Technical Support Document

For the Modeling and Weight of Evidence (WOE) Portions of the Document
Entitled “Cecil County, Maryland

8-Hour Ozone

State Implementation Plan and Base Year Inventory

SIP Revision:

07-05

June 15, 2007

                                                                        
                                                         

                                                                        
                                                        

TSD Prepared June, 2012

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 22, 2012

_________________

Date Signed

Technical Support Document

For the Modeling and Weight of Evidence (WOE) Portions of the Document
Entitled “Cecil County, Maryland

8-Hour Ozone

State Implementation Plan and Base Year Inventory

SIP Revision:

07-05

June 15, 2007”

Purpose of the Technical Support Document

This Technical Support Document (TSD) describes the Environmental
Protection Agency’s (EPA’s) evaluation of the modeling and WOE
portions of Maryland’s State Implementation Plan (SIP) entitled
“Maryland State Implementation Plan for Attainment of the 8-Hour Ozone
National Ambient Air Quality Standard Reasonable Further Progress and
Attainment Demonstration, June 2007”, hereafter referred to as the
Maryland SIP.  Maryland is part of the Philadelphia-Wilmington-Atlantic
City ozone nonattainment area (Philadelphia area).  The Philadelphia
area is comprised of 18 counties in Pennsylvania, New Jersey, Delaware
and Maryland.  Classified as a “moderate” nonattainment area, the
Philadelphia area is required to attain the NAAQS by June 2010, in
effect, by the ozone season of 2009.  

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
Maryland SIP.      

Introduction to the Maryland State Implementation Plan for Ozone

The Maryland SIP includes plans to reduce ozone-causing emissions for
Maryland’s portion of the Philadelphia Area.  The Plan also includes
modeling that will predict whether the area will meet the ozone standard
by the due date.  This TSD reviews modeling and WOE portions of the
Maryland SIP.  This TSD reviews Maryland’s documentation of modeling
and WOE that attempts to show attainment of the eight-hour ozone
standard by the 2009 ozone season.  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.

Maryland believes that their SIP modeling when combined with additional
supporting analyses (Weight of Evidence) (WOE) “Demonstrates that the
entire Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD moderate
non-attainment area will attain the 8-hour ozone NAAQS in 2009”.  

What Are The Components Of A Modeled Attainment Demonstration?

Modeling Process Overview                                               
                                                                        
                  

The OTC Modeling Committee 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 ozone precursors and
a sophisticated meteorological model to produce ozone concentrations
over the eastern United States.  The meteorological data used in the
meteorological model was for the base year ozone 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 ozone concentrations in a
relative sense and not rely solely on the concentrations the model
predicts for the attainment year (2009).  The relative response factor
(RRF) used in the modeled attainment test is computed by taking the
ratio of the mean of the 8-hour daily maximum predictions in the future
to the mean of the 8-hour daily maximum predictions with baseline
emissions, over all relevant days. The base year ozone design values at
each monitor are then multiplied by the monitor-specific RRF to produce
an attainment year design value.  If the result is less than or equal to
84 ppb, at all locations, the modeling system will have predicted
attainment of the ozone air quality standard. 

The Regulatory Framework

Section 110 (a) (2) (k) of the Clean Air Act requires states to prepare
air quality modeling to show how they will meet ambient air quality
standards.   EPA determined that areas classified as ‘moderate’ or
above must use photochemical grid modeling or any other analytical
method determined by the Administrator to be at least as effective to
demonstrate attainment of the ozone health-based standard by the
required attainment date (40 CFR 51.908, published at 70 FR 71612 on
November 29, 2005).  In 40 CFR 51.903, published at 69 FR 23951 on April
30, 2004, EPA specified how areas would be classified with regard to the
eight-hour ozone standard set by EPA in 1997.  At 69 FR 23858, on April
30, 2004, EPA followed these procedures and classified the
Philadelphia-Wilmington-Trenton, PA-NJ-DE-MD and ozone nonattainment
area as moderate, so they must attain the 1997 eight-hour ozone standard
by June 2010.  Since the attainment date is June 2010 for moderate
areas, states must achieve emission reductions by the ozone season of
2009 in order for ozone concentrations to be reduced, and show
attainment, during the last complete ozone season before the 2010
deadline.  

The modeling guidance lists nine steps for preparing modeling to
demonstrate attainment of the ozone 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 Maryland Address All Of The Components Of A Modeled Attainment
Demonstration?

