Technical Support Document (TSD)

For the Modeling and Weight of Evidence (WOE) Portions of the Document Entitled 

“Revision to the Allegheny County Portion of the Pennsylvania State Implementation 

Plan Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

April 2011

TSD Prepared October 2011

Timothy A. Leon Guerrero

Office of Air Monitoring & 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 & Analysis (3AP40)

October 24, 2011

_________________

Date Signed
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

Page 2 of 16

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) portions 

of Pennsylvania’s State Implementation Plan (SIP) entitled “Attainment Demonstration 

for the Liberty-Clairton PM2.5 Nonattainment Area”.

The Liberty-Clairton, PA PM-2.5 nonattainment area is comprised of a small portion of 

Allegheny County that includes the boroughs of Glassport, Liberty, Lincoln, Port Vue, 

and the City of Clairton (see figure below). The area was designated as nonattainment 

for the 1997 PM-2.5 National Ambient Air Quality Standard (NAAQS) in the January 5, 

2005 Federal Register [70 FR 944], effective April 5, 2005.

EPA requires states with nonattainment areas to submit an attainment demonstration and 

associated air-quality modeling, adopted state regulations to reduce emissions of PM-2.5

and its precursors, and other supporting information demonstrating that the area will 

attain the standards as expeditiously as practical. The Allegheny County Health 
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

Page 3 of 16

Department (ACHD) prepared its PM-2.5 SIP in cooperation with the Pennsylvania 

Department of Environmental Protection to comply with the CAAA of 1990 and with 

EPA requirements for the nonattainment area as stated in EPA’s 2005 designation of the 

PM-2.5 nonattainment area and EPA’s Clean Air Fine Particle Implementation Rule [72 

FR 20586, 25APR2007].

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 should consult the ACHD’s

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan 

(April 2011) for the Liberty-Clairton, PA PM-2.5 nonattainment area.

The Regulatory Framework

EPA established the PM-2.5 NAAQS on July 18, 1997 (62 FR 36852). This included an 

annual PM-2.5 standard of 15.0 μg/m3based on an annual arithmetic mean, averaged 

over 3 years, and a 24-hour (or daily) standard of 65 μg/m3based on a 3-year average of 

the 98th percentile of 24-hour concentrations. These standards were decided upon after 

reviewing numerous health studies demonstrating that serious health effects are 

associated with exposures to PM-2.5.

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 PM-2.5 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 PM-2.5 NAAQS (70 FR 

944), based on air-quality monitoring data for calendar years 2001-03.

The nonattainment designation for an area starts the process whereby a state or tribe must 

develop an implementation plan that includes, among other things, a demonstration 

showing how it will attain the ambient standards by the attainment dates required in the 

CAA. Under section 172(b), states have up to three years after the EPA’s final 

designations to submit their SIPs to EPA. These SIPs were due on April 5, 2008, three

years from the effective date of the designations.

Section 172(a)(2) of the Act requires states to attain the standards as expeditiously as 

practicable but within 5 years of designation (i.e. attainment date of April 5, 2010 based 

on air quality data for 2007–09), or within up to 10 years of designation (i.e. to April 

2015) if the EPA Administrator extends an area’s attainment date by 1–5 years based 

upon the severity of the nonattainment problem or the feasibility of implementing control 

measures.
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

Page 4 of 16

Introduction to the Liberty-Clairton, PA PM-2.5 State Implementation Plan

Pennsylvania’s SIP for the Liberty-Clairton, PA PM-2.5 nonattainment area outlines 

plans to reduce emissions that contribute to PM-2.5 nonattainment. The SIP includes a 

modeling demonstration that is used to show that the Liberty-Clairton area will meet the 

1997 annual PM-2.5 standard as expeditiously as practical. The Liberty-Clairton 

nonattainment area has some of the highest annual and 24-hour design values in the 

United States. This TSD reviews the modeling and WOE portions of Pennsylvania’s SIP 

for the Liberty-Clairton, PA PM-2.5 nonattainment area.

Pennsylvania’s PM-2.5 SIP includes a modeling demonstration that shows that the 

Liberty-Clairton area will comply with the annual PM-2.5 standard as expeditiously as 

practical. The modeling demonstration consists of results from the Community

Multiscale Air Quality (CMAQ) Model coupled with a local-scale modeling analysis 

using EPA’s CALPUFF model. Pennsylvania and the ACHD believe the results from the 

modeling analysis as well as the WOE supplemental analyses present overwhelming 

evidence that the Liberty-Clairton, PA PM-2.5 nonattainment area will attain the 1997 

annual PM-2.5 NAAQS by 2015, which is as expeditiously as practical considering the 

area’s elevated base year design values. Model base year design values (2000-02) were 

21.4 μg/m3for the annual NAAQS and 63 μg/m324-hour NAAQ at the Liberty monitor.

