Commonwealth of Pennsylvania

DESIGNATION RECOMMENDATIONS 

FOR THE 2010 1-HOUR SULFUR DIOXIDE

NATIONAL AMBIENT AIR QUALITY STANDARD

JUNE 2011

Bureau of Air Quality

Pennsylvania Department of Environmental Protection

P.O. Box 8468

Harrisburg, PA 17105-8468

717-787-9495

www.depweb.state.pa.us
This page left blank to enable two-sided copying.
Designation Recommendations

For the 2010 1-Hour Sulfur Dioxide 

National Ambient Air Quality Standard

Table of Contents

PAGE

Overview of this document................................................................................................. 1

What is SO2 and why was a new standard necessary?........................................................ 1

What is the process for designating areas and attaining the standard? ............................... 2

What would be the effects of designation as nonattainment?......................................... 4

Designation methodology ................................................................................................... 4

EPA guidance for designation boundaries...................................................................... 4

Designation Recommendations .......................................................................................... 5

Attainment Areas............................................................................................................ 5

Nonattainment Areas ...................................................................................................... 6

Unclassifiable Areas ....................................................................................................... 6

Discussion of related factors........................................................................................... 8

1. Air quality .............................................................................................................. 8

2. Emissions............................................................................................................. 10

3. Current level of emission controls....................................................................... 12

4. Geography/topography and meteorology ............................................................ 15

5. Jurisdictional and other boundaries ..................................................................... 51

Acronyms and Terms........................................................................................................ 52

References......................................................................................................................... 53

APPENDIX A. 

Pennsylvania Facilities with Reported SOx Emissions greater than 100 TPY (2007-2009)
TABLES AND FIGURES

TABLES

Table Title Page

Table 1 Recommended SO2 Designations in Pennsylvania 7

Table 2 Design Values by Monitor 2008-2010 9

Table 3 Pennsylvania SO2 Emissions - 2008 11

Table 4 SO2 Emissions from EGUs 2007-2010 13

Table 5 Controls on Electric Generating Units over 100 tons per year of SO2

Emissions

13

FIGURES

Figure Title Page

Figure 1 Recommended Nonattainment Areas (map) 8

Figure 2 Design Values by Monitor 2008-2010 (map) 10

Figure 3 Pennsylvania SO2 Emissions by County (map) 12

Warren County Analyses

Figure 4 Warren County Topographical Map 16

Figure 5 Warren-Overlook Monitor Topographical Map 17

Figure 6 Warren-Overlook Monitor Location 18

Figure 7 Wind Rose for the Warren-Overlook Monitor 19

Figure 8 Warren-Overlook Local Terrain 20

Figure 9 Warren-Overlook Wind Rose Data for Exceedance Hours 21

Figure 10 Warren-Overlook Time of Day for SO2 Exceedances 22

Beaver County Analyses

Figure 11 Beaver County Topographical Map 23

Figure 12 Brighton Township Monitor Topographical Map 24

Figure 13 Brighton Township Monitor Location 25

Figure 14 Wind Rose for the Brighton Township Monitor 26

Figure 15 Brighton Township Monitor Local Terrain 27

Figure 16 Brighton Township Monitor Wind Rose Data for Exceedance Hours 28

Figure 17 Brighton Township Time of Day for SO2 Exceedances 29

Figure 18 Hookstown Monitor Topographical Map 30

Figure 19 Hookstown Monitor Location 31

Figure 20 Wind Rose for the Hookstown Monitor 32

Figure 21 Hookstown Monitor Local Terrain 33

Figure 22 Hookstown Monitor Wind Rose Data for Exceedance Hours 34

Figure 23 Hookstown Monitor Time of Day for SO2 Exceedances 35

Allegheny County Analyses

Figure 24 Allegheny County Topographical Map 36

Figure 25 Allegheny County Airport Topographical Map 37

Figure 26 Liberty Monitor Topographical Map 38

Figure 27 Liberty Monitor Location 39
Figure 28 Wind Rose for the Liberty Monitor 40

Figure 29 Liberty Monitor Local Terrain 41

Figure 30 Liberty Monitor Wind Rose Data for Exceedance Hours 42

Figure 31 Liberty Monitor Time of Day for SO2 Exceedances 43

Indiana County Analyses

Figure 32 Indiana County Topographical Map 44

Figure 33 Strongstown Monitor Topographical Map 45

Figure 34 Strongstown Monitor Location 46

Figure 35 Wind Rose for the Strongstown Monitor 47

Figure 36 Strongstown Monitor Local Terrain 48

Figure 37 Strongstown Monitor Wind Rose Data for Exceedance Hours 49

Figure 38 Strongstown Monitor Time of Day for SO2 Exceedances 50
This page left blank to enable two-sided copying.
1

Overview of this document

The federal Clean Air Act (CAA) provides a mechanism for states to make 

recommendations to the United States Environmental Protection Agency (EPA) on the 

designation of areas meeting and not meeting the National Ambient Air Quality 

Standards (NAAQS). Section 107(d)(1) of the CAA establishes requirements and 

procedures for designating areas as “attainment,” “nonattainment” or “unclassifiable” (if 

adequate data is not available) following EPA’s promulgation of the NAAQS. 42 U.S.C. 

§ 7409(d)(1). 

In June 2010, EPA revised the NAAQS for sulfur dioxide (SO2) (signed June 2, 2010, 

published June 22, 2010 at 75 FR 35,520). A new 1-hour primary standard of 75 parts 

per billion (ppb) was established, and the existing 24-hour and annual primary standards 

were revoked. The 1-hour standard is based on the 3-year average of the annual 99th

percentile of 1-hour daily maximum concentrations. 

Following the promulgation of a NAAQS, each state submits NAAQS designation

recommendations to EPA for all areas within its borders one year after the promulgation 

of the revised NAAQS; designation recommendations for the SO2 NAAQS are due to 

EPA by June 3, 2011. The CAA authorizes the EPA Administrator to modify the 

designation recommendations and to provide an opportunity for states to demonstrate 

why the proposed modification is not appropriate.

In this document, the Department of Environmental Protection (DEP or Department) is 

making recommendations to EPA on behalf of the Commonwealth of Pennsylvania 

concerning the designation of attainment and nonattainment areas in Pennsylvania for the 

2010 SO2 NAAQS. The designation recommendations are based primarily on air quality 

monitoring data for 2008-2010. EPA anticipates making initial final designations by 

June 2012. The Department will continue to work with EPA during the SO2 NAAQS 

designation process, which is described in more detail below.

What is SO2 and why was a new standard necessary?

SO2 is one of a group of highly reactive gasses known as “oxides of sulfur.” 

Current scientific evidence links health effects with short-term exposure to SO2 ranging 

from 5-minutes to 24-hours. Adverse respiratory effects include narrowing of the 

airways which can cause difficulty breathing and increased asthma symptoms. These

effects are particularly important for asthmatics during periods of faster or deeper 

breathing (e.g., while exercising or playing). Studies also show an association between 

short-term SO2 exposure and increased visits to emergency departments and hospital 

admissions for respiratory illnesses--particularly in at-risk populations including children, 

the elderly and asthmatics. 
2

EPA sets the NAAQS based on its review of existing scientific knowledge about the 

adverse health and welfare effects. The CAA requires EPA to review and update 

periodically, if necessary, the NAAQS to “protect public health with an adequate margin 

of safety” based on the latest, best-available science. EPA’s evaluation of the scientific 

information and the risks posed by breathing SO2 indicate that this new 1-hour standard 

will protect public health by reducing people’s exposure to high short-term (5-minutes to 

24-hours) concentrations of SO2. The revised primary standard is consistent with the 

advice and recommendations of EPA’s principal independent science advisors on 

NAAQS: the Clean Air Scientific Advisory Committee.

EPA estimates that the revised standard will yield health benefits valued between $13 

billion and $33 billion, including reduced hospital admissions, emergency room visits, 

work days lost due to illness, and cases of aggravated asthma and chronic bronchitis, 

among other benefits.

