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Illinois-Indiana-Wisconsin

Supplement

Area Designations for the 2008

Ozone National Ambient Air Quality Standards

On December 9, 2011, EPA sent letters to Governor Pat Quinn of 

Illinois, Governor Mitchell E. Daniels, Jr. of Indiana, and 

Governor Scott Walker of Wisconsin, providing that EPA intended 

to designate as “unclassifiable/attainment” all parts of the 

States of Illinois, Indiana, and Wisconsin not otherwise noted 

in those letters and accompanying enclosures as intended 

nonattainment areas for the 2008 8-hour ozone National Ambient 

Air Quality Standards (2008 8-hour ozone NAAQS or standards).1 

All counties in the Chicago-Naperville-Michigan City, IllinoisIndiana-Wisconsin (IL-IN-WI) Combined Statistical Area (CSA) 

were identified in these letters as intended 

unclassifiable/attainment areas.

Based on new information submitted by the State of Illinois just 

prior to issuance of those letters, EPA is now revising its 

intended designation for many of the counties in the ChicagoNaperville-Michigan City, IL-IN-WI CSA. In a letter dated 

December 7, 2011, the State of Illinois submitted a letter 

stating that it had submitted certified ozone air quality data 

for 2011. That information was not submitted in sufficient time 

for EPA to consider it in the analyses provided in the December 

9, 2011 letters. The newly submitted data, when considered in 

conjunction with data from the previous two years (2009 and 

2010) indicate that a monitor (the Zion monitor) located in Lake 

County, Illinois is violating the 2008 8-hour ozone NAAQS. 

Based on that new information, EPA recently completed an 

analysis (provided below) to determine the area it intends to 

designate as nonattainment based on the violation of the 2008 8-

hour ozone standard at the Zion monitor. The intended 

nonattainment designation for the counties identified in this 

Technical Support Document (TSD) replaces the intended 

designation of unclassifiable/attainment for these counties 

provided in the December 9, 2011 letters and enclosures. This 

document does not change or modify the intended designations 

 

1 The primary 8-hour ozone standard, set to protect human health, was revised 

on March 27, 2008 (73 FR 16436) from 0.08 parts per million to 0.075 parts 

per million (ppm) (75 parts per billion (ppb)). The secondary ozone 

standard, set to protect human welfare and the environment, was revised to be 

consistent with the primary standard in all respects.
2

identified in the December 9, 2011 letters and enclosures for 

any other counties in the States.

The table below identifies the counties or parts of counties in 

Illinois, Indiana, and Wisconsin that EPA intends to designate 

as nonattainment as part of the Chicago-Naperville, IL-IN-WI 

nonattainment area for the 2008 8-hour ozone NAAQS. In 

accordance with section 107(d) of the Clean Air Act (CAA), EPA 

must designate an area as “nonattainment” if it is violating the 

2008 8-hour ozone NAAQS or if it contributes to a violation of 

the 2008 8-hour ozone NAAQS in a nearby area. The technical 

analyses supporting the boundaries for this nonattainment area 

are provided below.

Table 1. Intended Chicago-Naperville, IL-IN-WI Nonattainment 

Area for the 2008 Ozone NAAQS

State State Recommended 

Nonattainment Counties

EPA’s Intended 

Nonattainment Counties†

Illinois Cook

DuPage

Kane

Lake

McHenry

Will

Kendall – Partial

 Oswego Township

Grundy – Partial

 Aux Sable Township

 Goose Lake Township

Cook

DuPage

Kane

Lake

McHenry

Will

Kendall – Partial

 Oswego Township

Grundy – Partial

 Aux Sable Township

 Goose Lake Township

Indiana Lake Lake

Porter

Jasper

Wisconsin None Kenosha

† Nonattainment for both primary and secondary 2008 8-hour 

ozone standards.

The analysis below provides the technical and qualitative bases 

for the intended boundaries of the Chicago-Naperville, IL-IN-WI 

ozone nonattainment area under the 2008 8-hour ozone NAAQS. It 

relies on our analysis of whether and which monitors are 

recording violations of the 2008 8-hour ozone NAAQS, based on 

state-certified air quality monitoring data from 2009-2011 for 

the State of Illinois and from 2008-2010 for ozone monitors in 

Indiana and Wisconsin and on an evaluation of whether nearby 

areas are contributing to such violations. EPA has evaluated 

contributions from nearby areas (counties within the ChicagoNaperville-Michigan City, IL-IN-WI CSA) based on a weight-ofevidence analysis considering the factors identified below. EPA 

issued guidance on December 4, 2008 that identified these 
3

factors as ones EPA would consider in determining nonattainment 

area boundaries, and recommended that states consider these 

factors in making their designation recommendations to EPA.2

1. Air quality data, including the ozone design value3

calculated for each Federal Reference Method (FRM) or 

Federal Equivalent Method (FEM) monitor in the area;

