(REF: OZPMRH-5-97)

MEMORANDUM

SUBJECT: Guidance for Implementing the 1-Hour Ozone and Pre-Existing PM10 NAAQS

FROM: Richard D. Wilson, Acting Assistant Administrator

 for Air and Radiation (6101)

TO: Regional Administrator, Regions I-X

As you know, on July 18, 1997, EPA replaced the 1-hour ozone standard with an 8-hour

standard at a level of 0.08 parts per million (ppm). The Agency also revised the primary and

secondary national ambient air quality standards (NAAQS) for particulate matter (PM) by

establishing annual and 24-hour PM2.5 standards and by changing the form of the existing 24-hour

PM10 standard. The existing annual PM10 standard is retained; however, for the revised PM

NAAQS, the standard conditions of temperature and pressure adjustment have been removed. 

These new standards became effective September 16, 1997.

Guidance for continuing the implementation of the Clean Air Act (Act) requirements for

the 1-hour ozone and pre-existing PM10 NAAQS following EPA's promulgation of the new 8-

hour ozone and PM NAAQS is attached. This guidance is intended to ensure that momentum is

maintained by the States in their current programs while moving toward developing their plans for

implementing the new NAAQS, and it applies to all areas now subject to the 1-hour ozone

standard and the pre-existing PM10 standard regardless of attainment status. On July 16, 1997,

President Clinton issued a directive to Administrator Browner on implementation of the new

standards for ozone and PM. In that directive, the President laid out a plan on how these new

standards, as well as the current 1-hour ozone and pre-existing PM standards, are to be

implemented. The attached guidance reflects the Presidential Directive. 

Although the 8-hour ozone standard replaces the 1-hour standard, the 1-hour standard will

continue to apply to an area for an interim period until EPA makes a determination that the area

has air quality meeting the 1-hour standard. As a consequence, under the Act, the provisions of

subpart 2 of part D of title I, which govern implementation of the 1-hour ozone standard in

nonattainment areas, will continue to apply in those areas until EPA makes a determination that

the area has air quality meeting the 1-hour standard. Similarly, the provisions of subpart 4 of part

D of title I, which govern implementation of the pre-existing PM-10 standards in nonattainment

areas, will continue to apply for an interim period until the pre-existing PM10 standard is revoked. 

Guidance on how EPA will revoke the applicability of the 1-hour ozone and pre-existing PM10

standards is also in the attachment. 
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The EPA interprets the Act to provide that the detailed provisions of subpart 2 of part D

of title I are clearly and explicitly tied to the ozone NAAQS in existence at the time of the

enactment of the 1990 Amendments to the Act. Moreover, the provisions of subpart 4 of part D

apply only to PM10 NAAQS (this includes pre-existing and revised PM10 NAAQS). Thus, the

provisions of subparts 2 and 4 would not govern the implementation of the 8-hour ozone and

PM2.5 NAAQS. Instead, the general planning requirements of part A of title I and the

nonattainment planning requirements of subpart 1 of part D of title I govern the implementation of

the new 8-hour ozone standard and the PM2.5 standard. The EPA will prepare guidance and

proposed regulations on implementing these new standards in the near future. 

The purpose of this guidance is to set forth EPA’s current views on the issues discussed

herein. These issues will be addressed in future rulemakings as appropriate, e.g., actions

approving or disapproving State implementation plans submittals. In those rulemakings, EPA will

propose to take a particular action based in whole or in part on its views of the relevant issues,

and the public will have an opportunity to comment on EPA’s interpretations during the

rulemakings. When EPA issues final rules based on its views, those views will be binding on the

States, the public, and EPA as a matter of law. 

 If you have any questions during implementation of this guidance, please contact John

Seitz, Director of the Office of Air Quality Planning and Standards. The staff contacts are Sharon

Reinders (ozone) at 919/541-5284 and Robin Dunkins (PM) at 919/541-5335.

Attachment

cc: Air Division Director, Regions I-X

Air Programs Manager, Regions I-X

William Hunt, EMAD

Margo Oge, OMS

Rich Ossias, OGC

Sally Shaver, AQSSD 

John Seitz, OAQPS

Lydia Wegman, OAQPS

EPA:OAR:OAQPS:AQSSD:OPSG:SREINDERS\LTilley:NCM RM 510A:(MD-15)1-5526

File Name: I:\SEC\REINDERS\IIG1223.FIN December 23, 1997

Coordinated w/ the all Regions, Gay MacGregor w/ OMS, Rich Ossias of OGC. Please note that

Sally Shaver and Lydia Wegman have cleared this. 
1

Guidance for Implementating the 1-Hour Ozone and Pre-Existing PM10 NAAQS

PREFACE

The purpose of this guidance is to set forth EPA’s current views on the issues discussed

herein. These issues will be addressed in future rulemakings as appropriate, e.g., actions

approving or disapproving State implementation plans submittals. In those rulemakings, EPA will

propose to take a particular action based in whole or in part on its views of the relevant issues,

and the public will have an opportunity to comment on EPA’s interpretations during the

rulemakings. When EPA issues final rules based on its views, those views will be binding on the

States, the public, and EPA as a matter of law. 

