 52.21(m).  

	In 1980, EPA adopted regulations that included pollutant-specific SMCs
as a screening tool for sources to determine whether they should conduct
site-specific preconstruction ambient monitoring.  We explained our
position that it was appropriate to exempt sources from preconstruction
monitoring requirements for a pollutant if the source could demonstrate
that its ambient air impact was less than a value known as the
Significant Monitoring Concentration or SMC.  At the time the SMCs were
adopted, EPA described them as “air quality concentration de minimis
level[s] for each pollutant … for the purpose of providing a possible
exemption from monitoring requirements.”  The EPA explained that it
believed there was “little to be gained from preconstruction
monitoring” where a source could show that its projected impact of a
pollutant within the affected area was below the de minimis
concentration for that pollutant.  45 FR 52676, August 7, 1980, at
52710).  

	One commenter (0040) opposed our proposed establishment of any SMC for
PM2.5, claiming that SMCs in general are contrary to the Act.  The
commenter stated that “in Section 165(e) Congress mandated a full year
of continuous air quality monitoring for each major source subject to
the PSD program.”  With this in mind, the commenter indicated that
there are no exceptions, other than the limited statutory provisions,
discussed above, which allow for less than a year’s worth of
monitoring based on a determination that a complete and adequate
analysis of such purposes may be accomplished in a shorter period.  The
commenter then argued that “the allowance for a ‘shorter period’
hardly amounts to authority to waive monitoring entirely, which is what
EPA’s SMC proposal would do.”

	As with the SMCs adopted by EPA in 1980, the SMCs that we proposed for
PM2.5 are supported by the de minimis doctrine set forth in the Alabama
Power v. Costle opinion.  Like the other pollutants for which EPA has
promulgated SMCs, EPA believes there is little to be gained from
preconstruction monitoring of PM2.5 concentrations when the increased
emissions of PM2.5 from a proposed source or modification have a de
minimis impact on ambient concentrations of PM2.5.  If a source can show
through modeling of its emissions alone that its impacts are less than
the corresponding SMC, there is little to be gained by requiring that
source to collect additional monitoring data on PM2.5 emissions to
establish background concentrations for further analysis.  

	Therefore, in developing the three proposed options for an SMC, EPA
sought to use methods that would identify levels representing a de
minimis or insignificant impact on PM2.5 ambient air quality that makes
the collection of additional monitoring data extraneous.  

Level of the SMC

	As indicated earlier, the SMC for PM2.5 in this final rule is 4 μg/m3,
24-hour average.  This value may be used by permitting authorities to
determine when they may exempt a proposed major stationary source or
major modification for PM2.5 from the air quality monitoring
requirements for PM2.5 under 40 CFR 51.166.  The EPA and its delegated
state/local programs will also use this new value under the federal PSD
program at 40 CFR 52.21.  

	We proposed three options for developing the SMC for PM2.5; each option
yielded a notably different concentration value.  In choosing between
the three options, EPA proposed to select the option that reflected the
degree of ambient impact on PM2.5 concentrations that could be
considered truly de minimis and used to justify exempting a source from
the requirement to gather 1 year of ambient monitoring data for PM2.5. 
Ultimately, we have selected the “lowest detectable concentration”
approach (Option 1) that relies directly upon ambient monitoring
measurement sensitivity and precision.  That is, if the predicted source
impact or estimated existing air quality in an area is estimated to be
below a concentration that can be accurately measured, then it would not
be reasonable to require a source to attempt to collect such ambient
data.  

	In 1980, EPA determined the SMCs based on the then current capability
of providing a meaningful measure of ambient pollutant concentrations. 
The EPA promulgated values that represented five times the lowest
detectable concentration in ambient air that could be measured by the
instruments available for monitoring the pollutants.  45 FR 52710.  The
factor of “five” took into account the measurement errors associated
with the monitoring of these low pollutant levels or small incremental
changes in concentration.  These measurement errors were said to arise
from various sources, such as sample collection, analytical measurement,
calibration, and interferences.  See the internal EPA memorandum from
Rehme, K. A., to Warren Peters dated May 20, 1980, contained in the
docket for this rulemaking.  Accordingly, in the 2007 proposal for
PM2.5, we voiced our belief that this was a reasonable approach, since
it was also used for PM10 and TSP. Id.

	Eight commenters expressed support for the SMC based on Option 1,
albeit at the higher level as originally proposed.  In some cases, it is
not clear whether these commenters supported the particular approach
(i.e., link to lowest detectable level) or the fact that the calculated
value was simply the highest value of the values proposed under three
options.  Clearly, some of the commenters indicated their support for
the approach because it is consistent with the approach used for setting
the original SMCs in 1980.  Two commenters opposed the use of Option 1
because it resulted in a value that was too high.  These latter
commenters noted that the SMC derived via Option 1 (10 µg/m3, 24-hour
average) was greater than the proposed 24-hour PM2.5 increment for Class
II areas and argued that such an outcome is inappropriate.  We believe
that this important concern is adequately addressed by the new level of
the SMC.

	Several commenters supported the levels derived from either Option 2 or
Option 3, but were concerned that the justification for choosing either
of these values would need to be further explained.  Some of these
commenters were specifically concerned about the use of a 0.8
PM2.5-to-PM10 emissions ratio which, they argued, relied on inventory
data that did not adequately address all sources that would likely
affect ambient concentrations of PM2.5 in an area.

	We conclude that Option 1 is the most supportable option for defining
the SMC for PM2.5.  The ability to accurately measure ambient PM2.5
concentrations is not related to a ratio of PM2.5 to PM10 either
directly in terms of emissions or as expressed by the respective NAAQS,
which were used to define the SMC for PM2.5 under Options 2 and 3,
respectively.  Our original concern was that, while Option 1 linked the
SMC directly to the concept of a minimum detectable concentration (in
order to identify de minimis monitoring circumstances), the value
originally derived from that approach in the 2007 NPRM was high in
relationship to the concentrations of PM2.5 defined by the existing
NAAQS and increments for PM2.5.  

	In considering the use of Option 1 for developing the SMC in the final
rules, however, we recognized during the administrative process after
publication of the proposed rule that it was necessary to re-examine the
assumptions that we relied upon in 1980 to develop the numerical values
for the original SMCs so that we could most accurately reflect current
monitoring techniques for PM2.5.  Our re-examination utilized the most
current information concerning the physical capabilities of the PM2.5
Federal Reference Method Samplers, and addresses uncertainties
introduced to the measurement of PM2.5 due to variability in the
mechanical performance of the PM2.5 samplers and the micro-gravimetric
analytical balances that weigh filter samples.  

	The minimum detection limit (MDL) of 2 µg/m3, originally used in 1980
for the SMC for PM and promulgated for PM2.5 in 1997 (see 40 CFR part
50, Appendix L, section 3.1), has been reaffirmed by 9 years of field
blank data collected by EPA through the PM2.5 Performance Evaluation
Program.  However, we found that new data exist to “indicate a
conservative estimate of the aggregate uncertainty factor is no greater
that ‘2’ at the concentration equal to the MDL of 2 µg/m3.” 
Accordingly, the lowering of the uncertainty factor from “five” to
“two” under Option 1 yields an SMC of 4 µg/m3 PM2.5, 24-hour
average, rather than the proposed concentration of 10 µg/m3.  

	We conclude that the modified level of 4 µg/m3 PM2.5, 24-hour average,
for the SMC under Option 1, based upon a more current understanding of
monitoring precision for PM, especially fine PM, addresses commenter
support for the use of a method that is consistent with the way other
SMCs were developed and most directly reflects monitoring capability for
the pollutant of concern, while at the same time responding to the
concern of other commenters that a value in the lower range of proposed
SMC values is most reasonable considering the levels of the NAAQS and
increments for PM2.5. 