2. Emissions and emissions-related data, including locations 

of sources, population, amounts of emissions and emission 

controls, and growth patterns; 

3. Meteorology (weather/pollutant transport patterns);

4. Geography and topography (mountain ranges and other air 

basin boundaries affecting ozone levels and ozone precursor 

transport); and,

5. Jurisdictional boundaries, e.g. counties, air districts, 

existing ozone nonattainment areas, Indian country, 

Metropolitan Planning Organizations (MPOs) and their 

covered areas.

Ground-level ozone is generally not emitted directly into the 

air, but is created by chemical reactions involving Nitrogen 

Oxides (NOx) and Volatile Organic Compounds (VOC) in the 

presence of sunlight.4 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 

five factors with respect to the counties in the larger of the 

CSA or Core Based Statistical Area (CBSA) associated with the 

 

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-Related Data,” which results 

in 5 main categories of factors used to evaluate potential nonattainment area 

boundaries.

3 Average of the annual fourth-highest daily maximum 8-hour ozone 

concentrations during a three-year period with complete data that the state 

has quality assured/quality controlled and certified. In evaluating the 

attainment status of an area, EPA generally considers complete ozone data for 

the most recent three-year period.

4 Peak ozone concentrations generally occur downwind of source areas on 

relatively sunny days with high temperatures and relatively low wind speeds.
4

violating monitor(s).5 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 NAAQS, 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 8-hour ozone NAAQS. 

Congress required a similar approach in 1990 for areas 

classified as serious and above for the 1-hour ozone standard 

and EPA used the same approach in the designation process for 

the 1997 ozone NAAQS. Where a violating monitor is not located 

in a CSA or CBSA, EPA’s September 4, 2008 guidance recommends 

using the boundary of the county containing the violating 

monitor as the starting point for considering the nonattainment 

area’s boundary.

Technical Analysis for the Chicago-Naperville-Michigan City, ILIN-WI CSA

Figure 1 is a map of the intended Chicago-Naperville, IL-IN-WI 

ozone nonattainment area. The map provides other relevant 

information, including the locations of ozone monitors, county 

and other jurisdictional boundaries, Chicago-Naperville-Michigan 

City, IL-IN-WI CSA boundary, and major transportation arteries.

Figure 1. Chicago-Naperville, IL-IN-WI Area

 

5 Lists of the 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).
5

For purposes of the 1997 ozone NAAQS, as noted in Figure 1, 

portions of this area were designated nonattainment as parts of 

the Chicago-Gary-Lake County, IL-IN and Milwaukee-Racine, WI 

ozone nonattainment areas. The boundary of the Chicago-GaryLake County, IL-IN ozone nonattainment area for the 1997 ozone 

NAAQS included the entire counties of Cook, DuPage, Kane, Lake, 

McHenry, and Will in Illinois and Lake and Porter in Indiana. 

This nonattainment area also included parts of Kendall (Oswego 

Township) and Grundy (Aux Sable and Goose Lake Townships) in 

Illinois. Kenosha County in Wisconsin was designated as 

nonattainment, but was included in the Milwaukee-Racine, 

Wisconsin ozone nonattainment area for the 1997 ozone NAAQS. 

Although Kenosha County was designated as part of the MilwaukeeRacine, WI ozone nonattainment area, the Chiwaukee Prairie 

monitoring site in Kenosha County was used as the ozone design 

value site for both the Chicago-Gary-Lake County, IL-IN ozone 

nonattainment area and the Milwaukee-Racine, WI ozone 

nonattainment area for both the 1997 8-hour ozone standard and 

the 1-hour ozone standard.
6

La Porte County, Indiana was designated as a separate 

nonattainment area for the 1997 ozone NAAQS. All other counties 

in the Chicago-Naperville-Michigan City, IL-IN-WI CSA were 

designated as attainment/unclassifiable for the 1997 ozone 

NAAQS.

In March 2009, the Illinois Environmental Protection Agency 

(IEPA) recommended that Cook, DuPage, Kane, Lake, McHenry, 

Kendall (Oswego Township only), Grundy (Aux Sable and Goose Lake 

Townships only), and Will Counties be designated as 

nonattainment for the 2008 8-hour ozone NAAQS based on air 

quality data for 2006-2008. Illinois recommended that all other 

Illinois counties in the Chicago-Naperville-Michigan City, ILIN-WI CSA be designated as attainment for the 2008 ozone NAAQS. 