The Maryland 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 ozone, accounting for emissions and photochemistry. 
The Maryland SIP describes the climatology that produces high ozone
concentrations in the Philadelphia area.  On warm sunny days, winds from
the southwest and west blow emissions from sources of ozone-forming
chemicals both at the surface and aloft toward the Philadelphia area. 
In addition, emissions from large combustion sources in the Ohio Valley
and other areas are brought eastward by upper level winds to the east
coast, augmenting the ozone formed locally.  A complete conceptual
description of the ozone problem in the Philadelphia area is contained
in Section 12.1 of the Maryland SIP.

Modeling/analysis protocol

The Ozone Transport Commission’s (OTC’s) Modeling Committee
developed a protocol for modeling the ozone problem in the northeastern
United States.  The modeling protocol is located in Appendix H-1 of the
Maryland SIP.  It adequately describes how the photochemical grid model
will be used in the ozone attainment plans. 

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 Maryland.  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 12.2 of the Maryland SIP.

Meteorological Time Periods Used in the Modeling

Section 12.2 of the Maryland SIP notes that the OTC Modeling Committee
agreed to model the entire ozone season of 2002.  Using the entire ozone
season of 2002 covers many different kinds of ozone episodes and exceeds
EPA’s recommendations for episode selection.  2002 was a good year to
model because it was the base year for the attainment plans and as a
whole is representative of meteorological conditions conducive to
elevated concentrations of ozone.

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.  A summary of the MM5 application is contained in Section 12.2 of
the Maryland SIP. 

 

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 ozone formation 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 area 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 ozone
patterns experienced in the ozone transport region (OTR).  The OTC
Modeling Committee chose to use a 12 kilometer grid resolution based on
its states’ experiences with the one-hour ozone attainment modeling
that indicated that modeling at finer resolutions than 12 kilometers
would not result in increased model accuracy.  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.  The grid resolution, modeling domain and boundary
conditions are described in Section 12.2 of the Maryland SIP.

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 grid resolution used in the
modeling is described in Section 12.2 of the Maryland SIP.  The vertical
resolution used in the modeling exercise followed EPA’s modeling
guidance and therefore adequately represents the atmosphere where ozone
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 the Northeast
States for coordinated Air Use Management (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.

Details of emissions processing are provided in Appendices H-10 of the
Maryland SIP.

Base Case Run Model Performance Evaluation

NY DEC performed a model evaluation for the OTC to determine how well
CMAQ reproduced the Philadelphia nonattainment area’s 2002 ozone
season concentrations.  Model evaluation followed performance statistics
outlined in EPA modeling guidance.

The OTC’s evaluation included performance statistics for all monitors
inside the Philadelphia nonattainment area.  The model performance
evaluation results are presented in included in Appendix H-12 the
Maryland SIP.  The analysis indicates the modeling system does an
adequate job of estimating the eight-hour surface ozone concentrations
throughout the Philadelphia area.

2009 Control Case Modeling and the Modeled Attainment Test

The photochemical grid model used with projected emissions for 2009,
including emission changes due to regulations the states are planning to
implement and expected growth by the 2009 ozone season.   

Meteorological conditions from 2002, the same as the base year modeling,
were used in the 2009 modeling. Using the base case meteorology allows
the effect of changes in states’ emissions to be determined without
being influenced by yearly fluctuations in meteorology and is consistent
with EPA guidance.    

As described earlier in this TSD, the attainment test used in the
Philadelphia area                    modeling demonstration involved the
application of model-based RRFs to base year design values at each
monitor to produce projected future year design values (2009).  The
projected 2009 design values represent design values that should result
from emission controls Maryland and other states planned to have in
place in 2009.  The 2009 design values should be less than or equal to
84 ppb at all monitoring stations to meet the attainment test.  The SIP
modeling predicts that in 2009, Philadelphia area will not pass the
attainment test since design values are projected to be over the 84 ppb
standard (see Table 1 below). 

