Technical Support Document (TSD)

For the Modeling and Weight of Evidence (WOE) Portions of the Document
Entitled “Delaware State Implementation Plan

For Attainment of the PM2.5 Annual National Ambient Air Quality
Standard,”        January 3, 2008

TSD Prepared May, 2010

Todd A. Ellsworth

Office of Air Monitoring and Analysis , 3AP40

U.S. Environmental Protection Agency, Region 3

1650 Arch Street

Philadelphia, Pennsylvania 19103

/s/

____________________________________________

Reviewed by Walter Wilkie, Associate Director,

Office of Air Monitoring and Analysis (3AP40)

June 15, 2010

_________________

Date Signed

Technical Support Document for the Modeling Portion Of the State of
Delaware’s Ozone State Implementation Plan (SIP) Entitled “Delaware
State Implementation Plan

For Attainment of the PM2.5 Annual National Ambient Air Quality
Standard, January 3, 2008”

Purpose of the Technical Support Document

This Technical Support Document (TSD) describes the Environmental
Protection Agency’s (EPA’s) evaluation of the modeling and weight of
evidence (WOE) portion of Delaware’s State Implementation Plan (SIP)
revision entitled “Delaware State Implementation Plan For Attainment
of the PM2.5 Annual National Ambient Air Quality Standard, January 3,
2008.”  This SIP revision will hereafter be referred to as the
Delaware PM2.5 SIP.

In April 2005, EPA designated 126 areas of the country as
“non-attainment” under the annual fine particle (PM2.5) National
Ambient Air Quality Standard (NAAQS).  Among those non-attainment areas
is the Philadelphia-Wilmington, PA-NJ-DE PM2.5 Non-Attainment Area
(NAA).  This NAA includes:  New Castle County Delaware, Burlington and
Camden Counties in New Jersey and Bucks, Chester, Delaware, Montgomery
and Philadelphia Counties in Pennsylvania. According to the federal
Clean Air Act (CAA) and the EPA Implementation Rule, this entire NAA
must attain compliance with the annual PM2.5 NAAQS by 2010.

The purpose of this TSD is to provide more detailed information than can
be contained in the official notice published in the Federal Register. 
Readers who need more information than we provide in this TSD or want to
review the modeling in more detail should read the above referenced
Delaware SIP.  

The Regulatory Framework 

On July 18, 1997 (62 FR 36852), EPA established PM2.5 NAAQS, including
an annual standard of 15.0 µg/m3 based on a 3-year average of annual
mean PM2.5 concentrations, and a 24-hour (or daily) standard of 65
µg/m3 based on a 3-year average of the 98th percentile of 24-hour
concentrations.  EPA established the standards based on significant
evidence and numerous health studies demonstrating that serious health
effects are associated with exposures to PM2.5.

Following promulgation of a new or revised NAAQS, EPA is required by the
CAA to designate areas throughout the United States as attaining or not
attaining the NAAQS; this designation process is described  in section
107(d)(1) of the CAA.  In 1999, EPA and State Air-quality Agencies
initiated the monitoring process for the 1997 PM2.5 NAAQS, and, by
January 2001, established a complete set of air-quality monitors.  On
January 5, 2005, EPA published initial air-quality designations for the
1997 PM2.5 NAAQS (70 FR 944), based on air-quality monitoring data for
calendar years 2001-2003.

On April 14, 2005, EPA published a final supplemental rule amending the
Agency’s initial designations (70 FR 19844).  EPA did not consider
modifications made in this rule to be “re-designations” because the
changes were made before April 5, 2005, the effective date of the
initial designations.  As a result of the final supplemental rule, PM2.5
nonattainment designations are in effect for 39 areas, comprising 208
counties within 20 States (and the District of Columbia) nationwide,
with a combined population of about 88 million.  The Delaware portion of
the Philadelphia-Wilmington, PA-NJ-DE PM2.5 NAA   which is the subject
of this proposed rulemaking, is included in the list of areas not
attaining the 1997 PM2.5 NAAQS.  The only Delaware County included in
the Philadelphia-Wilmington, PA-NJ-DE PM2.5 NAA is New Castle County.

