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Technical Support Document (TSD)

Illinois

Area Designations For the 

2010 SO2 Primary National Ambient Air Quality Standard

Summary

Pursuant to section 107(d) of the Clean Air Act (CAA), EPA must designate areas as either 

“nonattainment,” “attainment,” or “unclassifiable” for the 2010 one-hour sulfur dioxide (SO2) 

primary national ambient air quality standard (NAAQS). The CAA defines a nonattainment area 

as one that does not meet the NAAQS or that contributes to poor air quality in a nearby area that 

does not meet the NAAQS. Table 1 below identifies the counties or portions of counties (or 

tribal areas) in Illinois that EPA intends to designate “nonattainment” for the primary 2010 SO2

NAAQS.

Illinois submitted recommendations on June 2, 2011. On February 6, 2013, EPA sent out a letter 

with intended designations for Illinois. Illinois did not respond to EPA’s intended designation. 

Table 1 below lists Illinois’s June 2, 2011 recommendations and identifies the counties or 

portions of counties in Illinois that EPA is initially designating “nonattainment” based on 

monitored violations. EPA is not yet prepared to designate other areas in Illinois, and will 

address them in subsequent rounds of designation.

Table 1. Nonattainment Area Designations for Illinois

Area Illinois Recommended 

Designation of Areas/ 

Counties

EPA's Designation of 

Areas/ Counties

Pekin, IL

 Tazewell County (partial)

 - Cincinnati Township, 

 - Pekin Township

 Peoria County (partial)

 - Hollis Township

Nonattainment

Unclassifiable

Nonattainment

Nonattainment

Lemont, IL

 Cook County (partial)

 - Lemont Township

 Will County (partial)

 - Dupage Township

 - Lockport Township

Nonattainment

Nonattainment

Nonattainment

Nonattainment
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Background

On June 3, 2010, EPA revised the primary SO2 NAAQS (75 FR 35520, June 22, 2010) by 

establishing a new 1-hour standard at a level of 75 parts per billion (ppb), which is met at an 

ambient air quality monitoring site when the 3-year average of the annual 99th percentile of the 

daily maximum 1-hour average concentration at each monitor in an area does not exceed 75 ppb, 

as determined in accordance with Appendix T of 40 CFR part 50. 40 CFR 50.17(a)-(b). EPA 

has determined that this is the level necessary to provide protection of public health with an 

adequate margin of safety, especially for children, the elderly and those with asthma. These 

groups are particularly susceptible to the health effects associated with breathing SO2. The 

Agency is revoking the two prior primary standards of 140 ppb evaluated over 24-hours, and 30 

ppb evaluated over an entire year because the standards will not add additional public health 

protection given a 1-hour standard at 75 ppb. Accordingly, EPA is not designating areas in this 

process on the basis of either of these two prior primary standards. Similarly, the secondary 

standard for SO2 has not been revised, so EPA is not designating areas in this process on the 

basis of the secondary standard.

EPA’s SO2 Designation Approach

Section 107(d) of the CAA provides that not later than 1 year after promulgation of a new or 

revised NAAQS, state Governors may submit their recommendations for designations and 

boundaries to EPA. For the 2010 SO2 NAAQS, this deadline was June 3, 2011. Section 107(d) 

also requires EPA to provide a notification to states of no less than 120-days prior to 

promulgating an initial area designation that is a modification of a state’s recommendation. 

EPA has reviewed the State’s recommendations and has notified the State Commissioner through 

letter signed by the Regional Administrator of any intended modifications. [While language in 

section 107 specifically addresses states, we intend to follow the same process for tribes, 

pursuant to section 301(d) of the CAA and Tribal Authority Rule (40 CFR Part 49). Therefore, 

we intend to designate tribal areas, in consultation with the tribes, on the same schedule as state 

designations.] If a State or Tribe did not submit designation recommendations, EPA is to

promulgate the designations that it deems appropriate. If a state or tribal government disagrees 

with EPA’s intended area designations, it had an opportunity to demonstrate why any proposed 

modification is inappropriate. 