Correction of Cross Reference in PSD Ambient Monitoring Requirements

	In the 2007 NPRM, we proposed to take final action to correct a cross
reference contained in paragraph (i) of the part 51 and 52 PSD
regulations.  Specifically, at the time of the proposal, paragraphs (ii)
and (iii) in 40 CFR 51.166(i)(5), and paragraph (ii) in 40 CFR
52.21(i)(5), each referred to concentrations listed in paragraph
(i)(8)(i) of both regulations.  However, there is no paragraph (i)(8)(i)
in existing 40 CFR 51.166, and no concentration values are contained in
existing section (i)(8)(i) of 40 CFR 52.21.  The cross reference in
these provisions was intended to reference the SMCs in paragraph
(i)(5)(i) of the two PSD regulations, but EPA failed to make this change
when the paragraphs were renumbered in an earlier rulemaking.  We did
not receive any comments concerning this proposed corrective action.  We
made the necessary correction as part of the May 16, 2008 final rule for
PM2.5 NSR implementation (see 73 FR 28321 at 28348 and 28349); therefore
it is not necessary to take any further action in this final rule with
regard to the proposed correction.  

Dates Associated With Implementation of the Final Rule

	This section describes the key dates that we have established for
implementing the final rule.  In the 2007 NPRM, we indicated that
different dates appeared to be appropriate for implementing the PM2.5
increments, each date depending on the legal authority that we relied
upon to promulgate them.  We described and took comment on some
alternative effective dates for increments, as well.  In addition, we
discussed and took comment on potential implementation dates for the
SILs and SMC components of the proposed rule, which we indicated were
not subject to the same statutory considerations as the increments.  

	We received a number of comments on the different proposed dates.  We
carefully considered these comments in selecting the dates described
below for the final rule.  Some of the significant comments and our
responses to those comments are provided below.  The remaining comments
and our responses are contained in the Response to Comments document
included in the docket for this rulemaking. 

Effective Date of the Final Rule

	In the 2007 NPRM, we took comments on the effective date of the final
rule by presenting the different options available for implementing the
PM2.5 increments.  Under Option 1 for developing the increments, we
stated that section 166(b) of the Act specifies that new increments
promulgated pursuant to section 166(a) are to become effective 1 year
following their promulgation.  In contrast, there is no such 1-year
delay or any other date prescribed for increments promulgated in
accordance with section 166(f) of the Act, upon which we based Options 2
and 3 for the annual PM2.5 increments.  Thus, increments promulgated
under Option 1, which relies on the procedural provisions of section
166(b) of the Act, would normally be subject to a 1-year delay in
implementation, while increments promulgated under either Option 2 or 3,
relying on section 166(f) of the Act, could follow a 30- or 60-day
effective date, typical of the effective date for most new rules in
general.  In either case, our consideration of the effective date for
the new increments assumed that the selected date would also be the
effective date of the final rule.  

	In the 2007 NPRM, we took comment on some alternative approaches to
establishing the effective date for PM2.5 increments.  Specifically,
while proposing a 1-year effective date under Option 1, we requested
comment on whether we could promulgate these increments under section
166(a) of the Act with an effective date of only 60 days.  See 72 FR
54142.

	Nine commenters supported our proposal to establish the effective date
of the part 51 and 52 PSD regulations for PM2.5 as 1 year from the date
of publication.  Alternately, two commenters encouraged us to apply the
60-day effective date, while three other commenters supported other
effective dates, as described in this section.

	Seven industry and industry association commenters supported our
proposal to make the final rule for PM2.5 increments effective 1 year
after promulgation.  Most of these commenters cited the additional time
necessary to develop the needed PM2.5 inventories needed for
implementation of the PM2.5 PSD program.

Two of the commenters urged EPA to allow state programs sufficient time
to adopt increments, particularly if condensable particulate matter is
included in the increment and its analysis.  These commenters stated
that the federal rule should not be effective for 1 year.  (They also
stated that states should have 3 years for the associated SIP
revisions.)  These same commenters added that this delay would provide
time for sources that have permits in the pipeline or are just about to
submit an application to be able to complete the permitting process
without undue delay.  One of the commenters specifically voiced support
for Option 1 for the effective date of the final rule (1 year) and
Option 2B for the period granted for SIP revisions (3 years).  This
commenter also explained that this additional time may give the Agency
time to promulgate better measurement methods for sources of condensable
particulate matter.

	Another of these commenters noted that, at the time of the proposal,
the NSR portion of the CAFPIR had not yet been promulgated, and that
states would need time to incorporate that rule as well as the
requirements of the proposal into their SIPs.  This commenter added that
making the PM2.5 increments effective before states and sources have had
a reasonable opportunity to begin, let alone complete, the SIP process
for the two related rulemakings would unnecessarily complicate an
already-complex regulatory process.  

  	In contrast, the two commenters supporting the shorter effective date
encouraged us to apply the 60-day period for the effective date under
whatever option is finalized.  One of these commenters urged us to take
measures to expedite the implementation of the PM2.5 final rule and
suggested that we choose the shortest of the proposed effective dates
which are allowed under any of the applicable regulations.  This
commenter indicated that in light of the excessive delay in the
implementation of the PM2.5 PSD program since the NAAQS were
promulgated, the 60-day effective date should be applied under EPA’s
preferred option. 

	In light of our decision to promulgate PM2.5 increments under the
authority of section 166(a) of the Act (proposed Option 1), we are faced
with the decision as to how to most effectively implement the
long-awaited PM2.5 increments, recognizing that the Act provides for a
1-year implementation delay.  We have concluded that it is most
appropriate to follow the plain language of the Act which calls for a
1-year effective date for implementing new increments developed under
section 166(a) of the Act.  We agree with the commenters who suggested
that a shortened implementation delay was desirable because of the
substantial delay in the promulgation of measures to prevent significant
air quality deterioration with respect to PM2.5.  Nevertheless, we
believe it would be inappropriate in this action to disregard the
statutory language which plainly calls for a 1-year delay.  Accordingly,
we are setting the effective date of the PM2.5 increments at 1 year from
the date of promulgation of this final rule.  We are doing this by
setting the “trigger date” for PM2.5 as [INSERT DATE 1 YEAR AFTER
DATE OF PUBLICATION IN THE FEDERAL REGISTER].  See new 40 CFR
51.166(b)(14)(i)(c) and (ii)(c), and new 40 CFR 52.21(b)(14)(i)(c) and
(ii)(c).  At the same time, we are establishing an effective date for
the other provisions, i.e., the SILs and SMC for PM2.5, in this final
rule as [INSERT DATE 60 DAYS FROM THE DATE OF PROMULGATION IN THE
FEDERAL REGISTER], which is 60 days from the date of promulgation.  This
will enable the implementation of these key elements of this rule under
the federal PSD program as soon as possible.    

State PSD Programs 

	In this final rule, we are establishing the final PM2.5 increments as
minimum program elements for all state PSD programs.  Accordingly,
states must submit for EPA’s approval revised SIPs that incorporate
the final PM2.5 increments or alternative measures that can be
demonstrated to EPA’s satisfaction to provide an equivalent level of
protection as the PM2.5 increments.  In accordance with section 166(b)
of the Act, we are requiring states to submit revised implementation
plans to EPA for approval within 21 months of promulgation, that is, by
[INSERT DATE 21 MONTHS AFTER DATE OF PUBLICATION IN THE FEDERAL
REGISTER].  Section 166(b) also specifies that we must approve or
disapprove these revisions within 25 months of promulgation (4 months
from the statutory deadline for SIP submittal).  We regard these
statutory deadlines as maximum allowed timeframes for action.  Moreover,
we do not believe that the Act restricts our ability to approve SIP
revisions requested by a state at any time before these deadlines.  In
this final rule, we are amending the regulatory provisions at 40 CFR
51.166(a)(6)(i) to articulate the deadline set forth by the statute for
the SIP submittals involving the PM2.5 increments pursuant to section
166(a) of the Act.