What Are The Components Of A Modeled Attainment Demonstration?

Modeling Process Overview 

EPA’s Guidance on the Use of Models and Other Analyses for Demonstrating Attainment 

of Air Quality Goals for Ozone, PM2.5, and Regional Haze (2007) describes how to 

construct a model attainment demonstration. The air quality modeling used in the 

Liberty-Clairton area’s attainment demonstration consisted of two components; a 

regional photochemical grid model and a local-scale model with sufficient resolution to 

examine the impacts of local emission sources. Model results were used in a “relative” 

rather than “absolute” sense. Following this methodology the ratio of the model’s future 

to current (baseline) predictions at both of the nonattainment area’s PM-2.5 monitors

determines if the Liberty-Clairton SIP’s proposed local and regional emission controls 

are likely to lead to compliance with the 1997 PM-2.5 NAAQS.

The Liberty-Clairton modeling demonstration used a regional photochemical grid model

(CMAQ) for part of its modeling demonstration. Baseline and future CMAQ modeling 

scenarios were run by the Bureau of Air Quality Analysis and Research Division of Air 

Resources New York State Department of Environmental Conservation with emissions 

information compiled by the Mid-Atlantic/Northeast Visibility Union Regional Planning 

Organization (MANE-VU). CMAQ provided results for the chemically reactive PM-2.5 

species such as sulfates and nitrates.
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

Page 5 of 16

Local sources in the Liberty-Clairton nonattainment area create steep gradients in the 

PM-2.5 concentrations. These gradients cannot be properly resolved in CMAQ whose 

model grid cells are roughly twelve square kilometers. Local scale meteorology is also 

not well simulated by the regional model due to steep topography within the 

nonattainment area that often contributes to strong temperature inversions and complex 

flow patterns within the valleys. A local-scale model, CALPUFF, was used in the 

attainment demonstration to better gauge the local impacts of direct PM-2.5 emissions 

and provide some meteorological enhancements within the nonattainment area. ACHD 

was responsible for running CALPUFF.

Steps Required in a Modeled Attainment Demonstration

EPA guidance1encourages states to take certain steps when preparing a modeling

analysis to demonstrate attainment of the PM-2.5 NAAQS. Recommendations include 

the following nine steps: 

1) Formulate a conceptual description of an area’s nonattainment problem.

2) Develop a modeling/analysis protocol.

3) Select an appropriate air quality model to use.

4) Select appropriate meteorological episodes to model.

5) Choose a modeling domain with appropriate horizontal and vertical resolution and 

establish the initial and boundary conditions to be used.

6) Generate meteorological and air quality inputs to the air quality model.

7) Generate emissions inputs to the air quality model.

8) Evaluate performance of the air quality model and perform diagnostic tests, as 

necessary.

9) Perform future year modeling (including additional control strategies, if 

necessary) and apply the attainment test.

How Did Allegheny County Address All of the Modeled Attainment Demonstration

Components?

ACHD’s PM-2.5 SIP for the Liberty-Clairton, PA PM-2.5 nonattainment area addressed

all of the modeled attainment demonstration elements. Each of these elements will be 

discussed in the following sections.

Conceptual Description of the Problem

"Particulate matter," also known as particle pollution or PM, is a complex mixture of 

extremely small particles and liquid droplets. Particle pollution is made up of a number 

 

1

See section 10.0 of EPA’s Guidance on the Use of Models and Other Analyses for Demonstrating 

Attainment of Air Quality Goals for Ozone, PM2.5, and Regional Haze Attainment of Air Quality Goals for 

Ozone, PM2.5, and Regional Haze, April 2007 (EPA -454/B-07-002)
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

Page 6 of 16

of components, including acids (such as nitrates and sulfates), organic chemicals, metals, 

and soil or dust particles. Particle pollution exposure is linked to a variety of health 

problems, including increased respiratory symptoms, such as irritation of the airways, 

coughing, or difficulty breathing, decreased lung function, aggravated asthma,

development of chronic bronchitis, irregular heartbeat, nonfatal heart attacks, and 

premature death in people with heart or lung disease.