Emissions that lead to high concentrations of SO2 generally also lead to the formation of

other oxides of sulfur. Reducing SO2 emissions is expected to have the important cobenefit of reducing the formation of fine sulfate particles that pose significant public 

health threats.

EPA also revised the monitoring network requirements when it promulgated the 1-hour 

standard. All newly sited SO2 monitors must be operational by January 1, 2013. 

Therefore, EPA will be basing its initial designations upon monitors in operation prior to 

2012 and upon any refined air quality modeling completed by the states or EPA. 

Nationally, the largest sources of SO2 emissions are fossil fuel combustion units at power 

plants and other industrial facilities. Smaller sources of SO2 emissions include industrial 

processes such as extracting metal from ore, and the burning of high-sulfur fuels by home 

heating equipment, locomotives, large ships, and non-road equipment. 

According to information compiled for 2008 emissions, large stationary sources 

contribute almost 90 percent of the SO2 emissions in the Commonwealth, with most of 

those emissions coming from electric generation units. The latest year for which 

emissions for all sectors is available is 2008. Only large stationary sources are required 

to provide emissions information annually. 

What is the process for designating areas and attaining the standard?

Section 107(d)(1)(B) of the CAA requires EPA to designate areas as nonattainment, 

attainment or unclassifiable after promulgating a new NAAQS. 42 U.S.C. 

§ 7407(d)(1)(B). Following promulgation of new or revised air standards, Governors are 

required to submit recommendations for attainment, nonattainment and unclassifiable 

areas. Governors’ recommendations for attainment, nonattainment and unclassifiable 

designations are to be submitted to EPA by June 3, 2011, one year after the promulgation 

of the revised NAAQS. EPA may make modifications and promulgate all or part of a 

Governor’s recommendations. If EPA determines that a modification to the 
3

recommendation is necessary, EPA will notify the state no later than 120 days prior to 

promulgating the designation (120-day letter), and must give the state an opportunity to 

demonstrate why the potential modification is inappropriate. The CAA requires EPA to 

make final designations within two years of promulgation of a NAAQS unless there is 

insufficient information, in which case EPA may extend the time period by one year. 

EPA stated in the preamble to the 2010 NAAQS that due to the generally localized 

impacts of SO2, EPA has not historically considered monitoring alone to be an adequate 

nor the most appropriate tool to identify all maximum concentrations of SO2. Therefore, 

EPA expects it will integrate air quality dispersion modeling into all phases of the SO2

NAAQS implementation. Dispersion modeling uses mathematical formulations to 

characterize the atmospheric processes that disperse a pollutant emitted by a source. 

Based on emissions and meteorological inputs, a dispersion model can be used to predict 

concentrations at selected downwind receptor locations.

Because of the expected reliance upon dispersion modeling in ultimately determining the 

boundaries of designated areas, EPA indicated it would provide additional guidance to 

states for designations and plans. However, EPA stated in its preamble to the 2010 

NAAQS that it will take time for EPA to issue the guidance, and that it may not be 

available for states to use in their initial recommendations. EPA suggested that initial 

state designation recommendations of unclassifiable would not be unexpected for areas 

without violations at an air quality monitor. In its March 24, 2011 memorandum, Area 

Designations for the 2010 Revised Primary Sulfur Dioxide National Ambient Air Quality 

Standards, EPA also indicated that even the first round of designations may not identify 

all areas where NAAQS violations may be occurring, and that states would address any 

such areas in the course of developing State Implementation Plan (SIP) revisions under 

Section 110(a) of the Clean Air Act.

The CAA requires states to submit Section 110(a) SIP revisions describing how the state 

will implement, maintain and enforce the new SO2 NAAQS. This obligation applies to 

all areas, whatever their designation. In the case of SO2, the preamble to the NAAQS 

promulgation explains the analytical framework states are expected to use in submitting 

these SIP revisions. To qualify areas as attainment, states are expected to describe how 

the standard will be maintained. For designated nonattainment areas, states are required 

to submit attainment demonstration SIP revisions, including implementation of all 

reasonably available control measures, incremental reductions showing reasonable 

further progress, emission inventories and contingency measures. All SIP revisions are 

subject to public review and comment, including a public hearing.

Designated nonattainment areas are required to attain the standard as expeditiously as 

practicable, but no later than five years from the effective date of designation.
4

Anticipated milestones for the 1-hour SO2 NAAQS are: 

June 3, 2011 State recommendations due to EPA

February 3, 2012 EPA notifies Pennsylvania if EPA intends to modify recommendations for 

areas with existing monitoring networks and sufficient data

February 20, 2012 EPA anticipates opening a 30-day public comment period of intended 

designations

April 3, 2012 State deadline for response to EPA notification 

June 2012 EPA makes final designations for areas based on existing monitoring 

network

January 2013 Additional monitoring to be operational

June 2013 Section 110(a) SIPs due for all areas

February 2014 Attainment demonstration SIP revisions due to EPA for nonattainment areas 

(18 months from the effective date of designation)

Mid-2015 Three years of data from new monitors become available to evaluate any 

additional monitored violations.

August 2017 Latest date by which nonattainment areas designated in 2012 must attain the 

NAAQS (5 years from the effective date of designations)

What would be the effects of designation as nonattainment?

The CAA contains different requirements for new and modified stationary sources in 

areas designated as nonattainment. In addition, the “general conformity” provisions of 

the CAA apply only in nonattainment and maintenance areas; the requirements of these

provisions require federally-funded actions and projects must conform to the SIP in order 

not to interfere with NAAQS attainment and maintenance. Due to the relatively small 

amounts of sulfur in gasoline and on-road diesel fuel, transportation conformity (which 

addresses only highway vehicle emissions) does not apply to the SO2 NAAQS. 

Designation methodology

EPA guidance for designation boundaries. 

Section 107(d)(1) of the CAA defines an area as nonattainment if it does not meet the 

NAAQS or if it is contributing to ambient air quality in a nearby area that does not meet 

the NAAQS. 42 U.S.C. § 7407(d)(1). 

EPA stated in the June 22, 2010 rulemaking that the expected presumptive boundary for 

any area designated nonattainment would be the county boundary associated with a 

violation. States may provide additional information for larger or smaller nonattainment 

areas; the additional information would most likely be refined dispersion modeling. In its 

March 24, 2011 memorandum, Area Designations for the 2010 Revised Primary Sulfur 

Dioxide National Ambient Air Quality Standards, EPA also recommended defining 

nonattainment boundaries with the use of well-defined jurisdictional lines or immovable 

landmarks or other readily identifiable boundaries. 
5

EPA did not identify other specific factors in the preamble to the June 22, 2010 

rulemaking that states should consider in their designation recommendations, but it did so 

in its March 24, 2011, memorandum. Because 1-hour SO2 violations are generally 

associated with a large specific source (usually a stationary source), not all of the factors 

associated with regional pollutants such as ozone or fine particulates are appropriate 

considerations for this pollutant, such as population growth. EPA is recommending states 

base boundary recommendations on five factors, and other available data: 

1. air quality data

2. emissions-related data

3. meteorology

4. geography and topography

5. jurisdictional and other boundaries

The Department has not yet conducted dispersion modeling for its SO2 sources to be used 

in informing designation recommendations, because EPA guidance was not issued in 

sufficient time. The Department will conduct dispersion modeling in accordance with 

EPA guidance for many of its SO2 sources to be able to respond to EPA before EPA 

makes its final designations in June 2012, including responding to the notice EPA must 

provide 120 days before the final designations if EPA intends to modify our 

recommended designations. Modeling will enable the Department to better consider the 

five factors recommended by EPA for boundary recommendations. The Department will 

aim to fulfill its obligations to submit Section 110(a) SIP revisions by June 2013 and 

submit attainment demonstrations in February 2014. 