On October 17, 2006, EPA strengthened the 24-hour PM2.5 NAAQS to 35
µg/m3, and retained the level of the annual PM2.5 standard at 15.0
µg/m3 (see 71 FR 61144).  On November 13, 2009, EPA designated areas as
either attainment/unclassified or nonattainment with respect to the
revised 24-hour NAAQS (see 74 FR 58688).  In the November 2009
designation action, EPA established a deadline of December 14, 2012, for
States to submit attainment plans for areas designated as nonattainment
for the revised 24-hour PM2.5 NAAQS.  Therefore the Delaware PM2.5 SIP
does not address the current 24-hour PM2.5 NAAQS.

Of relevance to the proposed rulemaking herein, 74 FR 58688 clarified
designations for the 1997 PM2.5 NAAQS by relabeling the existing
designation tables to identify designations for the annual NAAQS, and by
providing a separate table identifying designations for the 1997 24-hour
NAAQS (i.e., 65 µg/m3).  In that table, the Philadelphia-Wilmington,
PA-NJ-DE PM2.5 NAA is designated as attaining the 1997 

24-hour PM2.5 NAAQS. 

 

  

Introduction to the Delaware State Implementation Plan for the Annual
Average PM 2.5 Standard

On July 18, 1997, EPA established a health based PM2.5 NAAQS at 15.0
micrograms per cubic meter (µg/m3), annual average.  New Castle County,
Delaware was designated by the EPA as being in non-attainment for this
annual PM2.5 NAAQS in April 2005.  Kent and Sussex Counties were
designated as attainment; however, sources within these counties emit
PM2.5 and PM2.5 precursors which contribute to PM2.5 non-attainment in
New Castle County. 

 

The PM2.5 SIP includes plans to reduce PM2.5 emissions for Delaware’s
portion of the Philadelphia-Wilmington, PA-NJ-DE PM2.5 NAA.  The SIP
also includes modeling that will predict whether the area will meet the
PM2.5 standard by the attainment date.  This TSD reviews Delaware’s
documentation of modeling that shows attainment of the annual average
PM2.5 standard by the 2010 attainment date.  All of the States in the
northeastern United States cooperated via the Ozone Transport
Commission’s (OTC) Modeling Committee to prepare the modeling that was
performed by the New York State Department of Environmental Conservation
(NYSDEC) and supporting organizations.

Delaware believes that their PM2.5 SIP demonstrates that all of the CAA
and Rule requirements associated with the annual PM2.5 NAAQS have been
met;  and that Delaware and the entire Philadelphia-Wilmington-DE-PA-NJ
NAA will attain compliance with the annual PM2.5 NAAQS as expeditiously
as practicable, and not later than 2010.  

What Are The Components Of A Modeled Attainment Demonstration?

Modeling Process Overview                                               
                                                                        
                  

Delaware is a member of the Mid-Atlantic/Northeast Visibility Union
(MANE-VU) Regional Planning Organization (RPO).  The MANE-VU RPO was
tasked with the assignment of preparing a PM-2.5 modeling platform that
all member states could use to demonstrate compliance with the 1997
PM2.5 NAAQS.

The New York State Department of Environmental Conservation (NYSDEC) was
the lead agency for coordinating and running the modeling platform used
by the MAVE-VU RPO.  Modeling centers responsible for running the
platform included the NYSDEC, the University of Maryland at College Park
(UMD), the Northeast States for Coordinated Air Use Management
(NESCAUM), the New Jersey Department of Environmental Protection (NJ
DEP), and the Virginia Department of Environmental Quality (VA DEQ). 
Each modeling center was responsible for installing the modeling
platform, conducting diagnostic tests and completing a benchmark run to
ensure accurate results.   

                                                                        
                                                              

The MANE-VU RPO used the Community Multi-scale Air Quality model (CMAQ)
version 4.4 as its photochemical grid model.  The model uses simulations
of chemical reactions, emission of PM2.5 and PM2.5 precursors and a
sophisticated meteorological model to produce PM2.5 concentrations over
the eastern United States.  The meteorological data used in the
meteorological model was for the base year PM2.5 season of 2002.  The
photochemical grid model was run with the base year meteorology and base
year emissions to determine if the model performance was satisfactory. 
Once the model performance was determined to be adequate, 2009 ozone
concentrations were modeled by running the model with projected
emissions for 2009 and the original 2002 meteorology.  The meteorology
was held constant so that the results of changing the emissions would
not be influenced by changing meteorology.