	It is very unlikely that states will be able to revise their SIPs and
submit them to EPA for approval prior to the effective date of the PM2.5
increments in this final rule, which is [INSERT DATE 1 YEAR AFTER DATE
OF PUBLICATION IN THE FEDERAL REGISTER].  Therefore, there is likely to
be a period of time after [INSERT DATE OF PUBLICATION IN THE FEDERAL
REGISTER] when state laws will not require PSD applicants otherwise
subject to PSD for PM2.5 to complete an increment analysis for the PM2.5
increments, even though the PM2.5 increments, major source baseline
date, and trigger date have been established as a result of this final
rule.  Similarly, it is not clear whether states will have the authority
to consider such applicants as having triggered the minor source
baseline date during this interim period before their revised PSD rules
containing the new PM2.5 increments and relevant baseline dates become
effective.  

	The EPA does not intend to prescribe the implementation timeline for
state programs; rather, each state will need to determine how increment
consumption and the setting of the minor source baseline date for PM2.5
will occur under its own PSD program.  Nevertheless, regardless of when
a state begins to require PM2.5 increment analyses and how it chooses to
set the PM2.5 minor source baseline date, the emissions from sources
subject to PSD for PM2.5 on which construction commenced after [INSERT
DATE OF PUBLICATION OF THIS FEDERAL REGISTER] (the major source baseline
date) will consume PM2.5 increment and must be included in increment
analyses occurring after the minor source baseline date is established
for an area under the state’s revised PSD program.  

Federal PSD Program

	The federal PSD regulations under 40 CFR 52.21 apply where states do
not have approved PSD programs and in Indian lands.  In such cases,
either EPA implements the PSD program or the state will implement it
under authority granted by EPA through a delegation agreement.  

	We proposed to begin implementing the federal PSD program for PM2.5 on
the effective date of the final rule, i.e., either 1 year from the date
of publication in the Federal Register or 60 days from date of
publication, if we developed the new increments pursuant to proposed
Option 1.  Alternatively, we requested comment on whether we should
delay implementation of the federal PSD program until 25 months after
promulgation, which is the latest date by which EPA is required to
approve state SIP revisions.  This is the same approach we took in 1988
to implement the then new NO2 increments.  See 53 FR 40658, October 17,
1988.  We did not propose the 24-month delay for the PM2.5 increments
because of the significant delay that had already occurred between the
time we promulgated the PM2.5 NAAQS and the time the PM2.5 increment
rulemaking would be finalized.  However, we sought comment on this
alternative approach because we recognized that it might not be
equitable to begin implementation of the new program requirements in
those few areas where the federal program applies before the majority of
states are required to implement the program.  

	Two commenters (0026, 0043) urged EPA to hold off implementation of
state programs administered under the federal PSD program in order to
provide a uniform and consistent national approach.  One state agency
(0015) supported implementing the federal PSD program with a delayed
effective date of 1 year after the effective date of the final rule
instead of 60 days.

	We have decided to begin implementing the revised federal PSD program
as set out previously in our introductory discussion of this issue in
section VIII.A.  That is, the revised regulations at 40 CFR 52.21 will
become effective in 60 days, on [INSERT DATE 60 DAYS AFTER DATE OF
PUBLICATION IN THE FEDERAL REGISTER].  This will allow EPA or the
delegated state agency to begin using the SILs and SMC for PM2.5 on that
date, as described in section VIII.C of this preamble.  However, the
date established in the regulations for the trigger date will ensure
that the PM2.5 increments do not become effective for 1 year, consistent
with section 166(b) of the Act, and that the minor source baseline date
cannot be established until the PM2.5 increments become effective. 
However, PSD sources subject to PM2.5 that receive their PSD permit
after the date of publication of this final rule will be considered to
consume PM2.5 increments by virtue of the fact that they will commence
construction after the major source baseline date for PM2.5, which is
the date of publication of this final rule.  

	Thus, sources in an area subject to the federal PSD program for PM2.5
will be able to use the SILs and SMC as screening tools for the required
PM2.5 NAAQS compliance demonstration, but in most cases will not be
required to submit a PM2.5 increment analysis as part of a complete PSD
permit application for a federal PSD permit unless the application is
submitted on or after [INSERT DATE 1 YEAR AFTER DATE OF PUBLICATION IN
THE FEDERAL REGISTER].  On or after that date, when an applicant submits
a complete PSD permit application that is required to address PM2.5
under the federal PSD program, that first application will establish the
minor source baseline date for PM2.5 in the applicable attainment or
unclassifiable area.  

	As with the state PSD program requirements, prior to the establishment
of the minor source baseline date in an area, emissions increases from
minor sources in the area will be counted toward the baseline
concentration, rather than to the PM2.5 increment.  As described
earlier, the emissions from major stationary sources that commence
construction after the major source baseline date, regardless of the
date on which their PSD application is submitted, must be counted toward
consumption of the PM2.5 increments.  While these sources will not be
required to submit an increment analysis for PM2.5 as part of their
complete application as long as they receive their PSD permit before the
trigger date for PM2.5 (see discussion that follows in section VIII.B),
the emissions increases resulting from the permitting of these sources
ultimately must be counted toward the PM2.5 increments when the first
PSD permit application submitted after the trigger date establishes the
minor source baseline date for the area of concern, and in all
subsequent PM2.5 increment analyses for that area.

Transition Period 

	In the 2007 NPRM, we proposed a transition period to clarify when PSD
permit applications must contain an increment analysis demonstrating
compliance with the PM2.5 increments following the date the PM2.5
increments become effective in any state or federal PSD program. 
Specifically, we proposed to establish a grandfathering provision to
allow complete applications submitted before the increment effective
date, but for which the permit had not yet been issued by the effective
date, to continue being processed using the PM10 Surrogate Policy to
satisfy the requirement to demonstrate compliance with the new PM2.5
requirements.  The grandfathering provision for PM2.5 was originally
proposed in the 2007 NPRM at 40 CFR 51.166(i)(10) and 40 CFR
52.21(i)(11) for state and federal PSD programs, respectively.  See 72
FR 54112, September 21, 2007, at 54149 and 54154.	

	Three commenters (0015, 0022, 0026) supported the proposed
grandfathering provision for sources that submitted a complete
application before the effective date of the applicable PSD rules. 
Another commenter (0043) felt that it was reasonable to allow states a
choice between using PM10 or PM2.5 increments during a transition period
including SIP approval, where applicable.

	During the time since the proposal of this rule in 2007, we have
reconsidered the need for the proposed transition period in the federal
PSD program to effectively implement the PM2.5 increments.  In light of
the importance of preventing significant deterioration of PM2.5 air
quality and the amount of time that has passed since the initial
promulgation of the PM2.5 NAAQS, we do not believe that further delay is
warranted.  We expect that most permits issued after [INSERT DATE 1 YEAR
AFTER DATE OF PUBLICATION IN THE FEDERAL REGISTER] will be from sources
that submitted their PSD applications after the major source baseline
date for PM2.5, which is defined as the date of publication of this
final rule, so that they will be increment-consuming sources. 
Therefore, when these sources apply for their PSD permits, they will
have had significant advance notice of when the new increments will
become effective, i.e., 1 year from the date of publication of this
final rule.  The review and permitting of permit applications submitted
prior to the publication date of this final rule should generally be
completed prior to the effective date of PM2.5 increments and thus
effectively have a transition period of 1 year to complete processing.

