1

Illinois

Area Designations for the 

2008 Ozone National Ambient Air Quality Standards

The table below identifies the areas and associated counties or parts of counties in Illinois that EPA 

intends to designate as nonattainment for the 2008 ozone national ambient air quality standards (2008

NAAQS). In accordance with section 107(d) of the Clean Air Act, EPA must designate an area (county 

or part of a county) “nonattainment” if it is violating the 2008 ozone NAAQS or if it is contributing to a 

violation of the 2008 ozone NAAQS in a nearby area. The technical analyses supporting the boundaries 

for this nonattainment area are provided below.

Table 1. Intended Nonattainment Areas in Illinois

Area

Illinois’ Recommended 

Nonattainment Counties

EPA’s Intended Nonattainment 

Counties

St. Louis-St CharlesFarmington, MO-IL*

Madison County

Monroe County

St. Clair County

Madison County

Monroe County

St. Clair County

St. Louis-St. Charles-Farmington, MO-IL is a multi-state nonattainment area. Table 2 below identifies 

the counties in Missouri that EPA intends to designate as part of the nonattainment area.

EPA intends to designate the remaining counties in Illinois that are not listed in the table above as 

“unclassifiable/attainment” for the 2008 ozone NAAQS. 

The analysis below provides the basis for intended nonattainment area boundaries. It relies on our 

analysis of whether and which monitors are violating the 2008 ozone NAAQS, based on certified air 

quality monitoring data from 2008-2010 and an evaluation of whether nearby areas are contributing to 

such violations.1 EPA has evaluated contributions from nearby areas based on a weight of evidence 

analysis considering the factors identified below. EPA issued guidance on December 4, 2008, that 

identified these factors as ones EPA would consider in determining nonattainment area boundaries and 

recommended that states consider these factors in making their designations recommendations to EPA.

2

 

1. Air quality data (including the design value calculated for each Federal Reference Method 

(FRM) or Federal Equivalent Method (FEM) monitor in the area);

2. Emissions and emissions-related data (including location of sources and population, amount of 

emissions and emissions controls, and urban growth patterns);

3. Meteorology (weather/transport patterns);

4. Geography and topography (mountain ranges or other basin boundaries);

5. Jurisdictional boundaries (e.g., counties, air districts, existing nonattainment areas, Indian 

country, metropolitan planning organizations (MPOs))

Ground-level ozone is generally not emitted directly into the air, but is created by chemical reactions 

between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. 

 1 On December 7, 2011 Illinois submitted certified air quality monitoring data for 2011. Given the timing of this submission, 

EPA was not able to consider the 2011 data in this Technical Support Document. EPA will evaluate the implications of the 

2011 data as soon as possible.

2 The December 4, 2008 guidance memorandum “Area Designations for the 2008 Revised Ozone National Ambient Air 

Quality Standards” refers to 9 factors. In this technical support document we have grouped the emissions-related factors 

together under the heading of “Emissions and Emissions-Related Data,” which results in 5 categories of factors.
2

Because NOx and VOC emissions from a broad range of sources over a wide area typically contribute to 

violations of the ozone standards, EPA believes it is important to consider whether there are contributing 

emissions from a broad geographic area. Accordingly, EPA chose to examine the 5 factors with respect 

to the larger of the Combined Statistical Area (CSA) or Core Based Statistical Area (CBSA) associated 

with the violating monitor(s).

3 All data and information used by EPA in this evaluation are the latest 

available to EPA and/or provided to EPA by states or tribes.

In EPA’s designations guidance for the 2008 ozone NAAQS4 EPA recommended examining 

CSA/CBSAs because certain factors used to establish CSAs and CBSAs are similar to the factors EPA is 

using in this technical analysis to determine if a nearby area is contributing to a violation of the 2008

ozone NAAQS. Congress required a similar approach in 1990 for areas classified as serious or above 

for the 1-hour ozone standard and EPA used the same basic approach in the designation process for the 

1997 ozone NAAQS. Where a violating monitor is not located in a CSA or CBSA, EPA’s guidance 

recommended using the boundary of the county containing the violating monitor as the starting point for 

considering the nonattainment area’s boundary. 

