MEMORANDUM:

From: Suzanne Rudzinski, Director

Transportation and Regional Programs Division

Office of Transportation and Air Quality

Lydia Wegman, Director

Air Quality Strategies and Standards Division

Office of Air Quality Planning and Standards

To: EPA Regional Air Directors, Regions I - X

Subject: Guidance for Determining the “Attainment Years” for Transportation Conformity

in New 8-Hour Ozone and PM2.5 Nonattainment Areas.

The attached document provides guidance for 8-hour ozone and PM2.5 nonattainment areas in

selecting attainment dates for use in transportation conformity determinations both before and

after state implementation plans (SIPs) are submitted. This guidance also describes some

flexibilities that are available to areas using interim emission or budget tests in choosing which

years to perform a regional emissions analysis and applies to all 8-hour ozone and PM2.5

nonattainment areas. We request that you share this guidance with the States.

The Clean Air Act requires areas to attain the national ambient air quality standards as

expeditiously as practicable, but no later than specified dates. To demonstrate attainment, an

area must predict that emissions during the “season” preceding the attainment date will meet the

level of the standard. Ozone pollution is a problem during the hotter months of the year and for

most areas the ozone season runs from mid-spring to mid-fall, although for some warm-weather

areas (e.g., certain areas in Texas and California), the ozone season runs all year. For PM2.5, the

season is the entire year. In general, the attainment dates for 8-hour ozone are in June. Thus, the

relevant ozone season for predicting attainment will be the ozone season in the calendar year

preceding the attainment date. Similarly, the attainment dates for PM2.5 will be in April, so the

relevant PM2.5 season for predicting attainment will also be in the preceding calendar year. 

Because the maximum attainment dates fall relatively early in the calendar year, the final season

considered for purposes of attainment will fall in the preceding calendar year for those areas that

need the maximum time frame to attain. This situation is different than the situation created by

the 1-hour ozone standard and PM10 standard following enactment of the Clean Air Act

Amendments of 1990. The Amendments established attainment dates near the end of the relevant

ozone and PM10 seasons and thus the maximum attainment date fell within the same year as the

final season considered for purposes of attainment. Thus, the confusion some areas have had
about which calendar year to analyze as their attainment year for transportation conformity

purposes did not arise for purposes of the 1-hour ozone and PM10 standard. 

Finally, many areas designated nonattainment for the 8-hour ozone standard also have existing 1-

hour ozone budgets which they will be required to use and which bring with them their own

requirements for analysis years in transportation conformity determinations. EPA is issuing the

attached guidance to provide clarification on these issues. 

The guidance indicates that if there are further questions, the States should contact the

transportation conformity staff person responsible for the state at the appropriate EPA regional

office. A listing of regional offices, the states they cover, and contact information for EPA

regional conformity staff can be found at the following website:

http://www.epa.gov/otaq/transp/conform/contacts.htm.

General questions about this guidance can be directed to Joe Pedelty at EPA’s Office of

Transportation and Air Quality, via his email address: pedelty.joe@epa.gov or phone number:

734-214-4410. 
Air and Radiation EPA420-B-05-002

March 2005

Guidance for Determining

the “Attainment Year” for

Transportation Conformity in

New 8-Hour Ozone and PM2.5

Nonattainment Areas
EPA420-B-05-002

March 2005

Guidance for Determining the “Attainment Year” for

Transportation Conformity in New 8-Hour Ozone and

PM2.5 Nonattainment Areas

Transportation and Regional Programs Division

Office of Transportation and Air Quality

U.S. Environmental Protection Agency
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Guidance for Determining the “Attainment Year” for Transportation Conformity in New

8-Hour Ozone and PM2.5 Nonattainment Areas.

I. Background Information

The purpose of this guidance is to explain what year is to be an area’s attainment year for

the purpose of transportation conformity in the new 8-hour ozone and PM2.5

nonattainment areas, both before and after state implementation plans (SIPs) are

submitted. This guidance also describes some flexibilities that are available to areas

using interim emission or budget tests in choosing which years to perform a regional

emissions analysis.