On December 7, 2011, the Illinois Environmental Protection 

Agency submitted confirmation that the State had certified air 

quality data for 2011. The State did not provide a revised 

ozone nonattainment area recommendation in conjunction with 

these new data.

In March 2009, Indiana recommended that Lake County be 

designated as nonattainment for the 2008 8-hour ozone NAAQS 

based on a monitored violation of NAAQS in this county during 

2006-2008, and that Porter, La Porte, Jasper, and Newton 

Counties be designated as attainment for the 2008 ozone NAAQS 

based on a lack of monitored violations of the 2008 ozone NAAQS 

in these counties during 2006-2008. 

In March 2009, Wisconsin recommended that Kenosha County be 

designated as attainment for the 2008 ozone NAAQS despite the 

fact that violations of the 2008 8-hour ozone NAAQS were 

monitored in this county during 2006-2008.6

After considering these recommendations and the new certified 

air quality data submitted by the State of Illinois, and based 

 

6 Letter from Douglas P. Scott, Director, Illinois Environmental Protection 

Agency, to Bharat Mathur, Acting Regional Administrator, U.S. Environmental 

Protection Agency, Region 5, regarding Illinois’ recommended ozone 

nonattainment boundaries (March 9, 2009); Letter from Thomas W. Easterly, 

Commissioner, Indiana Department of Environmental Management, to Bharat 

Mathur, Acting Regional Administrator, U.S. Environmental Protection Agency, 

Region 5, regarding: Recommendations Concerning Air Quality Designations for 

the 2008 Revised 8-Hour Ozone National Ambient Air Quality Standard (March 

11, 2009); and, Letter from Governor Jim Doyle, State of Wisconsin, to Lisa 

Jackson, Administrator, U.S. Environmental Protection Agency, regarding: 

Designation of 8-Hour Ozone Nonattainment Areas in Wisconsin (March 12, 

2009). 
7

on EPA’s technical analysis described below, EPA intends to 

designate the counties in Illinois, Indiana, and Wisconsin, and 

the partial counties in Illinois identified in Table 1 as 

“nonattainment” for the 2008 8-hour ozone NAAQS as part of the 

Chicago-Naperville, IL-IN-WI nonattainment area. We intend to 

designate all other portions of the Chicago-Naperville-Michigan 

City, IL-IN-WI CSA as unclassifiable/attainment for the 2008 8-

hour ozone NAAQS.

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 ChicagoNaperville-Michigan City, IL-IN-WI CSA. We used the most recent 

three-years of certified air quality data, and, thus, considered 

ozone data for the 2008-2010 period for Indiana and Wisconsin 

and for the 2009-2011 period for Illinois. We also provide the 

ozone design values for counties in Illinois based on air 

quality data for 2008-2010 to provide a complete view of the 

ozone air quality in this area for this three-year period. 

A monitor’s ozone design value is the metric or statistic that 

indicates whether that monitor attained the ozone air quality 

standard. The 2008 8-hour ozone NAAQS are met at a monitor when 

the annual fourth-highest daily maximum 8-hour ozone 

concentrations, averaged over three years is 0.075 ppm or less. 

A design value is valid only if minimum data completeness 

requirements 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 individual design value.

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 4.10) and operating with a FRM or 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 monitor 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 40 CFR part 58 Appendix A 

(quality assurance requirements) or Appendix E (probe and 

monitoring path siting criteria) were not met.
8

The 2008-2010 and 2009-2011 ozone design values for monitors and 

counties in the Chicago-Naperville-Michigan City, IL-IN-WI CSA 

are given in Table 2.

Table 2. Ozone Air Quality Data for the Chicago-NapervilleMichigan City, IL-IN-WI CSA

State/County Site Number 2008-2010 8-Hour

Ozone Design Value

(ppm)

2009-2011 8-Hour 

Ozone Design Value 

(ppm)

Illinois:

Cook 170317002 0.063 0.069

Cook 170310032 0.068 0.072

Cook 170310064 0.064 0.068

Cook 170310076 0.067 0.069

Cook 170314002 0.065 0.069

Cook 170311601 0.070 0.069

Cook 170314007 0.059 0.062

Cook 170314201 0.068 0.072

Cook 170310001 0.069 0.071

Cook 170311003 0.066 0.067

DuPage 170436001 0.060 0.063

Kane 170890005 0.066 0.069

Lake 170971007 0.074 0.076†

McHenry 171110001 0.065 0.067

Will 171971011 0.062 0.063

Indiana:

Lake 180892008 0.067 NA

Lake 180890030 0.064 NA

Lake 180890022 0.061 NA

Porter 181270026 0.062 NA

Porter 181270024 0.067 NA

La Porte 180910010 0.065 NA

La Porte 180910005 0.065 NA

Wisconsin:

Kenosha 550590019 0.074 NA

† Monitored violation of the 2008 8-hour ozone NAAQS.