Designation Recommendations 

The Department has determined that the EPA presumptive county boundary approach is 

reasonable for Pennsylvania.

EPA stated in the preamble to the 1-hour SO2 NAAQS rulemaking that, for these initial 

designation recommendations, states should use monitoring data from the existing SO2

network for the years 2008-2010. The Department and the local air quality agencies in 

Philadelphia and Allegheny counties operated 28 monitors in 20 counties during the 

period 2008-2010. Two of the monitors are special purpose monitors which do not meet 

the required network design criteria for the SO2 NAAQS. The Department will provide 

EPA with any updated information available (for example, monitoring data for 2011 and 

a design value for 2009-2011) in response to EPA’s 120-day letter expected in February 

2012.

Attainment Areas

Of the 26 network monitors, 21 monitors in 16 counties did not show violations of the 1-

hour SO2 standard (including 3 monitors where data is incomplete). EPA stated in the 

preamble to the NAAQS rulemaking that absent monitoring data and air quality modeling 

results showing no violations, it expects that the initial designations will be unclassifiable 

as required by the Clean Air Act. Since the Department has not completed any dispersion 
6

modeling for designation purposes, no areas are being recommended as attainment at this 

time. If Department-conducted or evaluated dispersion modeling for sources in these 

counties can demonstrate attainment of the 1-hour standard, the Department will revise 

its recommendations from unclassifiable to attainment.

Nonattainment Areas

Monitors in Allegheny, Beaver, Indiana and Warren counties are violating the 1-hour SO2

NAAQS using monitoring data from 2008-2010. The Department is recommending that 

these counties be designated as nonattainment areas. 

In addition, Section 107(d)(1)(C)(i) of CAA, regarding designations by operation of law, 

provides that an area designated as nonattainment with respect to any air pollutant before 

November 1990 is designated as a nonattainment area for that pollutant. Portions of 

Armstrong County (Madison, Mahoning, Boggs, Washington and Pine townships) are 

designated as nonattainment for the 3-hour and annual SO2 NAAQS. Therefore, the 

Department expects EPA to include these townships in its designations as nonattainment 

for the 1-hour SO2 standard. 

Unclassifiable Areas

At this time, the Department is recommending that all other counties in Pennsylvania be 

designated as unclassifiable.

The Department will be conducting or evaluating refined air quality dispersion modeling 

for sources. However, in Pennsylvania, there are more than 100 facilities with SO2

emissions more than 100 tons per year (tpy) (determined by the maximum annual 

emissions in 2007, 2008 or 2009) and as many as 1,300 facilities with any reported SO2

emissions. Modeling for these sources will be an enormous and resource intensive 

undertaking. EPA guidance was not provided in sufficient time to ensure modeling for a 

June 2011, submission of recommendations conforming to the guidance.

The Department may revise its recommendations regarding unclassifiable areas to 

recommend that designations be revised to either nonattainment or attainment based upon 

that modeling. There is little doubt that there are modeled violations in the 

Commonwealth associated with large sources of SO2 emissions outside those counties 

with violating monitors. For example, of the five facilities with 2007-2009 maximum 

annual emissions of 100,000 tpy or greater, only one is in a county that is monitoring 

nonattainment.

Dispersion modeling to support the Department’s 1-hour SO2 designation 

recommendations will follow the United States Environmental Protection Agency 

(USEPA) March 24, 2011 memorandum, Area Designations for the 2010 Revised 

Primary Sulfur Dioxide National Ambient Air Quality Standards. The Department 

intends to make available to the public the results of any modeling that has been 

completed by February 2012. EPA has indicated it would also provide an opportunity for 

public comment at that time of its intended designations and responses to state 

recommendations. 
7

Table 1 summarizes the Commonwealth’s recommendations by county. Figure 1 is a 

map showing the recommended nonattainment areas. 

Table 1. Recommended SO2 Designations in Pennsylvania

PA Counties Recommendation PA Counties Recommendation

Adams County Unclassifiable Lackawanna County Unclassifiable

Allegheny County Nonattainment Lancaster County Unclassifiable

Armstrong County Unclassifiable Lawrence County Unclassifiable

Beaver County Nonattainment Lebanon County Unclassifiable

Bedford County Unclassifiable Lehigh County Unclassifiable

Berks County Unclassifiable Luzerne County Unclassifiable

Blair County Unclassifiable Lycoming County Unclassifiable

Bradford County Unclassifiable McKean County Unclassifiable

Bucks County Unclassifiable Mercer County Unclassifiable

Butler County Unclassifiable Mifflin County Unclassifiable

Cambria County Unclassifiable Monroe County Unclassifiable

Cameron County Unclassifiable Montgomery County Unclassifiable

Carbon County Unclassifiable Montour County Unclassifiable

Centre County Unclassifiable Northampton County Unclassifiable

Chester County Unclassifiable Northumberland County Unclassifiable

Clarion County Unclassifiable Perry County Unclassifiable

Clearfield County Unclassifiable Philadelphia County Unclassifiable

Clinton County Unclassifiable Pike County Unclassifiable

Columbia County Unclassifiable Potter County Unclassifiable

Crawford County Unclassifiable Schuylkill County Unclassifiable

Cumberland County Unclassifiable Snyder County Unclassifiable

Dauphin County Unclassifiable Somerset County Unclassifiable

Delaware County Unclassifiable Sullivan County Unclassifiable

Elk County Unclassifiable Susquehanna County Unclassifiable

Erie County Unclassifiable Tioga County Unclassifiable

Fayette County Unclassifiable Union County Unclassifiable

Forest County Unclassifiable Venango County Unclassifiable

Franklin County Unclassifiable Warren County Nonattainment

Fulton County Unclassifiable Washington County Unclassifiable

Greene County Unclassifiable Wayne County Unclassifiable

Huntingdon County Unclassifiable Westmoreland County Unclassifiable

Indiana County Nonattainment Wyoming County Unclassifiable

Jefferson County Unclassifiable York County Unclassifiable

Juniata County Unclassifiable
8

Figure 1. Recommended Nonattainment Areas.

Discussion of related factors

A general discussion of each factor and sources of information relevant to SO2

designations is provided in this section of the document. The Department is using this 

information in prioritizing and conducting its modeling for purposes of working with 

EPA on designations during the designation process. 

1. Air quality

The Department’s designation recommendations for the short-term SO2 NAAQS are 

based on the 2010 SO2 design values1(calculated using the 2008, 2009, and 2010

monitored data). 

 

1

 The design value for the 1-hour SO2 standard is based on the 3-year average of the annual 99th percentile 

of 1-hour daily maximum concentrations.
9

Table 2. Design Values by Monitor (2008-2010)

County Site

1-hour Design 

Value (ppb)

Allegheny Co. Avalon 63

Allegheny Co. Liberty 128

Allegheny Co. Pittsburgh (BAPC) 29*

Allegheny Co. Pittsburgh (Carnegie-DEP) special purpose

Allegheny Co. South Fayette 48

Allegheny Co. Stowe 66

Beaver Co. Brighton Twp 167

Beaver Co. Hookstown 101

Berks Co. Reading Airport 43

Blair Co. Altoona 47

Bucks Co. Bristol 27

Cambria Co. Johnstown 66

Centre Co. State College 29

Delaware Co. Chester 38

Erie Co. Erie 34

Greene Co. Holbrook special purpose

Indiana Co. Strongstown 90

Lawrence Co. New Castle 65

Luzerne Wilkes-Barre 26

Montgomery Co. Norristown 23

Northampton Co. Easton 50

Perry Co. Perry County 30

Philadelphia Co. AMS 29*

Philadelphia Co. Ritner 29*

Warren Co. Warren Overlook 123

Washington Co. Charleroi 67

Washington Co. Florence 60

York Co. York 71

 (* does not meet data completeness requirement)
10

Figure 2. Design Values by Monitor (2008-2010)

The DEP’s Ambient Air Monitoring Network Plan – 2011 (June 25, 2010), the 

Philadelphia Air Management Services’ (AMS) 2010/2011 Air Monitoring Network Plan

(July 1, 2010) and the Allegheny County Health Department’s (ACHD) “Monitoring 

Network Review” (July 1, 2010) describe the Commonwealth’s plans for additional SO2

monitoring. These documents are available on each of the respective agencies’ websites 

as listed in the reference section. However, since these monitors will not have three years 

of data by the time EPA makes its initial designations, the SO2 designation 

recommendations are based only upon the existing network. 