OZONE GUIDANCE

The following guidance presents EPA's view on key issues regarding the ongoing

programs implemented by State, local, and tribal air pollution control agencies to attain the 1-hour

ozone national ambient air quality standards (NAAQS). The purpose and intent are to ensure that

the momentum gained by States, local governments, and tribes to attain this NAAQS is not lost

when moving toward implementation and attainment of the new 8-hour NAAQS. The topics

covered are:

1. Continued Applicability of the 1-Hour Ozone NAAQS

2. Revocation of the 1-Hour Ozone NAAQS While Retaining the 8-Hour Ozone NAAQS 

3. Reclassifications and Attainment Date Extensions

4. Rate of Progress (ROP) Requirements for Serious and Above Areas

5. Substitution of Credits for ROP Emission Reductions

6. Findings of "Failure to Submit" Certain Planning Elements 

7. Attainment Demonstrations for the 1-hour Ozone NAAQS

a. State Implementation Plan Requirements for Serious and Higher Classified 

 Nonattainment Areas

b. States with Areas that are Bumped Up from Moderate to Serious

1. Continued Applicability of the 1-Hour Ozone NAAQS

On July 18, 1997 (62 FR 38856), EPA promulgated a regulation replacing the 1-hour

ozone NAAQS with an 8-hour NAAQS at a level of 0.08 ppm (40 CFR part 50). On that date,

EPA also announced that the 1-hour standard would no longer apply to an area once EPA

determines that the area has air quality meeting the 1-hour standard.

Subpart 2 of part D of title I of the Clean Air Act (Act) addresses the implementation

program for areas designated since 1991 as nonattainment for the 1-hour ozone standard. On

December 13, 1996, in the proposed interim implementation policy (61 FR 65764), EPA

proposed that the provisions of subpart 2 would not apply directly to the implementation of a new
2

ozone NAAQS, but would continue to apply during the interim period after promulgation of a

new NAAQS to the extent they are retained under a no-backsliding principle and to the extent

they are needed to comply with the general provisions of subpart 1. However, in light of the

comments received on that proposal, EPA reconsidered and now has determined that the

provisions of subpart 2 continue to apply directly as a matter of law to ozone nonattainment areas

for the purposes of achieving that standard. Therefore, in the July 18 rulemaking, the EPA

announced that the provisions of subpart 2 continue to apply to an area as a matter of law until

EPA determines that the area has air quality data meeting the 1-hour standard and revokes the

standard. The EPA will not revoke the 1-hour standard in an area that is violating that standard. 

The revocation process is discussed below.

Subpart 2 addresses the requirements for different classifications of nonattainment areas

for the 1-hour standard (i.e., marginal, moderate, serious, severe and extreme). For example,

these requirements include such items as mandatory control measures, annual rate of progress

requirements for emission reductions, attainment demonstrations and attainment dates, and offset

ratios for the emissions from new or modified stationary sources. The requirements in subpart 2

have contributed significantly to improvements in air quality since 1990. The EPA believes that

retaining the provisions of subpart 2 until areas have air quality meeting the 1-hour standard will

result in numerous benefits. Retention will provide continuity in implementation programs to

reduce ozone and protect public health and the environment, provide greater assurance that the

currently existing and required control measures will continue to be implemented, and position

nonattainment areas on the path toward eventual attainment of the new 8-hour NAAQS. 

Consistent with these goals, EPA intends to interpret section 110(l) of the Act to require that a

State may not remove, relax, or delay an ozone control measure or control measure commitment

that is included in the SIP unless the State has demonstrated that such removal, relaxation, or

delay will not adversely affect the ability of the State to prepare and submit a SIP that satisfies

requirements for reasonable further progress toward any NAAQS or attainment and maintenance

of any NAAQS, including the revised ozone NAAQS and new PM2.5 NAAQS. The continued

applicability of the 1-hour ozone standard is explained in the final regulation promulgating the

new ozone standard at 62 FR 38873 (July 18, 1997) and the Presidential Directive issued to the

EPA on July 16, 1997 (62 FR 38421). In certain cases where air quality data through 1997 show

nonattainment, EPA may be redesignating areas from attainment to nonattainment for the 1-hour

standard. Where this occurs, States should follow implementation guidance on the applicable

subpart requirements issued at the time of redesignation. 

2. Revocation of the 1-Hour Ozone NAAQS While Retaining the 8-Hour Ozone NAAQS

The EPA will publish a list of areas where the 1-hour standard is being revoked. That

determination will be based solely on air quality showing attainment of that NAAQS. At the

effective date of the determination, the 1-hour NAAQS will no longer be in effect for these areas

although the 8-hour ozone NAAQS continues in effect. Also, at the effective date of the

revocation, the existing area designations for such areas will no longer be applicable since the

purpose of the provisions of subpart 2 will have been achieved and those provisions will no longer
3

apply. As long as an area is violating the 1-hour standard, the provisions of subpart 2 and the 1-

hour standard continue to apply. In the future, the EPA intends to review areas eligible for

revocation of the 1-hour standard on an annual basis and take appropriate action. The

implications of revoking the 1-hour NAAQS on the Ozone Transport Region are not discussed in

this guidance. The EPA will issue separate guidance on these relationships.