	Thus, we are requiring each source that receives its PSD permit after
the effective date of the PM2.5 increments, regardless of when the
application was submitted, to provide a demonstration that the
source’s proposed emissions increase, along with other
increment-consuming emissions, will not cause or contribute to a
violation of the PM2.5 increments.  

Under this final rule, sources applying for a PSD permit under the
federal PSD program after the major source baseline date for PM2.5
(i.e., after the date of publication of this final rule), but before the
PM2.5 increments become effective (i.e., the date 1 year after
publication of this final rule), will be considered to consume PM2.5
increment.  While EPA will not require any such source to include a
PM2.5 increment analysis as part of its initial PSD application, an
increment analysis ultimately will be required before the permit may be
issued if the date of issuance will occur after the trigger date, when
the PM2.5 increments become effective under the federal PSD program.   
Finally, for the same reasons that we are not adopting the proposed
transition period that would have exempted PSD applicants with pending
permit applications from demonstrating compliance with the PM2.5
increment requirements under the federal PSD program, we have decided
not to provide an option for states to apply a transition period under
40 CFR 51.166.  We believe it is appropriate for all increment-consuming
sources subject to PM2.5 to demonstrate compliance with the PM2.5
increments when the required permit is issued after the PM2.5 increments
become effective in the state’s PSD regulations.    

SILs and SMC for PM2.5

	In the 2007 NPRM, we explained our position that SILs and SMCs are not
minimum required elements of an approvable SIP.  While these de minimis
values are widely considered to be useful components for implementing
the PSD program, they are not absolutely necessary for the states to
implement their PSD programs.  That is, states can satisfy the statutory
requirements for a PSD program by requiring each PSD applicant to submit
air quality monitoring data and to conduct a comprehensive air quality
impacts analysis for PM2.5 without using de minimis thresholds to exempt
certain sources from such requirements.  Because the de minimis values
for PM2.5 (and other pollutants) are not mandatory elements, we proposed
not to establish specific deadlines for submitting revisions to
incorporate the specific values for PM2.5 into SIPs.  

	One state/local commenter (0033) agreed that the SILs and SMCs should
not be a required element of the PSD SIP.  Another state/local commenter
(0015) agreed with our proposal, but stated that EPA has the authority
to include SILs and SMCs as minimum program requirements per the opinion
set forth in Alabama Power v. Costle.  This commenter added that the EPA
Environmental Appeals Board has affirmed EPA’s interpretation of the
Act to allow EPA to evaluate the significance of a source’s impact
when determining whether the source’s emissions would “cause or
contribute” to a NAAQS or increments violation under section 165(a)(3)
of the Act.  

	Two commenters (0035, 0037) disagreed with our proposed position and
argued that SILs and SMCs should be mandatory elements of a state PSD
program.  One of these commenters argued that the requirement to model
without the use of screening models with SILs and SMCs is so
unreasonable that EPA must require that states adopt the SILs and SMCs
to meet the Purpose clause of the Act, which requires a balancing of
environmental and economic considerations.  The other opposing commenter
stated that the increments, SILs, and SMCs need to be adopted as a
single regulatory approach because the SILs and SMCs define when
additional work is needed to ensure that PSD requirements, such as
maintaining adequate increment, are met.  This commenter added that
there is no reason for sources to be placed in the position of
conducting expensive modeling that can delay a project when it is
unnecessary from an air quality perspective.

	We agree that the SILs and SMCs used as de minimis thresholds for the
various pollutants are useful tools that enable permitting authorities
and PSD applicants to screen out “insignificant” activities;
however, the fact remains that these values are not required by the Act
as part of an approvable SIP program.  We believe that most states are
likely to adopt the SILs and SMCs because of the useful purpose they
serve regardless of our position that the values are not mandatory. 
Alternately, states may develop more stringent values if they desire to
do so.  In any case, states are not under any SIP-related deadline for
revising their PSD programs to add these screening tools. 

	Using the SILs for PM2.5, when a proposed major new source or major
modification of PM2.5 predicts (via air quality modeling) an impact less
than the PM2.5 de minimis value, the proposed source or modification is
not considered to have a significant air quality impact and would not
need to complete a cumulative impact analysis involving an analysis of
other sources in the area.  Also, a source with a de minimis ambient
impact would not be considered to cause or contribute to a violation of
either the PM2.5 NAAQS or increments.  

	The PM2.5 SILs will become effective under the federal PSD program on
the effective date of this final rule, that is, on [INSERT DATE 60 DAYS
AFTER DATE OF PUBLICATION IN FEDERAL REGISTER], when either EPA, or a
state acting under a delegation of EPA’s authority, implements the
revised PSD permitting requirements for PM2.5 pursuant to 40 CFR 52.21. 
The SILs will be for use initially with the compliance demonstration for
the PM2.5 NAAQS, and later for the PM2.5 increment analysis, under the
federal PSD program.  We emphasize, however, that the PM2.5 SILs are not
intended to be used as part of the determination of adverse impacts on
AQRVs for PM2.5 in Class I areas.  

	Similarly, we intend to use the PM2.5 SMC (4 µg/m3, 24-hour average)
as a screening tool in the federal PSD permit program beginning on
[INSERT DATE 60 DAYS AFTER DATE OF PUBLICATION IN THE FEDERAL REGISTER].
 Accordingly, when either the modeled PM2.5 impact of, or the existing
ambient air quality within the area of, the proposed new major source or
major modification is less than the PM2.5 SMC, the reviewing authority
may exempt the source or modification from the monitoring data
requirements for PM2.5 under 40 CFR 52.21(m).

Other Regulatory Changes

	The Act provides that the PSD regulations apply to areas designated as
“attainment” or “unclassifiable” as defined by the Act.  When
the original regulations were written, the Act provisions for
designating areas as either “attainment” or “unclassifiable”
were contained in sections 107(d)(1)(D) and (E), respectively.  In 1990,
Congress revised section 107 and changed the relevant paragraphs
defining “attainment” and “unclassifiable” areas to sections
107(d)(1)(A)(ii) and (iii), respectively.  In accordance with these
statutory changes, we are correcting the references to the statutory
classifications contained in the existing PSD rules to match the revised
paragraphs in the Act.  See revised 40 CFR 51.166(b)(14)(iii)(a) and
(15)(i) and (ii), and 40 CFR 52.21(b)(14)(iii)(a) and (15)(i) and (ii).

 	In adding the SILs for PM2.5 in this final rule, we restructured
paragraph (k) (“Source impact analysis”) in the existing PSD
regulations at 40 CFR 51.166 and 52.21.  Under the restructuring of
paragraph (k), old paragraph (k)(2) is now paragraph (k)(1)(b).  To
accommodate this restructuring change, we are also revising
grandfathering provisions that are contained in existing paragraphs
(i)(8) and (i)(9) at 40 CFR 51.166, and paragraphs (i)(9) and (i)(10) at
40 CFR 52.21, which contained references to requirements contained in
paragraph (k)(2).  As revised, the grandfathering provisions now
reference new paragraph (k)(1)(b).

Statutory and Executive Order Reviews

Executive Order 12866 - Regulatory Planning and Review

	Under Executive Order 12866 (58 FR 51735, October 4, 1993), this action
is a “significant regulatory action” because it raises novel legal
or policy issues arising out of legal mandates, the President’s
priorities, or the principle set forth in the Executive Order. 
Accordingly, EPA submitted this action to the Office of Management and
Budget (OMB) for review under Executive Order 12866 and any changes made
in response to OMB recommendations have been documented in the docket
for this action.