2. Emissions 

The counties that the Department is recommending as SO2 nonattainment areas contain 

the following number of large sources (over 100 tpy of SO2 in 2007, 2008 or 2009) of 

SO2:

Allegheny County: 7 facilities

Beaver County: 3 facilities

Indiana County: 3 facilities

Warren County: 1 facility
11

A list of sources emitting over 100 tpy of SO2 (maximum 2007-2009 reported emissions 

data) sorted by county is provided in Appendix A.

EPA expects active stationary sources to be the primary contributors to violations of the

1-hour SO2 NAAQS. Note that these sources are not the only sources of SO2 emissions. 

For example, the combustion of coal and oil for heating and industrial, commercial, or 

institutional purposes and the combustion of diesel for transportation purposes also 

contribute to SO2 emissions.

The Department prepares an emission inventory for all criteria pollutants from all sectors 

every three years. Only stationary source data is available every year; the most recent

full inventory was for the year 2008. 

Table 3. Pennsylvania SO2 Emissions – 2008

SECTOR Emissions 

Tons per Year

Emissions

Percent

Stationary 864,732 87.0%

 Electric Generating Unit (EGU) 

 Non-EGU

 819,015

 45,717

 (% of stationary)

 94.7%

 5.3%

Area stationary (includes small 

sources and home heating)

 125,855 12.7%

Highway 1,661 0.2%

Nonroad 2,183 0.2%

TOTAL 994,430
12

Figure 3. Pennsylvania SO2 Emissions By County (2008)

3. Current level of emission controls

As indicated above, EGUs contribute about 82 percent of the SO2 emissions in 

Pennsylvania. The EPA has included 40 EGUs operating in the Commonwealth in its 

National Electric Energy Data System (NEEDS). NEEDS 4.10 is the database of existing 

and planned-committed units which are in the EPA Base Case for the Integrated Planning 

Model (IPM) runs for the proposed Transport Rule (August 2, 2010). IPM is a multiregional, dynamic, deterministic linear programming model of the U.S. electric power 

sector.

The Clean Air Interstate Rule and acid rain programs have caused significant reductions 

to be made in Pennsylvania in SO2 emissions from sources affected by those programs in 

recent years.
13

Table 4. SO2 Emissions from EGUs

(Source: EPA Acid Rain Program)

YEAR SO2 (Tons)

2007 951,186.1

2008 831,914.9

2009 573,618.7

2010 393,196.4

Table 5 identifies EGUs in Pennsylvania and existing SO2 controls. 

Table 5. Controls on Electric Generating Units over 100 tons per year of SO2

Emissions (Max 2007-2009)

(Source: EPA National Electric Energy Data System v 410)

FACILITY FIRING COUNTY CONTROL

Cheswick Coal Steam Allegheny Wet Scrubber

Keystone Coal Steam Armstrong Wet Scrubber

Armstrong Power Station Coal Steam Armstrong

Bruce Mansfield Coal Steam Beaver Wet Scrubber

AES Beaver Valley Partners 

Beaver Valley Coal Steam Beaver Wet Scrubber

Titus Coal Steam Berks

Wheelabrator Falls

Munic solid 

waste Bucks Dry Scrubber

Colver Power Project Coal Steam Cambria Reagent Injection

Ebensburg Power Coal Steam Cambria Reagent Injection

Cambria Cogen Coal Steam Cambria Reagent Injection

Panther Creek Energy 

Facility Coal Steam Carbon Reagent Injection

Cromby Generating Station Coal Steam Chester Wet Scrubber

Cromby Generating Station O/G Steam Chester

Piney Creek Project Coal Steam Clarion Reagent Injection

Shawville Coal Steam Clearfield

Eddystone Generating 

Station Coal Steam Delaware Wet Scrubber

Eddystone Generating 

Station O/G Steam Delaware

Eddystone Generating 

Station O/G Steam Delaware

Hatfields Ferry Power Station Coal Steam Greene Wet Scrubber

Conemaugh Coal Steam Indiana Wet Scrubber

Homer City Station Coal Steam Indiana

Wet Scrubber on 1 of 3 coal 

sources

Seward Coal Steam Indiana Dry Scrubber

New Castle Coal Steam Lawrence

PPL Montour Coal Steam Montour Wet Scrubber
14

Table 5. Controls on EGUs continued

FACILITY FIRING COUNTY CONTROL

Portland Coal Steam Northampton

Northampton Generating 

Company Coal Steam Northampton Reagent Injection

PPL Martins Creek O/G Steam Northampton Shutdown*

Foster Wheeler Mt Carmel 

Cogen Coal Steam Northumberland Dry Scrubber

John B Rich Memorial Power 

Station Coal Steam Schuylkill Reagent Injection

WPS Westwood Generation 

LLC Coal Steam Schuylkill Reagent Injection

Wheelabrator Frackville 

Energy Coal Steam Schuylkill Reagent Injection

St Nicholas Cogen Project Coal Steam Schuylkill Reagent Injection

Sunbury Generation LP Coal Steam Snyder Wet Scrubber on 4 coal sources

Sunbury Generation LP Coal Steam Snyder

Reagent Injection on 2 coal 

sources

Scrubgrass Generating Coal Steam Venango Reagent Injection

Elrama Coal Steam Washington Wet Scrubber

Mitchell Power Station Coal Steam Washington Wet Scrubber

Mitchell Power Station O/G Steam Washington

PPL Brunner Island Coal Steam York Wet Scrubber

P H Glatfelter Coal Steam York

Reagent Injection on 1 of 4 

sources

*Included in EPA's database for analysis purposes

SO2 controls can include wet or dry scrubbers, also known as flue gas desulfurization 

(FGD) systems. SO2 scrubbers use chemical and physical absorption to remove SO2

from the flue gas. Wet scrubbers use a liquid sorbent to remove SO2 and the flue gas 

leaving the absorber is moisture saturated. With dry scrubbers the flue gas leaving the

absorber is not saturated. For circulating fluidized bed units (as shown in the "Firing" 

field), this field indicates whether reagent injection is used for SO2 control. Reagent 

injection involves adding finely crushed limestone to the fluidized bed. During 

combustion, the limestone is reduced to lime, the sulfur in the fuel is oxidized to form 

SO2, and, in the presence of excess oxygen, the SO2 reacts with the lime particles to form 

calcium sulfate, which can be removed with the bottom ash or collected with the fly ash 

by a downstream particulate matter control device.

Existence of SO2 controls does not necessarily equate to modeled attainment of the 1-

hour SO2 standard. EPA guidance recommends that dispersion modeling for designation 

purposes “should be based on the use of maximum allowable emissions or federally 

enforceable permit limits.” 

The Commonwealth has also proposed lower sulfur limits for commercial fuel oil, both 

for heating and industrial/commercial purposes. Finally, EPA has issued rules to reduce 

sulfur in fuel used in large commercial marine vessels (directly affecting the ports of 

Erie, Pittsburgh and Philadelphia, but with significant ambient air effects much farther 
15

inland). Beginning in 2015, fuel used by all vessels operating in these areas cannot 

exceed 0.1 percent fuel sulfur (1,000 ppm). This requirement is expected to reduce SO2

emissions by more than 85 percent. 

