Maintenance Plan for the

Chicago Nonattainment Area

for the 1997 PM2.5 

National Ambient Air Quality Standards

(Revised)

AQPSTR 11-07

August 17, 2011

Illinois Environmental Protection Agency

1021 North Grand Avenue East

Springfield, Illinois 62794-9276
i

TABLE OF CONTENTS

 Page

LIST OF TABLES . . . . . . . . . iii

LIST OF FIGURES . . . . . . . . . iv

EXECUTIVE SUMMARY . . . . . . . . 5

1.0 INTRODUCTION . . . . . . . . 6

1.1 Regulatory Background . . . . . . 6

1.2 Status of Air Quality . . . . . . . 8

2.0 REDESIGNATION AND MAINTENANCE PLAN REQUIREMENTS 9

3.0 PM2.5 MONITORING . . . . . . . 11

3.1 Monitored Design Values . . . . . . 11

3.2 Quality Assurance . . . . . . . 12

3.3 Continued Monitoring . . . . . . 12

4.0 EMISSIONS INVENTORY. . . . . . . 14

4.1 Attainment Year Inventory . . . . . . 14

4.2 Air Quality Improvements and Emissions Controls . . . 15

4.3 Emissions Projections. . . . . . . 16

4.4 Demonstration of Maintenance . . . . . 16

4.5 Provisions for Future Updates . . . . . 18

5.0 CONTROL MEASURES AND REGULATIONS . . . 19

5.1 Control Measures . . . . . . . 19

5.2 Reasonable Further Progress (RFP) and

Reasonably Available Control Technology (RACT) . . . 20

5.3 Controls to Remain in Effect . . . . . . 20

5.4 Provisions for Permitting New or Modified Emissions Sources . 21

5.5 Transportation Conformity . . . . . . 21

6.0 CONTINGENCY MEASURES . . . . . . 23

6.1 Contingency Measures . . . . . . 23

6.2 Commitment to Revise Plan . . . . . . 25

6.3 Public Participation . . . . . . . 25

6.4 Legal Authority to Implement and Enforce . . . . 26

7.0 CONCLUSIONS . . . . . . . . 27
ii

TABLE OF CONTENTS (Continued)

APPENDIX A Summary of Ambient Air Monitoring Data (2007-2009) 28

APPENDIX B Transportation Conformity 30
iii

LIST OF TABLES

Page

Table 4.1 2008 PM2.5, NOx and SO2 Emissions . . . . . 14 

Table 4.2 2002 PM2.5, NOx and SO2 Emissions . . . . . 15 

Table 4.3 2015 PM2.5, NOx and SO2 Emissions . . . . . 16 

Table 4.4 2020 PM2.5, NOx and SO2 Emissions . . . . . 17 

Table 4.5 2025 PM2.5, NOx and SO2 Emissions . . . . . 17 

Table 4.6 Comparison of 2008, 2015, 2020 and 2025 Emissions . . 17

Table 5.1 Proposed 2008 and 2025 Motor Vehicle Emissions Budgets

Chicago Nonattainment Area PM2.5 Maintenance Plan. . . 22

Table 6.1 Contingency Plan for the Chicago PM2.5 Nonattainment Area . 24
iv

LIST OF FIGURES

Page

Figure 1.1 Chicago PM2.5 Nonattainment Area . . . . . 7

Figure 3.1 PM2.5 Monitors in the Chicago Nonattainment Area . . . 11

Figure 3.2 Comparison of PM2.5 Design Values for the Chicago

Nonattainment Area Between 2000-2002 and 2007-2009 . . 13
5

EXECUTIVE SUMMARY

This document describes Illinois’ Maintenance Plan for the Illinois portion of the 

Chicago fine particulate matter (PM2.5) nonattainment area (NAA), hereafter referred to 

as the Chicago NAA. An approved Maintenance Plan is required before an area can be 

redesignated from nonattainment to attainment of a National Ambient Air Quality 

Standard (NAAQS). This document provides technical information required to support a 

request to redesignate the Chicago NAA to attainment of the 1997 annual PM2.5 NAAQS. 

This revision incorporates motor vehicle emissions estimates developed using the U.S. 

EPA’s MOVES model. The Indiana Department of Environmental Management 

(IDEM), has prepared a similar plan for the Indiana portion of the Chicago NAA.

PM2.5 air quality has improved in the Chicago area as a result of the implementation of 

State and Federal emissions control measures since the designation of the area as 

nonattainment in 2004. The air quality improvement is due to permanent and enforceable 

emissions control measures. The entire Chicago NAA has at least three years of 

complete, quality assured ambient air quality monitoring data for 2007-2009 that 

demonstrates compliance with the 1997 NAAQS. The U.S. EPA has made a 

determination that the Chicago NAA has attained the 1997 fine particle standard (40 CFR

52.74, p. 62243-62249).

This Maintenance Plan provides for continued attainment of the 1997 PM2.5 air quality 

standards for the Chicago nonattainment area for a period of at least ten years after U.S. 

EPA has formally redesignated the area to attainment. The Plan also provides assurances 

that, even if there is a subsequent violation of the air quality standard, contingency 

measures listed in the Plan will be triggered to prevent any future occurrences. Finally, 

the Plan includes on-road motor vehicle emissions budgets for the years 2008 and 2025

for use in transportation conformity determinations to assure that any increases in 

emissions from this sector do not jeopardize continued attainment of the PM2.5 standards

during the maintenance period.
6

1.0 INTRODUCTION

The Illinois Environmental Protection Agency (Illinois EPA) has prepared this document 

to describe Illinois’ PM2.5 Maintenance Plan for the Chicago NAA. This Maintenance 

Plan is required before the area can be redesignated from nonattainment to attainment of 

the annual National Ambient Air Quality Standard (NAAQS) for PM2.5 promulgated by 

the U.S. Environmental Protection Agency (U.S. EPA) in 1997. The Illinois EPA intends 

to submit such a request to the U.S. EPA in conjunction with this Maintenance Plan. The 

entire Chicago nonattainment area, including Lake and Porter counties in Indiana, has at 

least three years of complete, quality assured ambient air quality monitoring data for the 

most recent 3-year period, 2007-2009, demonstrating attainment of the annual PM2.5

NAAQS promulgated in 1997. U.S. EPA finalized its determination that the entire 

Chicago NAA attains the 1997 PM2.5 NAAQS in November 2009.

This document provides the technical information needed to support a request to 

redesignate the Chicago area to attainment of the 1997 annual PM2.5 NAAQS. Section 

107 of the Clean Air Act (CAA) establishes specific requirements to be met in order for a 

nonattainment area to be considered for redesignation. Before an area can be reclassified 

to attainment:

U.S. EPA must make a determination that the area has attained the NAAQS based 

on at least three complete years of ambient monitoring data. 

U.S. EPA must have approved a State Implementation Plan (SIP) for the area 

under Section 110 and Part D of the CAA. 

The state must demonstrate that the improvement in air quality is due to 

permanent and enforceable reductions in emissions resulting from implementation 

of the SIP and other federal requirements. 

The state must submit, and U.S. EPA must approve, a Maintenance Plan under 

Section 175(A) of the CAA, including provisions for contingency measures that 

will be implemented if future violations of the NAAQS are measured.

This Maintenance Plan provides for the continued attainment of the annual PM2.5

NAAQS for the Chicago NAA for a period of at least ten years after U.S. EPA has 

formally redesignated the area to attainment. The Plan also provides assurances that even 

if a subsequent violation of the annual PM2.5 NAAQS occurs, provisions in the Plan will 

prevent any future occurrences through the enactment of contingency measures that 

would be triggered upon such occurrence.

This document addresses the Maintenance Plan requirements established by the CAA and 

U.S. EPA, and includes additional information to support continued compliance with the 

PM2.5 NAAQS.