Table 1 Modeled Design Value

Monitor ID	Site Name	County	State	DVC (ppm)	RRF OTB/OTW V4	2009 Model DV
(ppm)	2009 Monitored   (ppm) 

100010002	Killens Pond	Kent	DE	88	0.8934	78	75

100031007	Lums Pond	New Castle	DE	91	0.8462	77	75

100031010	Brandywine	New Castle	DE	93	0.8781	81	78

100031013	Bellefonte	New Castle	DE	89	0.8759	77	74

100051002	Seaford	Sussex	DE	90	0.8462	76	76

100051003	Lewes	Sussex	DE	86	0.8956	77	76

240150003	Fair Hill	Cecil	MD	98	0.8336	81	84

340010005	Nacote Creek	Atlantic	NJ	88	0.8762	77	72

340070003	Camden	Camden	NJ	98	0.8996	88	87

340071001	Ancora State Hospital	Camden	NJ	100	0.8733	87	81

340110007	Millville	Cumberland	NJ	94	0.8486	79	78

340150002	Clarksboro	Gloucester	NJ	98	0.9004	88	83

340210005	Rider College	Mercer	NJ	97	0.8908	86	81

340290006	Colliers Mills	Ocean	NJ	107	0.8703	91	80

420170012	Bristol	Bucks	PA	99	0.8976	88	88

420290100	New Garden Airport	Chester	PA	94	0.8387	78	77

420450002	Chester	Delaware	PA	91	0.8705	79	77

420910013	Norristown	Montgomery	PA	92	0.8861	81	79

421010004	AMS Lab	Philadelphia	PA	72	0.9081	65	64

421010014	Roxboro	Philadelphia	PA	91	0.9070	82	81

421010024	NE Airport	Philadelphia	PA	97	0.9035	87	84

421010136	Elmwood	Philadelphia	PA	84	0.9070	76	82



Summary of Photochemical Grid Modeling Results

In summary, the basic photochemical grid modeling presented in the
Maryland SIP meets EPA’s guidelines and when used with the methods
recommended in EPA’s modeling guidance, is acceptable to EPA.  When
EPA’s attainment test is applied to the modeling results, the 2009
ozone design value is predicted to be 91 ppb in the
Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD ozone nonattainment
area.  Thus, based on EPA’s modeled attainment test, Philadelphia area
has not demonstrated that it will reach attainment of the ozone standard
in the 2009 attainment year with the modeled emission reduction
strategies committed to by the OTC states.  To make a case for
attainment, Maryland decided to use WOE to demonstrate attainment of the
ozone standard in the Philadelphia area.   

Weight of Evidence Demonstration

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 of the
eight-hour NAAQS for ozone.  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. 

The WOE portion of the Maryland SIP describes the analyses performed,
databases used, key assumptions and outcomes of each analysis, and why
the evidence, viewed as a whole, supports a conclusion that the
Philadelphia nonattainment area will attain the NAAQS despite the model
prediction that some monitors’ future design values exceed the current
eight-hour ozone standard.

Table 2 outlines under what circumstances a WOE demonstration is needed.
 Model-predicted design values are summarized above in Table 1.  Of the
twenty-two (22) ozone monitors in the Philadelphia nonattainment area
only eight (8) exceed the threshold (82 ppb) where the EPA modeling
guidance recommends a WOE demonstration.  Three of the monitors fall
within the 82-87 ppb threshold outlined in Table 1 and four others fall
within the last category listed in the WOE table included in the US EPA
guidance.   The Roxboro monitor is excluded from the WOE analysis since
its current design value is significantly lower than the eight-hour
standard (modeled 82 ppb, actual monitored 78 ppb).

The WOE analysis for the remaining seven monitors includes the
following:

A comparison of model-predicted 2009 ozone design values and monitored
design values for 2006 and 2009 

An analysis of recent ozone trends in the Philadelphia nonattainment
area,

Alternative methods for calculating the 2009 ozone design value.

Table 2.EPA Guidelines for Supplemental Analyses and Weight of Evidence
Determinations

Results of Modeled Attainment Test	Supplemental Analyses

Future Design Value < 82 ppb, all monitor sites	Basic supplemental
analyses should be completed to confirm the outcome of the modeled
attainment test

Future Design Value 82 - 87 ppb, at one or more sites/grid cells	A
weight of evidence demonstration should be conducted to determine if
aggregate supplemental analyses support the modeled attainment test

Future Design Value > 88 ppb, at one or more sites/grid cells	More
qualitative results are unlikely to support a conclusion differing from
the outcome of the modeled attainment test.