The EPA modeling guidance recommends that States use the modeled PM
concentrations in a relative sense and not rely solely on the
concentrations the model predicts for the attainment year (2009).  A
modeled attainment test is an exercise in which an air quality model is
used to simulate current and future air quality.  If future estimates of
PM2.5 concentrations are less than the NAAQS, then this element of the
attainment test is satisfied.  EPA’s recommended test is one in which
model estimates are used in a “relative” rather than “absolute”
sense.  Ratios of the model’s future (2009) predicted PM2.5
concentrations to base year (2002) predictions are calculated for all
PM2.5 monitor locations.  These ratios are called relative response
factors (RRF).  Future PM2.5 concentrations are estimated at existing
monitoring sites by multiplying a modeled relative response factor at
locations “near” each monitor by the observation-based,
monitor-specific, “baseline” design value.  The resulting predicted
“future concentrations” are compared to NAAQS.  The PM2.5 attainment
test is complicated and reflects the fact that PM2.5 is a mixture
species.  Therefore, the attainment test for PM2.5 is called the
Speciated Modeled Attainment Test (SMAT).  In the test, ambient PM2.5 is
divided into major components.  These are:

- mass associated with sulfates

- mass associated with nitrates

-mass associated with ammonium

- mass associated with organic carbon 

- mass associated with elemental carbon

- mass associated with particle bound water

- mass associated with “other” primary inorganic particulate matter

- and passively collected mass

A separate RRF is calculated for each of the PM2.5 components (except
passive mass).

Each of these site-specific ratios are called component-specific RRFs. 
Future PM2.5 design values are estimated at existing monitoring sites by
multiplying modeled relative response factors “near” each monitor
times the observed “component specific design value.”  This latter
quantity is estimated using measured site-specific design values for
PM2.5 in concert with available measured composition data.  Future
site-specific PM2.5 design values at a site are estimated by adding the
future year values of the seven PM2.5 components.  If all future
site-specific PM2.5 design values are less than or equal to 15.0
micrograms per cubic meter (µ/m3) at all locations, the test is passed
and the modeling system will have predicted attainment of the PM2.5
annual air quality standard. 

 

                                                                        
                                                       

Steps Required in a Modeled Attainment Demonstration

The modeling guidance lists nine steps for preparing modeling to
demonstrate attainment of the PM2.5 standard.  

1.  Develop a conceptual description of the problem to be addressed.

2.  Develop a modeling/analysis protocol.

3.  Select an appropriate model to support the demonstration.

4.  Select appropriate meteorological time periods to model.

5.  Choose an appropriate area to model with appropriate
horizontal/vertical resolution                                          
       

      and establish the initial and boundary conditions that are
suitable for the application.

6.  Generate meteorological inputs to the air quality model.

7.  Generate emissions inputs to the air quality model.

8.  Run the air quality model with base case emissions and evaluate the
performance.

     Perform diagnostic tests to improve the model, as necessary.

9.  Perform future year modeling (including additional control
strategies, if necessary)                         and apply the
attainment test.

How Did Delaware Address All Of The Components Of A Modeled Attainment
Demonstration?

The Delaware PM2.5 SIP addresses each of the elements of a modeled
attainment demonstration as follows:

Conceptual description of the problem

A conceptual model describes how weather patterns affect the formation
and transport of PM2.5, accounting for emissions and photochemistry. 

The conceptual model for the Delaware PM2.5 SIP is described in the
Attachment 1 entitled:  The Nature of the Fine Particle and Regional
Haze Air Quality Problems in the Mid-Atlantic Northeast Visibility
Union(MANE-VU) Region: A Conceptual Description (NESCAUM), November
2006.  This document was prepared by Northeast States for Coordinated
Air Use Management (NESCAUM) for use by the OTC member States, and it
provides the conceptual description of the fine particle issues in the
OTC states, consistent with the EPA’s guidance.