1.1 Regulatory Background

The CAA requires areas that fail to meet the NAAQS for PM2.5 to develop SIPs to 

expeditiously attain and maintain the NAAQS. Historically, one-year exceedances of the 

annual PM2.5 NAAQS have been monitored as recently as 2007 at one monitor in Cook 

County, but all monitors in the NAA are now in attainment of the PM2.5 NAAQS.
7

The Chicago NAA, which includes all of Cook, DuPage, Kane, Lake, McHenry and Will 

counties, as well as portions of Grundy and Kendall counties, was originally designated 

as nonattainment of the 1997 annual PM2.5 in 2004. The Chicago area was designated 

unclassifiable/attainment for the 24-hour PM2.5 standard that was also promulgated in 

1997, and revised in 2006. Since the Chicago area is not a nonattainment area for the 24-

hour PM2.5 NAAQS, any reference to the PM2.5 NAAQS in the remainder of this 

document refers only to the annual PM2.5 standard promulgated in 1997. Figure 1.1 

depicts the boundaries of the Chicago PM2.5 NAA in Illinois.

Figure 1.1- Chicago PM2.5 Nonattainment Area
8

The following is a list of the counties contained in the Chicago PM2.5 nonattainment area:

Cook County, IL

DuPage County, IL

Kane County, IL

Lake County, IL

McHenry County, IL

Will County, IL

Aux Sable and Goose Lake Townships in Grundy County, IL, and

Oswego Township in Kendall County, IL

As a result of the nonattainment designation, this area was subject to new requirements, 

including development of an attainment strategy that would allow the area to meet the 

federal PM2.5 NAAQS by June 15, 2010. The attainment strategy recognizes the 

importance of reducing both locally-generated as well as incoming (transported) PM2.5

and precursor emissions. State and Federal emissions control measures have reduced 

primary and secondary PM2.5 emissions both locally and regionally and have enabled the 

Chicago NAA to attain the PM2.5 NAAQS by the attainment deadline established by the 

U.S. EPA.

1.2 Status of Air Quality

PM2.5 monitoring data for the most recent three-year period, 2007 through 2009, 

demonstrates that air quality has met the 1997 PM2.5 NAAQS in the Chicago NAA.

Information regarding the air monitoring network and air quality monitoring data is

included in Section 3.0 and Appendix A.
9

2.0 REDESIGNATION AND MAINTENANCE PLAN REQUIREMENTS

Sections 107 and 110 of the CAA list a number of requirements that must be met by 

nonattainment areas prior to consideration for redesignation to attainment. One of those 

requirements is the development of a Maintenance Plan, which describes a state’s plan 

for maintaining the NAAQS for a minimum ten-year period after redesignation. The 

Illinois EPA developed this Maintenance Plan according to the guidance published by the 

U.S.EPA entitled “Procedures for Processing Requests to Redesignate Areas to 

Attainment” (September 4, 1992).

Before a redesignation to attainment can be promulgated, U.S. EPA must:

Determine that the NAAQS for PM2.5, as published in 40 CFR 50.4, has been 

attained. PM2.5 monitoring data must show that violations of the NAAQS are no 

longer occurring. This showing must rely on three consecutive years of data. The 

ambient air monitoring data must be quality assured in accordance with 40 CFR 

58.10, recorded in U.S. EPA’s Air Quality System (AQS) data base, and made

available to the public. U.S. EPA has already finalized and published a finding 

that the area has, in fact, attained the NAAQS. This finding was published in the 

Federal Register in November 2009. 

Approve the state’s plan for demonstrating attainment. The attainment plan, 

which is based on air quality modeling, must contain enforceable control 

measures and must be submitted as a revision to the state’s SIP after a public 

hearing.

Determine that the improvement in air quality between the year violations 

occurred and the year that attainment was achieved is based on permanent and 

enforceable emissions reductions.

Approve the state’s Maintenance Plan. The requirements for the Maintenance 

Plan are discussed below.

Determine that all other requirements applicable to the nonattainment area have 

been met.

A PM2.5 Maintenance Plan provides for the continued attainment of the PM2.5 NAAQS 

for a nonattainment area for a period of at least ten years after U.S. EPA has formally 

redesignated the area to attainment. To be approvable, the state is required to have a 

public comment period and provide the opportunity for a public hearing on the 

Maintenance Plan prior to adoption. The Maintenance Plan must contain the following 

elements:

A comprehensive “attainment year” emissions inventory of primary PM2.5 and the 

precursors of secondary PM2.5: oxides of nitrogen (NOx) and sulfur dioxide (SO2);
10

A projection of the emissions inventory forward to a year at least ten years after 

redesignation and a demonstration that the projected level of emissions is 

sufficient to maintain attainment of the PM2.5 NAAQS;

A commitment that, once redesignated, the state will continue to operate an 

appropriate monitoring network to verify maintenance of the attainment status;

A demonstration of legal authority to implement and enforce all control measures 

contained in the SIP;

Provisions for future updates of the inventory to enable tracking of emissions

levels, including an annual emissions statement from major sources;

Motor vehicle emissions budgets for transportation conformity for the ten-year 

maintenance period;

A commitment to submit a revised Maintenance Plan eight years after 

redesignation;

A commitment to enact and implement additional contingency measures 

expeditiously in the event that future violations of the NAAQS occur; and 

A list of potential contingency measures that would be implemented in such an 

event.

This Maintenance Plan has been prepared in accordance with the requirements specified 

in U.S. EPA’s guidance document and additional guidance received from U.S. EPA staff.

The following sections of this document describe how U.S. EPA’s requirements have 

been met.
11

3.0 PM2.5 MONITORING

U.S. EPA’s published guidance document, “Procedures for Processing Requests to 

Redesignate Areas to Attainment” (September 4, 1992), details specific requirements 

regarding the collection and use of ambient air monitoring data needed to support a 

redesignation request. Before the Chicago NAA can be redesignated, Illinois must 

demonstrate that the PM2.5 NAAQS has been attained. PM2.5 monitoring data must show 

that violations of the NAAQS are no longer occurring within the nonattainment area. 

This showing must rely on three complete, consecutive calendar years of quality assured 

data. Further, the air monitoring data must be quality assured in accordance with 40 CFR 

58.10, recorded in U.S. EPA’s AQS data base, and made available to the public. As 

previously mentioned, U.S.EPA has made a finding that the Chicago NAA has met these 

requirements and is attaining the 1997 PM2.5 NAAQS. Finally, Illinois must commit to

continue to operate an appropriate monitoring network to verify the maintenance of the 

attainment status, once the area has been redesignated.

The following subsections describe how each of these requirements has been addressed.

3.1 Monitored Design Values

Currently there are 19 PM2.5 monitors located in the nonattainment counties in the Illinois 

portion of the Chicago nonattainment area. Figure 3.1 shows the locations of these 

monitors. 

Figure 3.1 - PM2.5 Monitors in the Chicago Nonattainment Area
12

To determine whether the NAAQS has been met, the annual PM2.5 design value has been 

calculated for the 3-year period, 2007-2009. The current U.S. EPA method for 

calculating the annual PM2.5 design value is to average each monitor’s annual average 

values over a 3-year period and compare the calculated design values to the 15.0

microgram per cubic meter level of the NAAQS. The calculated annual PM2.5 design 

values for the monitors in the Chicago NAA for 2007-2009 are included as Appendix A 

of this report. Figure 3.2 compares the design values for 2000-2002, when the area was

initially recommended for designation as a nonattainment area, and the 2007-2009 period 

for monitoring stations in the Chicago region. The comparison shows that PM2.5 air 

quality has improved considerably since 2000-2002 throughout the Chicago NAA. The

2007-2009 data shows that the design values at all monitoring sites are less than the level 

of the annual PM2.5 NAAQS, demonstrating that the area attains the annual PM2.5 air 

quality standard.