Lake County (the Zion monitor) in Illinois shows a violation of 

the 2008 8-hour ozone NAAQS and confirms that at least one ozone 

monitor in the Chicago-Naperville-Michigan City, IL-IN-WI CSA 

violates this NAAQS. This supports the inclusion of Lake 

County, Illinois in the intended ozone 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 based on the weight-ofevidence of the five factors to determine whether it may have 

contributed to the nearby violation. 
9

It should be noted that historically the Chiwaukee Prairie 

monitoring site in Kenosha County, Wisconsin has been the high 

downwind monitoring site for the Chicago region. The Chiwaukee 

Prairie ozone design value was used to establish the 

classification for the Chicago-Gary-Lake County, IL-IN ozone 

nonattainment area under both the 1997 8-hour ozone standard and 

the 1-hour ozone standard. In addition, monitoring data from 

this monitoring site were historically used by the States of 

Illinois, Indiana, and Wisconsin in conjunction with modeled 

ozone concentrations to demonstrate that emission reductions in 

the Chicago area were sufficient to attain the 1-hour ozone 

standard and the 1997 8-hour ozone standard.

These considerations led us to further consider the peak ozone 

concentrations at the Chiwaukee Prairie site relative to those 

for the Zion, Illinois site.

Figure 2 considers the relationship between daily peak 1-hour 

ozone concentrations for the Chiwaukee Prairie and Zion 

monitoring sites for the 2000-2011 period.

Figure 2. Correlation Between Daily Peak 1-Hour Ozone 

Concentrations at Chiwaukee Prairie (Wisconsin) and 

Zion (Illinois) Monitoring Sites (2000-2011)
10

Figure 3 shows the comparison between 3-year ozone design values 

for the Chiwaukee Prairie and Zion monitoring sites for the 

2000-2011 period (note that the 2001 ozone monitoring data for 

Chiwaukee Prairie have been quality assured, but have not been 

certified by the State of Wisconsin).

Figure 3. Three-Year 8-Hour Ozone Design Values for Chiwaukee 

Prairie (Wisconsin) and Zion (Illinois) Monitoring 

Sites (2000-2011)
11

The data displayed in Figures 2 and 3 demonstrate both the 

strong correlation between the peak ozone concentrations at the 

Chiwaukee Prairie and Zion monitoring sites and the fact that 

the peak ozone concentrations at the Chiwaukee Prairie 

monitoring site generally exceed those at the Zion monitoring 

site. The two monitoring sites are approximately six miles 

apart, with the Chiwaukee Prairie monitoring site located very 

near the Illinois-Wisconsin border. The proximity of the two 

monitoring sites and the above data comparisons strongly suggest 

that it is likely that the Chiwaukee Prairie monitoring site 

will be determined to be violating the 2008 8-hour ozone NAAQS 

once certified data are submitted later this year. Preliminary 

data for the site suggest that the site may well be violating 

this ozone standard. 

Factor 2: Emissions and Emissions-Related Data

EPA evaluated emissions for ozone precursors (VOC and NOx) and 

other emissions-related data that provide information on area 

contributions to the ozone standard violation.
12

Emissions Data

EPA evaluated county-level emission data for NOx and VOC derived 

from the 2008 National Emissions Inventory (NEI), version 1.5. 

These are the most recently available NEI emissions data. (See 

http://www.epa.gov/ttn/chief/net/2008inventory.html) 

Significant emission levels in a nearby area indicate the 

potential for the area to contribute to the observed ozone 

standard violation.

Table 3 shows the 2008 emissions of VOC and NOx (tons per year 

(tpy)) for all counties in the Chicago-Naperville-Michigan City, 

IL-IN-WI CSA. This table also indicates which of the counties 

were recommended to be nonattainment for the 2008 ozone NAAQS by 

their respective states.