ACHD’s conceptual description of its PM-2.5 nonattainment problem is detailed in 

Appendix C (Modeling Protocol) of its SIP document. Two additional reports prepared 

by the ACHD are included in Appendix E present data from two speciated PM-2.5 

monitors in Allegheny County.

The Liberty-Clairton Area is made up of complex river valley terrain encompassing an 

area roughly three by five miles in size. It includes a four mile winding portion of the 

Monongahela River south of the City of Pittsburgh and is bordered on the east by the 

Youghiogheny River. The area includes rural land interspersed with densely populated 

residential areas and industrial facilities.

There are significant differences in terrain elevations within the nonattainment area; river 

valley elevations average just over 700 feet above mean sea level while adjacent hilltops 

can rise up to 1250 feet. Under weak synoptic forcing these sharp elevation differences 

can generate strong nocturnal temperature inversions. Temperature differences between

the valley floors and nearby hilltops can range from 2 to 7° F under these conditions. 

Cold air drainage flows often occur during these periods of strong nocturnal cooling. 

Under these circumstances air flows within the valleys can become quite complex with 

down slope flows reaching 3-4 mph and wind directions veering up to 180° within each 

valley’s vertical profile. 

Episodes of poor air quality often occur within the Liberty-Clairton, PA PM-2.5

nonattainment area during periods of strong nocturnal inversions. Under these 

conditions, air dispersion is often minimized allowing emissions to “build up” within the 

river valleys contributing to episodes of poor air quality, which lead to the nonattainment 

area’s high PM-2.5 design values. On some occasions PM-2.5 concentrations within the 

Liberty-Clairton area are significantly higher than concentrations in the nearby City of 

Pittsburgh. These differences in air quality are one of the reasons why the LibertyClairton, PA PM-2.5 nonattainment area was separated from the surrounding PittsburghBeaver Valley, PA PM-2.5 nonattainment area. 

ACHD performed source apportionment modeling for the Liberty and Lawrenceville 

monitors in Allegheny County using the Positive Matrix Factorization Model (PMF 

Version 1.1). The monitors are approximately eleven miles apart from each other with 

the Liberty monitor located in the Liberty-Clairton area and the Lawrenceville monitor 

located to the north near Pittsburgh.
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

Page 7 of 16

Local impacts were gauged by comparing both monitors’ speciation data with each other 

using PMF. ACHD’s analysis found that the Liberty monitor’s PM-2.5 concentrations 

are impacted by regional loading (mainly sulfates) based on similarities in both monitor’s 

speciation data. Sources near the Liberty monitor, both stationary and mobile, were 

thought to be responsible for the speciation differences observed between two Allegheny

County monitors. On peak concentration days at Liberty, carbons and ammonium are 

prominent species while chorine is more prominent on cold-weather peak days.

Models Used in the Attainment Demonstration

ACHD utilized two models in its attainment demonstration; a regional photochemical 

grid model used to simulate regional PM-2.5 concentrations and a local scale model used 

to simulate the effects of local sources of direct PM-2.5 emissions.

The photochemical grid model used in ACHD’s modeling demonstration is the CMAQ 

(version 4.5.1) model with CB4 chemistry, aerosol module for PM-2.5 and RADM cloud 

scheme. Photochemical modeling was performed by the Bureau of Air Quality Analysis 

and Research, New York State Department of Environmental Conservation (DEC).

The CMAQ modeling system has been designed to approach air quality as a whole by 

including state-of-the-science capabilities for modeling multiple air quality issues, 

including tropospheric ozone, fine particles, toxics, acid deposition, and visibility

degradation. This system includes input from both meteorological and emissions models, 

which are detailed in the following sections. 

EPA recommends using air-quality models such as CMAQ in a “relative” rather than 

“absolute” sense. That is, take the ratio of the model’s future to current (baseline) 

predictions at each monitor within the nonattainment area using relative response factors

(RRF), a ratio of model projected concentrations over model base-line concentrations. 

Future PM-2.5 concentrations are estimated at existing monitor sites by multiplying the 

modeled relative response factor at locations “near” each monitor by the observationbased, monitor-specific, “baseline” design value. The resulting predicted “future 

concentrations” are then compared to the NAAQS.