In the past, States with air quality data showing attainment have submitted, and EPA has

approved, redesignation requests and maintenance plans for these areas. From now on, because

the 1-hour standard and subpart 2 will no longer apply to an area once the area achieves that

standard, new redesignation requests as well as new maintenance plans for that standard will no

longer be required.

The EPA-approved maintenance plans remain effective for areas where the 1-hour

standard is revoked. However, EPA believes maintenance plans for areas that have been

redesignated to attainment for that standard may be revised to withdraw certain contingency

measure provisions that have not been triggered or implemented prior to EPA's determination of

attainment and revocation of that standard. Where the contingency measure is linked to the 1-

hour standard or air quality ozone concentrations, this measure may be removed from the

maintenance plan. Where the contingency measure is linked to a non-air quality element, such as

emission increases or vehicle miles traveled, this measure can only be removed if a demonstration

shows that its removal will not adversely affect the ability of the area to attain the 8-hour

standard. Contingency measure provisions linked to the 1-hour standard are designed to assure

that the States will promptly correct any violation of the 1-hour standard which occurs after the

redesignation of the area as an attainment area for that standard. After the 1-hour standard is

revoked for an area, the EPA believes that it would be permissible for States to revise their plans

to withdraw contingency measures related to the old standard and air quality for the area. 

Allowing such revisions would be consistent with section 110(l) of the Act since it would not

interfere with any applicable requirement concerning attainment and reasonable progress, or any

other applicable requirement of the Act. Since such contingency measures are designed to

address future violations of a standard which would no longer exist as to that area, it is no longer

necessary to retain them. Further, EPA believes that future attainment and maintenance planning

efforts should be directed toward the new 8-hour NAAQS. 

With respect, however, to contingency measures that were triggered and/or implemented

prior to EPA's revocation of the 1-hour standard, such measures were shown to be necessary to

correct violations that occurred while that standard was in existence for the area. Therefore, the

measures should be retained unless the State can show under section 110(l) that it would not

interfere with any applicable requirement concerning attainment and reasonable progress, or any

other applicable requirement of the Act.

The conformity provisions of section 176(c) of the Act apply to nonattainment and

maintenance areas. Because EPA-approved maintenance plans remain effective for areas where

the 1-hour standard is revoked, transportation and general conformity will continue to apply in
4

those areas with EPA-approved maintenance plans, even after the 1-hour ozone standard is

revoked. However, transportation and general conformity will no longer apply in those areas that

do not have EPA-approved maintenance plans and for which the 1-hour standard is revoked. 

Since these areas will no longer be designated nonattainment, and nothing in the ozone NAAQS

rule provides a basis for retaining conformity requirements for ozone, conformity will no longer

apply.

Nevertheless, EPA strongly encourages these areas to continue coordinating their

transportation planning and air quality planning processes. Air quality agencies should be

consulting with transportation agencies when developing the SIP, in order to ensure that the SIP

properly anticipates future motor vehicle emissions and adopts appropriate emission reduction

strategies. Likewise, as plans for transportation investments are subsequently developed, a

process for considering the long-term air quality impacts of proposed transporation investments is

a common-sense planning step that promotes the efficient use of state and local resources. 

Additionally, reconciling proposed transportation investments with the SIP’s goals and strategies

ensures that the standards are achieved on time and through an efficient allocation of emission

reductions among sources. Finally, the integration of air quality and transportation planning

emphasizes strategies that improve the efficiency of the transportation system, which in itself

offers long-term environmental benefits such as reducing greenhouse gas emissions.

The EPA recognizes that for other Federal actions normally subject to general conformity,

coordination with the State is usually initiated by the Federal agency when an action is expected

to occur. It is difficult for the State to coordinate in advance with each of 

the many Federal agencies that could potentially take an action. However, EPA does encourage

states to contact the major Federal facilities/activities in their nonattainment areas to ensure that

potential future Federal activities are considered when the SIP is developed.

Retaining the provisions contained in subpart 2 until EPA determines that an area has air

quality meeting the 1-hour standard helps areas to transition to attainment planning for the new

NAAQS and to avoid backsliding to degraded air quality. Although the provisions of subpart 2

will no longer apply to an area when EPA determines that the area has air quality meeting the 1-

hour standard, at which time the 1-hour standard will be revoked, EPA does not believe that the

revocation authorizes States to suspend, delay, or revoke any SIP measures adopted in response

to provisions of subpart 2 unless the State demonstrates under section 110(1) that such

suspension, delay, or revocation will not adversely affect the ability of the State to make

reasonable further progress or attain or maintain any NAAQS.

Designations for areas regarding the new 8-hour NAAQS will take place in the future. 