                                                                        
                                           Modeled Concentrations vs.
Monitored Design Values

Table 3 below lists the OTC modeled 2009 design values and the 2006-2011
monitored design values.  Maryland did not have access monitored ambient
ozone data from 2007-2011ambient data when it wrote its SIP. Because the
modeled 2009 and projected 2006 design values are surprisingly close to
one another with most modeled concentrations only slightly lower than
the monitored 2006 design values, Maryland SIP suggests that additional
reductions over the next three ozone seasons might bring several of the
monitors that are currently just over the eight-hour ozone standard into
attainment by the attainment date.  Classified as a “moderate”
nonattainment area, the Philadelphia area is required to attain the
NAAQS by June 2010, in effect, by end of 2009 ozone season.   As shown
in Table 3 by the end of the 2009 ozone season only two ozone monitors
(Bristol & Camden) were still monitoring nonattainment. However the 4th
high monitored 8-hour values in 2009 were less than or equal to 84 ppb,
the level needed to qualify for a one year extension of the attainment
date.  As a result, the EPA granted the Philadelphia area a one year
extension of the attainment date to June 2011 or effectively by the end
of the 2010 ozone season.

Additionally, the 2009 data presented Table 3 and earlier in Table 1
show that the model is over predicting the monitored design values by
anywhere from 1-13 ppb in 19 out of the 22 cases.    

Table 3.  Modeled vs. Monitored Design Values  

Monitor	Site ID Number	2009 Modeled   DV	2006 Monitored DV	2007
Monitored DV 	 2008  Monitored DV	2009  Monitored DV	2010  Monitored DV
2011  Monitored DV

Fairhill - CECIL CO, MD	240150003	81	90	93	90	84	80	81

Colliers Mills - OCEAN CO, NJ	340290006	91	93	92	87	80	81	81

Rider College - MERCER CO, NJ	340210005	86	87	91	87	81	78	78

Ancora State Hospital - CAMDEN CO, NJ	340071001	87	89	88	86	81	80	80

Camden - CAMDEN CO, NJ	340070003	88	84	88	87	87	83

	Clarksboro - GLOUCESTER CO, NJ	340155001	88	86	91	87	83	81	82

Bristol - BUCKS CO, PA	420170012	88	86	92	92	88	83	80

Northeast Airport - PHILADELPHIA CO, PA	421010024	87	90	91	89	84	82	83



                                                                        
                                                                        
    Design Value Trends

The Maryland SIP states that there have been significant declines in the
Philadelphia nonattainment area’s eight-hour ozone design values over
the last several decades.  Significant declines did occur after
enactment of the NOx SIP Call in the 2003/2004 period.  The data in
Table 4 show that ozone design values have decreased sharply after 2003.
 EPA’s study of the effect of the NOx SIP Call has documented the
beneficial effects of the NOx SIP Call emission reductions that were in
place by the 2004 ozone season across the eastern United States 

 

Since 2004, design values have not continued to decrease as sharply for
several reasons.  First, the 2004 ozone season was cooler than normal,
so the decreases in ozone due to additional controls have been offset
somewhat by higher concentrations as the areas have returned to more
typical summertime conditions.  Second, current reductions in ozone and
precursors transported from the Midwest are not as large as the
decreases that occurred while the NOx SIP Call was implemented.  However
additional emission reductions have continued to occur due mostly local
controls in each nonattainment area and a few reductions in major
sources due to States’ initiatives in the Ozone Transport Region.  

As Table 4 shows, the monitored ozone design values for each of the
Philadelphia area monitors continued to decline and now show attainment
beginning in 2010 and continue to show attainment in 2011.  

 

Table 4. Recent Ozone Design Value Trends for Philadelphia Area Monitors

Monitor ID	Site Name	2003	2004	2005	2006	2007	     2008	      2009	    
2010	     2011