ACHD’s analysis of its PM-2.5 monitors within Allegheny County showed significant 

local impacts in the Liberty-Clairton PM-2.5 nonattainment area. A more detailed 

modeling analysis was needed to account for these important local source impacts. As 

noted previously, atmospheric circulation in the Liberty-Clairton area during periods of 

high PM-2.5 concentrations is quite complex and beyond the resolution capabilities of

most regional photochemical models, which typically contain model grid cells on the 

order of twelve square kilometers. Additionally, regional scale photochemical models 

are unable to fully resolve important local topographic features that influence emission 

dispersion. Important spatial relationships between local sources and the affected 

monitors within the Liberty-Clairton, PA PM-2.5 nonattainment area are also not 
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

Page 8 of 16

properly resolved in the regional photochemical grid model. For these reasons, ACHD 

decided to do local scale modeling using EPA’s CALPUFF modeling system to help 

better resolve local atmospheric circulation, local terrain features and local emission 

source contributions.

The CALPUFF modeling system was used to create near-field and some long range 

transport simulations for the Liberty-Clairton area. CALPUFF Version 5.8 (dated June 

29, 2007) is the most recent EPA-approved version for regulatory applications. 

CALPUFF is currently not EPA’s preferred near-field model to use for sources within 50 

kilometers of the affected monitor (see August 14, 2008 EPA Clarification Memo entitled 

“Clarification of Regulator Status of CALPUFF for Near-field Applications”). The use 

of CALPUFF in this SIP, however, was granted since the modeling protocol outlining the 

modeling methodology was established before the issuance of this EPA memorandum.

The CALPUFF modeling system is comprised of CALMET (meteorological model), 

CALPUFF (dispersion model), geophysical data preprocessors, meteorological data 

preprocessors, and several postprocessors such as CALPOST. The CALPro GUI (dated 

June 29, 2007) comprises CALPUFF and associated preprocessors and postprocessors in 

a central interface and was utilized for the near field modeling analysis.

ACHD followed modeling procedures outlined in its PM-2.5 Model Protocol (Appendix 

C) for the Liberty-Clairton, PA PM-2.5 nonattainment area and EPA’s modeling 

guidance. The modeling analysis utilized a combination of regional CMAQ modeling 

using the MANE-VU inventory and local CALPUFF modeling using a local revised 

ACHD inventory (for direct PM-2.5 emissions only). ACHD listed several deviations 

from its original modeling protocol in section 7.1.1 of its main SIP document. These 

were necessary to account for several issues that came up during the modeling 

demonstration.

ACHD’s modeling methodology for its attainment demonstration followed roughly the 

same methodology used in the Philadelphia Air Toxics study. Average impacts from the 

uncorrected MANE-VU inventory across an “equivalent grid” were subtracted from the 

CMAQ impacts on a concurrent basis. The corrected ACHD inventory impacts for 

Liberty and Clairton were then added to the CMAQ results.

Meteorological Time Periods Used in the Modeling

The EPA’s 2007 Modeling Guidance recommends modeling an entire year or, at a 

minimum, several days in each quarter of a year, to adequately represent the range of 

meteorological conditions that contribute to elevated levels of fine particulate matter. 

MANE-VU regional modeling efforts were based on a base year of 2002. This was the 

year used for all PM-2.5 modeling efforts in EPA’s Region 3 and was also used in the 

modeling demonstration submitted for the Liberty-Clairton, PA PM-2.5 nonattainment 

area.
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

Page 9 of 16

Meteorological Models Used in the Air Quality Model

Meteorological data for the regional photochemical grid model and local scale model 

were constructed for the modeling demonstration. The regional photochemical grid 

model was driven by output from the Pennsylvania State University/National Center for 

Atmospheric Research (PSU/NCAR) Mesoscale Meteorological Model, also known as 

MM5. The meteorological model for the local scale modeling was derived using 

CALMET, which used a combination of MM5 data coupled with local observations from 

nearby met stations. The MM5 simulation included “nudging”, which uses observations 

in the tendency equations to force the model solution closer to observed values.

Additional information regarding the MM5 set up can be found in Appendix K-2 of 

ACHD’s SIP document.

The following is a short list of MM5 options used in the modeling demonstration 

simulation:

 Kain-Fritsch (1993) convective scheme for both 36 and 12 km domains with some 

adjustments to correct diurnal phase shifts in surface winds and temperatures

 Explicit moisture scheme (without the mixed phase) containing prognostic 

equations for cloud water (ice) and rainwater (snow)

 Modified version of the Blackadar PBL scheme

 Simple radiative cooling scheme

 Multi-layer soil model to predict land surface temperatures using the surface

energy budget equation 

MM5 met data was also used in the near field analysis using CALPUFF though the 

CALMET processor. CALMET was initialized with MM5 met fields and supplemented 

with meteorological data from the Liberty monitoring site, the Allegheny County Airport 

and USX Clairton. The CALMET processor is used to try and recreate some of the more 

complex atmospheric flows in the Liberty-Clairton nonattainment area that cannot be 

resolved in the MM5 simulation. Further details of the meteorological data processing 

for CALMET can be found in Appendix D of ACHD’s SIP document.