Implementation of the new 8-hour standard will be governed by the provisions of subpart 1 of

part D of title I of the Act. Designations, implementation guidance and regulations for the new 8-

hour NAAQS are not addressed in this memo. The EPA plans to address implementation of the

new NAAQS during the next year.
5

3. Reclassification and Attainment Date Extensions

Retention of subpart 2 subjects States with areas failing to attain the 1-hour NAAQS to

reclassification to a higher class and to the mandatory requirements of the higher class. With

respect to moderate areas that did not attain the 1-hour NAAQS by the attainment date in the

Act, those areas are subject to: (1) the reclassification requirements in section 181(b)(2) of the

Act, which state that areas will be reclassified (bumped up) to the next higher classification or

classification associated with the area's design value; and (2) all the requirements of the

classification to which they are bumped as specified in section 182. Section 181(b)(2) provides

that this bump-up action is to occur unless the area is granted an extension of its attainment date

by EPA in accordance with section 181.

The EPA recently initiated individual rulemaking actions proposing that certain moderate

nonattainment areas failed to attain the 1-hour NAAQS by November 15, 1996 as required by the

Act (62 FR 46233, and 62 FR 46238), in addition to publishing a final rulemaking action on a

moderate nonattainment area (62 FR 60001). The reader is referred to these notices for

additional information. With respect to extensions for attainment dates, EPA will continue to

consider granting up to two 1-year extensions as specified in the Act. 

4. Rate of Progress (ROP) Requirements for Serious and Above Ozone Areas

In numerous earlier guidance documents, the EPA has interpreted the section 182(c)(2)

reasonable further progress requirement as mandating volatile organic compounds (VOC) or

nitrogen oxides (NOx) reductions of 3 percent per year, averaged over a 3-year period, for

serious and above ozone nonattainment areas that were designated and classified under the 1-hour

0.12 ppm ozone NAAQS. The EPA refers to these reductions as the rate-of-progress (ROP)

requirement. After promulgation of the new NAAQS, the continuation of the ROP requirement is

grounded in both the retention of the 1-hour 0.12 ppm ozone NAAQS and the requirements of

section 182(c)(2)(B) in subpart 2. The ROP requirements continue until the area has air quality

meeting the 1-hour standard. Accordingly, areas with ROP plans approved by EPA should

continue to implement the ROP requirements of their plans, and areas that have not submitted

plans remain subject to the requirement.

5. Substitution of Credits for ROP Emission Reductions

The EPA previously proposed some additional flexibility for a nonattainment area as it

attempts to meet its annual ROP emission reductions. This flexibility expanded the geographic

size of the area from which States could obtain emission reductions to meet their annual average 3

percent per year ROP requirement. Specifically, EPA proposed that an area in nonattainment for

the 1-hour NAAQS should be allowed to take credit for emissions reductions obtained from

sources outside the designated nonattainment area for the post-1999 ROP requirement as long as

the sources are no farther than 100 km (for VOC sources) or 200 km (for NOx sources) away

from the nonattainment area. The proposal restricted credits to emission reductions from
1

 For purposes of this notice, the core part of the OTAG domain consists of the following

States: Alabama, Connecticut, District of Columbia, Delaware, Georgia, Illinois, Indiana,

Kentucky, Maine, Massachusetts, Maryland, Michigan, Missouri, North Carolina, New

Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, South Carolina,

Tennessee, Vermont, Virginia, Wisconsin, and West Virginia.

6

measures not otherwise mandated by the Act. Because the ROP requirement is a general ROP

requirement for at least 3 percent-per-year and not a requirement for specific programs or

measures such as vehicle inspection and maintenance, this flexibility would continue to provide

the same ROP in terms of reducing emissions. As explained in the proposed policy, EPA believes

that this additional flexibility for crediting reductions outside nonattainment areas is consistent

with the Act.

Under this approach, the geographic area for substitution of VOC emission reductions

remains at 100 km from the nonattainment area and the geographic area for substitution of NOx

reductions remains at 200 km from the nonattainment area with the possibility for additional

expansion of the NOx substitution area as follows. Based on its review of the public comments,

EPA believes that it should expand the allowable area for NOx substitutions up to the entire State

for those States in the core part of the Ozone Transport Assessment Group (OTAG) domain1, i.e.,

the fine grid area, if they so choose. (The OTAG modeling results provide an adequate technical

justification for statewide NOx emission substitutions for ROP.) All other States implementing a

NOx substitution strategy for ROP would be restricted to a distance of 200 km from the

nonattainment area, unless a substitution for a greater distance is accompanied by adequate

technical justification. There are some cases in the western portions of the United States where

100 km for VOC substitution or 200 km for NOx substitution from the nonattainment areas are

not appropriate for ROP credit. In those cases, States should obtain approval from the

appropriate Regional Office to verify credit and applicability prior to implementing such a

substitution.

The reductions obtained outside the nonattainment area are subject to the same use

restrictions as if they were obtained inside the nonattainment area. For example, the same

reduction should not be double counted for ROP credit and for new source growth offsets. EPA

believes that emissions from the source(s) outside the nonattainment area that are involved in the

substitution must be included in the baseline ROP emissions and target ROP reduction calculation. 

Emissions from source(s) outside the nonattainment area that are not involved in the substitution

would not have to be inventoried or included in the baseline ROP emissions and target ROP

calculation. Under this approach, States will need to track and 

record emission reductions and certify to EPA the amount of emission reductions achieved for

ROP. 