100010002	Killens Pond	0.089	0.084	0.080	0.080	0.081	0.081	0.075	0.074
0.071

100031007	Lums Pond	0.093	0.084	0.080	0.078	0.082	0.080	0.075	0.075
0.075

100031010	Brandywine	0.093	0.089	0.082	0.082	0.083	0.083	0.078	0.076
0.075

100031013	Bellefonte	0.090	0.085	0.082	0.081	0.081	0.078	0.074	0.075
0.077

100051002	Seaford	0.091	0.085	0.082	0.080	0.082	0.081	0.076	0.077	0.076

100051003	Lewes	0.088	0.085	0.084	0.082	0.082	0.079	0.076	0.077	0.075

240150003	Fair Hill	0.100	0.094	0.088	0.090	0.093	0.090	0.084	0.080
0.081

340010005	Nacote Creek	0.091	0.085	0.092	0.079	0.077	0.074	0.072



340070003	Camden	0.101	0.093	0.085	0.084	0.088	0.087	0.087	0.083

	340071001	Ancora State Hospital	0.101	0.095	0.091	0.088	0.089	0.086
0.081	0.080	0.080

340110007	Millville	0.095	0.89	0.084	0.083	0.083	0.081	0.078	0.076	0.071

340150002	Clarksboro	0.099	0.095	0.088	0.086	0.087	0.087	0.083	0.081
0.082

340210005	Rider College	0.100	0.092	0.086	0.087	0.091	0.087	0.081	0.078
0.078

340290006	Colliers Mills	0.109	0.102	0.094	0.093	0.092	0.087	0.080	0.081
0.081

420170012	Bristol	0.100	0.093	0.086	0.086	0.092	0.092	0.088	0.083	0.080

420290100	New Garden Airport	0.100	0.094	0.087	0.086	0.085	0.082	0.077
0.076	0.074

420450002	Chester	0.093	0.089	0.082	0.083	0.085	0.083	0.077	0.074	0.073

420910013	Norristown	0.094	0.089	0.086	0.085	0.086	0.084	0.079	0.078
0.077

421010004	AMS Lab	0.075	0.068	0.063	0.062	0.068	0.067	0.064	0.066	0.068

421010014	Roxboro	0.093	0.086	0.081	0.078	0.080	0.078	0.081



421010024	NE Airport	0.097	0.095	0.090	0.090	0.091	0.089	0.084	0.082
0.083

421010136	Elmwood	0.083	0.079	0.070	0.074	0.077	0.081	0.082





                                                                        
                                                                        
                                                                        
                                                                        
                                                            

Alternative Baseline Design Value     

                                                                        
                                                                        
                          Seven monitors within the Philadelphia area
are projected to exceed the current eight-hour ozone standard following
the US EPA’s recommended method.  The recommended baseline
concentration used in the attainment demonstration is the average of the
three eight-hour ozone design values that include the emission base year
(2002).  Thus the baseline concentration is the average of the 2002,
2003 and 2004 eight-hour ozone design values.

Many States in the Philadelphia area believe that by using the US EPA
recommended method for calculating a monitor’s baseline concentration,
undue weight is placed on the 2002 ozone season, one of the worst ozone
seasons since the late 1990s.  As alternative to the US EPA’s baseline
concentration calculation, a straight average of the 4th highs over the
same years (2000-2004) was used to calculate the baseline concentration.
 This approach weighs each year equally.  

EPA guideline method baseline = 105.7 ppb 

Maryland’s alternative baseline = 104.2 ppb

Table 5 lists the alternative baseline value and the projected 2009
concentration for the seven monitors that are projected to exceed the
current eight-hour ozone standard in 2009.  This reduces the modeled
2009 values slightly but the model is still over predicting the actual
monitored 2009 design values in six out of the seven cases.    

Table 5. Alternative Baseline Concentration Analysis

Site Name	State	Alternative Baseline	OTW/OTB V4

RRF	Alternate 2009	2009 Monitored Design Value

Camden	NJ	94.0	0.8996	84	87

Ancora S.H.	NJ	98.6	0.8733	86	81

Clarksboro	NJ	96.4	0.9004	86	83

Rider College	NJ	95.6	0.8908	85	81

Colliers Mills	NJ	104.2	0.8703	90	80

Bristol	PA	96.6	0.8976	86	88

NE Phila	PA	94.6	0.9035	85	84



Alternative RRF

Maryland calculated 2009 modeled ozone design values by multiplying the
modeling baseline design values with a relative response factor (RRF) as
recommended by EPA’s photochemical modeling guidance.  At each
monitoring site, the state calculates the RRF associated with the
maximum eight-hour ozone concentration in the nine grid cells nearest
with the monitoring site on high ozone days.  Lower RRFs produce larger 
 decreases in ozone between the base and future years.  

RRFs were calculated for several different ozone levels; 2002 baseline
model concentrations ( 85 ppb, 2002 baseline model concentrations ( 90
ppb and 2002 baseline model concentrations ( 95 ppb.  The idea is to see
if the air-quality model predicts more reductions on days with higher
ozone concentrations (more benefit on the worst days).  Table 6 contains
the different RRFs based on the 2002 baseline model concentrations.

The projected modeled 2009 design values were recalculated using the
most beneficial alternative RRFs.  This reduces the modeled 2009 values
slightly but the model is still over predicting the actual monitored
2009 design values in six out of the seven cases.   