4. Geography/topography and meteorology

Local terrain and meteorology affect the direction of transport and the dispersion of 

pollutants. The recommended model for SO2 modeling, AERMOD, contains modules 

that account for terrain and meteorology. Meteorological data must be spatially and 

climatologically (temporally) representative of the area of interest. The

representativeness of the data is dependent on: (1) the proximity of the meteorological 

monitoring site to the area under consideration; (2) the complexity of the terrain; (3) the 

exposure of the meteorological monitoring site; and (4) the period of time during which 

data are collected. Because most of the largest SO2 sources have been through relatively 

recent plan approval processes that required air quality modeling, the Department 

believes that it has representative meteorological data in-house for its modeling efforts 

related to designations.

Air quality impact analysis must also consider how terrain features influence the behavior 

of air pollution plumes. AERMOD uses a terrain preprocessor to generate elevation data 

for each model receptor. It also provides information that allows the dispersion model to 

simulate the effects of air flowing over hills or splitting to flow around hills. 

The Department has conducted initial meteorological and topographic analyses for the 

monitors in the four recommended nonattainment areas. The analysis confirms that the 

county nonattainment area is the most reasonable boundary for Warren, Beaver and 

Allegheny counties, because the sources of the violations are most likely within the 

county. For Indiana County, the analysis indicated that, while a county boundary is 

reasonable, further analysis through modeling may be necessary to assess whether the

nonattainment boundaries should be refined. Overall, the prominent westerly winds and 

stronger wind speeds are indicating that the driving source of the higher SO2

concentrations may be coming from the larger SO2 sources to the west of Strongstown. 

These types of sources generally have taller stacks and higher emission rates which helps 

in the downwind transport of pollution. Until this analysis is completed, the Department 

is recommending a county nonattainment boundary for Indiana County. 

Warren County

Warren County is situated within the western flank of the Appalachian Mountain chain. 

Figure 4 below displays a topographical overview of all of Warren County. There is one 

major river that runs through the county. The Allegheny River flows from the Allegheny 

Reservior (in the far northeastern portion of the county, south and eastward toward Forest 

County on its way into Pittsburgh. Otherwise, the county is marked by its higher terrain. 

When combined with the Allegheny River, this higher terrain is what helps drive the 

meteorological pattern within the county. 
16

Figure 4. Warren County Topographical Map
17

Warren-Overlook SO2 Monitoring Location

Warren-Overlook is situated on a portion of the higher terrain in the eastern side of 

Warren County. Figure 5 displays the location of the Warren-Overlook monitor with 

respect to the major SO2 sources. In addition, Figure 2 highlights the terrain above the 

anemometer of height of the Warren-Overlook meteorological tower (anemometer is at 

10 meters plus base elevation of tower at 580 meters). Therefore, the measurements 

being taken by the Warren-Overlook meteorological tower are likely to be influenced by 

the higher terrain to its east.

Figure 5. Warren-Overlook Topographical Map
18

Figure 6 (courtesy of Google Earth) displays a zoomed in look at the actual WarrenOverlook monitoring location with respect to the other regional SO2 sources.

Figure 6. Warren Overlook Monitoring Location
19

The impact of the topography near Warren-Overlook can also be seen by looking at the 

wind measurements that were collected at the Warren-Overlook air monitoring station 

(meteorological data, including wind direction and speed, are continuously measured). 

Figure 7 (courtesy of Google Earth) displays the wind data measured at WarrenOverlook’s meteorological tower from January 2008 to December 2010 (a full three year 

dataset).

Figure 7. Wind Rose for the Warren-Overlook Monitor 

The wind is primarily out of the west and southwest. There is also a secondary maximum 

out of the north and east. This wind profile follows the synoptic wind flow over northern 

Pennsylvania. Stronger winds exist out of the southwest than out of the northeast 

because the winds out of the southwest are undergoing less friction (the main river that 

runs through Warren County runs off to the south of the monitoring station). The wind 

undergoes more friction from the northeast due to the higher terrain in that direction. 
20

Taking a cross section look (in three dimensions within Google Earth) at the local area in 

Figure 8 below, one can see the relationship of the local terrain with respect to the major 

SO2 sources in the region and the Warren-Overlook air monitor station.

Figure 8. Local Terrain

From Figure 8 (which looks south to north), one can see that the Warren-Overlook air 

monitoring station sits on the side of a hill. The main SO2 source in the region sits down 

within the river valley.

Also from Figure 8 above, one can see that the Warren-Overlook monitor lies to the west

of the major SO2 source. The Warren-Overlook monitor acquires SO2 samples from the 

air continuously every hour, which results in approximately 8760 hours of samples every 

year. The latest design value year, 2010 (which is based on data from 2008 to 2010), 

showed the Warren-Overlook monitor exceeding the new SO2 standard with a 

concentration of 123 ppb. The Department analyzed the data to focus in on the hours in 

which the SO2 concentrations exceeded the new 1-hour SO2 standard. 112 hours were 

found to exceed this threshold. Out of those 112 hours, 88 hours had complete 

corresponding meteorological data. Then, the Department analyzed the wind data and 

created a wind rose to coincide with the meteorological data collected on those 88 hours 

that were found to exceed the new 1-hour SO2 standard threshold. 
21

Figure 9 shows the results.

Figure 9. Wind Rose Data for Exceedance Hours

When comparing this figure with Figure 7 above, one will notice that the primary wind 

direction has changed. During the periods when there are high SO2 concentrations, the 

wind is primarily out of the north and east. In addition, wind speeds are generally 

stronger, out of the east, indicating that the winds are unimpeded (from the impact of 

higher terrain) from that direction. Rotating counter-clockwise, the winds become 

generally lighter as the winds undergo more friction (from the higher terrain to the north). 

The combination of the severe terrain within the Warren-Overlook area combined with 

northeasterly component of the wind would indicate that a local source within the valley 

is creating the high SO2 concentrations. 
22

The time of the day when the SO2 concentrations are occurring is also of importance. 

Figure 10 illustrates when the Warren-Overlook monitor is experiencing the high 1-hour 

SO2 concentrations.

Figure 10. Time of Day for SO2 Exceedamces

All of the high SO2 concentrations are occurring in the late evening to early morning 

hours (from 7 PM to 9 AM). The timing of these exceedances coupled with the fact that 

the Warren-Overlook monitoring site is situated within a valley increases the likelihood 

that meteorological inversions are assisting in driving SO2 concentrations higher. Once 

an inversion forms and the wind near the surface decreases, localized air pollution 

becomes trapped near the surface. Therefore, there is even more likelihood that the high 

SO2 concentrations are driven by an SO2 source in close proximity to monitor. 

Due to the nature of the high SO2 concentrations around the Warren-Overlook monitor, 

the Department is recommending that Warren County be designated nonattainment for 

the new SO2 standard. 

Beaver County

Beaver County is situated to the west of the Appalachian Mountain chain. Figure 11 

below displays a topographical overview of all of Beaver County. There are two major 

rivers that run through the relatively high terrain of Beaver County. The Ohio River, 

which flows into the county from Pittsburgh, runs from east to west across the county. 

The Beaver River, flows from south to north from Lawrence County into the Ohio River 

Warren-Overlook Air Monitoring Station

Number of Observations of High SO2 Concentrations vs. Time

0

2

4

6

8

10

12

14

02468

10121416182022

Hour

Number of Observations

Trend of Hourly SO2
23

near the city of Monaca. When combined with the higher topography, these rivers help 

drive the meteorological pattern witnessed within the county. 

Figure 11. Beaver County Topographical Map
24

Brighton Township SO2 Monitoring Location

Brighton Township is situated on higher terrain while being within a mile of the Ohio 

River (which lies to the south of the monitor). Figure 12 displays the location of the 

Brighton Township monitor with respect to the major SO2 sources. In addition, Figure 2 

highlights the terrain above the anemometer of height of the Brighton Township 

meteorological tower (anemometer is at 10 meters plus base elevation of tower at 366 

meters). Therefore, the measurements being taken by the Brighton Township 

meteorological tower are not very influenced by any of the terrain in its immediate 

vicinity.