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

Conditions

MM5 (version 3.6) was run by the University of Maryland in consultation with New 

York DEC staff. The model was applied using a Lambert conformal map projection. 

The two nested domain consisted of coarse (36 km) and fine (12 km) mesh corresponding 

to 149 x 129 and 175 x 175 grids respectively. The Lambert projection used in this work 

followed the Regional Planning Organization (RPO) national domain setup.
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

Page 10 of 16

MM5 uses a terrain following σ-coordinate system with the pressure at each σ-level 

determined from a reference state that is estimated using the hydrostatic equation from a 

given sea-level pressure and temperature with a standard lapse rate. There are 30 

unevenly spaced σ-levels yielding 29 vertical layers with higher resolution within the 

planetary boundary layer (PBL). The surface layer was set at about 10 m, the level at 

which surface winds were typically observed, and the model top was set at 50 hPa with a 

radiative top boundary condition.

CMAQ simulations were performed using a one-way nesting approach for a continental 

simulation at 36 km grid spacing with a finer 12 km grid centered over the eastern portion 

of the US. Both domains utilized 22 layers in the vertical extending to about 16 km with 

16 layers placed within the lower three kilometers.

The continental CMAQ simulation utilized clean initial conditions with boundary

conditions extracted from a GEOS-CHEM global chemical model simulation. The 

CMAQ 36 km simulation was initiated from December 15, 2001 with the first 15 days 

used as a spin up period and terminated on December 31, 2002. RPO emissions data 

from 2002 was used with corresponding MM5 meteorological fields developed by the 

University of Maryland.

Hourly boundary fields for the 12 km CMAQ domain were obtained from the 

concentration fields generated by the 36 km CMAQ simulation. The 12 km simulations 

for both base and future year were assigned the boundary conditions based on the 36 km 

CMAQ simulation with clean initial conditions. A more detailed description of the 

CMAQ runs can be found in Appendix K-4 of ACHD’s SIP document.

Model resolution for CALPUFF, the near field model, was on a much finer scale than the 

regional model. CALPUFF grid spacing for the 150 km regional source analysis domain 

was one kilometer and 100 meters for the 20 kilometer local scale analysis domain. Both 

CALPUFF runs contained 11 vertical layers spaced within the first three km. More 

information on ACHD’s CALPUFF settings can be found in Appendix I of ACHD’s SIP 

document.

Emissions Used in the Air Quality Models

Northeastern US emissions inventories for all source classifications were developed by 

MANE-VU for use in regional analyses and SIPs. The MANE-VU emission inventory was 

originally developed for regional haze but was also used for ozone and PM-2.5 modeling

efforts in the Northeast. A report by MARAMA located in Appendix G of the SIP document 

provides additional details on the regional emission inventories.

The year 2002 was used for the baseline emissions inventory and 2014 for the projected 

inventory for the Liberty-Clairton area. Regional projections utilized on-the-books/on-theway (OTB/W) controls through the 2012 timeframe. Since no additional projections were 

available at the time, and since Liberty-Clairton controls focus on direct PM-2.5 emissions, 
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

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regional projections for 2012 were used for precursors and non-point PM-2.5 emissions in 

combination with local projections for 2014 for stationary point PM-2.5 emissions.

A more detailed inventory was developed by the ACHD for the extended Liberty-Clairton 

area as part of its near scale modeling analysis. This inventory was limited to direct PM-2.5 

emissions and was developed from both the regional MANE-VU inventories and projections 

along with ACHD’s inventories for stationary point sources. These emissions represent

“actual” values based on pollutant emission factors and throughputs or capacities of each 

emission source. Emission values do not necessarily represent permitted or “allowable” 

limits.

Regional controls for SO2 and NOx in the MANE-VU inventory were based on CAIR. On 

July 6, 2011, EPA finalized a rule that protects the health of millions of Americans by 

helping states reduce air pollution and attain clean air standards. This rule, known as the 

Cross-State Air Pollution Rule (CSAPR or Cross State Rule)

2

, requires 27 states to 

significantly improve air quality by reducing power plant emissions that contribute to 

ozone and/or fine particle pollution in other states.