3.2 Quality Assurance

The Illinois EPA has quality assured all monitoring data shown in Appendix A for all 

sites located in Illinois in accordance with 40 CFR 58.10 and the Illinois EPA’s Quality 

Assurance Plan, which describes Illinois EPA’s standard operating procedures for 

operating the ambient monitoring network and validating the data. The Illinois EPA has 

recorded the monitoring data in the U.S. EPA’s AQS database, which is available to the 

public.

3.3 Continued Monitoring

Illinois commits to continue monitoring PM2.5 levels according to a U.S. EPA approved 

monitoring plan, as required to ensure maintenance of the PM2.5 NAAQS. Should 

changes in the location of a PM2.5 monitor become necessary, the Illinois EPA will work 

with U.S. EPA to ensure the adequacy of the monitoring network. The Illinois EPA will

continue to quality assure the monitoring data to meet the requirements of 40 CFR 58. 

The Illinois EPA will continue to enter all data into AQS on a timely basis in accordance 

with federal guidelines.
13

Figure 3.2 - PM2.5 Design Values for the Chicago Nonattainment Area

Between 2000-2002 and 2007-2009

 2000-2002 Design Values 2007-2009 Design Values
14

4.0 EMISSIONS INVENTORY

A redesignation request must contain a demonstration that the improvement in air quality 

between the year that violations occurred and the year that attainment was achieved is 

based on permanent and enforceable emissions reductions. As described previously in 

Section 3.0, a three-year monitoring period is used to evaluate whether actual air quality 

attainment has been achieved. In this Section, the “attainment year” refers to the midpoint year (2008) of the three-year period (2007-2009) used to demonstrate attainment. 

As required by U.S.EPA redesignation guidance, this request also includes a projection 

of the emissions inventory to a year at least 10 years following redesignation, a 

demonstration that the projected level of emissions is sufficient to maintain the PM2.5

NAAQS, and a commitment to provide future updates of the inventory to enable tracking 

of emissions levels during the 10-year maintenance period.

4.1 Attainment Year Inventory

The Illinois EPA has prepared a comprehensive emissions inventory for the Chicago 

PM2.5 nonattainment area, including point, area, and on-road and off-road mobile sources 

for primary PM2.5 as well as precursors of PM2.5 (NOx and SO2) for the year 2008. The 

Illinois EPA selected 2008 emissions data to represent the “attainment year” since it is 

the middle year of the 3-year period (2007-2009) which demonstrates monitored 

attainment. This inventory is based on actual activity levels. Point source information 

was compiled from 2008 Annual Emissions Reports (AERs) submitted to the Illinois 

EPA by emissions sources. Area source emissions were calculated using the most 

recently available methodologies and emissions factors from U.S. EPA along with 

activity data (typically population, employment, fuel use, etc.) specific to 2008. On-road 

mobile source emissions were calculated using U.S. EPA’s MOVES emissions model 

with 2008 vehicle miles traveled (VMT) data provided by the Illinois Department of 

Transportation (IDOT). Off-road mobile source exhaust emissions, such as those from 

lawn and garden equipment, agricultural equipment, and construction equipment were 

calculated for summer 2008 using U.S. EPA’s NONROAD emissions model. Emissions 

sources such as commercial marine vessels, locomotives and aircraft were not included in 

the NONROAD model and were calculated separately. Biogenic emissions were not 

included in these summaries. 

Table 4.1 summarizes the 2008 emissions estimates for the Chicago PM2.5 nonattainment 

area.

Table 4.1

2008 PM2.5, NOx, and SO2 Emissions (tons per year)

Source Category PM2.5 NOx SO2

Point Sources 3,859 35,939 90,706

Area Sources* 9,189 32,318 4,109

On-Road Mobile Sources 5,100 127,951 537

Off-Road Mobile Sources 3,653 51,184 779

Total 21,800 247,391 96,130

*does not include fugitive dust emissions from construction (residential, road and other) and 

agricultural tilling
15

4.2 Air Quality Improvements and Emissions Controls

The Chicago area was designated as nonattainment of the 1997 PM2.5 NAAQS in 2004. 

Since that time, permanent and enforceable reductions of primary PM2.5 and secondary 

PM2.5 precursor emissions have contributed to improvements in PM2.5 air quality and to 

the attainment of the PM2.5 NAAQS. Some of these emissions reductions were due to the 

application of tighter federal emissions standards on motor vehicles and fuels, and some 

due to the requirements of the federal NOx SIP Call. Section 5.0 of this report describes 

these reductions in more detail, along with an explanation of their regulatory status. In 

this subsection, the 2008 attainment year emissions levels are compared to the base year 

2002 emissions levels.

The U.S. EPA’s PM2.5 Emissions Inventory Guidance requires that states with PM2.5

nonattainment areas prepare and submit a 2002 base year inventory of anthropogenic 

sources of direct PM2.5 and precursors of secondary PM2.5 emissions, namely NOx and 

SO2. This base year inventory included emissions from point, area, on-road mobile and 

off-road mobile emissions. The Illinois EPA prepared and submitted this inventory in 

May 2006. Table 4.2 summarizes 2002 emissions by major source category and by 

pollutant for the Chicago NAA. This summary has been revised to incorporate emissions 

estimates for on-road mobile sources using U.S. EPA’s MOVES model.

Table 4.2

2002 PM2.5 NOx, and SO2 Emissions (tons per year)

Source Category PM2.5 NOx SO2

Point Sources 2,757 54,050 121,598

Area Sources 22,356 32,325 3,290

On-Road Mobile Sources 6,573 187,632 4,472

Off-Road Mobile Sources 4,834 87,426 3,743

Total 36,520 361,433 133,103

Comparing the 2002 inventory to that for 2008 indicates that the total direct PM2.5 

emissions in the Chicago area were reduced by 14,720 tons per year. NOx emissions in 

the Chicago area decreased significantly, by 114,042 tons per year, during the same time 

period. These reductions were primarily from on-road and off-road mobile sources. SO2

emissions in the Chicago area decreased by 36,973 tons per year, due largely to 

reductions from point sources. These sizeable emissions reductions in direct PM2.5

emissions and secondary PM2.5 precursor emissions, as well as corresponding reductions 

in upwind areas in Illinois and other nearby states resulted in a substantial improvement 

in PM2.5 air quality in the Chicago area, ultimately resulting in attainment of the 1997 

PM2.5 NAAQS.
16

4.3 Emissions Projections

A Maintenance Plan must contain a demonstration that the level of emissions projected

for the ten-year period following redesignation are sufficient to maintain the NAAQS. 

Accordingly, Illinois EPA has projected PM2.5, NOx, and SO2 emissions for the Chicago 

NAA for 2025. Illinois EPA has also projected emissions to 2015 and 2020 to represent 

midpoint years during the maintenance period. Emissions for these projection years are 

compared to emissions levels in 2008 to determine if emissions are sufficient to maintain 

the NAAQS during this period.

Chicago area point and area source emissions for 2015, 2020, and 2025 were estimated 

using the 2008 base year inventory and growth factors appropriate for each source 

category. Off-road emissions projections were developed using the growth factors 

contained in U.S. EPA’s NONROAD model. On-road motor vehicle emissions were 

estimated using U.S. EPA’s MOVES motor vehicle emissions model. The figures 

assume the continued use of reformulated gasoline, the continued phase-in of the Tier 2 

motor vehicle emissions standards, and operation of an enhanced vehicle inspection and 

maintenance program. Total vehicle miles of travel (VMT) for 2015, 2020 and 2025

were assumed to increase at a rate of 1.5 percent per year from 2008.

Tables 4.3, 4.4 and 4.5 include the direct NOx, PM2.5 and SO2 emissions estimates for the 

years 2015, 2020 and 2025 respectively, for the Chicago nonattainment area.