The NESCAUM document contains a conceptual description that explains how
elevated regional PM2.5 peak concentrations in the summer differ
significantly from the largely urban peak concentrations observed during
winter.  On average, summertime concentrations of sulfate in the
northeastern United States are more than twice that of the next most
important fine particle constituent, organic carbon (OC), and more than
four times the combined concentration of nitrate and black carbon (BC)
constituents.  Episodes of high summertime sulfate concentrations are
consistent with stagnant meteorological flow conditions upwind of the
Philadelphia-Wilmington, PA-NJ-DE PM2.5 NAA and the accumulation of
airborne sulfate (via atmospheric oxidation of SO2) followed by
long-range transport of sulfur emissions from industrialized areas
within and outside the area.  National assessments have indicated that
in the winter, sulfate levels in urban areas are higher than background
sulfate levels across the eastern U.S., indicating that the local urban
contribution to wintertime sulfate levels is significant relative to the
regional sulfate contribution from long-range transport.  A network
analysis for the winter of 2002 suggests that the local enhancement of
sulfate in urban areas of the MANE-VU region ranges from 25 to 40% and
that the long-range transport component of PM2.5 sulfate is still the
dominant contributor in most eastern cities.

In the winter, urban OC and sulfate each account for about a third of
the overall PM2.5 mass concentration observed in Philadelphia and New
York City areas.  Nitrate also makes a significant contribution to urban
PM2.5 levels observed in the northeastern United States during the
winter months.  Wintertime concentrations of OC and nitrate in urban
areas can be twice the average regional concentrations of these
pollutants, indicating the importance of local source contributions. 
This is likely because winter conditions are more conducive to the
formation of local inversion layers which prevent vertical mixing. Under
these conditions, emissions from tailpipe, industrial and other local
sources become concentrated near the Earth’s surface, adding to
background pollution levels associated with regionally transported
emissions. 

The Model Used in the Attainment Demonstration

By agreement of the OTC, NYSDEC ran the Community Multi-scale Air
Quality Model version 4.4 (CMAQ) for the States in the northeast ozone
transport region, including Delaware.  CMAQ is an acceptable model,
listed in the photochemical modeling guidance as a currently used
photochemical grid model.  EPA agrees CMAQ is appropriate for this
modeling demonstration.  The inputs to the model are described in
Section 7 of the Delaware PM2.5 SIP.  

Meteorological Time Periods Used in the Modeling

The Delaware PM2.5 SIP notes that the OTC Modeling Committee agreed to
model all days in 2002.  Modeling an entire year covers many different
kinds of PM episodes and exceeds EPA’s recommendations for episode
selection.  Due to the fact that the attainment demonstration is being
conducted using a resource intensive photochemical grid model, EPA
accepts the use of a single, recent “representative” year to be used
for an annual model simulation.  Two factors were used in selecting 2002
as the “representative” year - the observed annual mean
concentrations of PM2.5 are close to the 3-year observed design value at
all, or most monitoring sites, and the pattern of quarterly mean values
is similar to the pattern of quarterly mean concentrations averaged over
3 years.

Meteorological Data Used in the Air Quality Model

The OTC Modeling Committee decided to use a prognostic meteorological
model that provides life-like meteorological inputs to the photochemical
grid model.  The Pennsylvania State University/National Center for
Atmospheric Research Mesoscale Meteorological Model (MM5) version 3.6
was chosen for the modeling analysis.  The MM5 model provides a
reasonable representation of weather conditions at the surface and
aloft.  

Domain of the Model, Horizontal/Vertical Resolution and the Initial and
Boundary Conditions

The modeling domain extends from Maine to Florida and out in the
Atlantic Ocean on the east and west to the Mississippi River.  The size
of the modeling domain was made large enough to include all emission
sources that affect PM2.5 concentration in the northeastern United
States.  Even this boundary is defined by a larger photochemical
modeling domain that covers much of North America.  Over the
northeastern United States, the model used 12 kilometer grid cells. The
Philadelphia-Wilmington, PA-NJ-DE PM 2.5 NAA is included in the 12
kilometer grid cell area.  The OTC Modeling Committee used a
12-kilometer grid size for the areas in and near its states to provide a
fine enough grid resolution to adequately capture the PM patterns
experienced in the ozone transport region (OTR).  Outside the local
areas the grid resolution used in the modeling is 36 kilometers.  The
selection of model domains and horizontal grid resolution was deemed
acceptable to EPA.  