Paperwork Reduction Act 

	The information collection requirements in this rule have been
submitted for approval to the OMB under the Paperwork Reduction Act, 44
U.S.C. 3501 et seq.  The information collection requirements are not
enforceable until OMB approves them. 

	Pursuant to title I, part C, of the Act, the PSD program requires the
owner or operator to obtain a permit prior to either constructing a new
major stationary source of air pollutants or making a major modification
to an existing major stationary source.  The information collection for
sources under PSD results from the requirement for owners or operators
to submit applications for NSR permits.  In some cases, sources must
conduct preconstruction monitoring to determine the existing ambient air
quality.  For reviewing authorities, the information collection results
from the requirement to process permit applications and issue permits,
and to transmit associated information to EPA.  The EPA oversees the PSD
program, and the information collected by sources and reviewing
authorities is used to ensure that the program is properly implemented.

	The final rule will increase the PSD permitting burden for owners and
operators of major stationary sources of PM2.5 emissions by adding PM2.5
increments to the list of existing increments for which air quality
impact analyses must be carried out to track the amount of increment
consumed by the proposed source and other sources in the area.  Over the
3-year period covered by the Information Collection Request (ICR), we
estimate an average annual burden totaling about 29,000 hours and $2.8
million for all industry entities that will be affected by the final
rule.  For the same reasons, we also expect the final rule (when fully
implemented) to increase burden for the state and local authorities
reviewing PSD permit applications.  In addition, there will be
additional burden for state and local agencies to revise their SIPs to
incorporate the proposed changes.  Over the 3-year period covered by the
ICR, we estimate that the average annual burden for all state and local
reviewing authorities will total about 7,500 hours and $581,000.  Burden
is defined at 5 CFR 1320.3(b).

	An agency may not conduct or sponsor, and a person is not required to
respond to, a collection of information unless it displays a currently
valid OMB control number.  The OMB control numbers for EPA’s
regulations in 40 CFR are listed in 40 CFR part 9.  When this ICR is
approved by OMB, the Agency will publish a technical amendment to 40 CFR
part 9 in the Federal Register to display the OMB control number for the
approved information collection requirements contained in this final
rule.

Regulatory Flexibility Act 

	The Regulatory Flexibility Act (RFA) generally requires an agency to
prepare a regulatory flexibility analysis of any rule subject to notice
and comment rulemaking requirements under the Administrative Procedure
Act or any other statute unless the Agency certifies that the rule will
not have a significant economic impact on a substantial number of small
entities.  Small entities include small businesses, small organizations,
and small governmental jurisdictions. 

	For purposes of assessing the impacts of this rule on small entities,
“small entity” is defined as: (1) a small business as defined by the
Small Business Administration’s regulations at 13 CFR 121.201; (2) a
small governmental jurisdiction that is a government of a city, county,
town, school district or special district with a population of less than
50,000; and (3) a small organization that is any not-for-profit
enterprise which is independently owned and operated and is not dominant
in its field.

	After considering the economic impacts of this final rule on small
entities, I certify that this action will not have a significant
economic impact on a substantial number of small entities.  This final
rule will not impose any requirements on small entities because small
entities are not subject to the requirements of this rule.

Unfunded Mandates Reform Act 

	This action contains no federal mandates under the provisions of Title
II of the Unfunded Mandates Reform Act of 1995 (UMRA), 2 U.S.C.
1531-1538 for state, local, or tribal governments or the private sector.
 The action imposes no enforceable duty on any state, local or tribal
governments or the private sector.  The final rules adds only a
relatively small number of new requirements to the existing permit
requirements already in place under the PSD program, since states are
currently implementing a PM10 surrogate program pursuant to EPA
guidance.  Thus, this action is not subject to the requirements of
sections 202 or 205 of UMRA.

	This rule is also not subject to the requirements of section 203 of
UMRA because it contains no regulatory requirements that might
significantly or uniquely affect small governments.  The final rule
applies only to new major stationary sources and to major modifications
at existing major stationary sources.

Executive Order 13132 - Federalism 

	This final rule does not have federalism implications.  It will not
have substantial direct effects on the states, on the relationship
between the national government and the states, or on the distribution
of power and responsibilities among the various levels of government, as
specified in Executive Order 13132.  The final rule makes relatively
minor changes to the established PSD program, simply making it possible
for states to implement PSD for PM2.5 instead of relying on PM10 as a
surrogate.  Thus, Executive Order 13132 does not apply to this rule.  In
the spirit of Executive Order 13132, and consistent with EPA policy to
promote communications between EPA and state and local governments, EPA
specifically solicited comment on the proposed rule from state and local
officials.

Executive Order 13175 - Consultation and Coordination with Indian Tribal
Governments

	This action does not have tribal implications, as specified in
Executive Order 13175 (65 FR 67249, November 9, 2000).  The final rule
provides the elements to implement a PM2.5 PSD program in attainment
areas.  The Act provides for states to develop plans to regulate
emissions of air pollutants within their jurisdictions.  The Tribal Air
Rule (TAR) under the Act gives tribes the opportunity to develop and
implement Act programs to attain and maintain the PM2.5 NAAQS, but
leaves to the discretion of the tribes the decision of whether to
develop these programs and which programs, or appropriate elements of a
program they will adopt.  Thus, Executive Order 13175 does not apply to
this action.

	The EPA did reach out to national tribal organizations in 2006 to
provide a forum for tribal professionals to provide input to the
rulemaking.  However, not much participation or input was received.

Executive Order 13045 - Protection of Children from Environmental Health
and Safety Risks 

	This action is not subject to Executive Order 13045 (62 FR 19885, April
23, 1997) because it is not economically significant as defined in
Executive Order 12866, and because the Agency does not believe the
environmental health or safety risks addressed by this action present a
disproportionate risk to children.  One of the basic requirements of the
PSD program is that new and modified major sources must demonstrate that
any new emissions do not cause or contribute to air quality in violation
of the NAAQS.

Executive Order 13211 - Actions That Significantly Affect Energy Supply,
Distribution, or Use 

	This action is not a “significant energy action” as defined in
Executive Order 13211 (66 FR 28355, May 22, 2001) because it is not
likely to have a significant adverse effect on the supply, distribution,
or use of energy.  Further, we have concluded that this rule is not
likely to have any adverse energy effects.

National Technology Transfer and Advancement Act 

	Section 12(d) of the National Technology Transfer and Advancement Act
of 1995 (NTTAA), Public Law No. 104-113, 12(d) (15 U.S.C. 272 note)
directs EPA to use voluntary consensus standards in its regulatory
activities unless to do so would be inconsistent with applicable law or
otherwise impractical.  Voluntary consensus standards are technical
standards (e.g., materials specifications, test methods, sampling
procedures, and business practices) that are developed or adopted by
voluntary consensus standards bodies.  The NTTAA directs EPA to provide
Congress, through OMB, explanations when the Agency decides not to use
available and applicable voluntary consensus standards. 

	This action does not involve technical standards.  Therefore, EPA did
not consider the use of any voluntary consensus standards.

Executive Order 12898 – Federal Actions to Address Environmental
Justice in Minority Populations and Low-Income Populations

	Executive Order 12898 (59 FR 7629, Feb. 16, 1994) establishes federal
executive policy on environmental justice.  Its main provision directs
federal agencies, to the greatest extent practicable and permitted by
law, to make environmental justice part of their mission by identifying
and addressing, as appropriate, disproportionately high and adverse
human health or environmental effects of their programs, policies, and
activities on minority populations and low-income populations in the
United States.  