1. Q. How is this guidance organized?

A. This document is organized by questions and answers under the following headings:

I. Background Information (Questions 1 - 5)

II. Conformity Requirements

A. Areas With Adequate or Approved Budgets for the 8-Hour Ozone or

PM2.5 Standards (Question 6)

B. 8-Hour Ozone Nonattainment Areas with 1-Hour Ozone SIP Budgets 

(Question 7)

C. 8-Hour Ozone Nonattainment Areas With No Existing Adequate or

Approved Budgets and PM2.5 Nonattainment Areas (Questions 8 -

9).

III. General Information

A. Does this Guidance Create New Requirements? (Question 10)

B. Who to Contact for More Information (Question 11).

2. Q. To which areas does this guidance apply?

A. This guidance applies to all 8-hour ozone and PM2.5 nonattainment areas. We note

that the effective date of the nonattainment designation for early action compact (EAC)

areas has been deferred. EAC areas are not subject to transportation conformity for the

8-hour ozone standard unless and until an 8-hour designation of nonattainment becomes

effective. 

3. Q. Why is this guidance document needed?

A. The purpose of this guidance is to clarify which calendar years an area must use to

analyze as their attainment year for transportation conformity. The CAA requires areas

to attain the relevant standards by the area’s maximum attainment date. For purposes of

the 8-hour ozone standard and the PM2.5 standard, a determination of attainment after the
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attainment date has passed is based on the most recent three complete years of data prior

to the area’s attainment date. Thus, where an area has a maximum attainment date in

April (for PM2.5) or June (for 8-hour ozone), the most recent three years of data will be

from the three preceding calendar years. For example, if an area’s maximum attainment

date is April or June of 2010, then air quality monitoring data from 2007, 2008 and 2009

would be considered for the purpose of determining whether the area has met its

attainment date. Moreover, for purposes of predicting attainment of the standard through

a modeling demonstration, states would need to predict that air quality in the last ozone

or PM2.5 “season” (i.e., 2009) would meet the standard. For that reason, EPA’s

implementation rule for the 8-hour ozone standard requires areas to implement all the

measures necessary to demonstrate attainment as expeditiously as practicable, but no

later than the start of the final complete ozone season preceding the area’s attainment

date (40 CFR §51.908). We anticipate that the implementation rule for the PM2.5

standard will have a similar requirement. 

This situation is different from the situation created by the 1-hour ozone and PM10

standard, where areas had a maximum attainment date in November. For 1-hour

ozone and PM10, the final season considered for purposes of demonstrating or

determining attainment was in the same calendar year as the attainment date. 

Because the maximum attainment date for 8-hour ozone and PM2.5 is not in the

same calendar year as the final season that must be considered for purposes of

ascertaining attainment, there has been some confusion regarding which calendar

year areas should use for purposes of transportation conformity. 

4. Q. What are the maximum attainment dates for 8-hour ozone areas?

A. The maximum attainment dates for 8-hour ozone areas are as follows. 

Subpart 1 (“Basic”) - June 15, 2009

Marginal - June 15, 2007

Moderate - June 15, 2010

Serious - June 15, 2013

Severe 15 - June 15, 2019

Severe 17 - June 15, 2021

These dates stem from CAA section 172(a)(2) and EPA’s regulations at 40 CFR

§51.904(b) for “Basic” areas and from CAA section 181(a)(1) and (2) and EPA’s

regulations at 40 CFR §51.903(a) for subpart 2 (marginal and above) areas.

5. Q. What are the attainment dates for the PM2.5 areas?

A. The effective date for PM2.5 designations is April 5, 2005. SIPs will be due in April

2008, 3 years from the date of designation. Per CAA section 172(a)(2), all PM2.5

nonattainment areas will have an initial maximum statutory attainment date of April 5,

2010.
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II. Conformity Requirements

A. Areas With Adequate or Approved Budgets for the 8-Hour Ozone or PM2.5 Standards

6. Q. What attainment year will areas use for conformity once motor vehicle emission

budgets from an attainment demonstration SIP addressing the 8-hour ozone or PM2.5

standard are adequate or approved?