Table 3. Total 2008 VOC and NOx Emissions (tons/year) in the 

Chicago-Naperville-Michigan City, IL-IN-WI CSA

State/County State Recommended 

Nonattainment?

VOC Emissions

(tpy)

NOx Emissions

(tpy)

Illinois:

Cook Yes 129,466 143,372

DeKalb No 4,395 4,637

DuPage Yes 30,508 30,412

Grundy Yes (partial) 3,291 4,577

Kane Yes 13,893 15,161

Kankakee No 5,179 6,941

Kendall Yes (partial) 3,970 4,642

Lake Yes 19,978 24,549

McHenry Yes 9,012 9,138

Will Yes 19,255 39,878

Illinois Totals 235,347 283,307

Indiana:

Jasper No 2,845 19,788

Lake Yes 21,266 46,808

La Porte No 5,555 8,875

Newton No 1,913 841

Porter No 8,100 27,055

Indiana Totals 39,679 103,367

Wisconsin:

Kenosha No 5,370 6,788

Total CSA 

Emissions

283,996 393,462

Emissions Observations by State
13

Illinois:

From the Illinois emissions in Table 3, it can be seen that 

comparatively high emissions originate in the following 

counties: Cook, DuPage, Kane, Lake, McHenry, and Will. 

Emissions from these counties, in 2008, account for 94.4 percent 

of the total Illinois VOC emissions and 92.7 percent of the 

total Illinois NOx emissions for the Illinois portion of the 

Chicago-Naperville-Michigan City, IL-IN-WI CSA. These same 

counties account for 78.3 percent of the total VOC emissions and 

66.7 percent of the total NOx emissions for the entire ChicagoNaperville-Michigan City, IL-IN-WI CSA.

Indiana:

From the Indiana emissions data in Table 3, it can be seen that 

comparatively high VOC emissions originate in Lake and Porter 

Counties, and comparatively high NOx emissions originate in 

Jasper, Lake, and Porter Counties. These counties account for 

74.0 percent of the total VOC emissions and 90.6 percent of the 

total NOx emissions for the Indiana portion of the ChicagoNaperville-Michigan City, IL-IN-WI CSA. These same counties 

account for 10.3 percent of the total VOC emissions and 23.8 

percent of the total NOx emissions for the entire ChicagoNaperville-Michigan City, IL-IN-WI CSA.

Wisconsin:

The VOC and NOx emissions in Kenosha County are comparatively 

small; they are comparable to the emissions from the lowemissions counties in the Illinois and Indiana portions of the 

Chicago-Naperville-Michigan City, IL-IN-WI CSA. 

Population, Population Density, and Degree of Urbanization

EPA evaluated the county-specific populations, population 

trends, and vehicle use characteristics for the ChicagoNaperville-Michigan City, IL-IN-WI CSA 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 that may contribute to 

violating ozone monitors. Rapid population growth in a county 

on the urban perimeter signifies increasing integration with the 

urban core area, and indicates that it may be appropriate to 
14

include this county in the ozone nonattainment area, 

particularly if this county already has moderate or higher VOC 

and/or NOx emissions. Table 4 shows the 2010 population, 

population density, and population growth information for each 

county in the Chicago-Naperville-Michigan City, IL-IN-WI CSA

Table 4. Population and Population Growth in the ChicagoNaperville-Michigan City, IL-IN-WI CSA

State/County State 

Recommended 

Nonattainment?

2010 

Population

2010 

Population 

Density 

(1,000 per 

square 

mile)

Change in 

Population

(2000-

2010)

Population 

Percent 

Change 

(2000-

2010)

Illinois:

Cook Yes 5,194,675 5.43 -182,417 -3

DeKalb No 105,160 0.17 15,839 18

DuPage Yes 916,924 2.73 10,269 1

Grundy Yes (partial) 50,063 0.12 12,388 33

Kane Yes 515,269 0.98 107,749 26

Kankakee No 113,449 0.17 9,573 9

Kendall Yes (partial) 114,736 0.36 59,529 108

Lake Yes 703,462 1.50 55,288 9

McHenry Yes 308,760 0.51 46,890 18

Will Yes 677,560 0.80 169,531 33

Indiana:

Jasper No 33,478 0.06 3,296 11

Lake Yes 496,005 0.99 11,516 2

La Porte No 111,467 0.18 1,309 1

Newton No 14,244 0.04 -298 -2

Porter No 164,343 0.39 17,188 12

Wisconsin:

Kenosha No 166,426 0.60 16,352 11

Sources: U.S. Census Bureau population estimates for 2010 as of 

August 4, 2011.