	The EPA has determined that this final rule will not have
disproportionately high and adverse human health or environmental
effects on minority or low-income populations because it does not affect
the level of protection provided to human health or the environment. 
This final rule will provide regulatory certainty for implementing the
preconstruction NSR permitting program for PM2.5.  However, the
requirements are similar to the existing requirements of the PM10
program and hence do not impact the human health or environmental
effects.

Congressional Review Act

	The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the
Small Business Regulatory Enforcement Fairness Act of 1996, generally
provides that before a rule may take effect, the agency promulgating the
rule must submit a rule report, which includes a copy of the rule, to
each House of the Congress and to the Comptroller General of the United
States.  The EPA will submit a report containing this rule and other
required information to the U.S. Senate, the U.S. House of
Representatives, and the Comptroller General of the United States prior
to publication of the rule in the Federal Register.  A major rule cannot
take effect until 60 days after it is published in the Federal Register.
 This action is not a “major rule” as defined by 5 U.S.C. 804(2). 
Nevertheless, this rule needs to be reviewed for the new increments
being promulgated herein so that they can be scrutinized by Congress as
intended under section 166(b) of the Act.  Even though the PM2.5
increments will not become effective for 1 year, the final rule will
become effective 60 days from the date of publication, that is, on
[INSERT DATE 60 DAYS AFTER THE DATE OF PUBLICATION IN THE FEDERAL
REGISTER], for the screening tools (SILs and SMC) being established in
this rule.

Judicial Review

	Under section 307(b)(1) of the Act, petitions for judicial review of
this action must be filed in the United States Court of Appeals for the
District of Columbia Circuit by [INSERT DATE 60 DAYS AFTER DATE OF
PUBLICATION IN THE FEDERAL REGISTER].  Any such judicial review is
limited to only those objections that are raised with reasonable
specificity in timely comments.  Filing a petition for reconsideration
by the Administrator of this final rule does not affect the finality of
this rule for the purposes of judicial review nor does it extend the
time within which a petition for judicial review may be filed, and shall
not postpone the effectiveness of such rule or action.  Under section
307(b)(2) of the Act, the requirements of this final action may not be
challenged later in civil or criminal 

Page 200 of 216 – Prevention of Significant Deterioration (PSD) for
Particulate Matter Less Than 2.5 Micrometers (PM2.5) – Increments,
Significant Impact Levels (SILs) and Significant Monitoring
Concentration (SMC)

proceedings brought by us to enforce these requirements. 

Statutory Authority

	The statutory authority for this final action is provided by sections
101, 160, 163, 165, 166, 301, and 307(d) of the Act as 

amended (42 U.S.C. 7401, 7470, 7473, 7475, 7476, 7601, and 7607(d)).

List of Subjects

40 CFR Part 51

	Administrative practices and procedures, Air pollution control,
Environmental protection, Intergovernmental relations.

40 CFR Part 52

	Administrative practices and procedures, Air pollution control,
Environmental protection, Intergovernmental relations.

___________________________                                             
                                                           

Dated:

__________________________

Lisa P. Jackson,

Administrator. 

	

  SEQ CHAPTER \h \r 1 For the reasons set out in the preamble, title
40, chapter I of the Code of Federal Regulations is amended as follows:

PART 51 - [Amended]

	1.  The authority citation for part 51 continues to read as follows:

	Authority: 23 U.S.C. 101; 42 U.S.C. 7401 - 7671q.

Subpart I - [Amended]

	2.  Section 51.165 is amended by revising the table in paragraph (b)(2)
to read as follows:

§51.165  Permit requirements.

* * * * *

	(b)  * * *

	(2)  * * *

Pollutant	Annual	Averaging time (hours)



24	8	3	1

SO2	

PM10	

PM2.5	

NO2	

CO		1.0 µg/m3	

1.0 µg/m3	

0.3 µg/m3	

1.0 µg/m3	

		5 µg/m3	

5 µg/m3

1.2 µg/m3	

			

0.5 mg/m3	25 µg/m3	

		

2 mg/m3



* * * * *

	3.  Section 51.166 is amended as follows:

  SEQ CHAPTER \h \r 1 By revising paragraph (a)(6)(i);	

By revising paragraph (b)(14)(i)(a);

By removing the period at the end of paragraph (b)(14)(i)(b) and adding
“; and” in its place;

By adding paragraph (b)(14)(i)(c);

By revising paragraph (b)(14)(ii)(a);

By removing the period at the end of paragraph (b)(14)(ii)(b) and adding
“; and” in its place;

By adding paragraph (b)(14)(ii)(c);

By revising paragraph (b)(14)(iii)(a);

By revising paragraph (b)(15)(i) and paragraph (b)(15)(ii) introductory
text;

By revising the table in paragraph (c)(1);

By revising paragraph (c)(2);

By revising paragraph (i)(5)(i)(c);

By redesignating existing paragraphs (i)(5)(i)(d) through (j) as
paragraphs (i)(5)(i)(e) through (k);

By adding new paragraph (i)(5)(i)(d);

By removing “(k)(2)” from paragraph (i)(8) and adding
“(k)(1)(b)” in its place;

By removing in two places “(k)(2)” from paragraph (i)(9) and adding
“(k)(1)(b)” in those places;

By revising paragraph (k);

By removing the words “particulate matter” in the last sentence of
paragraph (p)(4) and adding in their place “PM2.5, PM10,”; and

By revising the table in paragraph (p)(4).

§51.166 Prevention of significant deterioration of air quality.

	(a) * * *

	(6) * * *  

	(i) Any State required to revise its implementation plan by reason of
an amendment to this section, with the exception of amendments to add
new maximum allowable increases or other measures pursuant to section
166(a) of the Act, shall adopt and submit such plan revision to the
Administrator for approval no later than 3 years after such amendment is
published in the Federal Register.  With regard to a revision to an
implementation plan by reason of an amendment to paragraph (c) of this
section to add maximum allowable increases or other measures, the state
shall submit such plan revision to the Administrator for approval within
21 months after such amendment is published in the Federal Register. 

* * * * *  

	(b)  * * *

	(14)(i)  * * *

	(a)	In the case of PM10 and sulfur dioxide, January 6, 1975;

* * * * *

	(c)  In the case of PM2.5, [INSERT DATE OF PUBLICATION IN THE FEDERAL
REGISTER].

	(ii)  * * *

	(a)	In the case of PM10 and sulfur dioxide, August 7, 1977;

* * * * *

	(c)  In the case of PM2.5, [INSERT DATE 1 YEAR AFTER DATE OF
PUBLICATION IN THE FEDERAL REGISTER].

	(iii) * * *

(a) The area in which the proposed source or modification would
construct is designated as attainment or unclassifiable under section
107(d)(1)(A)(ii) or (iii) of the Act for the pollutant on the date of
its complete application under 40 CFR 52.21 or under regulations
approved pursuant to 40 CFR 51.166; and

* * * * *

	(15)(i) Baseline area means any intrastate area (and every part
thereof) designated as attainment or unclassifiable under section
107(d)(1)(A)(ii) or (iii) of the Act in which the major source or major
modification establishing the minor source baseline date would construct
or would have an air quality impact for the pollutant for which the
baseline date is established, as follows: equal to or greater than 1
µg/m3 (annual average) for SO2, NO2, or PM10;, or an air quality impact
equal or greater than 0.3 µg/m3 (annual average) for PM2.5.