Technical Analysis for St. Louis-St. Charles-Farmington, MO-IL

Figure 1 is a map of the St. Louis-St. Charles-Farmington, MO-IL intended nonattainment area. The 

map provides other relevant information including the locations and design values of air quality 

monitors, county and other jurisdictional boundaries, St. Louis-St. Charles-Farmington, MO-IL CSA 

boundary, existing nonattainment boundary for 1997 ozone NAAQS, and major transportation arteries. 

 3 Lists of CBSAs and CSAs and their geographic components are provided at 

www.census.gov/population/www/metroareas/metrodef.html . The lists are periodically updated by the Office of 

Management and Budget. EPA used the most recent update, based on 2008 population estimates, issued on December 1, 

2009 (OMB Bulletin No. 10-02). 4 See Appendix [x] for a copy of the guidance memorandum.
3

Figure 1.

For purposes of the 1997 8-hour ozone NAAQS, portions of this area were designated nonattainment. 

The boundary for the nonattainment area for the 1997 ozone NAAQS included the entire counties of 

Jersey, Madison, Monroe and St. Clair Counties in Illinois and St. Louis City and Franklin, Jefferson, St.

Charles and St. Louis Counties in Missouri.

 

Illinois submitted its designation recommendations in a March 9, 2009, letter from Douglas P. Scott, 

Director of the Illinois Environmental Protection Agency, which included enclosures containing an 

analysis of data supporting the States recommendations. In this submission Illinois recommended that 

Madison, Monroe and St. Clair Counties be designated as “nonattainment” for the 2008 ozone NAAQS

based on air quality data from 2006-2008. Missouri submitted its designation recommendations in a 

March 11, 2009 letter from Mark N. Templeton, Director of the Missouri Department of Natural 

Resources, which included enclosures containing an analysis of data supporting the State’s 

recommendations. Missouri revised its recommendations and MDNR requested EPA to act on the 

revisions in a letter dated December 5, 2011. In its updated submittal, Missouri recommended that St. 

Louis City and Jefferson, St. Charles and St. Louis Counties be designated as “nonattainment” for the 

2008 ozone NAAQS based on air quality data from 2006-2008. These data are from FRM or FEM

monitors sited and operated in accordance with 40 CFR Part 58. 
4

After considering these recommendations and based on EPA's technical analysis described below, EPA 

intends to designate the areas in Illinois and Missouri listed in Table 2 below as “nonattainment” for the 

2008 ozone NAAQS as part of the St. Louis-St. Charles-Farmington, MO-IL multi-state nonattainment 

area. 

Table 2. State's Recommended and EPA’s Intended Designated Nonattainment Counties for St. LouisSt. Charles-Farmington, MO-IL Area.

St. Louis-St. CharlesFarmington, MO-IL 

Area

State-Recommended 

Nonattainment Counties

EPA Intended

Nonattainment Counties

Illinois

Madison County

Monroe County

St. Clair County

Madison County

Monroe County

St. Clair County

Missouri

Franklin County

Jefferson County

St. Charles County

St Louis County

St Louis City

Franklin County

Jefferson County

St. Charles County

St Louis County

St Louis City

Factor Assessment

Factor 1: Air Quality Data 

For this factor, we considered 8-hour ozone design values (in ppm) for air quality monitors in counties 

in the St. Louis-St. Charles-Farmington, MO-IL CSA based on data for the 2008-2010 period (i.e., the 

2010 design value), which are the most recent years with fully-certified air quality data.

5 A monitor’s 

design value is the metric or statistic that indicates whether that monitor attains a specified air quality 

standard. The 2008 ozone NAAQS are met at a monitor when the annual fourth-highest daily maximum 

8-hour average concentration, averaged over 3 years is 0.075 ppm or less. A design value is only valid 

if minimum data completeness criteria are met. See 40 CFR part 50 Appendix P. Where several 

monitors are located in a county (or a designated nonattainment area or maintenance area), the design 

value for the county or area is determined by the monitor with the highest level.

Note: Monitors that are eligible for providing design value data generally include State and Local Air 

Monitoring Stations (SLAMS) that are sited in accordance with 40 CFR Part 58, Appendix D (Section 

4.1) and operating with a federal reference method (FRM) or federal equivalent method (FEM) monitor 

that meets the requirements of 40 CFR part 58, appendix A. All data from a special purpose monitor 

(SPM) using an FRM or FEM which has operated for more than 24 months is eligible for comparison to 

the NAAQS unless the monitoring agency demonstrates that the data came from a particular period 

during which the requirements of appendix A (quality assurance requirements) or appendix E (probe and 

monitoring path siting criteria) were not met.