(http://factfinder2.census.gov/faces/tableservices/jsf/pages/pro

ductview.xhtml?pid=DEC_10_PL_GCTPL2.STO5&prodType=table) and 

U.S. Census Bureau GIS files for the county boundaries.

Population Observations By State

Illinois:

For Illinois, the population data show that Cook, DuPage, Kane, 

Lake, McHenry, and Will Counties have comparatively large 

populations and population densities and, therefore, are more 

urbanized than the other Illinois counties in this CSA. This 
15

indicates that the population-related VOC and NOx emissions in 

these counties are relatively high. In addition, the population 

change levels for 2000-2010 in Kane, Kendall, Lake, McHenry, and 

Will Counties significantly exceed those of other Illinois 

counties in the CSA, suggesting that these “fast growing”

counties are becoming increasingly urbanized and integrated with 

the urban core of the Chicago-Naperville-Michigan City, IL-IN-WI 

CSA. This further indicates that the population-related 

emission contributions from these counties are increasing 

compared to those from other counties in the Chicago-NapervilleMichigan City, IL-IN-WI CSA. 

The population densities of DeKalb, Grundy, and Kankakee 

Counties are relatively small compared to those of other 

counties in the Chicago-Naperville-Michigan City, IL-IN-WI CSA, 

indicating that the population-related VOC and NOx emissions in 

these counties contribute significantly less to high ozone 

concentrations in this CSA.

Indiana:

In the Indiana portion of the Chicago-Naperville-Michigan City, 

IL-IN-WI CSA, the populations and population densities of Lake, 

Porter, and La Porte Counties are significantly larger than 

those of Jasper and Newton Counties. This indicates that 

population-related VOC and NOx emissions in Jasper and Newton 

Counties contribute less to high ozone concentrations in this 

CSA.

The population and population density of La Porte County are 

comparable to those DeKalb and Kankakee Counties in Illinois, 

indicating that the population-related VOC and NOx emissions in 

this county contribute significantly less to high ozone 

concentrations in this CSA.

Finally, it is concluded that the population-related emissions 

of Lake and Porter Counties are more significant, from an ozone 

formation standpoint, than those of other counties in the 

Indiana portion of the Chicago-Naperville-Michigan City, IL-INWI CSA, indicating that population-related VOC and NOx emissions 

in these counties do contribute significantly to high ozone 

concentrations in this CSA.

Wisconsin:

Kenosha County has a moderately low 2010 population compared to 

those of higher populated counties in the Chicago-Naperville-
16

Michigan City, IL-IN-WI CSA. However, the population density of 

Kenosha County is relatively high, showing that this county is 

significantly urbanized and that population-related VOC and NOx 

emissions in this county can significantly contribute to high 

downwind ozone concentrations.

Traffic and Commuting Patterns

EPA evaluated the total VMT for each county in the ChicagoNaperville-Michigan City, IL-IN-WI CSA. In combination with the 

population/population density data and the location of main 

transportation arteries (see the above area map), this 

information helps identify the probable location of non-point 

source emissions. A county with high VMT is generally an 

integral part of the urban area and indicates the presence of 

relatively high motor vehicle (on-road mobile source) emissions 

that may significantly contribute to ozone formation and 

transport in the urban area. This implies 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 area (in the CSA/CBSA).

Table 5 shows the traffic levels, total 2008 VMT, in each county 

in the Chicago-Naperville-Michigan City, IL-IN-WI CSA.

Table 5. Traffic Levels in the Chicago-Naperville-Michigan 

City, IL-IN-WI CSA

State/County State Recommended 

Nonattainment?

2008 VMT

(million miles)*

Illinois:

Cook Yes 32,755

DeKalb No 883

DuPage Yes 8,443

Grundy Yes (partial) 678

Kane Yes 3,628

Kankakee No 945

Kendall Yes (partial) 769

Lake Yes 5,638

McHenry Yes 2,169

Will Yes 5,713

Indiana:

Jasper No 732

Lake Yes 4,915

La Porte No 936

Newton No 219

Porter No 1,640

Wisconsin:

Kenosha No 1,354
17

* Mobile source VMT are those input into the NEI version 1.6 

used to compute the mobile source portion of the NEI emissions 

summarized above in Table 3.

VMT Observations By State

Illinois:

For Illinois, the VMT data show that VMT levels in Cook County 

are significantly higher than those for other counties in the 

Chicago-Naperville-Michigan City, IL-IN-WI CSA. The VMT levels 

for DuPage, Kane, Lake, McHenry, and Will Counties are 

comparatively higher than those of the other Illinois counties 

in the Chicago-Naperville-Michigan City, IL-IN-WI CSA and, 

cumulatively, are a significant portion of the total VMT for the 

Chicago-Naperville-Michigan City, IL-IN-WI CSA.