Base Case Run Model Performance Evaluation

Model performance evaluations were done for MM5 and the regional CMAQ runs as 

well as the local scale runs using CALPUFF. Regional model performance was based on 

matrices outlined in EPA’s Guidance on the use of models and other analyses for 

demonstrating attainment of air quality goals for ozone, PM-2.5, and regional haze

(EPA-454/B-07-002) and was summarized in Appendix K-1.

NY DEC examined the MM5 output to determine how well the simulation was 

performing. Only meteorological fields from the ozone season (May through September) 

were examined. The nudging process used National Weather Service data so as expected 

the model did relatively well compared with this data set. Meteorological data from the 

Clean Air Status and Trends Network or CASTNET was also used to assess model 

accuracy since this data set was not included in the nudging process. Vertical parameters 

were also included in the analysis as well as cloud cover data, precipitation and simulated 

calm periods.

The meteorological assessment showed that in general, MM5’s performance was 

reasonable both at the surface and in the vertical. It was therefore concluded that MM5 

performed adequately and the data could be used in the CMAQ simulations.

Regional model evaluation statistics for the entire 2002 simulation were calculated over a 

wide region for PM-2.5 mass and major species. In general, CMAQ did a reasonable job 

simulating daily average PM-2.5 and SO4 (sulfate) mass. CMAQ, however, did not 

appear to be able to reproduce the day-to-day or seasonal variation in other species like 

 

2

http://www.epa.gov/airtransport
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

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NO3, OM, EC, or crustal mass. The model appeared to meet model performance criteria 

for PM-2.5 reasonably well over the Ozone Transport Region (OTR) as a whole but not 

as well if one focused on an emissions-dense, complex urban setting such as the New 

York City area. This finding appears to support ACHD’s local scale modeling efforts for 

the Liberty-Clairton area.

ACHD examined CALPUFF’s ability to simulate local monitor concentrations, 

specifically the model’s ability to simulate the strong diurnal variations that contribute to 

the area’s high PM-2.5 design values. A comparison of CALPUFF hourly averaged 

modeled and TEOM (monitor) concentrations showed the local scale modeling generally 

provided a better simulation of the strong diurnal contrasts (high overnight 

concentrations) than did the regional model though the CALPUFF model tended to over 

predict PM-2.5 concentrations. This over prediction, however, was not considered a 

problem since the local scale modeling was used in a relative sense for attainment 

demonstration purposes. CALPUFF model performance using EPA matrices was judged 

to be adequate overall with the 2nd and 3rd quarters showing better performance than the 

1

st and 4th quarters.

2014 Control Case Modeling and the Modeled Attainment Test

The monitored attainment test for PM-2.5 utilizes both PM-2.5 and individual PM-2.5 

component species. EPA refers to the attainment test for PM-2.5 as the Speciated 

Modeled Attainment Test (SMAT). A separate relative response factor (RRF) is 

calculated for each PM-2.5 species.

In order to perform the recommended modeled attainment test, it is recommended that 

states divide observed mass concentrations of PM-2.5 into seven (7) components plus 

passive mass:

- 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

To apply the test, states must first run an air quality model at least twice to simulate 

current emissions and to simulate future year emissions. RRF values are then calculated 

for each PM-2.5 species. These RRF values are then multiplied by the base year 

concentrations for each monitor within the nonattainment area.
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

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Data analyses by Frank3have noted that the FRM monitors do not measure the same 

components and do not retain all of the PM-2.5 that is measured by routine speciation 

samplers. EPA recommends using the sulfate, adjusted nitrate, derived water, inferred 

carbonaceous material balance approach or SANDWICH to account for these differences 

in the SMAT. A more detailed description of this process can be found in EPA’s 

Guidance on the Use of Models and Other Analyses for Demonstrating Attainment of Air 

Quality Goals for Ozone, PM-2.5, and Regional Haze, EPA -454/B-07-002 April 2007.

ACHD’s modeled attainment test included an additional step to account for the two 

models used in its analysis. The direct PM-2.5 component was taken from the CALPUFF 

modeling while CMAQ provided results for the other PM-2.5 components.

The Liberty-Clairton nonattainment area has two PM-2.5 monitoring sites, Liberty and 

Clairton. Speciation data from Liberty was used for the Clairton monitor since this site 

does not collect speciation data. Details on how the modeling attainment demonstration 

was conducted are included in section 8 of the main PM-2.5 SIP document.