Further, whereas the initial Agency proposal disallowed ROP credit from measures

mandated by the Act and implemented by States outside of their nonattainment areas to reduce
7

precursors of ozone, EPA now believes that it should allow ROP credit for such reductions of

ozone precursors. That is, creditable reductions achieved outside a nonattainment area should

include those occurring from measures such as those proposed by EPA in its regional NOx State

implementation plan call (signed by the Administrator on October 10, 1997) for States to reduce

interstate pollution transport, even though these reductions are not specifically required by the

Act. Also now creditable outside the nonattainment area are those reductions mandated by the

Act. Examples are credit for maximum achievable control technology standards controlling

hazardous air pollutants that are precursors of ozone or the Act’s title IV NOx emission reduction

requirements. (These are merely illustrative examples of such programs, not an inclusive list of all

such programs.) This is consistent with EPA’s previous interpretations of section 182(c)(2)(B)

and related provisions regarding the creditability of reductions inside nonattainment areas toward

ROP.

The EPA is clarifying its proposal for areas having approved NOx waivers granted under

section 182(f). EPA believes that the NOx reductions achieved outside the nonattainment area

with waivers may be substituted for VOC reductions within the nonattainment area if

accompanied by adequate technical justification at the time of submittal. In general, EPA believes

that substitutions in waiver areas may be allowed only if EPA determines that the substitution

would result in a reduction in ozone concentrations in the nonattainment area with waivers. For

most areas, NOx waivers were granted because the areas were already attaining the ozone

NAAQS and are not at issue for ROP. For other areas, NOx waivers were granted based on

modeling showing that NOx reductions were not needed to attain or resulted in ozone disbenefits. 

Accordingly, although EPA generally intends to allow the substitution policy as described above

to apply in nonattainment areas that received NOx waivers, EPA does not believe that it should

allow NOx reductions from within such areas to be substituted for required VOC reductions

without certain technical assurances in cases where the waiver was granted based on a showing

that NOx reductions resulted in ozone disbenefits or otherwise provided no benefits. Thus, in

order for substitutions to be allowed in such ozone disbenefit waiver areas, the technical

justification should be accompanied by an adequate showing that the NOx reductions will lead to

lower ozone concentrations in the nonattainment area and should also be accompanied by an

amended NOx waiver request with modeling data supporting the revised NOx waiver.

The EPA believes that the start date of the expanded locality-based substitution credit for

ROP is changed from post-1999 ROP requirements to post-1996 requirements. EPA does not

believe that it may allow credit for substitutions to complete or revise the 15 percent ROP

requirement for VOC emission reductions in nonattainment areas through 1996. Although the

start date for application of ROP substitution reductions from outside the nonattainment area

would apply to post-1996 ROP requirements, consistent with past Agency policy, States would

be able to bank excess earlier reduction credits (NOx or VOC) to apply to post-1996 and later

requirements.

The EPA believes the Act does not allow States to substitute other controls for

specifically mandated measures such as inspection/maintenance or reasonably achievable control
8

technology that are required by the Act due to the area classification or location within the Ozone

Transport Region. In these cases, the measures are prescribed, required controls that the Act

does not allow EPA discretion to remove. 

Substitutions are restricted to intrastate areas unless two or more States involved reach

mutual agreement. Similarly, application of credits from substitutions should be limited to only

one nonattainment area unless two or more areas involved reach agreement on dividing the credit

between them, such that the same emission reductions are not credited toward the progress

requirements for more than one area. Interstate substitutions, like intrastate substitutions, must be

enforceable by the States in which the affected sources are located. 

6. Findings of "Failure to Submit" Certain Planning Elements 

By notice published July 10, 1996 (61 FR 36292), EPA issued three types of findings for

nine nonattainment areas in ten States and the District of Columbia and thereby started sanctions

clocks for these areas. These findings were for failure to submit: (1) a SIP provision requiring

emissions reductions of 9 percent in ozone precursors from the end of 1996 to 1999, (2) a SIP

commitment to adopt any additional regulations needed to complete the requirements for ROP

reductions after 1999 and until the attainment date, and (3) a SIP commitment to adopt additional

measures needed for attainment of the 1-hour 0.12 ppm NAAQS. Note that areas classified as

serious only received the first and third findings. 

In addition, EPA issued two types of findings to the Commonwealth of Pennsylvania for

the Philadelphia area and, thereby, started sanctions clocks for that area (62 FR 27201, May 19,

1997). These findings were for failure to submit: (1) a SIP commitment to adopt any additional

regulations needed to complete the requirements for ROP reductions after 1999 and until the

attainment date, and (2) a SIP commitment to adopt additional measures needed for attainment of

the 1-hour 0.12 ppm NAAQS.

Because the provisions of subpart 2, section 182(c)(2), that relate to ROP plans and

attainment demonstrations continue to apply to areas not attaining the 1-hour ozone standard, all

findings made by EPA and associated sanctions and Federal implementation plan clocks continue

to apply. Also, because the current subpart 2 implementation program is retained, all other

previously-issued findings pertaining to required elements in the Act's ozone program are carried

forward.