 5 On December 7, 2011 Illinois submitted certified air quality monitoring data for 2011. Given the timing of this submission, 

EPA was not able to consider the 2011 data in this Technical Support Document. EPA will evaluate the implications of the 

2011 data as soon as possible.
5

The 2010 design values for the ozone NAAQS for counties in the St. Louis-St. Charles-Farmington, 

MO-IL CSA are shown in Table 3. 

Table 3. Air Quality Data for Counties in the St. Louis-St. Charles-Farmington, MO-IL CSA.

County State Recommended 

Nonattainment?

2008-2010 Design Value

(ppb)

Illinois:

 Bond County No

 Calhoun County No

 Clinton County No

 Jersey County No 69

 Macoupin County No 66

 Madison County Yes 72

 Monroe County Yes

 St. Clair County Yes 68

Missouiri:

 Franklin County Yes

 Jefferson County Yes 72

 Lincoln County No 72

 St. Charles County Yes 77

 St. Francois County No

 St. Louis County Yes 71

 St. Louis City Yes 69

 Warren County No

 Washington County No

St Charles County in Missouri shows a violation of the 2008 ozone NAAQS, therefore this county is

included in the nonattainment area. A county (or partial county) must also be designated nonattainment 

if it contributes to a violation in a nearby area. Each county without a violating monitor that is located 

near a county with a violating monitor has been evaluated, as discussed below, based on the five factors 

to determine whether it contributes to the nearby violation. 

Factor 2: Emissions and Emissions-Related Data

EPA evaluated emissions of ozone precursors (NOx and VOC) and other emissions-related data that 

provide information on areas contributing to violating monitors.

Emissions Data

EPA evaluated county-level emission data for NOx and VOC derived from the 2008 National Emissions 

Inventory (NEI), version 1.5. This is the most recently available NEI. (See

http://www.epa.gov/ttn/chief/net/2008inventory.html) Significant emissions levels in a nearby area 

indicate the potential for the area to contribute to the observed ozone standard violation. Table 4 shows 

2008 emissions of NOx and VOC (in tons per year) for all counties in the St. Louis-St. CharlesFarmington, MO-IL CSA. This table also indicates which of the counties were recommended to be 

nonattainment for the 2008 ozone NAAQS by their respective states.
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Table 4. Total 2008 NOx and VOC Emissions.

County State Recommended

Nonattainment? NOx (tpy) VOC (tpy)

Illinois:

 Bond County No 1,422 1,181

 Calhoun County No 607 1,057

 Clinton County No 4,409 2,515

 Jersey County No 1,125 1,166

 Macoupin County No 2,286 2,147

 Madison County Yes 23,109 12,351

 Monroe County Yes 2,410 1,551

 St. Clair County Yes 10,804 8,719

Illinois total: 46,172 30,687

Missouri:

 Franklin County Yes 14,094 4,939

 Jefferson County Yes 11,769 6,729

 Lincoln County No 1,855 2,081

 St. Charles County Yes 15,894 11,652

 St. Francois County No 2,030 2,349

 St. Louis County Yes 36,455 41,894

 St. Louis City Yes 17,576 14,027

 Warren County No 1,749 2,064

 Washington County No 678 862

Missouri total: 102,100 86,597

Areawide: 148,272 117,284

The emissions data in Table 4 show that, for Illinois, comparatively high 2008 NOx and VOC

emissions originate in Madison and St. Clair Counties. In 2008, these counties account for 73% of the 

NOx emissions and 69% of the VOC emissions for the Illinois portion of the area. Monroe County in 

Illinois is located between St. Clair County in Illinois and Jefferson County in Missouri (see Figure 1). 

Since Jefferson County also has relatively high 2008 NOx and VOC emissions, including Monroe 

County, Illinois as part of the area designated as nonattainment would maintain a contiguous area. 

