1

Technical Support Document for the Modeling Portion Of the 

Commonwealth of Pennsylvania’s Fine Particulate Matter State 

Implementation Plan (SIP) Entitled “ State Implementation Plan 

Revision: Attainment Demonstration and Base Year Inventory

Pennsylvania Portion of the Philadelphia-Wilmington, PA-NJ-DE Fine 

Particulate Nonattainment Area April 2010”

TSD Prepared October, 2011 by

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 Andrew Hass, Acting Associate Director,

Office of Air Monitoring and Analysis (3AP40)

October 11, 2011

_________________

Date Signed

 

 

 
2

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 portion of Pennsylvania’s State 

Implementation Plan (SIP) revision entitled “State Implementation Plan Revision: 

Attainment Demonstration and Base Year Inventory Pennsylvania Portion of the 

Philadelphia-Wilmington, PA-NJ-DE Fine Particulate Nonattainment Area April 2010”. 

This SIP revision will hereafter be referred to as the Philadelphia Area PM2.5 SIP.

In April 2005 the Environmental Protection Agency (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 PhiladelphiaWilmington, PA-NJ-DE Fine Particulate Nonattainment Area (NAA). The PhiladelphiaWilmington, PA-NJ-DE Nonattainment Area (Philadelphia Area) is comprised of 9 

counties in Pennsylvania, New Jersey and Delaware. The Pennsylvania counties 

included in this NAA are: Bucks, Chester, Delaware, Montgomery and Philadelphia 

counties (five-county Philadelphia area). According to the federal Clean Air Act (CAA) 

and the EPA Implementation Rule1, this entire NAA must attain compliance with the 

annual PM2.5 NAAQS by 2010. Figure 1 displays a map of the Philadelphia Area.

Figure 1: Map of the Philadelphia-Wilmington, PA-NJ-DE 

PM2.5 Nonattainment Area

 

1 Environmental Protection Agency, Clean Air Fine Particle Implementation Rule, 40 CFR Part 51, 

March 29, 2007.

 
3

 

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 Philadelphia Area PM2.5 SIP. 

The Regulatory Framework

On July 18, 1997 (62 FR 36852), EPA established PM2.5 NAAQS, including an annual 

standard of 15.0 μg/m3based on a 3-year average of annual mean PM2.5 concentrations, 

and a 24-hour (or daily) standard of 65 μg/m3based 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 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 2001-03.

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 Philadelphia-Wilmington, PA-NJ-DE PM2.5 Nonattainment Area, which is 

the subject of this proposed rulemaking, is included in the list of areas not attaining the 

1997 PM2.5 NAAQS.

On October 17, 2006, EPA strengthened the 24-hour PM2.5 NAAQS to 35μg/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 Philadelphia Area 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 Nonattainment Area is designated as 

attaining the 1997 24-hour PM2.5 NAAQS.
4

 

Introduction to the Philadelphia Area PM2.5 State Implementation Plan for the 

Annual Average PM2.5 Standard

On July 18, 1997 the US Environmental Protection Agency (EPA) established a health 

based fine particulate matter (PM2.5) National Ambient Air Quality Standard (NAAQS) at 

15.0 micrograms per cubic meter (μg/m3), annual average. The Pennsylvania counties of 

Bucks, Chester, Delaware, Montgomery and Philadelphia counties were designated by

the EPA as being in non-attainment for the annual PM2.5 NAAQS in April 20052. 

The Philadelphia Area PM2.5 SIP includes plans to reduce PM2.5 emissions within the

Philadelphia-Wilmington, PA-NJ-DE PM2.5 Nonattainment Area. The Plan also includes 

modeling that will predict whether the area will meet the PM2.5 standard by the attainment

date. This TSD reviews Pennsylvania’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.

Pennsylvania believes that the Philadelphia Area PM2.5 SIP demonstrates that all of the 

CAA and Rule requirements associated with the annual PM2.5 NAAQS have been met; 

and that Philadelphia-Wilmington, PA-NJ-DE PM2.5 Nonattainment Area 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 

Pennsylvania 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 PM2.5 modeling platform that all member states could use to 

demonstrate compliance with the 1997 PM-2.5 NAAQS.