7. Attainment Demonstrations for the 1-Hour Ozone NAAQS

a. State Implementation Plan Requirements for Serious and Higher Classified

Nonattainment Areas
2 Exceptions are international border areas, where States are allowed to defer the

adoption of plans to attain and maintain the 1-hour NAAQS due to emissions emanating from

outside the United States and beyond their control. The EPA has previously issued guidance for

these areas, and this guidance remains applicable. The General Preamble provided SIP guidance

for international border areas (57 FR 13569, April 16, 1992). 

3 Note that EPA addressed ROP and attainment plans for serious classified nonattainment

areas in the Nichols policy statement mentioned above. That policy states that remaining

regulations needed for serious classified nonattainment areas to attain should be adopted and

implemented in time for those areas to meet their attainment date of November 1999.

9

The Act requires attainment demonstrations for the 1-hour NAAQS.2 In an earlier policy

statement issued on March 2, 1995 by Mary D. Nichols, titled “Ozone Attainment

Demonstrations,” the EPA provided guidance on attainment demonstrations for the 1-hour

NAAQS for serious and higher classified nonattainment areas. That policy was closely tied to the

progress of the OTAG, which was a group of States assembled to assess the transport of ozone

across the eastern portion of the United States. The policy indicated that States participating in

the OTAG would have until mid-1997 to submit attainment demonstrations to EPA. The

additional time beyond 1994 was necessary to provide States with time to: (1) participate in the

OTAG assessment of ozone transport and its impact, (2) review and complete the assessment of

transported ozone and precursors, and (3) complete local-area modeling needed to support

attainment demonstrations.

Because the conclusion of the OTAG assessment was delayed for approximately 9

months, in this guidance, EPA now believes States should have until April 1998 to submit

attainment demonstrations. On or before that date, States with serious and higher classified

nonattainment areas should forward to the appropriate EPA Regional Office their attainment

demonstrations for the 1-hour standard, modeling analysis, and supporting documentation. In

addition, the submittal should contain the following five elements: 

(1) Evidence that all measures and regulations required for the nonattainment area by

subpart 2 of title I of the Act to control ozone and its precursors have been adopted and

implemented or are on an expeditious schedule to be adopted and implemented.

(2) A list of measures and regulations and/or a strategy including technology forcing

controls needed to meet ROP requirements and attain the 1-hour NAAQS.

(3) For severe and higher classified nonattainment areas, a SIP commitment to submit a

plan on or before the end of 2000 which contains (a) target calculations for post-1999 ROP

milestones up to the attainment date3 (unless already submitted to satisfy EPA’s previous findings

of failure to submit) and (b) adopted regulations needed to achieve the post-1999 ROP

requirements up to the attainment date and to attain the 1-hour NAAQS. (Note that for many

States, EPA has proposed in its regional NOx SIP call to require submittal of NOx reduction
10

programs by the earlier date of September 1999 and that reductions from these programs can

contribute to achieving ROP.) 

(4) A SIP commitment and schedule to implement the control programs and regulations

in a timely manner to meet ROP and achieve attainment.

(5) Evidence of a public hearing on the State submittal.

The modeling analysis now due in April 1998 should demonstrate attainment of the 1-hour

NAAQS by the date required in the Act. States may wish to conduct additional modeling

analyses to support the attainment demonstration; however, EPA is not requiring any additional

modeling and will accept as sufficient existing modeling analyses performed in the OTAG

assessment and/or local area modeling that is already available. States that are covered by EPA’s

proposed NOx SIP call can submit a modeling analysis that reflects boundary conditions that are

consistent with the regional reductions required in EPA's proposed NOx SIP call. In the event the

final SIP call changes significantly from what was proposed, States will be permitted to adjust

their attainment demonstrations to reflect the effects of the final SIP call. All States should

document the boundary conditions assumed in the analysis and quantify the percent of VOC and

NOx reductions needed to attain the 1-hour standard.

The modeling analysis should be based on the guidance documents issued by the EPA

titled "Guideline for Regulatory Application of the Urban Airshed Model," July 1991, and

"Guidance on Urban Airshed Model Reporting Requirements for Attainment Demonstrations,"

March 1994. States may base the attainment test on the document titled "Guidance on Use of

Modeled Results to Demonstrate Attainment of the Ozone NAAQS" issued by EPA in June 1996. 

Taken together, these documents address regulatory model application, modeling reporting

requirements, and the use of corroborative data such as air quality monitored trends and results

from observational models and/or other photochemical grid models for demonstrating attainment.

b. States with Areas that are Bumped Up from Moderate to Serious

In accordance with the Act, areas designated as moderate ozone nonattainment were

required to submit to EPA a SIP with specific annual reductions in ozone precursors sufficient to

attain the 1-hour NAAQS by November 15, 1996. As discussed previously, failure to attain by

the Act's required date subjects the moderate area to reclassification (bump up) to a higher

classification and new control requirements.