Designations guidance was issued by EPA through a March 24, 2011, memorandum from 

Stephen D. Page, Director, U.S. EPA, Office of Air Quality Planning and Standards, to Air 

Division Directors, U.S. EPA Regions I-X. This memorandum identifies factors EPA intends to 

evaluate in determining boundaries for areas designated nonattainment. These 5 factors include: 

1) Air quality data; 2) Emissions and emissions-related data (location of sources and potential 

contribution to ambient SO2 concentrations); 3) Meteorology (weather/transport patterns); 4) 

Geography/topography (mountain ranges or other air basin boundaries); and 5) Jurisdictional 

boundaries (e.g., counties, air districts, pre-existing nonattainment areas, reservations, 

metropolitan planning organization), among any other information deemed relevant to 

establishing appropriate area designations and boundaries for the 1-hour SO2 NAAQS.
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The March 24, 2011, designations guidance memo recommended that area boundaries be 

defaulted to the county boundary unless additional provided information justifies a larger or 

smaller boundary than that of the county. EPA believes it is appropriate to evaluate each 

potential area on a case-by-case basis, and to recognize that area-specific analyses conducted by 

states, tribes and/or EPA may support a different boundary than a default county boundary.

In this TSD, EPA discusses its review and technical analysis of the recommendations submitted 

by Illinois for designations of the 1-hour SO2 standard and any modifications from these 

recommendations.

Definition of important terms used in this document:

1) Designated nonattainment area – an area which EPA has determined, based on a state 

recommendation and/or on the technical analysis included in this document, has violated the 

2010 SO2 NAAQS, based on the most recent three years of air quality monitoring data from 

2009-2011, or contributes to a violation in a nearby area. 

2) Recommended nonattainment area – an area that a state or tribal government has 

recommended to EPA to be designated as nonattainment.

3) Violating monitor – an ambient air monitor meeting all methods, quality assurance and citing 

criteria and requirements whose valid design value exceeds 75 ppb, as described in Appendix T 

of 40 CFR part 50.

4) 2010 SO2 NAAQS - 75 ppb, national ambient air quality standard for SO2 promulgated in 

2010. Based on the 3-year average of the 99th percentile of the annual distribution of daily 

maximum 1-hour average concentrations

5) Design Value – a statistic computed according to the data handling procedures of the 

NAAQS (in 40 CFR 50 Appendix T) that, by comparison to the level of the NAAQS, indicates 

whether the area is violating the NAAQS.

Technical analysis for the Lemont, IL Area

Introduction 

This technical analysis for the Lemont, IL area identifies Cook County with a monitor, in 

Lemont, that violates the 2010 SO2 NAAQS, and evaluates nearby counties for contributions to 

SO2 concentrations in the area. EPA has evaluated this county and nearby counties based on the 

evidence for the factors recommended in the March 24, 2011 EPA guidance. 

Figure 1 is a map of the area showing the locations and design values of air quality monitors in 

the area, and the counties surrounding any violating air quality monitors. Notably, a monitor in 
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Lemont Township in Cook County recorded a 2009 to 2011 design value of 98 ppb. Multiple 

other monitors in Cook County and a monitor in Will County showed design values below the 

standard, with values ranging from 18 to 30 ppb. 

Figure 1. Map of sources and monitors in the Chicago area and the Lemont, IL nonattainment 

area

Illinois analyzed the sources that might be contributing to the monitored violation in Lemont. 

Based on this assessment, Illinois recommended that an area consisting of DuPage and Lockport 

Townships in Will County and Lemont Township in Cook County be designated as 

nonattainment. This recommendation reflected Illinois’ view that no significant sources are 

located in Cook County near Lemont but that three significant sources are located nearby in Will 

County.