Indiana:

For Indiana, the VMT data show that VMT levels in Lake and 

Porter Counties are comparatively higher than those of the other 

Indiana counties in the Chicago-Naperville-Michigan City, IL-INWI CSA, and, cumulatively, are a significant portion of the 

total VMT for the Chicago-Naperville-Michigan City, IL-IN-WI 

CSA.

Wisconsin:

The VMT level in Kenosha County is similar to the VMT level in 

Porter County, Indiana. This indicates that the ozone impact of 

mobile source emissions in Kenosha County should be similar to 

that of Porter County.

Factor 3: Meteorology (Weather/Transport Patterns)

EPA evaluated available meteorological data to help determine 

how meteorological conditions, particularly transport 

conditions, affect the fate and transport of ozone and ozone 

precursors contributing to ozone formation in the ChicagoNaperville-Michigan City, IL-IN-WI CSA. The data available for 

this evaluation were presented by the States of Illinois and 

Wisconsin as part of their March 2009 ozone designation 

recommendation submittals. Indiana conducted no meteorological 

analyses to assess the impacts of transported ozone and ozone 

precursors for monitors outside of Indiana, and presented 

minimal discussions on pollutant transport for ozone monitors 

inside of Indiana.
18

In Illinois’ March 9, 2009 ozone designation recommendation 

submittal, the IEPA notes that the predominant wind direction 

across the State is from south/southwest, with an average wind 

speed of approximately 11 miles per hour. The State notes that 

ozone monitors in the Chicago area that exceed the 2008 8-hour 

ozone standard based on 2006-2008 data show strong evidence of 

regional (i.e., longer-range) contributions to high ozone 

levels. The State also presents a pollution wind rose 

(direction percent frequency) for days in 2006-2008 with peak 8-

hour ozone concentrations exceeding 75 ppb, with wind data

collected at the Alsip monitoring site (Cook County). These 

data show that, on high ozone days, the wind blew from the south 

through southwest. Some high ozone day winds were also recorded 

with winds from east-northeast through south-southeast and westsouthwest through west. Virtually no high ozone day wind 

directions were recorded for wind directions for west-northwest 

through northeast. 

In Wisconsin’s March 12, 2009 ozone designation recommendation 

submittal technical support document, the Wisconsin Department 

of Natural Resources (WDNR) summarized the wind directions for 

days (2006-2008) when 1-hour ozone concentrations at the 

Chiwaukee Prairie monitoring site in Kenosha County exceeded 75 

ppb. This analysis indicated that, on 57.9 percent of these 

high ozone days winds were from the southeast through south, 

which is where the Chicago-Gary-Lake County, IL-IN ozone 

nonattainment area for the 1997 8-hour ozone standard is 

located. On 15.8 percent of the high ozone days, winds were 

from the southwest, indicating that emissions in Walworth County 

contributed to the high ozone concentrations in Kenosha County.

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 air-shed, and, 

therefore, the distribution of ozone over the area.

The Chicago-Naperville-Michigan City, IL-IN-WI 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
19

Once we identified the general area that we anticipated we would 

recommend as nonattainment for the 2008 8-hour ozone NAAQS, we 

then considered existing jurisdictional boundaries for purposes 

of providing a clearly defined legal boundary and to help 

identify the area appropriate for carrying out the air quality 

planning and enforcement functions for an ozone nonattainment 

area. Examples of jurisdictional boundaries include existing or 

prior nonattainment boundaries, air district boundaries, 

township boundaries, areas covered by metropolitan planning 

organizations, state lines, and Reservation boundaries. Where 

existing jurisdictional boundaries are not adequate or 

appropriate to describe the nonattainment area, other clearly 

defined and permanent landmarks or geographic coordinates may be 

considered.

The Chicago-Naperville-Michigan City, IL-IN-WI CSA has 

previously established ozone nonattainment boundaries associated 

with both the 1-hour and 8-hour ozone NAAQS. The Chicago 

nonattainment boundary for the 1-hour ozone NAAQS included Cook, 

DuPage, Kane, Lake, McHenry, and Will Counties and Lake and 

Porter Counties in Indiana in their entireties and partial 

counties for Grundy (Aux Sable and Goose Lake Townships) and 

Kendall (Oswego Township) Counties in Illinois. Kenosha County, 

Wisconsin was part of the Milwaukee 1-hour ozone nonattainment 

area. All of these areas were designated as nonattainment for 

the 1997 8-hour ozone NAAQS. 