Table 4.3

2015 PM2.5, NOx, and SO2 Emissions (tons per year)

Source Category PM2.5 NOx SO2

Point Sources 4,169 27,082 58,092

Area Sources 9,676 32,997 4,266

On-Road Mobile Sources 3,071 68,491 504

Off-Road Mobile Sources 2,995 35,927 866

Total 19,911 164,497 63,727

4.4 Demonstration of Maintenance

Table 4.6 provides a comparison of emissions for the years 2008, 2015, 2020, and 2025. 

The table demonstrates that the level of emissions projected through the maintenance 

period are less than emissions estimated for the attainment year and are, therefore,

sufficient to maintain the PM2.5 NAAQS. As shown in the table, both SO2 and NOx 

emissions within the nonattainment area are expected to decrease significantly between 

2008 and 2025 with PM2.5 decreasing slightly. Projected emissions of those pollutants 

for the mid-point years of 2015 and 2020, are also less than their respective emissions 

levels in 2008. Based on these emissions trends it is expected that air quality will 

continue to meet the PM2.5 NAAQS throughout the maintenance period.
17

Table 4.4

2020 PM2.5, NOx, and SO2 Emissions (tons per year)

Source Category PM2.5 NOx SO2

Point Sources 4,391 28,500 53,452

Area Sources 10,009 33,277 4,332

On-Road Mobile Sources 2,119 40,599 477

Off-Road Mobile Sources 2,398 28,271 919

Total 18,918 130,648 59,180

Table 4.5

2025 PM2.5, NOx, and SO2 Emissions (tons per year)

Source Category PM2.5 NOx SO2

Point Sources 4,604 29,638 56,310

Area Sources 10,377 33,687 4,407

On-Road Mobile Sources 2,067 38,456 488

Off-Road Mobile Sources 2,267 27,173 1,215

Total 19,316 128,954 62,420

Table 4.6

Comparison of 2008, 2015, 2020 and 2025 Emissions

(Emissions stated in tons per year)

2008 2015 2020 2025 Decrease

(2008-2015)

Decrease 

(2008-2020)

Decrease 

(2008-2025)

PM2.5 21,800 19,911 18,918 19,316 1,889 2,882 2,484

NOx 247,391 164,497 130,648 128,954 82,894 116,743 118,437

SO2 96,130 63,727 59,180 62,420 32,403 36,950 33,710

In addition to the overall emissions reductions projected to occur within the 

nonattainment area, significant reductions of statewide NOx and SO2 emissions resulting 

from implementation of Illinois’ multi-pollutant standards affecting electric utilities 

during the maintenance period, will also help to ensure continued attainment of the PM2.5

NAAQS.

It should also be noted that the emissions projections included here do not reflect the 

reductions expected from a range of measures being implemented to reduce diesel 

emissions in the Chicago NAA. These measures have been funded through sources such 

as the:

U.S. EPA’s Midwest Clean Diesel Initiative 

Congestion Mitigation and Air Quality Improvement (CMAQ) Program 

Diesel Emissions Reduction Act (DERA)
18

American Recovery and Reinvestment Act of 2009

Various Supplemental Environmental Projects 

These projects include the installation of particulate filters, diesel oxidation catalysts, 

closed-crankcase ventilation systems, and direct-fired heaters on school and transit buses, 

and municipally-owned utility vehicles, repowering diesel locomotive engines with 

generator sets, upgrading diesel construction engines with engines meeting more 

stringent emissions standards, and installing auxiliary power units on over-the-road 

trucks to reduce idling. We anticipate DERA and CMAQ funding to continue to support 

additional diesel emissions reduction projects in the near future.

4.5 Provisions for Future Updates

As required by Section 175A(b) of the CAA, Illinois commits to submit to U.S. EPA, 

eight years after redesignation, a revised version of this Maintenance Plan. The revision 

will contain Illinois’ plan for maintaining the PM2.5 NAAQS for ten years beyond the 

initial maintenance period.
19

5.0 CONTROL MEASURES AND REGULATIONS

This section provides specific information on the control measures implemented in the 

Chicago NAA. These include CAA requirements, and other state and federal measures. 

These control measures have been fully promulgated, and will provide emissions

reductions in future years. Illinois EPA commits to keep these measures in effect after 

redesignation, or to maintain equivalent emissions levels using alternate measures. 

Illinois’ SIP contains acceptable provisions to provide for preconstruction review of new 

emissions sources. After redesignation to attainment, Prevention of Significant 

Deterioration (PSD) requirements will apply to the construction of new major sources 

and to significant modifications of existing sources. Illinois has accepted delegation from 

U.S. EPA of this program. Illinois further commits to continue to require that all future 

regional transportation plans for the Chicago area conform to the SIP.

5.1 Control Measures

A variety of control measures are in place that reduce emissions of direct PM2.5, NOx and 

SO2, and have contributed to the attainment of the annual fine particle standard. The 

emissions reduction measures for demonstrating attainment of the PM2.5 standard are as 

follows:

NOx SIP Call 

New Source Performance Standards (NSPS) and National Emissions Standards 

for Hazardous Air Pollutants (NESHAPS)/Maximum Achievable Control 

Technology (MACT) Standards 

VOM Solvent Categories: Aerosol Coatings, Architectural and Industrial 

Maintenance (AIM) Coatings, Consumer Solvents

Vehicle Inspection & Maintenance Program 

Reformulated Gasoline 

Tier 2 Motor Vehicle Emissions Standards and Gasoline Sulfur Control 

Requirements

On-Highway Heavy-Duty Engine and Vehicle Standards and Highway Diesel 

Fuel Sulfur Control Requirements

Federal Emissions Standards for Off-Road Equipment (e.g., Nonroad Diesel 

Engine Rule, Evaporative Large Spark Ignition and Recreational Vehicle 

Standards) incorporated into NONROAD Model

Tier 4 Nonroad Diesel Engine Standards and Diesel Fuel Sulfur Content 

Restrictions 

Marine Compression-Ignition Engine Standards and Locomotive Engine 

Standards 

Consent Decrees (CITGO and ExxonMobil)
20

5.2 Reasonable Further Progress (RFP) and Reasonably Available Control 

Technology (RACT)

Since U.S. EPA has published an attainment finding for the Chicago area for the 1997 

PM2.5 standard, the requirements for Illinois to submit an attainment demonstration, 

RACM, RFP, contingency measures, and any other planning SIP’s related to attainment 

are suspended as long as the area continues to attain the 1997 PM2.5 NAAQS.

5.3 Controls to Remain in Effect

Illinois will maintain all of the control measures listed in this Section to ensure 

maintenance of the annual PM2.5 NAAQS. Any revisions to the control measures 

included as part of the Maintenance Plan will be submitted as a SIP revision to U.S. EPA 

for approval, and will be accompanied by a showing that such changes will not interfere 

with maintenance of the NAAQS.

In addition, clean construction standards are in place as part of Cook County Ordinance 

No. 09-O-36, 5-19-2009 (Article IX, Section 30-952) that mandates that contractors must 

use Ultra Low Sulfur Diesel fuel in diesel vehicles, nonroad vehicles, and stationary 

generators for Cook County government projects exceeding $2 million. Furthermore, by 

the start of 2014, any primary contractor working on a construction project in Cook 

County shall be required to meet a PM emission reduction of at least 85% from 

uncontrolled for any heavy duty diesel vehicle or diesel nonroad vehicle. This level of 

control of diesel vehicles must be met by subcontractors by the start of 2016. This is not 

included as a contingency measure, but is further evidence of current and future PM 

emissions reductions in the heart of the urban area.

The O’Hare Airport Modernization Program already has in place an Ultra Low Sulfur 

Diesel fuel requirement for all off-road diesel powered vehicles and equipment (both 

mobile and stationary) that are utilized on-site. (O’Hare Modernization Project Site 

Preparation, Project No. OH6126.200.50.023, specification no. 35491) This requirement 

is in place for the remainder of the project. 