Based on EPA's technical analysis described below, EPA is initially designating a Lemont 

nonattainment area consisting of Lemont Township in Cook County and DuPage and Lockport 

Townships in Will County as nonattainment for the 2010 SO2 NAAQS. Areas and sources that 

we are not yet prepared to conclude are contributing to monitored violations or to other possible 

violations are not included in this initial nonattainment area. Such sources and areas will be 

further addressed in a subsequent round of final designations.
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Detailed Assessment

Air Quality Data 

This factor considers the SO2 air quality monitoring data, including the design values (in ppb) 

calculated for all air quality monitors in the Chicago metropolitan area based on data for the 

2009-2011 period.

The 2010 SO2 NAAQS design values for the Chicago area within Illinois are shown in Table 2.

Table 2. Air Quality Data in the Chicago Area

County State Recommended

Nonattainment?

Monitor Air Quality 

System ID

Monitor Location SO2 Design Value, 

2009-2011 (ppb)

Cook No 17-031-0050 41.7076, -87.5686 20*

No 17-031-0063 41.877, -87.6343 18*

No 17-031-0076 41.7514, -87.7135 24

Yes 17-031-1601 41.6681, -87.9906 98

No 17-031-4002 41.8552, -87.7525 30

No 17-031-4201 42.1400, -87.7992 18*

Will No 17-197-0013 41.46, -88.182 28*

*Data are incomplete. Value is determined from available data for instrument identified as POC 2.

Monitors in Bold have the highest 2009-2011 design value in the respective county.

The Lemont monitor in Cook County shows a violation of the 2010 SO2 NAAQS. 

Emissions and Emissions-Related Data

Evidence of SO2 emissions sources in the vicinity of a violating monitor is an important factor 

for determining whether a nearby area is contributing to a monitored violation. For this factor, 

EPA evaluated county level emission data for SO2 and any growth in SO2 emitting activities

since the date represented by those emissions data.

Emissions

The most recent year for which national emissions information was compiled was 2008. Illinois 

did not provide more recent emissions information. Therefore, EPA relied on the 2008 National 

Emissions Inventory (NEI) emissions data (NEI08V3). 

Table 3 shows total emissions of SO2 (given in tons per year) for Cook County and for adjoining 

Will County. Table 3 also shows pertinent information for sources in these counties emitting

greater than 100 tons per year of SO2 according to the 2008 NEI. 
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Table 3. SO2 Emissions in the Chicago Area (NEI08V3)

County Facility in 

State 

Recommen

ded N.A. 

Area?

Facility Emissions 

NEI08V3

(tons per 

year)

Facility Location Distance 

to Lemont 

Monitor 

(km)

Total 

County SO2

Emissions 

(tons per 

year)

Cook No Crawford Station 6,627 tpy 41.8278, -87.7236 28 19,346

No Fisk Station 4,486 tpy 41.8408, -87.6533 34

No Corn Products 2,203 tpy 41.7751, -87.8224 18

No Koppers 823 tpy 41.8206, -87.7487 26

No O’Hare Airport 498 tpy 41.9772, -87.9044 35

No Saint-Gobain 

Containers 

345 tpy 41.6439, -87.6003 32

No Carmeuse Lime 321 tpy 41.7056, -87.5438 37

No Midway Airport 110 tpy 41.785, -87.7519 24

Will No MWG Joliet Station 18,281 tpy 41.4947, -88.125 22 63,967

Yes MWG Will County 

Station 

16,497 tpy 41.6344, -88.0592 7

No Exxon Mobil 16,404 tpy 41.4138, -88.1835 33

Yes Oxbow Midwest 

Calcining 

6,205 tpy 41.6622, -88.0379 4

Yes CITGO Petroleum 6,137 tpy 41.6444, -88.0559 6

The sources in Cook County are at considerable distances from the violating monitor. For 

example, the closest source is Corn Products Corporation, at about 18 kilometers from the 

monitor, with emissions of about 2,300 tons per year, and the highest emitting source in Cook 

County, Midwest Generation’s Crawford Station, is about 28 kilometers away, emitting about 

6,600 tons per year. Based on the distance of these sources from the violating monitor, EPA is 

not yet prepared to conclude that these sources contribute to the Lemont monitor’s design value. 