Taken together, in 2008 Madison, Monroe and St. Claire Counties account for 79% of the NOx

emissions and 74% of the VOC emissions in the Illinois portion of the area and 24% of the NOx

emissions and 19% of the VOC emissions for the entire St. Louis-St. Charles-Farmington, MO-IL CSA. 

The VOC and NOx emissions originating in Bond, Calhoun, Clinton, Jersey and Macoupin Counties are 

significantly smaller than those originating in the higher emitting counties elsewhere in the St. Louis-St. 

Charles-Farmington, MO-IL CSA. Taken together, in 2008 these counties account for only 6.6% of the 

NOx emissions and 6.9% of the VOC emissions for the St. Louis-St. Charles-Farmington, MO-IL CSA. 

Note that the comparative emissions levels in the Missouri portion of the St. Louis-St. CharlesFarmington, MO-IL CSA are discussed in the ozone designation technical support document for 

Missouri. 
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Population Density and Degree of Urbanization

EPA evaluated the population and vehicle use characteristics and trends of the area as indicators of the 

probable location and magnitude of non-point source emissions. These include ozone-creating 

emissions from on-road and off-road vehicles and engines, consumer products, residential fuel 

combustion, and consumer services. Areas of dense population or commercial development are an 

indicator of area source and mobile source NOx and VOC emissions. Rapid growth in population or 

Vehicle Miles Traveled (VMT) (see below) in a county on the urban perimeter signifies increasing 

integration with the core urban area, and indicates that it may be appropriate to include the area 

associated with area source and mobile source emissions as part of the nonattainment area. Table 5 

shows the population, population density, and population growth information for each county in the 

area.

Table 5. Population and Growth.

County

State 

Recommended 

Nonattainment?

2010 

Population

 2010

 Population

 Density

(1000 pop/sq mi)

 Absolute

 change

in population

(2000-2010)

Population 

% change

(2000-

2010)

Illinois:

 Bond County No 17,768 0.05 118 +1%

 Calhoun County No 5,089 0.02 -1 0%

 Clinton County No 37,762 0.08 2,233 +6%

 Jersey County No 22,985 0.06 1,330 +6%

 Macoupin County No 47,765 0.06 -1,224 -2%

 Madison County Yes 269,282 0.36 10,165 +4%

 Monroe County Yes 32,957 0.08 5,193 +19%

 St. Clair County Yes 270,056 0.40 13,852 +5%

Illinois total: 703,664 31,666 +5%

Missouri:

 Franklin County Yes 101,492 0.11 7,434 +8%

 Jefferson County Yes 218,733 0.33 19,995 +10%

 Lincoln County No 52,566 0.08 13,310 +34%

 St. Charles County Yes 360,485 0.61 74,322 +26%

 St. Francois County No 65,359 0.14 9,615 +17%

 St. Louis County Yes 998,954 1.91 -17,376 -2%

 St. Louis City Yes 319,294 4.83 -27,570 -8%

 Warren County No 32,513 0.07 7,793 +32%

 Washington County No 25,195 0.03 1,785 +8%

Missouri total: 2,174,591 +4%

Areawide: 2,878,255 0.31 120,974 +4%

Sources: U.S. Census Bureau population estimates for 2010 as of August 4, 2011

For Illinois, population data show that Madison and St. Clair Counties have comparatively high 

populations and population densities. This implies that the population-related NOx and VOC emissions 

in these counties are comparatively high. Monroe County in Illinois has the highest population percent 

change and third highest absolute change in population (behind St. Clair and Madison Counties) among 

the Illinois Counties in the CSA. Monroe County is located between St. Clair County in Illinois and 

Jefferson County in Missouri. Since Jefferson County also has relatively high population and 
8

population density, including Monroe County, Illinois as part of the area designated as nonattainment 

would maintain a contiguous area.

Note that the ozone designation technical support document for Missouri addresses the populationrelated emission contributions from the Missouri portion of the St. Louis-St. Charles-Farmington, MOIL CSA.

Traffic and Commuting Patterns

EPA evaluated the commuting patterns of residents in the area, as well as the total VMT for each 

county. In combination with the population/population density data and the location of main 

transportation arteries (see above), this information helps identify the probable location of non-point 

source emissions. A county with high VMT and/or a high number of commuters is generally an integral 

part of an urban area and indicates the presence of motor vehicle emissions that may contribute to ozone 

formation that contributes to nonattainment in the area. Rapid population or VMT growth in a county on 

the urban perimeter signifies increasing integration with the core urban area, and indicates that this 

county should be included in the ozone nonattainment area, particularly if the VOC and/or NOx

emissions in this county are a significant portion of the total emissions in the nonattainment area. 