Vertical resolution is the number of layers and the size of each layer
in the model.  The layers in the photochemical grid model were set up to
be compatible with the model that produced weather conditions for the
photochemical grid model.  The vertical resolution used in the modeling
exercise followed EPA’s modeling guidance and therefore adequately
represents the atmosphere where PM2.5 is emitted, forms and is
transported.  

Emissions Used in the Air Quality Model

The emissions data for 2002 were generated by individual States within
the OTR and assembled and processed through the Mid-Atlantic Northeast
Visibility Union (MANE-VU), a Regional Planning Organization (RPO). 
These emissions were then processed by NYSDEC using the SMOKE emissions
processor to provide CMAQ compatible inputs.   The 2002 emissions for
the non-OTR areas within the modeling domain were obtained from the
corresponding RPOs and were processed using SMOKE, in a manner similar
to that of the OTR emissions.

The OTR states, through MANE-VU, contracted MACTEC Federal Programs
(called Contractor) to develop 2009, 2012 and 2018 inventories based
upon 2002 inventories that the states had previously developed for use
in the base-year model work.  The Contractor, in consultation with the
States, developed the necessary growth and control factors and applied
to the 2002 inventory.  Emissions for mobile sources and the electric
energy generating units (EGUs) was not part of the Contractor’s
effort.  To generate on-road mobile emissions, the states provided the
Virginia Department of Environmental Quality (VADEQ) and NESCAUM with
appropriate MOBILE 6 input files along with the projected vehicle miles
traveled (VMT), which was coupled with hourly “gridded temperature”
information. As for the emissions from the EGU sector, the inter-RPO
work group utilized the Integrated Planning Model (IPM) to develop the
state and unit-level emissions.  These inventories are identified as
2009 on the way (2009OTW), since they reflect all emission control
measures that were promulgated or would become effective on or before
2009.

Emission inventory details are provided in Sections 3, 4 and 6.3.5 of
the Delaware PM2.5 SIP.

Base Case Run Model Performance Evaluation

NY DEC performed a model evaluation for the OTC to determine how well
CMAQ reproduced the Philadelphia-Wilmington, PA-NJ-DE PM2.5 NAA 2002
PM2.5 concentrations. 

CMAQ was employed to simulate PM2.5 for the calendar year 2002.  A
review of PM2.5 and its individual species was conducted for the study
domain.

The CMAQ model performance for surface PM2.5 is good with acceptable
bias and error.  Several observations can be made with respect to model
performance, including the following:

Approximately 80-90% of organic mass (OM) is in the primary fraction. 
Observed OM has distinct maximum during summer when secondary formation
is highest; CMAQ exhibits substantial under-prediction in secondary
organic aerosols (SOA).  The predicted primary OM is highest during the
winter.

CMAQ captures seasonal variation in SO4 well.

CMAQ appears to overestimate primary PM2.5 components (EC, soil, primary
OM), especially during colder months.

CMAQ appears to underestimate secondary OM during the summer.

These issues are not of great regulatory concern since attainment tests
are based on the application of relative response factors.  In summary,
the regional and local model performance is acceptable for PM2.5.  While
there are some differences between the spatial data between sub-regions,
there is nothing to suggest a tendency for the model to respond in a
systematically different manner between regions.  Examination of the
statistical metrics by sub-region confirms the absence of significant
performance problems arising in one area but not in another, building
confidence that the CMAQ modeling system is operating consistently
across the full OTC domain.  This confidence in the modeling results
allows for the modeling system to be used to support the State
Implementation Plan to meet the 24-hour and annual PM2.5 NAAQS.

2009 Control Case Modeling and the Modeled Attainment Test

QS include an annual standard of 15 μg/m3 based on the 3-year average
of annual mean PM2.5 concentrations.

The purpose of a modeling assessment is to determine if control
strategies currently being implemented (“on the books”) will lead to
attainment of the annual average NAAQS for PM2.5 by 2009.  The modeling
is applied in a relative sense, similar to the 8-hour ozone attainment
test.  However, the PM2.5 attainment test is more complicated and
reflects the fact that PM2.5 is a mixture.  In the test, ambient PM2.5
is divided into major components, with a separate relative response
factor (RRF) and future design value (DVF) calculated for each of the
PM2.5 components.  Since the attainment test is calculated on a per
species basis, the attainment test for PM2.5 is referred to as the
Speciated Modeled Attainment Test (SMAT).  The following sections
outline the process to determine that 2009 projections of PM2.5 will
meet the NAAQS from regional modeling, as suggested in EPA’s modeling
guidance.