Figure 12. Brighton Township (Beaver County) Topographical Map
25

Figure 13 (courtesy of Google Earth) displays a zoomed in look at the actual Brighton 

Township monitoring location with respect to the other regional SO2 sources.

Figure 13. Brighton Township Monitoring Location
26

The impact of the topography near Brighton Township can also be seen by looking at the 

wind measurements that were collected at the Brighton Township air monitoring station 

(meteorological data, including wind direction and speed, are continuously measured). 

Figure 14 (courtesy of Google Earth) displays the wind data measured at Brighton 

Township’s meteorological tower from January 2008 to December 2010 (a full three year 

dataset).

Figure 14. Wind Rose Data for the Brighton Monitor

The wind is primarily out of the west and northwest. This wind profile follows the 

synoptic wind flow over the region and is not surprising by referencing Figure 12 above, 

which shows that there is not any significant terrain that is influencing the wind 

measurements. 
27

Taking a cross section look (in three dimensions within Google Earth) at the local area in 

Figure 15 below, one can see the relationship of the local terrain with respect to the major 

SO2 sources in the region and the Brighton Township air monitor station.

Figure 15. Local Terrain

From Figure 15 (which looks south to north), once again one can see that the Brighton 

Township air monitoring station sits on top of a local hill, with many of the major SO2

sources sitting in the Ohio River valley. 

Also from Figure 15 above, one can see that the Brighton Township monitor lies to the 

north of these SO2 sources. The Brighton Township monitor acquires SO2 samples from 

the air continuously every hour, which results in approximately 8760 hours of samples

every year. The latest design value year, 2010 (which is based on data from 2008 to 

2010), showed the Brighton Township monitor exceeding the new SO2 standard with a 

concentration of 167 ppb. The Department analyzed the data to focus in on the hours in 

which the SO2 concentrations exceeded the new 1-hour SO2 standard. 183 hours were 

found to exceed this threshold. Out of those 183 hours, 110 hours had complete 

corresponding meteorological data. Then, the Department analyzed the wind data and 

created a wind rose to coincide with the meteorological data collected on those 110 hours 

that were found to exceed the new 1-hour SO2 standard threshold. 
28

Figure 16 shows the results.

Figure 16. Wind Rose Data for Exceedance Hours

When comparing this figure with Figure 14 above, one will notice that the primary wind 

direction has changed. During the periods when there are high concentrations of SO2, the 

wind is primarily out of the south, southwest. In addition, wind speeds are generally 

slower, indicating that a much more stable air mass is in place over the region when SO2

concentrations rise. A stable boundary layer would limit vertical mixing, thus allowing 

concentrations to build near the surface. Overall, the prominent southwesterly winds and 

lighter wind speeds are indicating that the driving source of the higher SO2concentrations 

is coming from the SO2 sources sitting within the Ohio River valley to the monitors 

south. 
29

The time of the day when the SO2 concentrations are occurring is also of importance. 

Figure 17 illustrates when the Brighton Township monitor is experiencing the high 1-

hour SO2 concentrations. 

Figure 17. Time of Day For SO2 Exceedances

Most of the high SO2 concentrations are occurring in the late evening to early morning 

hours (from 8 PM to 10 AM). The timing of these exceedances coupled with the fact that 

the Brighton Township monitoring site is situated within a valley increases the likelihood 

that meteorological inversions are assisting in driving SO2 concentrations higher. Once 

an inversion forms and the wind near the surface decreases (see Figure 6 for an example 

of this), localized air pollution becomes trapped near the surface. Therefore, there is even 

more likelihood that the high SO2 concentrations are driven by an SO2 source in close 

proximity to monitor. 

Hookstown SO2 Monitoring Location

Hookstown is situated on higher terrain while being within several miles of the Ohio 

River (which lies to the north of the monitor). Figure 18 displays the location of the 

Brighton Township monitor with respect to the major SO2 sources. In addition, Figure 18

highlights the terrain above the anemometer height of the Hookstown meteorological 

tower (anemometer is at 10 meters plus base elevation of tower at 366 meters). 

Therefore, the measurements being taken by the Hookstown meteorological tower are not 

very influenced by any of the terrain in its immediate vicinity.

Brighton Township Air Monitoring Station

Number of SO2 Concentration Exceedances vs. Time

0

2

4

6

8

10

12

02468

10121416182022

Hour

Number of Exceedances

Trend of Hourly SO2
30

Figure 18. Hookstown (Beaver County) Topographical Map
31

Figure 19 (courtesy of Google Earth) displays a zoomed in look at the actual Hookstown 

monitoring location with respect to the other regional SO2 sources.

Figure 19. Hookstown Monitor Location Map
32

The impact of the topography near Hookstown can also be seen by looking at the wind 

measurements that were collected at the Hookstown air monitoring station 

(meteorological data, including wind direction and speed, are continuously measured). 

Figure 20 (courtesy of Google Earth) displays the wind data measured at Brighton 

Township’s meteorological tower from January 2008 to December 2010 (a full three year 

dataset).

Figure 20. Wind Rose for the Hookstown Monitor

The wind is primarily out of the west and southwest. This wind profile follows the 

synoptic wind flow over the region and is not surprising by seeing Figure 18 above, 

which shows that there is not any significant terrain that is influencing the wind 

measurements. 
33

Taking a cross section look (in three dimensions within Google Earth) at the local area in 

Figure 21 below, one can see the relationship of the local terrain with respect to the major 

SO2 sources in the region and the Hookstown air monitor station.

Figure 21. Local Terrain

From Figure 21 (which looks south to north), once again one can see that the Hookstown

air monitoring station sits on top of a local hill, with the closest SO2 source in 

Pennsylvania sitting in the Ohio River valley off to the north and east of the Hookstown 

monitor. 

Also from Figure 21 above, one can see that the Hookstown monitor lies to the southwest 

of this SO2 source. The Hookstown monitor acquires SO2 samples from the air 

continuously every hour, which results in approximately 8760 hours of samples every 

year. The latest design value year, 2010 (which is based on data from 2008 to 2010), 

showed the Brighton monitor exceeding the new SO2 standard with a concentration of 

101 ppb. The Department analyzed the data to focus in on the hours in which the SO2

concentrations exceeded the new 1-hour SO2 standard. 74 hours were found to exceed 

this threshold. Out of those 74 hours, 74 hours had complete corresponding 

meteorological data. Then, the Department analyzed the wind data and created a wind 

rose to coincide with the meteorological data collected on those 74 hours that were found 

to exceed the new 1-hour SO2 standard threshold. 
34

Figure 22 shows the results. 

Figure 22. Wind Rose Data for Exceedance Hours

When comparing this figure with Figure 20 above, one will notice that the primary wind 

direction has changed. During the periods when there are high SO2 concentrations, the 

wind is primarily out of the west. In addition, wind speeds are generally stronger, 

indicating that the high SO2 concentrations are being driven in from out of state. 

Comparing the strong westerly component of the winds with the fact that there are no 

other major SO2 emissions sources within Pennsylvania in close proximity of the 

Hookstown monitor indicates that the Hookstown monitor is picking up on the intrastate 

transport of SO2. Overall, the prominent westerly winds and stronger wind speeds are 

indicating that the driving source of the higher SO2 concentrations is coming from the 

SO2 sources cited in states to our west.
35

The time of the day when the SO2 concentrations are occurring is also of importance. 

Figure 23 illustrates when the Hookstown monitor is experiencing the high 1-hour SO2

concentrations.

Figure 23. Time of Day for SO2 Exceedances

Most of the high SO2 concentrations are occurring in the middle of the day hours (from 9 

AM to 5 PM). The timing of these exceedances coupled with the fact that the Hookstown

monitoring site is situated on higher terrain increases the likelihood that intrastate 

transport is playing a role in the monitored SO2 concentration exceedances. The middle 

of the day is when the atmosphere is the most unstable, meaning that more horizontal and 

vertical mixing is occurring. The onset of this mixing usually occurs in the late morning 

when, after a cool night, the sun warms the surface. The air at the surface is then warmer 

and less dense than its surroundings so it wants to rise, inducing vertical motion. The top 

two hours when we see the most exceedances are 10 and 11 AM, when vertical mixing 

begins. Therefore, there is even more likelihood that the high SO2 concentrations are 

driven by SO2 sources by SO2 sources to the west of the Hookstown monitor. 