Table 6 shows traffic and commuting pattern data, including total 2008 VMT for each county, number 

of commuters in each county who drive to another county within the area, and the percent of total 

commuters in each county who commute to other counties within the area.

Table 6. Traffic and Commuting Patterns.

County

State 

Recommended 

Nonattainment?

2008 VMT*

(million miles)

Number Commuting 

to or within any 

violating counties**

Percent Commuting 

to or within any 

violating counties**

Illinois:

 Bond County No 284 20 0%

 Calhoun County No 40 109 5%

 Clinton County No 389 49 0%

 Jersey County No 192 125 1%

 Macoupin County No 415 36 0%

 Madison County Yes 2,839 1,126 1%

 Monroe County Yes 361 84 1%

 St. Clair County Yes 2,666 729 1%

Illinois total: 7,186

Missouri:

 Franklin County Yes 1,637 776 2%

 Jefferson County Yes 1,885 1,337 1%

 Lincoln County No 495 5,529 30%

 St. Charles County Yes 2,728 70,282 47%

 St. Francois County No 548 92 0%

 St. Louis County Yes 11,925 13,513 3%

 St. Louis City Yes 3,450 1,502 1%

 Warren County No 525 2,967 25%

 Washington County No 220 27 0%
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Missouri total: 23,413

Areawide: 30,599

* MOBILE model VMTs are those inputs into the NEI version 1.5. 

For Illinois, the VMT data show that VMT levels in Madison and St. Clair Counties are significantly 

higher than those in the other Illinois counties in the St. Louis-St. Charles-Farmington, MO-IL CSA. 

When including the VMT from Monroe County, together, these three counties account for 82% of the 

VMT in the Illinois portion of the St. Louis-St. Charles-Farmington, MO-IL CSA and 19 percent of the 

VMT in the entire CSA.

Factor 3: Meteorology (Weather/Transport Patterns)

EPA evaluated available meteorological data to help determine how meteorological conditions, such as 

weather, transport patterns and stagnation conditions, would affect the fate and transport of precursor 

emissions contributing to ozone formation. EPA examined the frequency distribution of wind directions 

during the summer by averaging National Weather Service direction-sorted wind directions for each 

county for a 30 year period. To apply the results of this data analysis to the St. Louis-St. CharlesFarmington, MO-IL CSA, we have considered the wind direction frequencies during the summer 

months (June-August) for St. Charles County in Missouri, the only county with a recorded violation of 

the 2008 ozone NAAQS (see Table 3). Table 7 shows the summertime 30-year averaged percentages of 

wind directions (winds blowing indo the subject county from the specified wind direction sector) for St. 

Charles County in Missouri.

Table 7. Averaged Summertime Wind Direction Percentages for St. Charles County, MO

Wind Direction Percentage

North-Northeast 9.82%

East-Northeast 7.24%

East-Southeast 13.66%

South-Southeast 14.41%

South-Southwest 20.01%

West-Southwest 14.64%

West-Northwest 12.84%

North-Northwest 7.39%

The wind direction percentages show that there is no “preferred” wind direction during the summertime. 

Transport winds can and do blow from all directions into the county with a recorded violation of the 

2008 ozone NAAQS. There is, however an indication that winds from the south-southwest may be 

slightly more prevalent than winds from other directions during the summertime, and there is a southerly 

component 62.72% of the time. 

The state provided wind direction data for days from 2006 through 2008 when ozone concentrations

were greater than 75 ppb at any monitor in the Illinois portion of the St. Louis-St. Charles-Farmington, 

MO-IL CSA. Wind data was taken from Edwardsville in Madison County, IL. This data is presented in 

Figure 2.
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Figure 2. Primary Wind Direction Percentages at Edwardsville in Madison County, IL for Days from 

2006 Through 2008 When Ozone Concentrations in the Illinois Portion of the St. Louis-St. CharlesFarmington, MO-IL CSA Were Greater Than 75ppb 

Data in Figure 2 indicate that when considering wind direction at Edwardsville in Madison County, IL 

for days from 2006 through 2008 when ozone concentrations in the Illinois portion of the St. Louis-St. 