Annual SMAT Results                                                     
                                            

Table 1 presents the results of the annual SMAT results for the PA-NJ-DE
nonattainment area. The SMAT results demonstrate that the projected
average annual arithmetic mean PM2.5 concentration calculated at each
FRM monitor attains the annual PM2.5 NAAQS.  Specifically, all future
design value (DVF) calculations are less than15 μg/m3.   Table 1
presents the results of the annual SMAT results for a suite of regional
modeling runs conducted by OTC each representing OTB/OTW – “On the
Books, On the Way” control measures.  All runs demonstrate compliance
with the annual NAAQS.

	

Table 1: Annual SMAT Results for PA-NJ-DE Nonattainment Area

2009 On-The-Books-On-The-Way Control Measures

AIRS ID	Site Name	County	State	2000-2004 DVB	2009





Q1	Q2	Q3	Q4	DVF

10-003-1003	Bellefonte	New Castle	DE	14.91	15.54	15.45	13.02	12.3

10-003-1007	Lums Pond	New Castle	DE	13.30	14.49	15.69	11.10	11.4

10-003-1012	Newark	New Castle	DE	15.56	15.00	15.75	13.57	12.5

10-003-2004	MLK	New Castle	DE	16.79	15.60	16.66	14.26	13.3

34-007-0003	Copewood E Davis	Camden	NJ	13.5	14.3	16.6	12.7	12.1

34-007-1007	Pennsauken TWP	Camden	NJ	14.0	14.0	15.7	13.6	12.2

34-015-0001	Gibbstown Municipal Bldg.	Gloucester	NJ	13.9	13.4	16.0	11.4
11.7

42-017-0012	Bristol	Bucks	PA	14.14	13.68	14.70	13.82	12.4

42-029-0100	Belmont Avenue	Chester	PA	14.44	14.07	16.72	14.12	12.8

42-045-0002	Chester	Delaware	PA	15.07	15.96	16.35	12.63	13.3

42-091-0013	Norristown	Montgomery	PA	13.61	13.77	14.90	12.71	12.0

42-101-0004	Philadelphia AMS	Philadelphia	PA	14.13	13.86	16.20	12.83
12.5

42-101-0020	Philadelphia Belmont Ave	Philadelphia	PA	14.0	14.4	15.4	13.1
12.0

42-101-0024	Philadelphia North East	Philadelphia	PA	12.43	12.37	15.56
11.45	11.0

42-101-0047	Philadelphia Broad Street	Philadelphia	PA	15.54	14.88	16.89
13.25	12.8

42-101-0136	Philadelphia Elmwood	Philadelphia	PA	13.75	13.04	15.75	11.93
11.5



Summary of Photochemical Grid Modeling Results

μg/m3 in the Philadelphia-Wilmington, PA-NJ-DE NAA.  Thus, based on
EPA’s modeled attainment test, the Philadelphia-Wilmington, PA-NJ-DE
PM2.5 NAA will reach attainment of the annual average PM2.5 standard in
2009 before the attainment date of April 5, 2010. 

Unmonitored Area Analysis

The modeled attainment test does not address future air quality at
locations where there is not a PM2.5 monitor nearby.  To guard against
the possibility that air quality levels could exceed the standard in
areas with limited monitoring, EPA suggests that additional review is
necessary, particularly in nonattainment areas where the PM2.5
monitoring network just meets or minimally exceeds the size of the
network required to report data to Air Quality System (AQS).  This
review is intended to ensure that a control strategy leads to reductions
in PM2.5 and its constituent pollutants at other locations that could
have baseline (and future) design values exceeding the NAAQS were a
monitor deployed there.  The test is called an “unmonitored area
analysis”.  The purpose of the analysis is to use a combination of
model output and ambient data to identify areas that might exceed the
NAAQS if monitors were located there. 

 

It is important to note that Delaware currently operates a network of
six PM2.5 monitors. Four of these monitors are in New Castle County,
which is part of the PA-NJ-DE nonattainment area.  Some of these
monitors were established as State and Local Air Monitoring Stations
(SLAMS).  These SLAMS monitors were selected based on specific
monitoring objectives (background concentration, area of highest
concentration, high population, source impact, transport, and rural
impact) as required by EPA and siting scales (micro, middle,
neighborhood, urban, and regional) established by EPA.  