 

Table 6. Alternative Projected 2009 Modeled Values Using Alternative
RRFs

Site	Alt RRF	DV Base	Alt Projected 2009	2009 Monitored Design Value

Camden	0.8915	98.0	87	87

Ancora S.H.	0.8723	99.7	86	81

Clarksboro	0.8875	98.0	86	83

Rider	0.8908	97.7	86	81

Colliers Mills	0.8703	105.7	91	80

Bristol	0.8892	99.0	88	88

NE Airport	0.8991	96.7	86	84



Combining Alternative Baseline Concentrations and Alternative RRFs

Table 7 contains the projected 2009 modeled design values from combining
the alternative baseline concentrations and the alternative RRF
calculations described in the previous two sections.  This reduces the
modeled 2009 values slightly but the model is still over predicting the
actual monitored 2009 design values in five out of the seven cases.    

Table 7. Combined Effects of Alternative Baseline Concentrations and
Alternative RRFs

Site	Alt RRF	Alt DV Base	Alt Projected 2009	2009 Monitored Design Value

Camden	0.8915	94.0	83	87

Ancora S.H.	0.8723	98.6	86	81

Clarksboro	0.8875	96.4	85	83

Rider	0.8908	95.6	85	81

Colliers Mills	0.8703	104.2	90	80

Bristol	0.8892	96.6	85	88

NE Airport	0.8991	94.6	85	84



In summary, with the benefit of having the 2009 monitored design values,
it’s obvious that the model is over predicting the actual
concentrations, even when model adjustments are made to account for
model over prediction.    

  

Summary of EPA’s Evaluation Maryland’s WOE Analysis

Maryland’s photochemical grid modeling results predict a 2009
projected design value well above the air quality health standard for
the Philadelphia ozone nonattainment area.  However, after taking into
account WOE arguments regarding model over prediction of the 2009
monitored design values and recent ozone design value trends, which show
attainment of the standard by 2010, the Maryland SIP has demonstrated
attainment of the ozone standard by the extended attainment date of June
2011.  

Summary of EPA’s Technical Findings

The result of the photochemical grid modeling analysis using EPA’s
recommended methods predicts that the Philadelphia area ozone
nonattainment area will not attain the standard in the attainment year
of 2009.  In response to this, a number of WOE arguments have been made
that when taken together with recent air quality trends show attainment
of the ozone standard by the extended date of June 2011.  EPA’s review
of the attainment demonstration portion of the Maryland SIP determined
the following:

The Maryland SIP modeling uses an appropriate photochemical grid model
and follows EPA’s guidance methods and does not predict attainment in
2009.

The Maryland SIP relies on emission reductions resulting from a
commitment to adopt and implement a number of regulations prior to the
start of the 2009 ozone season.  Some of these were included in the
photochemical grid modeling.  These regulations would provide for
additional reductions from boilers, refineries, power generation,
consumer products and portable fuel containers.  Maryland’s own
analysis shows that Maryland must adopt all these measures, and
additional measures as well to show attainment by 2009.   

In order to insure attainment, Maryland refers to additional measures
which were not included in the original photochemical modeling analysis.
 Most of these measures are not contained in the SIP and are not
committed to by Maryland as part of its attainment demonstration.  While
EPA encourages Maryland to continue to promote these worthwhile and
important emission reduction programs, the amount of tangible air
quality benefit is difficult to estimate with any degree of certainty. 
However, implementing these measures will move the State’s
nonattainment areas closer to attainment.   

 An evaluation of recent air quality data indicates that the
Philadelphia area has attained the 1997 8-hour ozone standard by the
applicable attainment date of June 2011.   

Recommendation of Approval of the Attainment Demonstration

EPA has carefully evaluated the information provided by Maryland and
other information it deems relevant to help understand what the air
quality was likely to be by the extended attainment date of June 2011 or
effectively by the end of the 2010 ozone season.  EPA concludes that
Maryland’s SIP satisfies the Clean Air Act’s requirement that State
Implementation Plans provide for attainment of the National Ambient Air
Quality Standard by the applicable attainment date.

Based on EPA’s review of the technical information provided in the
Maryland SIP, EPA concludes that the SIP demonstrates attainment of the
ozone standard by the June 2011 attainment date and EPA should approve
the attainment demonstration portion of the SIP.

 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, and specifically recommends a WOE analysis if modeled ozone
is greater than or equal to 82 ppb.

 PAGE   

 PAGE   1 