Charles-Farmington, MO-IL CSA were greater than 75ppb, prevailing winds were from the southsouthwest through the southeast approximately 40% of the time. Edwardsville is slightly to the east and 

south of the violating monitor in St. Charles County, Missouri. All of the counties proposed as 

nonattainment lie to the south of or even with the nonattainment monitor in St. Charles County. As 

shown in Figure 1, the Illinois counties of Madison, St. Clair and Monroe all border Missouri and thus 

range from directly south of the violating monitor in St. Charles County, to east of the violating 

monitor. 
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Factor 4: Geography/Topography (Mountain Ranges or Other Air Basin Boundaries)

The geography/topography analysis evaluates the physical features of the land that might affect the 

airshed and, therefore, the distribution of ozone over the area. The St. Louis-St. Charles-Farmington, 

MO-IL CSA does not have any geographical or topographical barriers significantly limiting air pollution 

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

Factor 5: Jurisdictional Boundaries

Once we identified the general areas we anticipated including in the nonattainment area, we then 

considered existing jurisdictional boundaries for the purposes of providing a clearly defined legal 

boundary and to help identify the areas appropriate for carrying out the air quality planning and 

enforcement functions for nonattainment areas. Examples of jurisdictional boundaries include 

existing/prior nonattainment area boundaries for ozone or other urban-scale pollutants, county lines, air 

district boundaries, township boundaries, areas covered by a metropolitan planning organization, state 

lines, and Reservation boundaries. 

The St. Louis, MO-IL area has previously established nonattainment boundaries associated with the 1-

hour and 1997 8-hour ozone NAAQS. The portion of the St. Louis-St. Charles-Farmington, MO-IL 

CSA that we are intending to designate as nonattainment for the 2008 ozone NAAQS is the same area 

that we designated as nonattainment under the 1-hour NAAQS. Under the 1997 8-hour ozone NAAQS, 

Jersey County, IL was also included in the nonattainment area due to a monitored violation of the 

standard in that county. 

Conclusion

Based on the assessment of factors described above, EPA has preliminarily concluded that the following 

Illinois counties meet the CAA criteria for inclusion in the St. Louis-St. Charles-Farmington, MO-IL

nonattainment area: Madison County, Monroe County, and St. Clair County. This is consistent with the 

recommendation submitted by Illinois. All three of these counties were included in the St. Louis, MOIL nonattainment area for the 1-hour ozone NAAQS. Under the 1997 ozone NAAQS, Jersey County, IL 

was also included in the nonattainment area due to a monitored violation of the NAAQS in that county. 

The monitor in Jersey County, IL is currently well below the standard and the other factors do not 

support inclusion of the county within the St. Louis-St. Charles-Farmington, MO-IL nonattainment area. 

There are no air quality monitors in Illinois counties indicating violations of the 2008 ozone NAAQS

based on the 2010 design values. Madison and St. Clair Counties are nearby counties that do not have 

violating monitors, but EPA has concluded that these areas contribute to the ozone concentrations in 

violation of the 2008 ozone NAAQS due to relatively high NOx and VOC emissions and relatively high 

VMT. Based on 2008 data, Madison County has the second highest NOx emissions and third highest 

VOC emissions in the St. Louis-St. Charles-Farmington, MO-IL CSA, and St. Clair County has the 

seventh highest NOx emissions and fifth highest VOC emissions in the St. Louis-St. CharlesFarmington, MO-IL CSA. Madison and St. Clair Counties have the second and fourth highest 2008 

VMT in the St. Louis-St. Charles-Farmington, MO-IL CSA, respectively. Monroe County, IL does not 

have especially high emissions or VMT, but it is located between St. Clair County, IL and Jefferson 

County, MO, both of which have comparatively high emissions and VMT. We support Illinois’ 

recommendation that Monroe County should be included as part of the designated nonattainment area as 

its inclusion will maintain a contiguous area. Comparatively low emissions, population, and VMT in the 

remaining Illinois counties supports the exclusion of these counties from the recommended ozone 

nonattainment area for the 2008 8-hour ozone NAAQS.