The New York State Department of Environmental Conservation (NYSDEC) was the 

lead agency for coordinating and running the modeling platform used by the MANE-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 

 

2 70 FR 944, January 5, 2005
5

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 PM2.5 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 guidance3recommends 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 in this case). 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 

satisfied11. 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 

 

3 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
6

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 Pennsylvania Address All Of The Components Of A Modeled Attainment 

Demonstration?

The Philadelphia Area 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 Philadelphia Area PM2.5 SIP is described in 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 NSCAUM 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 longrange transport of sulfur emissions from industrialized areas within and outside the area. 
7

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 organic carbon (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, that includes 

Pennsylvania. 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 V of the Philadelphia Area PM2.5 SIP. 

Meteorological Time Periods Used in the Modeling

The Philadelphia Area 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: 1. the observed annual mean concentrations of PM2.5 are close 

to the 3-year observed design value at all, or most monitoring sites, and 2. 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. 
8

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 (see Figure 2 below). 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 PhiladelphiaWilmington, PA-NJ-DE PM2.5 Nonattainment 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 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. 

Figure 2. OTC Modeling Study Domain

Outer grid at 36-kilometer resolution, inner grid at 12-kilometer resolution
9

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 (MANEVU), 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 (2009 OTW), 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 III and IV of the Philadelphia Area

PM2.5 SIP.

Base Case Run Model Performance Evaluation

NY DEC performed a model evaluation for the OTC to determine how well CMAQ 

reproduced 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:

1. 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.

2. CMAQ captures seasonal variation in SO4 well.

3. CMAQ appears to overestimate primary PM2.5 components (EC, soil, primary

OM), especially during colder months.

4. CMAQ appears to underestimate secondary OM during the summer.
10

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

As previously mentioned, the Philadelphia-Wilmington, PA-NJ-DE PM2.5 NAA has an 

attainment date of April 5, 2010. The PM2.5 NAAQS include an annual standard of 15 

μg/m3based 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)4. 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/m

3

. 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 PM2.5 NAAQS.

 

4 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. 
11

 

Table 1: Annual SMAT Results for Philadelphia-Wilmington, PA-NJ-DE PM 

2.5 Nonattainment Area On-The-Books-On-The-Way Control Measures

 

 

 

Summary of Photochemical Grid Modeling Results

In summary, the basic photochemical grid modeling, presented in the Philadelphia Area

PM2.5 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 annual-average PM2.5 design value is predicted to be 

13.5μg/m3in the Philadelphia-Wilmington, PA-NJ-DE PM2.5 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. 

AIRS 

ID

Site 

Name County State

2000-2004 DVB 2009

Q1 Q2 Q3 Q4 DVF

420170012 Bristol Bucks PA 14.14 13.69 14.73 13.85 12.1

420290100 New Garden Chester PA 14.39 14.73 16.36 13.76 12.4

420450002 Chester Delaware PA 15.07 15.96 16.34 13.74 13.3

420910013 Norristown Montgomery PA 12.68 13.62 13.96 12.34 11.3

421010004 AMS Lab Philadelphia PA 15.99 14.01 15.95 13.82 12.9

421010024 NE Airport Philadelphia PA 13.58 13.63 14.95 12.96 11.9

421010047 Broad Street Philadelphia PA 16.59 16.45 15.80 15.37 13.5

421010136 Elmwood Philadelphia PA 15.70 14.20 15.27 12.99 12.7

100031003 Bellefonte New Castle DE 14.87 15.16 15.50 13.13 12.6

100031007 Lums Pond New Castle DE 13.16 14.37 16.05 10.66 11.3

100031012 Newark New Castle DE 15.27 14.91 16.53 13.14 12.6

100032004 MLK New Castle DE 16.41 15.40 17.61 14.04 13.3

340070003 Camden Camden NJ 13.99 14.54 15.76 12.47 12.3

340071007 Pennsauken Camden NJ 13.99 14.00 14.75 13.59 12.3

340155001 Gibbstown Gloucester NJ 13.92 13.43 15.08 11.39 11.7
12

It is important to note that the Philadelphia-Wilmington, PA-NJ-DE PM2.5 NAA currently 

has an operating network of fifteen PM2.5 monitors. EPA believes that the density of the 