The Illinois EPA has the necessary resources to enforce any violations of its rules or 

permit provisions. After redesignation, it intends to continue enforcing all rules that 

relate to the emissions of primary PM2.5 and precursors to secondary PM2.5 in the Chicago

nonattainment area.

5.4 Provisions for Permitting New or Modified Emissions Sources

Illinois has longstanding and fully implemented programs for the review of new major 

sources and significant modifications of existing sources. The PSD program, which 

includes requirements for Best Available Control Technology (BACT) on major new 

sources or significant modifications of existing sources, will be applicable in the Chicago
21

area once the area has been redesignated to attainment. Illinois has been delegated full 

authority to implement the PSD program by U.S. EPA.

5.5 Transportation Conformity

The purpose of this section is to describe and establish the Chicago nonattainment area 

motor vehicle emissions budgets associated with the PM2.5 Maintenance Plan SIP. 

Annual motor vehicle emissions budgets are being proposed for the attainment year, 

2008, and for the final year of the Maintenance Plan, 2025, for primary PM2.5 and the 

precursor pollutant NOx. The Maintenance Plan also includes motor vehicle emissions 

estimates for the interim years 2015 and 2020 in order to demonstrate that total emissions 

from all sectors remain below the 2008 attainment year total; however, these interim year 

motor vehicle emissions estimates are not being proposed as formal motor vehicle 

emissions budgets. The Maintenance Plan also includes estimates of emissions of SO2, 

however, as motor vehicles have not been identified as a significant source of SO2, motor 

vehicle emissions budgets are not being proposed for this pollutant. The proposed 2008 

and 2025 annual NOx and direct PM2.5 motor vehicle emissions budgets were 

developed consistent with the motor vehicle activity assumptions and emissions control 

strategies incorporated into the 8-hour ozone Attainment Demonstration and Maintenance 

Plan SIPs. The budgets reflect an emissions level determined using actual motor vehicle 

VMT for 2008 and VMT growth at an annual rate of 1.5% from year 2008 levels to 2025. 

A motor vehicle emissions budget is that portion of the total allowable emissions 

allocated to highway and transit vehicle use that are defined in the SIP for a certain year. 

The rules governing transportation conformity require certain transportation activities to 

be consistent with motor vehicle emissions budgets contained in control strategy 

implementation plans (40 CFR § 93.118). Section 93.101 of the rule defines a “control 

strategy [State] implementation plan revision” as a “plan which contains specific 

strategies for controlling the emissions and reducing ambient levels of pollutants in order 

to satisfy CAA requirements of reasonable further progress and attainment.” In order to 

demonstrate conformity to the motor vehicle emissions budget, emissions from the 

implementation of a transportation plan or a transportation improvement program must 

be less than or equal to the budget level (40 CFR § 93.118(a)).

The motor vehicle emissions budgets established and described herein were developed 

consistent with the methodology and control strategy assumptions in place in the region. 

The effects of motor vehicle control measures are incorporated into the emissions 

produced by the U.S. EPA’s MOVES model. These control measures include the 

implementation of national motor vehicle emissions standards, the operation of a vehicle 

inspection and maintenance (I/M) program, and the required use of reformulated gasoline 

and low sulfur gasoline and diesel fuel.

The U.S. EPA’s transportation conformity regulations allow for the use of a “safety 

margin” in the development of motor vehicle emissions budgets for Maintenance Plans. 

A safety margin is defined as “the amount by which the total projected emissions from all 

sources of a given pollutant are less than the total emissions that would satisfy the 
22

applicable requirement for reasonable further progress, attainment, or maintenance.” 

According to table 4.6, PM2.5 and NOx emissions for the end of the maintenance plan 

year 2025 are 2,484 and 118,437 tons per year, respectively, less than the year 2008 

attainment year levels. As year 2025 emissions levels are projected to be substantially 

less than the attainment year 2008 emissions, a 15% safety margin is being proposed to 

be added to the 2025 estimated motor vehicle emissions to make up the motor vehicle 

emissions budget. The 15% increase would equate to an increase of 310 tpy of PM2.5 and 

5,768 tpd of NOx. 

The motor vehicle emissions budgets, which reflect the VMT and control program 

assumptions and methodology described here, are listed in Table 5.1.

Table 5.1

Proposed Chicago PM2.5 Maintenance Plan

2008 and 2025

Motor Vehicle Emissions Budgets

(tons per year)

Estimated Emissions Safety Margin Motor Vehicle Emissions 

Budgets

Year PM2.5 NOx PM2.5 NOx PM2.5 NOx

2008 5,100 127,951 - - - - 5,100 127,951

2025 2,067 38,456 310 5,768 2,377 44,224

Complete details on the derivation of the motor vehicle emissions budgets, including 

discussion of the MOVES model inputs and assumptions are included in Appendix B of 

this report.
23

6.0 CONTINGENCY MEASURES

6.1 Contingency Measures

Section 175(A) of the CAA specifies the requirements for Maintenance Plans, including 

provisions for contingency measures that will be implemented if violations of the annual 

PM2.5 NAAQS are measured after redesignation to attainment. A list of potential 

contingency measures that would be implemented in such an event should also be 

included in the Maintenance Plan. Finally, the plan should provide a commitment to 

submit a revised Maintenance Plan eight years after redesignation to ensure continued 

maintenance for the next ten-year maintenance period.

Contingency measures are intended to provide further emissions reductions in the event 

that violations of the annual PM2.5 NAAQS occur after redesignation to attainment. 

While these measures do not need to be fully adopted by the Illinois Pollution Control 

Board (IPCB) prior to the occurrence of NAAQS violations, the contingency plan should 

ensure that the contingency measures are adopted expeditiously once they are triggered. 

The Maintenance Plan must identify the triggers that determine when contingency 

measures will be adopted, and the measures that the state will consider.

Illinois EPA’s contingency plan for the Chicago NAA is described in Table 6.1. 

Consistent with this plan, Illinois agrees to adopt and implement, as expeditiously as 

practicable, the necessary corrective actions in the event that violations of the annual 

PM2.5 NAAQS occur within the Chicago maintenance area after redesignation to 

attainment. As described in Section 5.0 of this report, Illinois has adopted and is 

continuing to implement a range of control measures that will greatly reduce precursor 

emissions, both locally and statewide. Illinois commits to continue to implement the 

identified control measures, although the Illinois EPA anticipates that these emissions

reductions will be sufficient to mitigate exceedances or violations of the NAAQS that 

may occur in the coming years without further regulatory action. 

The contingency plan provides for different levels of corrective responses should ambient

annual PM2.5 levels exceed the NAAQS in any year; if emissions in the NAA increase 

significantly above current attainment levels; or if the NAAQS is violated. A Level I 

response would occur in the event that: 1) the average of the annual PM2.5 concentration 

for the three most recent years at any monitoring site in the Illinois portion of the Chicago

NAA exceeds 15 micrograms per cubic meter, or 2) if total PM2.5, SO2 or NOx emissions 

increase more than 5% above the levels contained in the attainment year (2008) 

emissions inventory. If exceedances of the annual PM2.5 NAAQS are observed in Lake 

and Porter counties in Indiana, Illinois commits to work with the Indiana Department of 

Environmental Management (IDEM) to develop appropriate corrective measures. It 

should be noted that U.S. EPA does not require a state to implement contingency 

measures when occasional exceedances are recorded. The Illinois EPA’s voluntary 

commitment to initiate a Level I response is intended to prevent future violations of the 

NAAQS from ever occurring.
24

Table 6.1

Contingency Plan for the Chicago PM2.5 Nonattainment Area 

 

Contingency Measure 

Trigger Action to be Taken List of Potential Contingency Measures

Level I Trigger

Highest monitored 

PM2.5

concentration 

exceeding 15.0 

ug/m**3 in any 

year at any 

monitoring station 

in the Chicago

maintenance area.