	(ii) Area redesignations under section 107(d)(1)(A)(ii) or (iii) of the
Act cannot intersect or be smaller than the area of impact of any major
stationary source or major modification which:

* * * * *

	(c)  * * * 

	(1)  * * *

Pollutant	Maximum allowable increase (micrograms per cubic meter)

Class I Area

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10: 

Annual arithmetic mean	

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

1

2

4

8

2

5

25

2.5

Class II Area

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

Annual arithmetic mean	

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

4

9

17

30

20

91

512

25

Class III Area

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

Annual arithmetic mean	

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

8

18

34

60

40

182

700

50



* * * * *

	(2)  Where the State can demonstrate that it has alternative measures
in its plan other than an area classification plan, including maximum
allowable increases as defined under paragraph (c)(1) of this section,
that satisfy the requirements in sections 166(c) and 166(d) of the Act
for a regulated NSR pollutant for which the Administrator has
established maximum allowable increases pursuant to section 166(a) of
the Act, the requirements for an area classification plan and maximum
allowable increases for that pollutant under paragraph (c)(1) of this
section shall not apply upon approval of the plan by the Administrator. 
The following regulated NSR pollutants are eligible for such treatment:

	(i)  Nitrogen dioxide.

	(ii) PM2.5.

* * * * *

	(i)  * * *

	(5)  * * *

	(i)  * * *

	(c)  PM2.5—4 µg/m3, 24-hour average;

	(d)  PM10—10 µg/m3, 24-hour average;

* * * * *

	(k)  Source impact analysis.  

(1)  Required demonstration.  The plan shall provide that the owner or
operator of the proposed source or modification shall demonstrate that
allowable emission increases from the proposed source or modification,
in conjunction with all other applicable emissions increases or
reduction (including secondary emissions), would not cause or contribute
to air pollution in violation of:

	(i)  Any national ambient air quality standard in any air quality
control region; or

	(ii)  Any applicable maximum allowable increase over the baseline
concentration in any area.

	(2)  Significant impact levels.  The plan may provide that, for
purposes of PM2.5, the demonstration required in paragraph (k)(1) of
this section is deemed to have been made if the emissions increase from
the new stationary source alone or from the modification alone would
cause, in all areas, air quality impacts less than the following
amounts:

Pollutant	Averaging time	Class I 

Area	Class II 

Area 	Class III

Area 

PM2.5	Annual		0.06 µg/m3		0.3 µg/m3		0.3 µg/m3

	24-hour		0.07 µg/m3		1.2 µg/m3		1.2 µg/m3



* * * * *

	(p)  * * *

	(4)  * * *

Pollutant	Maximum allowable increase (micrograms per cubic meter)

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

Annual arithmetic mean	

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

4

9

17

30

20

91

325

25



* * * * *

	4.  Appendix S to part 51 is amended by revising the table in Section
III.A to read as follows:

Appendix S to Part 51—Emission Offset Interpretative Ruling

* * * * *

	III.  * * *

	A.  * * *

Pollutant	Annual	Averaging time (hours)



24	8	3	1

SO2	

PM10	

PM2.5	

NO2	

CO		1.0 µg/m3	

1.0 µg/m3

0.3 µg/m3	

1.0 µg/m3	

		5 µg/m3	

5 µg/m3

1.2 µg/m3	

			

0.5 mg/m3	25 µg/m3	

		

2 mg/m3



* * * * *

PART 52 - [Amended]

	5.  The authority citation for part 52 continues to read as follows:

	Authority: 42 U.S.C. 7401, et seq.

Subpart A - [Amended]

	6.  Section 52.21 is amended as follows:

  SEQ CHAPTER \h \r 1 By revising paragraph (b)(14)(i)(a);

By removing the period at the end of paragraph (b)(14)(i)(b) and adding
“; and” in its place; 

By adding paragraph (b)(14)(i)(c);

By revising paragraph (b)(14)(ii)(a);

By removing the period at the end of paragraph (b)(14)(ii)(b) and adding
“; and” in its place;

By adding paragraph (b)(14)(ii)(c);

By revising paragraph (b)(14)(iii)(a);

By revising paragraph (b)(15)(i) and paragraph (b)(15)(ii) introductory
text;

By revising the table in paragraph (c); 

By revising paragraph (i)(5)(i); 

By removing “(k)(2)” from paragraph (i)(9) and adding
“(k)(1)(b)” in its place;

By removing in two places “(k)(2)” from paragraph (i)(10) and adding
“(k)(1)(b) in those places;

By revising paragraph (k);

By removing the words “particulate matter” in the last sentence of
paragraph (p)(5) and adding in their place “PM2.5, PM10,”; and

By revising the table in paragraph (p)(5).

§52.21  Prevention of significant deterioration of air quality.

* * * * *

	(b)  * * *

	(14)(i)  * * *

	(a)	In the case of PM10 and sulfur dioxide, January 6, 1975;

* * * * *

	(c)  In the case of PM2.5, [INSERT DATE OF PUBLICATION IN THE FEDERAL
REGISTER].

	(ii)  * * *

	(a)	In the case of PM10 and sulfur dioxide, August 7, 1977;

* * * * *

	(c)  In the case of PM2.5, [INSERT DATE 1 YEAR AFTER DATE OF
PUBLICATION IN THE FEDERAL REGISTER].

	(iii) * * *

(a) The area in which the proposed source or modification would
construct is designated as attainment or unclassifiable under section
107(d)(1)(A)(ii) or (iii) of the Act for the pollutant on the date of
its complete application under 40 CFR 52.21 or under regulations
approved pursuant to 40 CFR 51.166; and

* * * * *

	(15)(i) Baseline area means any intrastate area (and every part
thereof) designated as attainment or unclassifiable under section
107(d)(1)(A)(ii) or (iii) of the Act in which the major source or major
modification establishing the minor source baseline date would construct
or would have an air quality impact for the pollutant for which the
baseline date is established, as follows: equal to or greater than 1
µg/m3 (annual average) for SO2, NO2, or PM10,; or an air quality impact
equal or greater than 0.3 µg/m3 (annual average) for PM2.5.

	(ii) Area redesignations under section 107(d)(1)(A)(ii) or (iii) of the
Act cannot intersect or be smaller than the area of impact of any major
stationary source or major modification which:

* * * * *

	(c)  * * * 

Pollutant	Maximum allowable increase (micrograms per cubic meter)

Class I Area

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

Annual arithmetic mean	

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

1

2

4

8

2

5

25

2.5

Class II Area

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

Annual arithmetic mean	

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

4

9

17

30

20

91

512

25

Class III Area

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

Annual arithmetic mean	

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

8

18

34

60

40

182

700

50



* * * * *

	(i)  * * *

	(5)  * * *

	(i)   The emissions increase of the pollutant from the new source or
the net emissions increase of the pollutant from the modification would
cause, in any area, air quality impacts less than the following amounts:

	(a)  Carbon monoxide—575 µg/m3, 8-hour average;

	(b)  Nitrogen dioxide—14 µg/m3, annual average;

	(c)  PM2.5—4 µg/m3, 24-hour average;

	(d)  PM10—10 µg/m3, 24-hour average;

	(e)  Sulfur dioxide—13 µg/m3, 24-hour average;

	(f)  Ozone;1 

	(g)  Lead—0.1 µg/m3, 3-month average;

	(h)  Fluorides—0.25 µg/m3, 24-hour average;

	(i)  Total reduced sulfur—10 µg/m3, 1-hour average;

	(j)  Hydrogen sulfide—0.2 µg/m3, 1-hour average;

	(k)  Reduced sulfur compounds—10 µg/m3, 1-hour average; or

	1 No de minimis air quality level is provided for ozone.  However, any
net emissions increase of 100 tons per year or more of volatile organic
compounds or nitrogen oxides subject to PSD would be required to perform
an ambient impact analysis, including the gathering of ambient air
quality data.

* * * * *

	(k)  Source impact analysis.  