A. Once an 8-hour ozone or PM2.5 attainment demonstration SIP is submitted and the

motor vehicle emissions budgets (“budgets”) are found adequate or approved, the SIP

will establish the attainment year that is used for conformity determinations. The

attainment year established by the SIP will be, at the latest, the calendar year of the final

season for determining attainment, which in the case of 8-hour ozone and PM2.5, will

generally be in the calendar year before the area’s maximum attainment date. Areas must

consider the attainment year established in the SIP as the attainment year for

demonstrating consistency and conducting conformity analyses as required by §93.118(b)

and (d) respectively of the conformity rule.

B. 8-Hour Ozone Nonattainment Areas with 1-Hour Ozone SIP Budgets

7. Q. What attainment year should be used for conformity before 8-hour ozone budgets are

found adequate or 8-hour ozone SIPs are approved?

A. 8-hour ozone nonattainment areas that have 1-hour ozone budgets are, in most cases,

subject to the regional emissions analysis requirements in §93.118 of the conformity rule.

(See §93.109(e)(2)(iv) and (v) for limited exceptions.) Prior to adequate or approved 8-

hour budgets in these areas, the attainment year that should be used for conformity to

meet §93.118 requirements for the 8-hour standard depends on an area’s 8-hour ozone

classification, as follows:

“Basic”, Moderate, Serious and Severe 8-Hour Ozone Areas

All “Basic”, moderate, serious and severe 8-hour ozone nonattainment areas that have 1-

hour ozone budgets have an option for addressing the conformity rule’s requirements to

demonstrate consistency (§93.118(b)) and to conduct a conformity analysis (§93.118(d))

for their 8-hour ozone attainment year. 

Specifically, before an 8-hour ozone SIP is adequate or approved, EPA believes that

these areas may consider either of the following to be the attainment year for the

purposes of §93.118:

• the year of the maximum attainment date or 

• the year prior to the maximum attainment date. 
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For example, a moderate area that has 1-hour ozone emissions budgets may perform a

regional emissions analysis and demonstrate consistency for either 2010, which is its

maximum attainment date, or 2009, which is the last possible year for which there will be

a full ozone season to consider for purposes of demonstrating attainment. 

These areas have a choice because prior to the development of the 8-hour SIP, no area

knows for certain its 8-hour ozone attainment date because the CAA requires that areas

attain “as expeditiously as practicable”(CAA section 172(a)(2)(A)). A date “as

expeditiously as practicable” cannot be known until an attainment demonstration is

completed. Therefore, it would be premature for EPA to require areas to use as their

attainment year in conformity any year earlier than the year in which the maximum

attainment date falls. EPA has historically interpreted the conformity regulations to

allow areas to presume that the attainment year will be the calendar year of the maximum

attainment date prior to the development of an attainment SIP and determination of the

actual attainment date. Based on this interpretation, areas that have already begun their

conformity analysis using the calendar year of the maximum attainment date may

complete their analysis using that date. 

As an alternative to the maximum attainment date, areas may, instead, analyze the year

prior to the maximum attainment date to satisfy the conformity requirement in §93.118 in

anticipation that the prior year will be the year for which the SIP will demonstrate

attainment and will be the year in which the final season considered for purposes of

determining attainment occurs. EPA acknowledges that in some areas the year prior to

the maximum attainment date may not be the final attainment year as the CAA requires

that attainment be reached as expeditiously as practicable. Therefore, an area’s ultimate

attainment date could be even earlier because areas cannot anticipate what their modeled

attainment demonstrations may conclude. It is appropriate for areas to rely on either the

calendar year of the maximum attainment date or the calendar year preceding the

maximum attainment date. 