These sources will be further addressed in a subsequent round of designations. 

Three of the sources in Will County are relatively close to the Lemont monitor and have 

sufficient emissions that Illinois recommended including the townships containing these sources 

in the Lemont nonattainment area. However, considering their emission levels and based on 

their distance from the monitor, EPA is not yet prepared to conclude that two other Will County 

sources, Midwest Generation’s Joliet Station and the Exxon-Mobil refinery, are contributing to 

the Lemont monitor’s design value. These two sources will also be further addressed in 

subsequent a round of designations.

Emissions Controls

The emissions data used by EPA in this technical analysis and provided in Table 3 represent 

emissions levels taking into account any control strategies implemented on stationary sources in 

this area up to and including 2008. EPA has not received any additional information on 

emissions reductions resulting from controls put into place after 2008.
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Meteorology (weather/transport patterns)

Evidence of source-receptor relationships between specific emissions sources and high SO2

values at violating monitors is another important factor in determining the appropriate 

contributing areas and the appropriate extent of the nonattainment area. Figure 2 shows the 

prevalent wind direction for the Lemont, IL area. 

Figure 2: Wind Rose for Lemont, IL

Source: IEPA Software: WRPLOT-Lakes Environmental Software

The wind rose above shows that winds are most likely to come from the south, west, and 

southwest directions, but also frequently come from all the northeast direction, and occasionally 

from the other directions. This shows that a source from any direction could contribute to the 

violation at the monitor. The three largest nearby emitters, MWG Will County Station, Oxbow 

Midwest Calcining, and CITGO Petroleum, are located to the west and southwest of the monitor, 

which are the frequent wind directions. 

Geography/topography (mountain ranges or other air basin boundaries)

The Lemont area does not have any geographical or topographical barriers significantly limiting 

air pollution transport within its airshed. Therefore, this factor did not play a significant role in 

determining the nonattainment boundary.

Jurisdictional boundaries 

Illinois does not have any current SO2 nonattainment areas under the prior SO2 NAAQS. 

Townships in Illinois have well established boundaries and are a suitable basis for defining 

nonattainment areas.
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Other Relevant Information

EPA did not receive additional information relevant to establishing a nonattainment area 

boundary for this area.

Conclusion

Illinois has adequately justified an initial nonattainment area, based on the violating monitor in 

Cook County, which includes the Lemont Township containing the monitoring site and two 

townships in Will County, DuPage and Lockport Townships, with sources that contribute to the 

monitored violation. Based on the distance from the violating monitor and wind rose analysis, 

EPA is not yet prepared to conclude that other sources in Cook County outside Lemont 

Township, as well as the Midwest Generation Joliet plant and the Exxon-Mobil refinery in Will 

County, contribute to the Lemont monitor’s design value. In a subsequent round of designations, 

EPA will make final designations decisions for areas and sources that are not currently included 

in the initial nonattainment area designation addressed in this TSD.

Technical analysis for the Pekin, IL Area

Introduction 

This technical analysis for the Pekin, IL area identifies a Tazewell County monitor that violates

the 2010 SO2 NAAQS. EPA has evaluated this county and nearby counties based on the 

evidence for the factors recommended in the March 24, 2011 EPA guidance.

Figure 3 is a map of the area showing the location and the design value of the air quality monitor

in the area, and the counties surrounding this air quality monitor. The monitor in Pekin

(Tazewell County) recorded a 2009 to 2011 design value of 211 ppb. A monitor in Peoria 

County recorded a 2009 to 2011 design value of 36 ppb, based on incomplete data. No other

SO2 monitor is located in these or any neighboring counties.
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Figure 3. Map of sources, monitors, and nonattainment area boundaries in the Pekin, IL area 

Illinois analyzed the sources that might be contributing to the monitored violation in Pekin. 