(1)  Required demonstration.  The owner or operator of the proposed
source or modification shall demonstrate that allowable emission
increases from the proposed source or modification, in conjunction with
all other applicable emissions increases or reductions (including
secondary emissions), would not cause or contribute to air pollution in
violation of:

	(i)  Any national ambient air quality standard in any air quality
control region; or

	(ii)  Any applicable maximum allowable increase over the baseline
concentration in any area.

	(2)  Significant impact levels.  For purposes of PM2.5, the
demonstration required in paragraph (k)(1) of this section is deemed to
have been made if the emissions increase from the new stationary source
alone or from the modification alone would cause, in all areas, air
quality impacts less than the following amounts:

Pollutant	Averaging time	Class I Area 	Class II 

Area	Class III

Area 

PM2.5	Annual		0.06 µg/m3		0.3 µg/m3		0.3 µg/m3

	24-hour		0.07 µg/m3		1.2 µg/m3		1.2 µg/m3



* * * * *

	(p)  * * *

	(5)  * * *

Pollutant	Maximum allowable increase (micrograms per cubic meter)

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

Annual arithmetic mean	

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

4

9

17

30

20

91

325

25



* * * * *

 We view “promulgation” to occur on the date that a final rule is
published in the Federal Register.  Hence, references in this preamble
to the date of promulgation of this final rule alternatively refer to
the date of publication of this final rule.

 We have delegated our authority to some states to implement the federal
PSD program.  The EPA remains the reviewing authority in non-delegated
states lacking SIP-approved programs and in Indian country.

 The basic monitoring exemption provision is part of the original
monitoring requirements adopted in the 1980 PSD rulemaking.  45 FR
52710, August 7, 1980.

 Baseline dates are pollutant specific.  That is, a complete PSD
application establishes the baseline date only for those regulated NSR
pollutants that are projected to be emitted in significant amounts (as
defined in the regulations) by the applicant’s new source or
modification.  Thus, an area may have different baseline dates for
different pollutants.  

 See EPA’s “Guideline on Air Quality Models” at 40 CFR part 51,
Appendix W.

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 h

 as Class I includes the fundamental purposes for which such lands have
been established and preserved by the Congress and the responsible
federal agency.  For example, under the 1916 Organic Act to establish
the National Park Service (16 U.S.C. 1), the purpose of such national
park lands ‘is to conserve the scenery and the natural and historic
objects and the wildlife therein and to provide for the enjoyment of the
same in such manner and by such means as will leave them unimpaired for
the enjoyment of future generations.’”  S. Rep. No. 95-127 at 36
(1977).

 Under the 2005 NOx regulation, states can adopt measures other than
increments as long as they can demonstrate that the measures selected
comply with the same criteria and goals of sections 166 (c) and (d) of
the Act that must be met for increments.

 We also believe that we clearly described how section 166(f) might
provide alternative authority for establishing increments for PM2.5
(see, e.g., 72 FR 54120 - 54121), but will not address that in detail
here because the increments in this rule are not based on section 166(f)
authority. 

 Even if such a waiver of the Class I increment is allowed upon a
finding of no adverse impact, the source must comply with such emissions
limitations as may be necessary to ensure that alternative increments
specified in the rules for SO2 or PM are not exceeded.  The alternative
increments are generally at the level of the Class II increments, with
the lone exception being a more restrictive 3-hour increment for SO2. 
Section 165(d)(2)(C)(iv).  The EPA made this provision applicable to the
PSD provisions for NOx at the level of the NO2 Class II increment (53 FR
3704; 53 FR 40656) and substituted the PM10 Class II increments for the
statutory alternative PM increments, which were based on TSP (58 FR
31622).  This final rule expands this provision to include the PM2.5
Class II increments as well.  See 40 CFR 51.166(p)(4) and 52.21(p)(5).

 In response to concerns that Class I increment would hinder growth in
areas surrounding the Class I area, Congress established Class I
increments as a means of determining where the burden of proof should
lie for a demonstration of adverse effects on AQRVs.  See Senate Debate,
June 8, 1977 (3 LH at 725).

 See S. Rep. 95-127, at 12, reprinted at 3 LH at 1386, 1410 (describing
the goal of protecting “air quality values” in “Federal lands –
such as national parks and wilderness areas and international parks,”
and in the next paragraph and subsequent text using the term “air
quality related values” to describe the same goal); id. at 35, 36
(“The bill charges the Federal land manager and the supervisor with a
positive role to protect air quality values associated with the land
areas under the jurisdiction of the [FLM]” and then describing the
statutory term as “air quality related values”).  H.R. Report 95-564
at 532 (describing duty of Administrator to consider “air quality
values” of the tribal and State lands in resolving an appeal of a
tribal or State redesignation, which is described in the final bill as
“air quality related values”).

 We have paraphrased these factors here and in other sections to
facilitate the explanation of our reasoning.  However, we recognize, as
we did in our regulation for NOx, that the statutory language is broader
than the shorthand we use here for convenience.

 Note that the PM10 increment may still be more limiting in areas where
much of that increment has already been consumed.

 The 24-hour PM2.5 NAAQS (35 µg/m3) is about 23 percent of the 24-hour
PM10 NAAQS (150 µg/m3).

 The review completed in 2006 updated the previous review, which began
in 1994 and resulted in revised standards for PM in 1997.

 It should be noted, however, that an increment does not allow air
pollution levels in an area to increase beyond the ambient concentration
of a pollutant that would exceed the level allowed by the NAAQS.

 Docket No. EPA-HQ-OAR-2006-0605 can be accessed on line at   HYPERLINK
"http://www.regulations.gov"  www.regulations.gov . 

 In the 2005 OAQPS Staff Paper reviewing the NAAQS for PM, EPA cited the
following accepted definition of “critical load”: “quantitative
estimate of an exposure to one or more pollutants below which
significant harmful effects on specified sensitive elements of the
environment do not occur according to present knowledge.”  See page
6-45.

 The commenter cited   HYPERLINK
"http://www.nps.gov/shen/naturescience/visibility_and_haze.htm" 
http://www.nps.gov/shen/naturescience/visibility_and_haze.htm  for
historic visibility in national parks.

 “A source will be considered to impact an area if it has an impact of
1 µg/m3 or more of SO2 or PM on an annual basis.  This figure has been
selected because it corresponds to levels of significance used in
previous Agency determinations for SO2 and PM.  45 FR 52676, August 7,
1980, at page 52716.  

 We note that, under the 2007 NPRM, we proposed that the SILs for PM2.5
would not be treated as a minimum program element for state PSD
programs; however, the proposed regulatory language incorrectly stated
the “the plan shall provide”, which would indicate that the use of
the SILs for PM2.5 was required in the state plan.  This final rule
corrects this error.

 See “Information Collection Request (ICR) for the Prevention of
Significant Deterioration for PM2.5 - Increments, Significant Impact
Levels and Significant Monitoring Concentration,” Docket No.
EPA-HQ-OAR-2007-0628.

 In 1985, the requirements now contained in 40 CFR 51.165(b) were
contained in 40 CFR 51.18(k), which was later part of a major
restructuring of the part 51 SIP requirements. 

 In the case of a NAAQS compliance analysis, all sources in the area are
considered to contribute to the air quality levels; for increments,
however, “all” refers only to those sources whose emissions, in
whole or in part, consume PSD increment for a particular pollutant.

 The provision for the monitoring exemption was originally promulgated
at 40 CFR 51.24(i)(8) and 52.21(i)(8); it should be noted, however, that
this provision is now found at 40 CFR 51.166(i)(5) and 52.21(i)(5). 

 This information is contained in a March 12, 2009 internal EPA
memorandum from Dennis Crumpler to Raj Rao, titled “PSD Monitoring De
Minimis Concentration for PM2.5,” which has been placed in the docket
for this rulemaking.

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