Illinois has recommended that the same full and partial counties 

in Illinois be included as part of the Chicago nonattainment 

area for the 2008 8-hour ozone NAAQS. Indiana has recommended 

that only Lake County be designated as nonattainment for the 

2008 ozone NAAQS. Finally, Wisconsin has recommended that 

Kenosha County be designated as attainment for the 2008 8-hour 

ozone NAAQS.

Conclusion

Illinois:

Based on the assessment of factors described above, EPA intends 

to include the following Illinois counties and partial counties 

in the Chicago-Naperville, IL-IN-WI ozone nonattainment area: 

Cook, DuPage, Kane, Lake, McHenry, and Will Counties in their 

entirety; and, Oswego Township in Kendall County, and Aux Sable 

and Goose Lake Townships in Grundy County. Based on the levels 

of VOC and NOx emissions, and other emissions-related data, 

including population and VMT levels, it is concluded that Cook, 
20

DuPage, Kane, Lake, McHenry, and Will Counties are significant 

sources of emissions that contribute to the high ozone levels at 

the Zion monitor. Based on the State of Illinois’ 

recommendation and on historical nonattainment boundary 

considerations, we also intend to include Oswego Township in 

Kendall County and Aux Sable and Goose Lake Townships in Grundy 

County as part of the Chicago-Naperville, IL-IN-WI ozone 

nonattainment area for the 2008 8-hour ozone standard.

Based on our analysis of the factors above, especially 

considering the emissions-related factors, we intend to 

designate the remaining Illinois counties, including the 

remaining portions of Kendall and Grundy Counties, in the 

Chicago-Naperville-Michigan City, IL-IN-WI CSA as attainment for 

the 2008 8-hour ozone NAAQS.

Indiana:

Based on the assessment of factors described above, EPA intends 

to include Lake, Jasper, and Porter Counties in the ChicagoNaperville, IL-IN-WI nonattainment area for the 2008 8-hour 

ozone NAAQS. This is based on the high emissions in these 

counties that contribute to high ozone concentrations at the 

Zion monitor. Meteorology on high ozone days in Chicago area 

favor the transport of ozone and ozone precursor emissions from 

these counties to the Zion monitor and other downwind portions 

of the Chicago area. 

The low emissions and emissions-related population and VMT data 

of Newton County favor the exclusion of this county from the 

nonattainment area. It is concluded that emissions from this 

county do not significantly contribute to the high ozone 

concentrations at the Zion monitor.

The VOC and NOx emissions of La Porte County are significantly 

lower than those of Lake and Porter Counties and those of 

recommended nonattainment counties in Illinois. In addition, it 

is recognized that historically La Porte County has been 

designated as a separate nonattainment area for the 1997 8-hour 

ozone standard. Based collectively on these factors, we intend 

to not include La Porte County in the Chicago-Naperville, IL-INWI ozone nonattainment area for the 2008 8-hour ozone NAAQS.

Wisconsin:

Kenosha County presents a more unique situation for this 

designation analysis. The VOC and NOx emissions in Kenosha 
21

County are relatively low and similar to those for counties 

recommended for exclusion from the intended ozone nonattainment 

area. In addition, it is noted that Illinois’ and Wisconsin’s 

wind direction analyses for high ozone days indicate that 

Kenosha County emissions are probably downwind of the violating 

Zion, Illinois monitor on high ozone days. These conclusions 

would support the exclusion of Kenosha County from the intended 

ozone nonattainment area.

Nonetheless, it is also recognized that the Chiwaukee Prairie 

monitoring site in Kenosha County has historically been the high 

downwind ozone monitoring site for the Chicago region. 

Chiwaukee Prairie ozone design values were used to establish the 

classification for the Chicago-Gary-Lake County, IL-IN ozone 

nonattainment area under both the 1997 8-hour ozone standard and 

the 1-hour ozone standard.

Based on the above considerations, at this time we are notifying 

the State of Wisconsin that we intend to include Kenosha in the 

Chicago-Naperville, IL-IN-WI ozone nonattainment area for the 

2008 8-hour ozone standard. If the State of Wisconsin submits 

certified data for 2009-2011 showing that Kenosha County is 

actually attaining the 2008 8-hour ozone standard, EPA’s 

conclusion regarding the designation for Kenosha County should 

be revisited.