Projected monitor concentrations were calculated for both monitors in the LibertyClairton area following EPA guidance. EPA has developed the Modeled Attainment Test 

Software (MATS) to automatically calculate design values and interpolate for 

unmonitored areas. Testing of MATS version 2.2.1 showed inconsistent results with the 

methodology given in the EPA Modeling Guidance. EPA’s MATS software, therefore, 

was not used by ACHD in this attainment demonstration though the general methodology

was followed to calculate the projected PM-2.5 concentrations.

Summary of the Combined Photochemical and CALPUFF Modeling Results

Annual and 24-hour PM-2.5 concentrations for both the Liberty and Clairton monitors 

were calculated from the quarterly base-year averaged monitor concentrations and the 

RRFs calculated from CMAQ and CALPUFF for each PM-2.5 species components. 

Results for the annual and 24-hour PM-2.5 NAAQS are summarized in the following

table and show that the projected 2014 annual and 24-hour design values are below the 

1997 PM-2.5 NAAQS.

 

3

 Frank, N., 2006: “Retained Nitrate, Hydrated Sulfates, and Carbonaceous Mass in 

Federal Reference Method Fine Particulate Matter for Six Eastern U.S. Cities” J. Air 

Waste Mange. Assoc., 56, 500-511.
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

Page 14 of 16

Model Projected PM-2.5 Concentrations

For the Liberty-Clairton, PA PM-2.5 Nonattainment Area

Monitor

Annual Standard 24-Hour Standard

Projected 1997 NAAQS Projected 1997 NAAQS

Liberty 14.3 μg/m315.0 μg/m342 μg/m365 μg/m3

Clairton 11.8 μg/m315.0 μg/m327 μg/m365 μg/m3

EPA’s CSAPR rule was published after ACHD submitted their PM-2.5 SIP for LibertyClairton. ACHD did provide an analysis of EPA’s Transport Rule, which had replaced 

EPA’s CAIR regional emission control proposal, in its Weight of Evidence (WOE) 

section (13.3). EPA’s Transport Rule was the proposal in effect at the time of the SIP 

document’s preparation.

EPA Region 3 suggests that ACHD submit an addendum to their current SIP document 

that examines EPA’s most recent regional emission control proposal (CSAPR) to ensure 

that its SIP modeling analysis is at least as controlled as EPA’s current proposal. This 

addendum should reexamine the elements included in section 13.3 of ACHD’s main SIP 

document and could additionally include a comparison of model results for the LibertyClairton area from EPA’s CAIR and CSAPR modeling analyses.

Local Area Analysis

EPA guidance calls for additional analyses in areas where large sources of primary

particulates could cause substantial spatial gradients in PM-2.5 concentrations. These are 

often referred to as “hot spots”, which could impact an area’s ability to comply with the 

NAAQS. Analysis of these hot spots could necessitate additional photochemical grid 

modeling using a finer modeling grid scale, down to 1 to 2 kilometers, or alternatively the 

use of a Gaussian dispersion model.

ACHD conducted a local area analysis using EPA’s CALPUFF model. This analysis 

examined the impacts on direct PM-2.5 emissions in the Liberty-Clairton, PA 

nonattainment area. These impacts were coupled with the regional CMAQ modeling 

analysis to demonstrate that the nonattainment area would comply with the 1997 PM-2.5 

NAAQS.

Unmonitored Area Analyses

The unmonitored area analysis is intended to be the primary means for identifying high 

PM-2.5 concentrations outside of traditionally monitored locations. The spatial resolution 

of the model that is the underlying basis of the unmonitored area analysis will determine 

how well it addresses primary PM-2.5 hotspots. 
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

Page 15 of 16

The size of the Liberty-Clairton, PA PM-2.5 nonattainment area is much smaller than 

most of the neighboring nonattainment areas. As a consequence of its size, the LibertyClairton, PA PM-2.5 nonattainment area has a much higher density of monitors within it. 

This partially negates the necessity of doing this analysis though ACHD detailed an 

assessment of the area in section 8.6 of its main SIP document.

ACHD examined modeled PM-2.5 reductions in the vicinity of the Liberty monitor. 

Several large sources of direct PM-2.5 emissions lie southwest of the monitor near steep 

terrain adjacent to the Monongahela River. ACHD examined percent reductions in these 

areas and noted that shutdowns and plant emission reductions would produce much 

greater improvements in air quality in these areas than what are projected to occur at the 

Liberty monitor itself.