Areas that have not yet begun their conformity analysis may choose to use the year prior

to their statutory attainment date as the attainment year for conformity purposes with the

assumption that this will be the attainment year determined by the SIP. By doing so, they

may complete some of the analysis that is required for future conformity determinations

(e.g., model development, data collection) and avoid analyzing a year that is not required

in future conformity determinations provided that the assumed attainment year does not

change during SIP development.

For example, a moderate 8-hour ozone nonattainment area, which has a maximum

attainment date of June 15, 2010, has 1-hour rate of progress (ROP) budgets for NOx and

VOCs established for the year 2005 and attainment budgets for NOx and volatile organic

compounds (VOCs) established for the year 2007. This area wants to perform an 8-hour

ozone conformity determination in 2005, prior to the development of its attainment

demonstration, for its 2005 - 2025 transportation plan. The conformity determination
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would need to show consistency with budgets (per §93.118(b)) for the following years:

• 2005, using the 1-hour ozone 2005 ROP budgets;

• 2007, using the 1-hour 2007 ozone attainment budgets;

• either 2009 or 2010 (8-hour ozone attainment year) budget test using the 1-hour

ozone 2007 maintenance budgets;

• 2015, (interim year) using the 1-hour ozone 2007 attainment budgets; and

• 2025, (last year of the transportation plan) using the 1-hour ozone 2007

attainment budgets.

For this conformity determination the area would need to perform regional emissions

analyses (per §93.118(d)) for the following years:

• 2005;

• either 2009 or 2010 (8-hour ozone attainment year);

• 2015 (interim year); and

• 2025 (the last year of the transportation plan).

Emissions estimates for the year 2007 can be generated by interpolating between years in

which a regional emissions analysis has been performed - in this case, between the years

2005 and, 2009 or 2010.

Marginal 8-Hour Ozone Areas

Marginal 8-hour ozone areas with 1-hour ozone budgets may use the year of their

maximum attainment date (2007) as the attainment year in their conformity

determinations. Alternatively, these areas may also assume the year 2006 as their

attainment year since the ozone season in 2006 would be the third ozone season (2004,

2005, 2006) considered for purposes of determining whether the area attained the 8-hour

ozone standard by the area’s maximum attainment date of June 2007. 

Because they are not required to submit an attainment demonstration, marginal areas may

choose either 2006 or 2007 as their attainment year for conformity purposes. Also, given

the short time prior to their maximum statutory attainment date, these areas are not likely

to establish an attainment year before 2006 or 2007. In cases where a marginal area

without an attainment demonstration analyzes 2006 as its attainment year for conformity

purposes, it should state why it has done so.

For example, a marginal 8-hour ozone area has 1-hour ozone NOx and VOC maintenance

budgets established for the years 2003 and 2013. The area wants to determine

conformity in 2005, prior to the development of an 8-hour ozone SIP, for its 2005 - 2025

transportation plan. For this conformity determination the budget test requirements

(§93.118(b)) would be satisfied by showing consistency for the following years:

• either 2006 or 2007 (assumed attainment year) using the 2003 1-hour ozone

maintenance plan budgets;

• 2013 (budget year) using the 2013 1-hour ozone maintenance budgets;

• 2015 (interim year) budget test using the 2013 1-hour ozone maintenance
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budgets;

• 2025 (last year of the transportation plan) using 2013 1-hour ozone maintenance

budgets. 

For this determination the area would need to perform regional emissions analyses (per

§93.118(d)) for the following years:

• either 2006 or 2007 (8-hour ozone attainment year);

• 2015 (interim year); and

• 2025 (the last year of the transportation plan).

In this example, emissions estimates for the year 2013 could be generated by

interpolating between years in which a regional emissions analysis has been performed -

in this case, between the years 2006 or 2007, and 2015.

In the case where a marginal area chooses to perform an attainment demonstration, the

date determined by that demonstration would then become the attainment year for

transportation conformity purposes.