The Chicago

maintenance area’s 

total PM2.5, NOx

or SO2 emissions 

increase more than 

5% above the 

levels included in 

the 2008 emissions 

inventories.

IL will evaluate air quality, or 

determine if adverse emissions trends 

are likely to continue. If so, IL will 

determine what and where controls 

may be required, as well as level of 

emissions reductions needed, to avoid a 

violation of the NAAQS. The study 

shall be completed within 9 months. If 

necessary, control measures shall be 

adopted within 18 months of

determination and implemented as 

expeditiously as practicable, taking into 

consideration the ease of 

implementation and the technical and 

economic feasibility of the selected 

measures. 

Point Source Measures

IL Multi-Pollutant Program for 

electric generating units

NOx RACT

Clean Air Transport Rule, after 

promulgation by U.S.EPA

Best Available Retrofit 

Technology (BART)

Broader geographic applicability 

of existing measures

Mobile Source Measures

Tier 2 Vehicle Standards and Low 

Sulfur Fuel

Heavy Duty Diesel Standards and 

Low Sulfur Diesel Fuel

High-enhanced I/M (OBDII)

Federal railroad/locomotive 

standards

Federal commercial marine vessel 

engine standards

Area Source Measures

Architectural/Industrial 

Maintenance (AIM) Coatings

Commercial and Consumer 

Products

Aerosol coatings

Portable fuel containers

Level II Trigger

A violation of the 

NAAQS at any 

monitoring station 

in the Chicago

maintenance area.

IL will conduct a thorough analysis to 

determine appropriate measures to 

address the cause of the violation. 

Analysis shall be completed within 6 

months. Selected measures shall be 

implemented within 18 months of a 

violation.

Illinois commits to compiling PM2.5, SO2, and NOx emissions inventories for the Chicago 

area every three years for the duration of the Maintenance Plan to facilitate the 

emissions trends analysis included in the contingency plan under Level I. The Illinois 

EPA will evaluate the causes of high PM2.5 levels or the emissions trends and to 

determine appropriate control measures needed to assure continued attainment of the 

annual PM2.5 NAAQS. Under Level I, measures that could be implemented in a short 

time would be selected so as to be in place quickly after the Illinois EPA is aware that 

corrective measures have been triggered. Control measures selected under Level I will be 

adopted in most cases within 18 months after a determination is made, and implemented, 

generally, within 24 months of adoption by the IPCB. 

A Level II response would be implemented in the event that a violation of the annual 

PM2.5 NAAQS were to be measured at a monitoring site within the Chicago maintenance 
25

area (including sites in Indiana and Illinois). In order to select appropriate corrective 

measures, the Illinois EPA will work with IDEM to conduct a comprehensive study to 

determine the causes of the violation and the control measures necessary to mitigate the 

problem. The analysis will examine the following factors:

the location and severity of the ambient PM2.5 exceedances;

the weather patterns contributing to the elevated PM2.5 levels;

potential contributing emissions sources;

the geographic applicability of possible contingency measures;

emissions trends, including timeliness of implementation of scheduled control 

measures;

current and recently identified control technologies; and

air quality contributions from outside the maintenance area.

Contingency measures will be selected from those listed in Table 6.1 or from any other 

measure deemed appropriate and effective at the time the selection is made. It is 

expected that implementation of only a few of these measures would be necessary. The 

selection between measures will be based upon cost-effectiveness, emissions reduction 

potential, ease and timing of implementation, and other appropriate factors. 

Implementation of necessary controls in response to a Level II trigger will take place as 

expeditiously as possible, but in no event later than 18 months after the Illinois EPA 

makes a determination, based on quality-assured ambient data, that a violation of the 

NAAQS has occurred.

Adoption of additional control measures is subject to necessary administrative and legal 

processes. The Illinois EPA will solicit input from all interested and affected persons in 

the area prior to selecting appropriate control measures. No contingency measure will be 

implemented without providing the opportunity for full public participation. This process 

will include publication of notices, an opportunity for public hearing, and other measures 

required by Illinois law.

6.2 Commitment to Revise Plan

As noted in Section 4.5 above, the Illinois EPA commits to review its Maintenance Plan 

eight years after redesignation, as required by Section 175(A) of the CAA. The 

Maintenance Plan revision is intended to ensure continued attainment of the annual PM2.5

NAAQS for an additional ten-year period.

6.3 Public Participation

In accordance with Section 110(a)(2) of the CAA, Illinois is required to have a public 

comment period and provide the opportunity for a public hearing on the Maintenance 

Plan prior to adoption. Public participation in the SIP process is provided for as follows:
26

Notice of availability of the Chicago PM2.5 Maintenance Plan document and the 

time and date of the public hearing was published in the Chicago Sun-Times on 

July 8, 2011.

If requested, the public hearing to receive comments on the Chicago Maintenance 

Plan was scheduled for August 18, 2011, at 1:00 p.m. in the Sangamo Room at 

the Illinois EPA’s Headquarters at 1021 N. Grand Ave. East, Springfield, Illinois. 

A 30-day public comment period was open after the public hearing to receive 

comments on the Maintenance Plan. A summary of the comments received and 

Illinois EPA’s responses thereto is included as part of the submittal to U.S. EPA.

6.4 Legal Authority to Implement and Enforce

The Maintenance Plan must contain a demonstration that the State of Illinois has the 

necessary legal authority to implement and enforce the measures relied upon to attain and 

maintain the NAAQS. Illinois has the legal authority to implement and enforce the 

requirements of this SIP submittal pursuant to the Illinois Environmental Protection Act.
27

7.0 CONCLUSIONS

The Chicago nonattainment area has attained the 1997 annual PM2.5 NAAQS and has 

complied with the applicable provisions of the CAA required of PM2.5 NAAs. Illinois 

has performed an analysis that demonstrates that the Chicago NAA has attained the 1997 

annual PM2.5 NAAQS and believes the air quality improvements are due to permanent 

and enforceable control measures. Supporting documentation is contained herein.

The Illinois EPA has prepared a Maintenance Plan that meets the requirement of the 

Clean Air Act. This Maintenance Plan provides for the continued attainment of the 1997 

annual PM2.5 NAAQS for a period of at least ten years after U.S. EPA has formally 

redesignated the area to attainment. This Maintenance Plan provides adequate 

contingency measures for potential, additional emissions reductions in the event that 

future violations of the 1997 annual PM2.5 NAAQS are observed in the area. 

The Illinois EPA has prepared a comprehensive emissions inventory of PM2.5 and its

precursors for the “attainment” year, 2008, and has prepared projections of the emissions

inventory to 2015, 2020 and 2025. These emissions projections indicate that emissions 

levels in the Chicago nonattainment area will continue to remain much lower than 

emissions from the attainment year 2008 levels, thereby maintaining the PM2.5 NAAQS 

in future years. The Illinois EPA commits to continue to operate an appropriate air 

quality monitoring network to verify the maintenance of the attainment status once the 

area has been redesignated. The Illinois EPA has the legal authority to implement and 

enforce all control measures.

Finally, the Chicago PM2.5 Maintenance Plan includes year 2008 and 2025 on-road motor 

vehicle emissions budgets for PM2.5 and NOx for use in transportation conformity 

determinations to assure that any increases in emissions from this sector do not 

jeopardize continued attainment of the annual PM2.5 standard during the ten-year 

maintenance period. The Chicago Maintenance Plan has been prepared in accordance 

with the requirements specified in U.S. EPA’s guidance document, and additional 

guidance received from U.S. EPA staff.
28

APPENDIX A

Summary of Ambient Air Monitoring Data 

(2007-2009)
29

Table A.1

2007-2009 Annual PM2.5 Design Values 

for Monitors in the Chicago Nonattainment Area

*- Annual Standard does not apply at these monitoring sites

Annual averages listed in underlined italics based on incomplete data.