Weight of Evidence Demonstration

ACHD conducted a Weight of Evidence (WOE) demonstration in accordance with

section 2.3 of EPA’s modeling guidance. The WOE demonstration is detailed in section 

13 of ACHD’s main SIP document. ACHD’s WOE demonstration consisted of an 

analysis of monitor trends, local and national emission control programs, population 

trends and monitoring concentrations during periods of low production. These results 

were used as further evidence supporting the ACHD’s conclusion that their SIP modeling 

analysis demonstrates compliance with the 1997 PM-2.5 NAAQS.

ACHD examined PM-2.5 monitoring trends within the nonattainment area and the 

surrounding region. PM-2.5 concentrations at most of the regional monitors appear to be 

declining though ACHD noted these trends may not be statistically significant at this 

time.

ACHD included a summary of various local and regional emission control programs 

being implemented in the area. Some of these control measures may extend beyond the 

Liberty-Clairton, PA PM-2.5 nonattainment area and therefore may have a lesser impact. 

Emission control programs noted in the WOE section include Pennsylvania’s enactment 

of a wood boiler rule, a wood stove change out program in southwest Pennsylvania,

EPA’s recently proposed Transport Rule, Allegheny County’s diesel fuel engine retrofit 

program, local and state anti-idling campaigns and Allegheny County’s grant program to 

reduce diesel particulate emissions. ACHD contends that the combined effects of these 

controls add additional support for their attainment demonstration.

Recent population trends are declining in the Pittsburgh region. ACHD noted that these 

population declines, if they continue, would help reduce emissions in the area that 

contribute to the nonattainment problem; fewer people equates to less driving and other 

activities that contribute to emissions in the area.
EPA Technical Support Document for the Modeling Portion of Pennsylvania’s 

Revision to the Allegheny County Portion of the Pennsylvania State Implementation Plan

Entitled “Attainment Demonstration for the Liberty-Clairton PM2.5 Nonattainment Area”

TSD Prepared October 2011

Page 16 of 16

ACHD also looked at the effect of lower emissions on its PM-2.5 monitoring network 

during the recent economic downturn. This was done by comparing TEOM data from 

2009, a period of lower production due to the economic downturn, to the unaffected 

2000-2008 time period. Production levels at the local and regional level have fallen due 

to the recent economic downturn. These emission reductions appear to have lowered

monitor concentrations when compared to previous time periods. ACHD interprets these 

declines as demonstrating the future effectiveness of their proposed local source emission 

controls. 

Recommendation of Conditional Approval of Liberty-Clairton PM-2.5 Attainment 

Demonstration

EPA has evaluated the information provided in the SIP document as well as other 

information relevant to assessing air quality in the Liberty-Clairton, PA PM-2.5 

nonattainment area. EPA concludes that attainment of the 1997 PM-2.5 NAAQS will 

likely occur by the proposed attainment date (2015). ACHD’s projected (modeled) 2014

design values are expected to be below 15.0 μg/m3and 65 μg/m3respectively indicating 

the nonattainment area satisfies the Clean Air Act’s requirement that State 

Implementation Plans provide for attainment of the NAAQS by the applicable attainment 

date.

As noted previously, ACHD’s regional CMAQ modeling included emission controls 

from EPA’s CAIR program. Since ACHD’s SIP submittal, EPA has proposed CSAPR to 

replace CAIR. To ensure that the modeling demonstration is still valid EPA is requesting 

that ACHD redo the analysis it included in section 13.3 of its main SIP document and 

consider examining the modeling technical support documents for CAIR and the recently 

proposed Cross State Rule to ensure that the more recently proposed rule provides at least 

the same or possibly lower model concentrations in the Liberty-Clairton area as the 

modeling analysis used in the April 2011 SIP modeling demonstration.

Based on the technical information provided in the Liberty-Clairton SIP document, EPA 

concludes that the modeling and WOE analyses demonstrate attainment of the 1997 PM2.5 NAAQS. EPA, therefore, should conditionally approve the model attainment 

demonstration portion of Liberty-Clairton, PA PM-2.5 SIP. Final approval of the model 

attainment demonstration portion of the SIP will be contingent on ACHD’s reanalysis of 

the elements included in section 13.3 of its main SIP document and an examination of 

modeled PM-2.5 concentrations from EPA’s proposed CSAPR Rule.