Based on this assessment, Illinois recommended that an area consisting of Cincinnati and Pekin 

Townships in Tazewell County be designated as nonattainment. 

EPA believes that Hollis Township in Peoria County also contributes to the violation monitored 

in Tazewell County. E.D. Edwards Station, a power plant operated by Ameren, is located in this 

township. This source emits approximately 11,000 tons of SO2 per year, in a location that is 

about 4.5 kilometers in a direction that is periodically upwind of the Pekin monitor. 

Based on EPA's technical analysis described below, and based on a monitored violation, EPA is 

initially designating a Pekin nonattainment area consisting of Cincinnati and Pekin Townships in 

Tazewell County and Hollis Township in Peoria County. Areas and sources that we are not yet 

prepared to conclude are contributing to the monitored violations are not included in this initial 

nonattainment area. Such areas and sources will be addressed in a subsequent round of final 

designations.

EPA received comments from Ameren and from the Illinois Environmental Regulatory Group 

objecting to the inclusion of Hollis Township in the nonattainment area, as well as comments 

from Citizens Against Ruining the Environment and the Respiratory Health Association 

generally supporting the intended designation. These comments are addressed in more detail in 

the response to comments document.
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Detailed Assessment

Air Quality Data 

This factor considers the SO2 air quality monitoring data, including the design value (in ppb) 

calculated for the air quality monitor in Tazewell County based on data for the 2009-2011

period. The only other monitor in this part of Illinois is located in Peoria County. The 2010 SO2

NAAQS design values for the Tazewell and Peoria County monitors are shown in Table 4.

Table 4. Air Quality Data in the Pekin Area

County State Recommended

Nonattainment?

Monitor Air Quality 

System ID

Monitor Location SO2 Design Value, 

2009-2011 (ppb)

Peoria No 17-143-0024 40.6874, -89.6069 36

Tazewell Yes 17-179-0004 40.5565, -89.654 211

The Tazewell County monitor shows a violation of the 2010 SO2 NAAQS. Therefore, some area 

in this county and possibly additional areas in surrounding counties must be designated 

nonattainment. The absence of a violating monitor alone is not a sufficient reason to eliminate 

nearby counties as candidates for inclusion in a nonattainment area.

Emissions and Emissions-Related Data

Evidence of SO2 emissions sources in the vicinity of a violating monitor is an important factor 

for determining whether a nearby area is contributing to a monitored violation. For this factor, 

EPA evaluated county level emission data for SO2 and any growth in SO2 emitting activities 

since the date represented by those emissions data.

Emissions 

The most recent year for which national emissions information was compiled was 2008. Illinois 

reported data indicating that emissions from pertinent sources in 2007 and 2009 were similar to 

emissions in 2008. Therefore, EPA relied on the 2008 National Emissions Inventory (NEI)

emissions data (NEI08V3). 

Table 5 shows total emissions of SO2 (given in tons per year) for Tazewell County and for 

adjoining Peoria County. Table 5 also shows pertinent information for sources in these counties 

emitting greater than 100 tons per year of SO2 according to the 2008 NEI. 
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Table 5. SO2 Emissions in the Pekin Area (NEI08V3)

County Facility Located 

in State 

Recommended 

Nonattainment

Area?