County Monitoring Site 2007 2008 2009 Design 

Value

Cook Blue Island 14.3 12.5 11.7 12.8

Cook Chicago-Com Ed 14.3 11.9 11.1 12.4

Cook Chicago-Springfield 15.2 12.0 11.3 12.8

Cook Chicago-Mayfair 15.5 12.2 12.7 13.5

Cook Chicago-SE Police 14.1 11.8 11.0 12.3

Cook Chicago-Washington 15.7 12.5 11.6 13.3

Cook Cicero 14.8 13.3 12.0 13.4

Cook Des Plaines 12.7 11.4 11.0 11.7

Cook McCook* 15.6 12.9 12.6 13.7

Cook Northbrook 13.2 10.1 9.3 10.9

Cook Schiller Park* 15.4 13.6 12.9 14.0

Cook Summit 14.8 12.0 11.6 12.8

Du Page Naperville 13.8 11.3 9.8 11.6

Kane Aurora 14.5 10.3 10.0 11.6

Kane Elgin 13.2 10.8 9.6 11.2

Lake Zion 11.9 9.3 8.8 10.0

McHenry Cary 11.6 10.1 9.6 10.4

Will Braidwood 12.1 10.3 8.7 10.4

Will Joliet 14.6 11.7 10.5 12.3

Lake IN Franklin School 14.4 12.0 11.3 12.6

Lake IN Griffith 13.2 11.7 11.0 12.0

Lake IN Madison St. 14.6 12.3 12.1 13.0

Lake IN Hammond-Purdue 13.8 11.7 15.9 13.8

Lake IN Clark HS 13.7 12.4 10.8 12.3

Porter IN Ogden Dunes 13.8 10.9 11.3 12.0
30

APPENDIX B

Transportation Conformity
31

TRANSPORTATION CONFORMITY

This section describes the development of the Chicago NAA motor vehicle emissions 

budgets associated with the PM2.5 Maintenance Plan SIP. Annual motor vehicle 

emissions budgets are being proposed for the attainment year, 2008, and 2025, the final 

year of the initial maintenance period for direct motor vehicle PM2.5 emissions and for the 

precursor pollutant NOx. These budgets were developed consistent with the motor 

vehicle activity assumptions and emissions control strategies incorporated into the PM2.5

maintenance plan analysis. 

Background

Section 176(c)(4) of the Clean Air Act (CAA) Amendments of 1990 requires that 

transportation plans, programs, and projects which are funded or approved under Title 23 

USC must be determined to conform with State or Federal air implementation plans. A 

motor vehicle emissions budget is that portion of the total allowable emissions allocated 

to highway and transit vehicle use that are defined in the SIP for a certain year. Section 

93.101 of the rule defines a “control strategy [State] implementation plan revision” as a 

“plan which contains specific strategies for controlling the emissions and reducing 

ambient levels of pollutants in order to satisfy CAA requirements of reasonable further 

progress and attainment.” In order to demonstrate conformity to the motor vehicle 

emissions budget, emissions from the implementation of a transportation plan or a 

transportation improvement program (TIP) must be less than or equal to the budget level 

(40 CFR § 93.118(a)).

Transportation conformity will be based on these submitted on road motor vehicle 

emissions budgets after the U.S. Environmental Protection Agency (“U.S.EPA”) 

determines that the budgets meet the adequacy criteria of the transportation conformity 

rule under §93.118(e). The motor vehicle emissions budgets in this submittal are 

adequate as each of the six criteria under §93.118(e) is satisfied. These six criteria 

include:

1. The submitted control strategy implementation plan revision or maintenance plan was 

endorsed by the Governor (or his or her designee) and was subject to a State public 

hearing.

2. Before the control strategy implementation plan or maintenance plan was submitted 

to EPA, consultation among federal, State, and local agencies occurred: full 

implementation plan documentation was provided to [US]EPA; and [US]EPA’s 

stated concerns, if any, were addressed;

3. The motor vehicle emissions budgets(s) is clearly identified and precisely quantified;

4. The motor vehicle emissions budget(s), when considered together with all other 

emission sources, is consistent with all applicable requirements for reasonable further 
32

progress, attainment, or maintenance (whichever is relevant to the given 

implementation plan submission);

5. The motor vehicle emissions budget(s) is consistent with and clearly related to the 

emissions inventory and the control measures in the submitted control strategy 

implementation plan revision or maintenance plan, and

6. Revisions to previously submitted control strategy implementation plans explain and 

document any changes to previously submitted budgets and control measures, 

impacts on point and area source emissions; any changes to established safety 

margins; and reasons for the changes (including the basis for any changes related to 

emission factors or estimates of vehicle miles traveled).

The PM2.5 attainment demonstration SIP and the associated motor vehicle emissions 

budgets have been developed by the Illinois Environmental Protection Agency (Illinois 

EPA), the designated air quality agency for the State of Illinois. The required public 

hearing to accept public comment on the proposed motor vehicle emissions inventory 

was held at 1:00 PM, on July 14, 2010 in Room 9-040 of the James R. Thompson Center 

in downtown Chicago. Notification of this hearing was printed in the Chicago Sun Times 

on June 11, 2010. Comments on the proposed attainment demonstration and motor 

vehicle emissions budgets were accepted for 30 days after the public hearing. A 

“Responsiveness Summary” which addresses the comments received was included in the 

final submission.

Regarding this revision to the Chicago PM2.5Maintenance Plan, notice of a comment 30-

day comment period was posted on the Illinois EPA’s website and printed in the Chicago 

Sun Times on July 8, 2011. A public hearing to discuss the revised Maintenance Plan 

and associated motor vehicle emissions budgets was to be held on August 18, 2011, if it 

was requested. Comments were required to be postmarked by August 8, 2011, unless a 

public hearing was requested. No request for a public hearing was received. All 

comments were addressed in the attached Responsiveness Summary. None of the 

comments affected the proposed motor vehicle emissions budgets.

In compliance with adequacy criterion #2, an interagency consultation meeting was held 

with members of the Chicago Metropolitan Agency for Planning (CMAP) Tier 2 

Consultation Team on June 25, 2010 in Chicago. At this meeting, the Illinois EPA 

representative discussed the requirements for the maintenance plan as they relate to 

transportation conformity and explained the derivation of the proposed motor vehicle 

emissions budgets. A follow-up meeting of the Tier 2 Conformity Consultation Team to 

discuss the revised MOVES-based motor vehicle emissions budgets was held at the 

CMAP offices on June 28, 2011.

Compliance with the remaining adequacy criteria is contained within the narrative of the 

attainment demonstration document and this transportation conformity section.

The motor vehicle emissions budgets proposed and described herein were developed 

consistent with the methodology and control strategy assumptions used in the 
33

development of the emissions estimates contained in the Chicago PM2.5 Maintenance 

Plan. The effects of these controls are incorporated into the emissions inventory 

estimates generated by the U.S.EPA’s MOVES2010 (MOVES) model. Following is a 

discussion of the inputs and assumptions used in the development of the motor vehicle 

emissions budgets.

Vehicle Miles Travelled: The attainment year 2008 motor vehicle emissions estimates 

contained Chicago PM2.5 Maintenance Plan incorporate county-and township-level 2008

annual vehicle miles traveled (VMT) levels from the Illinois Department of 

Transportation (IDOT). The 2008 annual VMT total for the 6-county-3-township 

Chicago NAA was approximately 58.8 billion miles. For future year emission estimates, 

VMT was grown to the target year at a compound growth rate of 1.5% per year. 

Applying this growth factor to the 2008 VMT level yields future year annual VMT 

projections of 65.2 billion for 2015, 70.3 billion for 2020, and 75.7 billion for 2025.

Meteorological Data: U.S. EPA guidance for the use of the MOVES model 

requires the use of representative local temperature and absolute humidity data. Average 

2008 maximum and minimum monthly temperatures for the region were obtained from 

the National Weather Service local climatological data (LCD) for O’Hare International 

Airport. Absolute humidities corresponding to the average temperatures were calculated 

from LCD information as well. These 2008 temperatures and absolute humidity values, 

shown below, were used in the year 2025 emissions modeling.