C. 8-Hour Ozone Areas with No Existing Adequate or Approved Budgets and PM2.5

Nonattainment Areas

8. Q. What are the conformity analysis year requirements for areas with no adequate or

approved budgets?

A. Nonattainment areas that do not have any adequate or approved budgets are not

required to demonstrate conformity and perform a regional emissions analysis for their

attainment year. Under §93.119(g)(1) of the conformity rule, nonattainment areas using

interim emission tests are required to perform a regional emissions analysis for only the

following years:

• a year no more than five years beyond the year in which the conformity

determination is being made;

• the last year of the transportation plan’s forecast period; and

• any additional years within the time frame of the transportation plan so that

analysis years are no more than ten years apart.

9. Q. Before a SIP is found adequate or approved, what year should be analyzed as the year

no more than five years beyond the year in which the conformity determination is being

made?

A. Areas are free to choose any analysis year that is not more than five years into the

future from the year in which the conformity determination is made. However, EPA

notes that selecting the calendar year of the final season that will be considered for

purposes of demonstrating attainment, if it is within the first five years from the

conformity determination date, may have certain benefits. For example, selecting the
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final ozone season calendar year may save work and valuable state and local resources

once a SIP has been submitted. In this case, the areas may be able to complete some of

the analysis (e.g., model development, data collection) that is needed for future

conformity determinations, should that year be selected as the attainment year in the SIP.

Examples:

An 8-hour basic ozone nonattainment area has a maximum attainment date of June 15,

2009. The area has no 1-hour ozone budgets and plans to make a conformity

determination in 2005 to update its 2005 - 2025 transportation plan. This area could

select the following analysis years to meet the conformity rule’s interim emission test

requirements in §93.119 for the 8-hour ozone standard:

2008 - near term year (within the first five years) and possible attainment date

determined by the SIP;

2015 - intermediate year so that the analysis years are no more than 10 years

apart;

2025 - last year of the transportation plan.

A PM2.5 nonattainment area has a maximum attainment date of April 5, 2010. The area

wants to make a conformity determination in 2005 for its upcoming 2006 - 2030

transportation plan. To meet the conformity rule’s interim emission tests requirements in

§93.119 for PM2.5 the area could analyze the following years:

2009 - near term year (within the first five years) and possible attainment date

determined by the SIP;

2015 - intermediate year so that analysis years are no more than ten years apart;

2025 - intermediate year so that analysis years are no more than ten years apart;

2030 - last year of the transportation plan.

III. General Information

10. Q. Does this guidance create new requirements?

A. No, this guidance is based on the existing Clean Air Act (CAA) and associated

regulations and does not create any new requirements. It merely explains how to fulfill

the conformity rule’s requirement to analyze the attainment year in 40 CFR §93.118,

given the attainment dates for the new 8-hour ozone and PM2.5 standards.

The statutory provisions and EPA regulations described in this document contain legally

binding requirements. This document does not substitute for those provisions or

regulations, nor is it a regulation itself. Thus, it does not impose legally binding

requirements on EPA, states, or the regulated community, and may not apply to a

particular situation based upon the circumstances. EPA retains the discretion to adopt

approaches on a case-by-case basis that may differ from this guidance, but still comply

with the statute and conformity regulations. Any decisions regarding a particular

conformity determination will be made based on the statute and regulations. This
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guidance is a living document and may be revised periodically without public notice.

11. Q. Who can I contact if I have further questions about attainment year requirements for

conformity under the new air quality standards?

A. If this guidance document does not answer a specific question, please contact the

transportation conformity staff person responsible for your state at the appropriate EPA

regional office. A listing of regional offices, the states they cover, and contact

information for EPA regional conformity staff can be found at the following website:

http://www.epa.gov/otaq/transp/conform/contacts.htm.

General questions about this guidance can be directed to Joe Pedelty at EPA’s Office of

Transportation and Air Quality, via his email address: pedelty.joe@epa.gov or phone

number: 734-214-4410.