Facility – Total SO2 Air

Emissions NEI08V3

(tons per year)

Facility Location Distance 

to Pekin 

Monitor 

(km)

Total County 

SO2 Emissions 

(tons per year)

Peoria No*

Ameren – E.D. Edwards 

Stn – 11,224 tpy

40.5958, -89.6631 4 14,603

No ADM – 3049 tpy 40.6756, -89.6073 14

No Keystone Steel & Wire –

138 tpy

40.6420, -89.6467 10

Tazewell Yes MWG – Powerton Stn. –

22,355 tpy

40.5408, -89.6786 3 34,358

Yes Aventine Renewable 

Energy – 11,830 tpy

40.5553, -89.6629 1

*This source is included in the nonattainment area that EPA is promulgating

The two significant sources in Tazewell County are located in Cincinnati and Pekin Townships, 

respectively, which Illinois has recommended including in the Pekin nonattainment area. Illinois 

did not recommend including any of Peoria County in this nonattainment area. However, EPA 

finds that Ameren’s E.D. Edwards power plant is only 4 kilometers from the monitor and has 

significant emissions with potential to have significant impact on recorded concentrations at the 

monitor. This source is located in Hollis Township, and so this township warrants consideration 

for its contributions to the violation measured in Pekin. Based on their distance from the 

violating monitor, EPA is not yet prepared to conclude that the other sources in Peoria County 

contribute to the violating monitor’s design value. These sources will be further addressed in a 

subsequent round of designations.

Emissions Controls

The emissions data used by EPA in this technical analysis and provided in Table 5 represent 

emissions levels taking into account any control strategies implemented on stationary sources in 

this area up to and including 2008. EPA has not received any additional information on 

emissions reductions resulting from controls put into place after 2008.

Meteorology (weather/transport patterns)

Evidence of source-receptor relationships between specific emissions sources and high SO2

values at violating monitors is another important factor in determining the appropriate 

contributing areas and the appropriate extent of the nonattainment area. Figure 4 shows the 

prevalent wind direction for the Lemont, IL area. 
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Figure 4: Wind Rose for Pekin, IL

Source: IEPA Software: WRPLOT-Lakes Environmental Software

The wind rose above suggests that winds come most frequently from the south, somewhat 

frequently from the northwest, and occasionally from the other directions. Focusing on days 

when concentrations are above the level of the standard, winds from the north (including variable 

winds that at least in part include north winds) occur with sufficient frequency to suggest that 

nearby significant sources located north as well as west and southwest of the monitor are 

contributing to violations measured in Pekin. As discussed in more detail in the response to 

comments document, winds from the north (including variable winds that at least in part include 

north winds) also occur in particular at times when the standard is exceeded at the Pekin monitor.

Geography/topography (mountain ranges or other air basin boundaries)

The Pekin area does not have any geographical or topographical barriers significantly limiting air 

pollution transport within its airshed. Therefore, this factor did not play a significant role in 

determining the nonattainment boundary.

Jurisdictional boundaries 

Illinois does not have any current SO2 nonattainment areas under the prior SO2 NAAQS. 

Townships in Illinois have well established boundaries and are a suitable basis for defining 

nonattainment areas.

Other Relevant Information

EPA did not receive additional information relevant to establishing a nonattainment area 

boundary for this area.
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Conclusion

Illinois’ recommendation to define the Pekin, IL nonattainment area to include Cincinnati and 

Pekin Townships of Tazewell County appropriately includes the portions of Tazewell County 

that are contributing to the measured violation. However, EPA has determined that the initial 

nonattainment area should also include Hollis Township in Peoria County, which includes 

Ameren’s E.D. Edwards Station. This source has substantial emissions relatively close to the 

monitor measuring a violation, and analysis of wind information supports a finding of 

contribution of emissions from the direction of this source to the violating monitor. Therefore, 

EPA believes that Hollis Township of Peoria County warrants inclusion in the initial Pekin 

nonattainment area. Thus, after considering the factors described above, EPA is initially 

designating an area that includes Cincinnati and Pekin Townships in Tazewell County and Hollis 

Township in Peoria County as the Pekin, IL nonattainment area for the 2010 SO2 NAAQS. In a 

subsequent round of designations, we will make final designations decisions for areas and 

sources that we are not yet prepared to conclude are contributing to the monitored violations or 

to other possible violations and that are not currently included in the initial nonattainment area 

designation addressed in this TSD.