Individual area bump ups will be addressed by EPA in separate regulatory actions. While

subpart 2 contains the general SIP requirements for serious areas, the details of the plan

requirements for areas bumped up from moderate to serious will be addressed in connection with

individual area bump ups. Similarly, SIP requirements for redesignated areas will be addressed
11

within the redesignation process for an individual area.

Several moderate areas submitted plans, including an attainment demonstration, for the 1-

hour NAAQS but did not in fact attain the NAAQS by the November 15, 1996 attainment

deadline in the Act. Where States submitted attainment demonstrations for areas that failed to

attain the 1-hour NAAQS or where these areas are bumped up to serious areas, such attainment

demonstrations are no longer relevant because their actual air quality data reflect nonattainment. 

Thus, these areas become subject to bump up to the serious classification and the statutory

requirements applicable to serious areas. Once such areas are bumped up, the obligation to

demonstrate attainment by the former attainment date will be superseded by the requirement to

demonstrate attainment by the serious area attainment deadline. In addition to the serious area

requirements, all of the statutory requirements for the moderate classification and regulations

submitted by States and approved by EPA, except for the requirement to demonstrate attainment

by November 15, 1996 remain in effect. 
4PM NAAQS refers to both PM10 and PM2.5 standards.

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PM GUIDANCE

The following guidance presents EPA’s view on key issues regarding the ongoing

programs implemented by State, local and tribal air pollution control agencies to attain the preexisting PM10 NAAQS. It is intended to ensure that the improvements in air quality achieved to

date are not lost when moving toward implementation and attainment of the new PM NAAQS. 

The topics covered are:

1. Retention of the PM10 Standard

2. Attainment Determinations

3. Areas Not Attaining the Pre-Existing PM10 NAAQS

4. Areas Attaining the Pre-Existing PM10 NAAQS

a. Designated Nonattainment Areas with an Approved Part D SIP in Place

b. Designated Nonattainment Areas that Do Not Have an Approved Part D SIP 

c. Attainment Areas

d. Unclassifiable Areas

1. Retention of the PM10 Standard

On July 18, 1997 (62 FR 38652), the Agency revised the primary and secondary NAAQS

for PM by establishing annual and 24-hour PM2.5 standards and by changing the form of the

existing 24-hour PM10 standard. In addition, the existing annual PM10 standard was retained. 

With respect to the newly-revised suite of PM NAAQS4, 40 CFR part 50, section 50.3, was

revised to remove the requirement to correct the temperature and pressure of measured PM

concentrations to standard reference conditions. The revised PM NAAQS and their associated

appendices became effective on September 16, 1997. Since it will take a number of years for

States to identify PM problems under the revised standards and to develop effective means for

addressing those problems, EPA believes it is necessary for all areas, including those that may

have already attained the pre-existing PM10 standards to maintain their current PM10

implementation efforts for the purpose of protecting public health during the transition to

implementing the revised PM standards. To provide for an effective transition from the preexisting PM standards to the revised PM standards (in light of the need to establish PM2.5

monitoring networks, designate areas, and develop control strategies for PM2.5), in 40 CFR part

50, section 50.6, the Administrator determined that the existing standards and associated

provisions will continue to apply for an interim period. The duration of the interim period will

depend on when the area in question has attained the pre-existing PM10 standards, has included all

state adopted and implemented PM10 measures in an EPA approved SIP, and has received EPA

approval of a SIP that must be submitted pursuant to section 110(a)(1) which will generally

provide for implementation, maintenance and enforcement of the revised PM NAAQS. For those

areas which have not attained the pre-existing PM10 NAAQS, that standard will remain until EPA
13

promulgates a rule pursuant to section 172(e) of the Act to assure that no backsliding occurs

during the interim period (for further information, see paragraph 3 below).

On September 16, 1997, the revised PM NAAQS became effective, triggering the

requirement for the collection and reporting of PM10 data at local temperature and pressure

conditions. However, consistent with guidance issued in EPA’s memo entitled “Collection and

Reporting of PM10 Data,” signed by William Hunt on September 15, 1997, collection and

reporting of data for the revised PM10 NAAQS at local ambient conditions will not be required

until January 1, 1998. Beginning January 1, 1998, all areas will be required to collect and report

ambient PM10 concentrations to AIRS-AQS at local temperature and pressure conditions. 

However, until the pre-existing PM10 NAAQS is revoked for an area, monitoring and reporting of

PM10 air quality data under both the pre-existing PM10 NAAQS methodology (i.e., corrected to

standard temperature and pressure) and the revised PM10 methodology (i.e., reported at local

temperature and pressure) are required. In order to accommodate this requirement, EPA is

adjusting the AIRS-AQS system to handle these dual data reporting requirements. The EPA

realizes the short-term burden this may place on the States but is committed to working with them

to revoke the standards as expeditiously as possible. Guidance on the technical details of this

process is in preparation. 