Due to the nature of the high SO2 concentrations around the Brighton Township and 

Hookstown monitors, the Department is recommending that Beaver County be 

designated nonattainment for the new SO2 standard. 

Hookstown Air Monitoring Station

Number of SO2 Concentration Exceedances vs. Time

0

2

4

6

8

10

12

14

16

02468

10121416182022

Hour

Number of Exceedances

Trend of Hourly SO2
36

Allegheny County

Allegheny County is situated to the west of the Appalachian Mountain chain. Figure 24 

below displays a topographical overview of all of Allegheny County. There are four 

major rivers that run through the relatively high terrain of Allegheny County. The 

Monongahela River, which runs from the Washington County line northward, and the 

Allegheny River, which runs from the Westmoreland County line southward, converges 

in Pittsburgh to form the Ohio River, which runs from Pittsburgh northwestward toward 

Beaver County. The Youghiogheny River, in southeastern Allegheny County, flows into 

the Monongahela River. When combined with the higher topography, these rivers help 

drive the meteorological pattern witnessed within the county. 

Figure 24. Allegheny County Topographical Map
37

Liberty SO2 Monitoring Location

Liberty is situated on higher terrain while being surrounded by two rivers: the 

Youghiogheny River to the east and the Monongahela River to the west. Figure 25 

displays the location of the Liberty monitor with respect to the major SO2 sources In 

addition, Figure 2 highlights the terrain above the anemometer of height of the Allegheny 

County Airport meteorological tower (anemometer is at 10 meters plus base elevation of 

tower at 380 meters). The measurements being taken by the Allegheny County Airport

meteorological tower are likely to not be influenced by any higher terrain.

Figure 25. Allegheny County Airport Topographical Map
38

The Liberty air monitoring station also collected meteorological data during the three 

year period (Jaunary 2008 to December 2010). However, the meteorological data set 

during that time frame was not complete, which is why the Allegheny County Airport’s 

meteorological data was utilized. Figure 26 highlights the terrain above the anemometer 

of height of the Liberty monitoring station (anemometer plus base elevation of tower at 

380 meters). If available, the measurements being taken by the Liberty meteorological 

tower are likely to be influenced by the local terrain. 

Figure 26. Liberty Monitor Topographical Map

The difference in elevation between the Allegheny County Airport and the Liberty air 

monitoring stations is approximately 55 meters. 
39

Figure 27 (courtesy of Google Earth) displays a zoomed in look at the actual Liberty 

monitoring location with respect to the other regional SO2 sources. 

Figure 27. Liberty Monitor Location Map
40

The impact of the topography near Liberty can also be seen by looking at the wind 

measurements that were collected at the Allegheny County Airport meteorological tower. 

Figure 28 (courtesy of Google Earth) displays the wind data measured at the Allegheny 

County Airport’s meteorological tower from January 2008 to December 2010 (a full three 

year dataset). 

Figure 28. Wind Rose for the Allegheny County Airport

The wind is primarily out of the west and south. There is also a secondary maximum out 

of the north. This wind profile follows the synoptic wind flow over southwestern 

Pennsylvania. Stronger winds exist at this monitoring station because the wind is not 

undergoing any friction because it is not impacted by higher terrain. 
41

Taking a cross section look (in three dimensions within Google Earth) at the local area in 

Figure 29 below, one can see the relationship of the local terrain with respect to the major 

SO2 sources in the region and the Liberty air monitor station. 

Figure 29. Local Terrain

From Figure 29 (which looks north to south), one can see that the Liberty air monitoring 

station sits on top of a hill. However, there is higher terrain surrounding the monitor, 

creating valley like influences. The main SO2 sources in the region are at lower elevation 

as they sit down within the river valley.

Figure 28 above shows that the Liberty monitor is centrally located between multiple 

major SO2 sources. The Liberty monitor acquires SO2 samples from the air continuously 

every hour, which results in approximately 8760 hours of samples every year. The latest 

design value year, 2010 (which is based on data from 2008 to 2010), showed the Liberty

monitor exceeding the new SO2 standard with a concentration of 128 ppb. The 

Department analyzed the data to focus in on the hours in which the SO2 concentrations 

exceeded the new 1-hour SO2 standard. 116 hours were found to exceed this threshold. 

Out of those 116 hours, 116 hours had complete corresponding meteorological data. 

Then, the Department analyzed the wind data and created a wind rose to coincide with 

the meteorological data collected on those 116 hours that were found to exceed the new 

1-hour SO2 standard threshold. 
42

Figure 30 shows the results. 

Figure 30. Wind Rose Data for Exceedance Hours

When comparing this figure with Figure 28 above, one will notice that the primary wind 

direction has changed. During the periods when there are high SO2 concentrations, the 

wind is primarily out of the south. In addition, wind speeds are generally stronger, 

indicating that the winds are unimpeded (from any terrain) from that direction. As Figure 

25 and Figure 26 displayed, the Allegheny County Airport location is not influenced by 

higher terrain while the Liberty location is. The Allegheny County airport 

meteorological tower is measuring winds at 55 meters above the Liberty meteorological 

tower. Therefore, the stronger winds at the Allegheny County airport could potentially 

signify the longer range transport issue affecting the Liberty monitor.
43

The time of the day when the SO2 concentrations are occurring is also of importance. 

Figure 31 illustrates when the Liberty monitor is experiencing the high 1-hour SO2

concentrations. 

Figure 31. Time of Day for SO2 Exceedances

Most of the high SO2 concentrations are occurring in the late evening to early morning 

hours (from 10 PM to 8 AM). The timing of these exceedances coupled with the fact that 

the Liberty monitoring site is situated within a valley increases the likelihood that 

meteorological inversions are assisting in driving SO2 concentrations higher. Once an 

inversion forms and the wind near the surface decreases (see Figure 6 for an example of 

this), localized air pollution becomes trapped near the surface. Therefore, there is even 

more likelihood that the high SO2 concentrations are driven by an SO2 source in close 

proximity to monitor. Note the rise in exceedances from 7 AM to 8 AM. This could 

signify the regional transport of SO2 in the region. Inversions usually begin to break 

down during the late morning (in the 8 AM to 11 AM time frame). As the inversion 

breaks, the air mass aloft mixes down toward the surface. If this air mass aloft has 

elevated SO2 concentrations within it, those higher concentrations will likely be picked 

up by the monitor at the surface.

Due to the nature of the high SO2 concentrations around the Liberty monitor, the 

Department is recommending that Allegheny County be designated nonattainment for the 

new SO2 standard.

Liberty Air Monitoring Station

Number of SO2 Concentration Exceedances vs. Time

0

2

4

6

8

10

12

14

16

18

02468

10121416182022

Hour

Number of Exceedances

Trend of Hourly SO2
44

Indiana County

Indiana County is situated within the western flank of the Appalachian Mountain chain. 

Figure 32 below displays a topographical overview of all of Indiana County. There is 

one major river that runs through the county. The Conemaugh River, which runs across 

southern Indiana County, forms the border between Indiana County and Westmoreland 

County. Otherwise, then a few tributary streams, the county is primarily land. 

Ultimately, the meteorological pattern is driven by the higher terrain in the eastern half of 

Indiana County.

Figure 32. Indiana County Topographical Map
45

Strongstown SO2 Monitoring Location

Strongstown is situated on a portion of the higher terrain in the eastern side of Indiana 

County. Figure 33 displays the location of the Strongstown monitor with respect to the 

major SO2 sources. In addition, Figure 2 highlights the terrain above the anemometer of 

height of the Strongstown meteorological tower (anemometer is at 10 meters plus base 

elevation of tower at 580 meters). Therefore, the measurements being taken by the 

Strongstown meteorological tower are likely to be influenced by the higher terrain to its 

east.