Motor Vehicle Emissions Controls: Beyond the U.S. EPA’s federal motor vehicle 

control program emissions standards, the primary local motor vehicle emissions control 

programs that were in place in the Chicago NAA in 2008, and are projected to still be 

required in 2025 are a vehicle inspection and maintenance (I/M) program and the 

required use of reformulated gasoline (RFG).

Inspection and Maintenance (I/M): The Illinois I/M program in effect since 

2007 requires biennial On-Board Diagnostics II (OBD) testing on all model year (MY) 

1996 and newer (MY96+) light-duty gasoline vehicles (cars and light-duty trucks), and 

biennial exhaust idle and gas cap testing on MY96+ heavy duty gasoline vehicles 

including gasoline-powered buses, registered in the I/M testable area. Motorcycles and 

diesel vehicles are not subject to I/M. The program includes a 4-year grace period for 

new vehicles. This post-2007 I/M program was established when the Illinois legislature 

Month Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec

Min, (oF) 15 16 27 39 45 61 64 64 57 47 32 14

Max, (oF) 32 30 43 60 66 81 84 82 75 62 46 32

Month Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec

AH, grains/lb 17 14 21 34 41 73 83 74 71 39 25 15

2008 Minimum and Maximum Temperatures for Chicago, from O'Hare NWS Data

2008 Absolute Humidity Corresponding to the Temperatures Above
34

amended the Illinois Vehicle Inspection law in 2005 to (a) end dynamometer testing of 

vehicles, (b) require an OBD-based program beginning in February 2007, and (c) remove 

the requirement for testing compliant pre-MY96 vehicles. 

The Chicago I/M program vehicle testing domain includes the urbanized areas in the 

Chicago NAA. An “I/M Coverage” percentage was developed based on the amount of 

VMT from vehicles subject to the inspection program compared to total area VMT. The 

I/M Coverage percentage for the Chicago 8-hour ozone NAA is 91.5%. 

Fuels: The use of federal RFG has been required in the Chicago NAA since 

1995. The 8-hour ozone Attainment Demonstration and original Maintenance Plan 

assumed the use of northern grade RFG in 2008 and beyond. RFG was and is assumed to 

contain 10% ethanol. The MOVES model can account for other fuels, such as E85, 

natural gas, methanol, etc, but for all practical purposes the gallons of such alternative 

fuels and hence the number of vehicles using them is very small compared to the number 

of gasoline and diesel vehicles, therefore, the use of such fuels was not considered.

Gasoline Sulfur: The federal Tier 2 regulations require gasoline sulfur levels to 

average no greater than 30 parts per million (ppm) with a maximum of 80 ppm 

beginning in 2007. There are no Illinois gasoline sulfur requirements, therefore, 

the MOVES default gasoline sulfur levels were used in the emissions modeling. 

Diesel Sulfur: The federal Tier 2 regulations limit the level of sulfur in diesel 

fuel requiring on- highway diesel fuel to 15 ppm beginning in 2006. There are no 

Illinois diesel sulfur requirements, therefore, the MOVES default diesel sulfur 

levels were used in the emissions modeling. 

Fuel Volatility: The volatility of summer RFG, measured as Reid vapor pressure 

(RVP), is not specifically regulated. However, a fuels’ RVP is one of the primary 

characteristics controlled by refiners in order to meet the RFG performance 

standards. The MOVES model contains default RVP levels for different seasons 

of the year based on fuel compliance testing. Therefore, the MOVES default 

RVP levels were used in the emissions modeling. 

Vehicle Registration Distribution: A Chicago area-specific vehicle registration 

distribution (RD) profile based upon 2008 information data was developed by Illinois 

EPA’s Division of Mobile Source Programs from vehicle age data for 2008 provided by 

the Illinois Secretary of State’s Department of Motor Vehicles. The RD is the fraction of 

vehicles of a given vehicle type and age in the fleet of vehicles of that type as a whole. 

Different vehicle types have different RDs Chicago-area RDs generally show fewer 

older vehicles than the nationwide average or default, because vehicles in the Chicago 

area tend to wear out faster than they do in the rest of the country due to rust from road 

salt and heavy city driving. 
35

Source Type Population represents the number of vehicles of each MOVES vehicle type 

in the fleet as a whole within the area under consideration. Accurate local source-type 

populations were not available; therefore the MOVES default fractions modified by 

VMTs by vehicle type were used.

VMT Temporal Fractions are the VMT fractions of annual VMT by month of the year, 

of weekly VMT by day of the week, and daily VMT by hour of the day. The Illinois 

EPA uses temporal fractions derived from data collected from continuous count stations 

and presented by IDOT. Temporal fractions vary by road type.

Speed distributions are the fractions of VMT on a given road type by given vehicle 

types in various speed ranges (bins). Thus, on a typical Urban Arterial, a small fraction 

of the vehicles are traveling at less than 10 mph (plus or minus 5 mph), more at 20 mph, 

more at 30mph, most at 40 mph, less at 50 mph, and so on. These fractions differ by 

hour of the day—in more congested conditions during rush hours, the maximum fraction 

might be in the 30 mph range rather than the 40 mph range. MOVES uses speed 

distributions when aggregating emissions (or emission rates) for vehicles at different 

speeds. The Illinois EPA used the speed distributions derived from the CMAP 

transportation demand model.

Ramp fraction is the fraction of total VMT on limited-access highways such as 

Interstates that is from on- and off-ramps to or from those highways. Driving on limitedaccess highways is more or less at uniform speed, but driving on ramps involves 

considerable acceleration and deceleration; and these speed changes affect emissions. 

The default MOVES Ramp Fractions are 15% on Rural Interstates, 10% on Urban 

Interstates, and 2% on Other Freeways and Expressways. Illinois does not have actual or 

observed Ramp Fraction data; therefore the MOVES default values were used.

Road Type Distribution is the (fraction of) VMT on different road categories within an 

area under consideration. The Illinois EPA uses VMT data by HPMS functional class 

(FC) published by IDOT as the basis of its emission calculations. The Road Type 

Distribution for Rural Interstates in a county is the county’s Rural Interstate VMT 

divided by the county’s total all-road-type VMT. Similar calculations can be made for 

MOVES road types and vehicle types.

Safety Margin: The U.S. EPA’s transportation conformity regulations allow for the 

use of a safety margin in the development of motor vehicle emissions budgets for 

Maintenance Plans. A Safety Margin is defined as “the amount by which the total 

projected emissions from all sources of a given pollutant are less than the total emissions 

that would satisfy the applicable requirement for reasonable further progress, attainment, 

or maintenance.” According to table 4.6, PM2.5 and NOx emissions for the end of the 

maintenance plan year 2025 are 2,484 and 118,437 tons per year, respectively, less than 

the year 2008 attainment year levels. As year 2025 emissions levels are projected to be 

substantially less than the attainment year 2008 emissions, a 15% safety margin is being 

proposed to be added to the 2025 estimated motor vehicle emissions to make up the 

motor vehicle emissions budget. The 15% increase would equate to an increase of 310 

tpy of PM2.5 and 5,768 tpd of NOx. 
36

The motor vehicle emissions budgets, which reflect the VMT, motor vehicle fleet 

characteristics, emissions and control program assumptions, and safety margin described 

herein, are identified below.

Proposed Chicago PM2.5 Maintenance Plan

2008 and 2025

Motor Vehicle Emissions Budgets

(tons per year)

Estimated Emissions Safety Margin Motor Vehicle Emissions 

Budgets

Year PM2.5 NOx PM2.5 NOx PM2.5 NOx

2008 5,100 127,951 - - - - 5,100 127,951

2025 2,067 38,456 310 5,768 2,377 44,224