monitoring network in NAA 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 

Philadelphia-Wilmington, PA-NJ-DE PM2.5 NAA are projected to exceed the annual 

PM2.5 NAAQS so it does not appear to be a necessary requirement in this circumstance to 

conduct the local area analysis. PADEP has observed enhancement of PM2.5

concentrations at the Chester monitor by local sources. Using emissions to distance 

ratios (Q/d) and local predominant wind directions; seven (7) sources were identified for 

possible analysis with a dispersion model to gauge the effect of local direct PM2.5

emissions on the North Braddock monitor. A local area analysis using a dispersion 

model, however, was not conducted since the modeled concentrations for the Chester 

monitor currently would attain the PM2.5 NAAQS. This does not preclude the 

Department from conducting a dispersion modeling analysis as part of a local area 

analysis in the future for the EPA’s revised 24-hour PM2.5 standard.

Supplemental Analyses and Weight of Evidence (WOE) Determination 

EPAs 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. EPAs 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.

EPA modeling guidance states that those modeling analyses that show that attainment 

with the NAAQS will be reached in the future with some margin of safety (i.e., estimated 

concentrations below 14.5 μg/m3for annual PM2.5 and 62 μg/m3for 24-hour PM2.5) need 

more limited supporting material. 
13

Due to the fact that the modeling results presented in Table 1 fall below the 

aforementioned “weight of evidence” thresholds established by EPA, a limited 

supplemental analysis was deemed necessary to support the 2009 attainment 

demonstration.

PM2.5 Design Values 

Table 2 (see below) shows the 2009 annual PM2.5 design value for all monitors in the 

Philadelphia-Wilmington, PA-NJ-DE PM2.5 NAA. It is clear from this figure that all the

monitors are currently attaining the NAAQS. All the monitors continue to attain in 2010.

 

 Table 2: 2008-2010 Philadelphia-Wilmington, PA-NJ-DE PM2.5 NAA 

Monitored PM2.5 Design Values

 

 

 

 

AIRS 

ID Site Name County

Sta

te

2008 2009 2010

Annual 

PM2.5 DV

Annual 

PM2.5 DV

Annua

l PM2.5 

DV

420170012 Bristol Bucks PA 12.6 12.2 11.3

420290100 New Garden Chester PA 13.4 13.9 13.8

420450002 Chester Delaware PA 14.1 13.7 13.1

420910013 Norristown Montgomery PA 12.3 11.7 10.5

421010004 AMS Lab Philadelphia PA 13.4 12.5 11.5

421010024 NE Airport Philadelphia PA 12.4 11.6 10.5

421010047 Broad Street Philadelphia PA 14.5 13.0 11.9

421010136 Elmwood Philadelphia PA 13.2 13.3 X

100031003 Bellefonte New Castle DE 12.9 12.2 11.1

100031007 Lums Pond New Castle DE 11.8 11.3 10.5

100031012 Newark New Castle DE 12.9 12.2 11.2

100032004 MLK New Castle DE 14.2 13.0 11.7

340070003 Camden Camden NJ 12.9 13.3 12.9

340071007 Pennsauken Camden NJ 12.7 11.7 10.3

340150004 Gloucester NJ 11.6 11.4 10.0

421010055 24th and Ritner Philadelphia PA 13.5 12.4 12.0

421010057 Fire Admin 

Building

Philadelphia PA 12.7 12.1 11.7
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Summary of EPA’s Evaluation Pennsylvania’s WOE Analysis

The reduction in PM2.5 precursor emissions, coupled with current annual PM2.5 design 

values that show attainment of the annual NAAQS, confirms the Commonwealth’s 

assertion that the Philadelphia-Wilmington, PA-NJ-DE PM2.5 NAA will be in compliance 

with the annual PM2.5 NAAQS by the attainment date. 

Summary of EPA’s Technical Findings

The result of the photochemical grid modeling analysis using EPA’s recommended 

methods predicts that the Philadelphia-Wilmington, PA-NJ-DE PM2.5 NAA will attain 

the annual PM2.5 standard by the attainment date of April 5, 2010. This result is 

confirmed by the 2010 air quality data presented in Table 2.

Recommendation of Approval of Attainment Demonstration

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

EPA concludes that Philadelphia Area PM2.5 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.
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Attachments:

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.