EPA believes that the density of the monitoring network in New Castle
County relieves the necessity of applying this additional analysis.

Local Area Analysis

EPA modeling guidance recommends that a local area analysis be performed
for those areas where local primary PM2.5 sources are thought to be
contributing to a monitor and causing non-attainment of the NAAQS.  At
this time, no monitors within the PA-NJ-DE nonattainment area are
projected to exceed the NAAQS so it does not appear to be a necessary
requirement in this circumstance to conduct the local area analysis. 
Furthermore, existing monitoring data suggests a uniform regional
pattern with respect to PM2.5 concentrations rather than any “hot
spot” monitors. 

Supplemental Analyses and Weight of Evidence (WOE) Determination 

EPA(s modeling guidance states that additional analyses are recommended
to determine if attainment will be likely, even if the modeled
attainment test is “passed.”  The guidance recommends supplementary
analyses in all cases.  EPA(s modeling guidance describes how to use a
photochemical grid model and additional analytical methods to complete a
WOE analysis to estimate if emissions control strategies will lead to
attainment.  A WOE analysis is a supporting analysis that helps to
determine if the results of the photochemical modeling system are
correctly (or not correctly) predicting future air quality. 

All models, including the CMAQ, model have inherent uncertainties. Over
or under prediction may result from uncertainties associated with
emission inventories, meteorological data, and representation of PM2.5
chemistry in the model. Therefore, EPA modeling guidance provides for
other evidence to address these model uncertainties so that proper
assessment of the probability to attain the applicable standards can be
made.

μg/m3 for annual PM2.5 and 62 μg/m3 for 24-hour PM2.5) need more
limited supporting material. 

Due to the fact that the modeling results presented in Table 1 fall well
below the aforementioned “weight of evidence” thresholds established
by EPA, a limited supplemental analysis was deemed necessary to support
the 2009 attainment demonstration.

  

Trends in PM2.5 Design Values  

Figure 1 below shows the annual PM2.5 design value trends for the period
2000-2009 for all monitors in the PA-NJ-DE PM2.5 NAA including the
monitors in Kent and Sussex Counties.  It is clear from this figure that
all the monitors show a downward trend in the annual PM2.5 design value.
 It is noteworthy that from 2008 and after the design values at all
monitors are in compliance with the annual PM2.5 standard.  Please note
that the 2009   PM2.5 design values represented in Figure 1 are
preliminary values. 

Figure 1

 

Summary of EPA’s Evaluation Delaware’s WOE Analysis

Design values at all monitors have trended downward since the year 2000.
This information coupled with current annual average PM2.5 design all
below the annual average PM2.5 standard since 2007 support the
demonstration of attainment by the 2010 attainment date.

  

Summary of EPA’s Technical Findings

The result of the photochemical grid modeling analysis using EPA’s
recommended methods predicts that the PA-NJ-DE PM 2.5 NAA will attain
the annual average PM2.5 standard by the attainment date of April 5,
2010.

Recommendation of Approval of Attainment Demonstration

EPA has carefully evaluated the information provided by Delaware PM2.5
SIP.



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ational Ambient Air Quality Standard by the applicable attainment date.

Attachment:

Attachment 1: The Nature of the Fine Particle and Regional Haze Air
Quality Problems in the Mid-Atlantic Northeast Visibility Union
(MANE-VU) Region: A Conceptual Description (NESCAUM), November 2006.

 	Environmental Protection Agency, Clean Air Fine Particle
Implementation Rule, 40 CFR Part 51, March 29, 2007.

  

 	  HYPERLINK
"http://www.epa.gov/fedrgstr/EPA-AIR/2005/January/Day-05/a001.htm"  70
FR 944 , January 5, 2005

 Guidance on the Use of Models and Other Analyses for Demonstrating
Attainment of Air Quality Goals for Ozone, PM2.5, and Regional Haze, EPA
-454/B-07-002, April 2007

 The guidance also states that additional analyses are recommended to
determine if attainment will be likely, even if the modeled attainment
test is “passed”.  The guidance recommends supplementary analyses in
all cases.  

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