Figure 33. Strongstown (Indiana County) Topographical Map
46

Figure 34 (courtesy of Google Earth) displays a zoomed in look at the actual Strongstown 

monitoring location with respect to the other regional SO2 sources.

Figure 34. Strongstown Monitoring Location
47

The impact of the topography near Strongstown can also be seen by looking at the wind 

measurements that were collected at the Strongstown air monitoring station 

(meteorological data, including wind direction and speed, are continuously measured). 

Figure 35 (courtesy of Google Earth) displays the wind data measured at Strongstown’s 

meteorological tower from January 2008 to December 2010 (a full three year dataset). 

Figure 35. Wind Rose for the Strongstown Monitor

The wind is primarily out of the west. There is also a strong influence of northeasterly 

winds. Generally, this wind profile follows the synoptic wind flow over the region and is 

not surprising by seeing Figure 34 above, which shows that there is not any significant 

terrain to the west of Strongstown that is influencing the wind measurements. 
48

Taking a cross section look (in three dimensions within Google Earth) at the local area in 

Figure 36 below, one can see the relationship of the local terrain with respect to the major 

SO2 sources in the region and the Strongstown air monitor station. 

Figure 36. Local Terrain

From Figure 36 (which looks south to north), once again one can see that the 

Strongstown air monitoring station sits on top of a local hill. 

From Figure 35 above, one can see that the Strongstown monitor lies to the east of 

several major SO2 sources. The Strongstown monitor acquires SO2 samples from the air 

continuously every hour, which results in approximately 8760 hours of samples every 

year. The latest design value year, 2010 (which is based on data from 2008 to 2010), 

showed the Strongstown monitor exceeding the new SO2 standard with a concentration of 

90 ppb. The Department analyzed the data to focus in on the hours in which the SO2

concentrations exceeded the new 1-hour SO2 standard. 25 hours were found to exceed 

this threshold. Out of those 74 hours, 23 hours had complete corresponding 

meteorological data. Then, the Department analyzed the wind data and created a wind 

rose to coincide with the meteorological data collected on those 23 hours that were found 

to exceed the new 1-hour SO2 standard threshold. 
49

Figure 37 shows the results. 

Figure 37. Wind Rose Data for Exceedance Hours

When comparing this figure with Figure 34 above, one will notice that the primary wind 

direction has generally stayed the same. During the periods when there are high SO2

concentrations, the wind continues to be primarily out of the west. In addition, wind 

speeds are generally stronger, indicating that the high SO2 concentrations are being 

driven in from further distances away. Comparing the strong westerly component of the 

winds with the fact that there are no other major SO2 emissions sources within 

Pennsylvania in close proximity of the Strongstown monitor indicates that the 

Strongstown monitor is picking up on the interstate transport of SO2. Overall, the 

prominent westerly winds and stronger wind speeds are indicating that the driving source 

of the higher SO2 concentrations is coming from the larger SO2 sources (these types of 

sources generally have taller stacks and higher emission rates which helps in the 

downwind transport of pollution) to the west of Strongstown.
50

The time of the day when the SO2 concentrations are occurring is also of importance. 

Figure 38 illustrates when the Strongstown monitor is experiencing the high 1-hour SO2

concentrations.

Figure 38. Time of Day for SO2 Exceedances

Most of the high SO2 concentrations are occurring in the middle of the day hours (from 9 

AM to 2 PM). The timing of these exceedances coupled with the fact that the 

Strongstown monitoring site is situated on higher terrain increases the likelihood that 

interstate transport is playing a role in the monitored SO2 concentration exceedances. 

The middle of the day is when the atmosphere is the most unstable, meaning that more 

horizontal and vertical mixing is occurring. The onset of this mixing usually occurs in 

the late morning when, after a cool night, the sun warms the surface. The air at the 

surface is then warmer and less dense than its surroundings so it wants to rise, inducing 

vertical motion. The top two hours when we see the most exceedances are 11 AM and 12 

PM, when vertical mixing begins. Therefore, there is even more likelihood that the high 

SO2 concentrations are driven by SO2 sources to the west of the Strongstown monitor. 

Due to the nature of the high SO2 concentrations around the Strongstown monitor, the 

Department is recommending that Indiana County be designated nonattainment for the 

new SO2 standard. 

Strongstown Air Monitoring Station

Number of SO2 Concentration Exceedances vs. Time

0

1

2

3

4

5

6

02468

10121416182022

Hour

Number of Exceedances

Trend of Hourly SO2
51

5. Jurisdictional and other boundaries 

At this time, the Department is recommending that county boundaries be used to define 

areas for designation purposes. EPA has indicated that the presumptive county boundary 

will serve as the nonattainment area unless evidence indicates that a different planning 

area is justified. Inventory data for non-point sources is more accurate and available on 

the county level which will be useful in meeting the requirements in nonattainment areas 

for emission inventory information and for reasonable further progress (incremental 

emission reductions). The Department is using EPA’s presumptive county assumption 

to recommend the boundaries of nonattainment areas associated with monitors violating 

the 1-hour SO2 standard. The Department will be conducting refined modeling to better 

characterize boundaries relating to nonattainment and attainment areas. 
52

Acronyms and Terms

AERMOD AMS/EPA Regulatory Model

AMS American Meteorological Society

CAA Clean Air Act

CFR Code of Federal Regulations

DEP Department of Environmental Protection (Pennsylvania)

EGU Electric Generating Unit

EPA Environmental Protection Agency (United States)

FGD flue gas desulfurization 

IPM Integrated Planning Model

MSA Metropolitan Statistical Areas 

NAAQS National Ambient Air Quality Standards

NEEDS National Electric Energy Data System 

OMB Office of Management and Budget (United States)

ppb parts per billion

SIP State Implementation Plan

SO2 Sulfur dioxide

tpy tons per year

U.S.C. United States Code
53

References

EPA, Final Rule, “Primary National Ambient Air Quality Standards for Sulfur 

Dioxide,” (75 FR 35,520; June 22, 2010)

EPA, Area Designations for the 2010 Revised Primary Sulfur Dioxide National 

Ambient Air Quality Standards, from Stephen D. Page, Director, EPA Office of 

Air Quality Planning and Standards, March 24, 2011.

The DEP’s “Ambient Air Monitoring Network Plan – 2011” (June 25, 2010) 

http://www.dep.state.pa.us/dep/deputate/airwaste/aq/aqm/principal.htm

The Philadelphia Air Management Services’ (AMS) “2010/2011 Air Monitoring 

Network Plan” (July 1, 2010) http://www.phila.gov/health/AirManagement/

The Allegheny County Health Department’s (ACHD) “Monitoring Network 

Review” (July 1, 2010) http://www.achd.net/air/index.html

EPA Aerometric Information Retrieval System (AIRS), Air Quality System, 

http://www.epa.gov/air/data/index.html

EPA National Electric Energy Data System (NEEDS) v.4.10

http://www.epa.gov/airmarkets/progsregs/epa-ipm/BaseCasev410.html#needs

Office of Management and Budget, notice of decision, 2010 Standards for Delineating 

Metropolitan and Micropolitan Statistical Areas (75 Fed. Reg. 37,246 (June 28, 2010 and 

corrected July 7, 2010). The updated list of statistical areas is available at the following 

website: www.census.gov/population/www/metroareas/metrodef.html

Office of Management and Budget, Bulletin No. 10-2, “Update of Statistical 

Area Definitions and Guidance on Their Uses,” December 2009.

U.S. Census Bureau, Geography Division, Cartographic Products Management Branch, 

Metropolitan and Micropolitan Statistical Areas Wall Maps, November 2008.

http://www.census.gov/geo/www/maps/msa_maps2008/us_wall_1108.html