2. Attainment Determinations

Consistent with 40 CFR part 50, Appendices K and J, for the pre-existing PM10 NAAQS,

attainment determinations are based on a calendar year of ambient monitored data corrected to

standard temperature and pressure, and are exceedance based. Under these regulations, an area is

considered to be in attainment if it meets the criteria of no more than one exceedance per calendar

year of the pre-existing PM10 NAAQS averaged over 3 consecutive years. Since the PM NAAQS

were revised mid-year (i.e., as of September 16, 1997), the Agency has concluded that in order to

comply with the requirement of a full calendar year of data, it will base attainment determinations

for the pre-existing PM10 NAAQS on ambient monitored data reported to the AIRS database for

the years 1994 - 1996. Thus, data covering these years will be used to identify those areas that

are attaining the pre-existing PM10 NAAQS. These data will also serve to identify the existing

PM10 areas that are not attaining the pre-existing PM10 NAAQS and, therefore, are subject to the

section 172(e) rulemaking to avoid backsliding in the maintenance of acceptable ambient air

quality. More details on this rulemaking are provided below. 

Also, consistent with the natural events policy issued by Mary Nichols on May 30, 1996, if

an attainment or unclassifiable area has data showing violations of the PM10 NAAQS due to

natural events and is complying with the policy by having in place or developing a natural events

action plan (NEAP), then EPA will not use those data in any air quality analysis to determine

whether that area is attaining or not attaining the pre-existing PM10 NAAQS. In the event an area

fails to comply with the natural events policy within the specified time frames, then the area will

be subject to the section 172(e) no backsliding rulemaking. Additionally, if an area has violations

of the PM10 NAAQS due to a significant contribution of nonanthropogenic emissions or would
14

attain but for the influence of PM10 emissions from another country and has an approved waiver

pursuant to section 188(f) or 179(B), respectively, of the Clean Air Act, then EPA will continue

application of the waivers, provided the data continue to support the initial finding that was the

basis for approving the waiver. Attainment provisions for the revised PM10 NAAQS are covered

in 40 CFR part 50, Appendices M and N, and are based on a 99th percentile form of the standard;

however, they will not be used for attainment determinations of the pre-existing PM10 NAAQS.

3. Areas Not Attaining the Pre-Existing PM10 NAAQS

For those areas that are not attaining the pre-existing PM10 standards as of September

16, 1997, the pre-existing standards will continue to apply until EPA has completed its

rulemaking under section 172(e) of the Act to assure that no backsliding occurs in the interim

period (62 FR 38701 and 62 FR 38429). Section 172(e) provides that, if the Administrator

relaxes a national ambient air quality standard, she shall, within 12 months after the relaxation,

promulgate requirements applicable to all areas that have not attained that standard as of the date

of the relaxation. Those requirements shall provide for controls that are not less stringent than the

controls applicable to areas designated nonattainment before such relaxation. The suite of revised

PM standards, when viewed as a whole, is more stringent than the set of pre-existing PM

standards; however, the shift from the pre-existing PM10 standards to the revised PM10 standards,

when viewed by itself, represents a relaxation of the existing PM10 standard. As a result, section

172(e) requires EPA to issue a rule within 12 months to apply implementation requirements no

less stringent than the currently-applicable requirements for those areas that had not attained the

existing PM10 standards by September 16, 1997. Pursuant to the Presidential Directive, EPA

plans to propose the section 172(e) rule for notice and comment in the near future and, therefore,

is deferring a detailed discussion of the implementation requirements for subject areas until that

time.

4. Areas Attaining the Pre-Existing PM10 NAAQS

For the areas that are attaining the pre-existing PM10 standards at the time of the effective

date of the revised PM standards, i.e., September 16, 1997, the pre-existing PM10 standards will

continue to apply until the areas have received EPA approval of a SIP that includes all control

measures which were adopted and implemented at the State level to meet the pre-existing PM10

NAAQS. As indicated in the Ozone Section with regard to contingency measures, EPA believes

that where the contingency measure is linked to the pre-existing PM10 standard or air quality PM10

concentrations, this measure may be removed from the maintenance plan. Where the contingency

measure is linked to a non-air quality element, such as emission increases or vehicle miles

traveled, this measure can only be removed if a demonstration shows that its removal will not

adversely affect the ability of the area to attain the revised PM10 standard or the PM2.5 standard. 

Contingency measure provisions linked to the pre-existing PM10 standard are designed to assure

that the States will promptly correct any violation of the pre-existing PM10 standard which occurs

after the redesignation of the area as an attainment area for that standard. After the pre-existing

PM10 standard is revoked for an area, EPA believes that it would be permissible for States to
15

revise their plans to withdraw contingency measures related to the old standard and air quality for

the area. Allowing such revisions would be consistent with section ll0(l) of the Act since it would

not interfere with any applicable requirement concerning attainment and reasonable progress, or

any other applicable requirement of the Act. Since such contingency measures are designed to

address future violations of a standard which would no longer exist as to that area, it is no longer

necessary to retain them. In addition, the NAAQS rule provides that before EPA revokes the preexisting PM10 standard, these areas must receive EPA approval of a SIP under section 110(a)(1)

that addresses the revised PM NAAQS.

The Act requires all States to submit SIPs under section 110(a)(1) within 3 years of the

promulgation of any NAAQS. The section 110 SIP must generally provide for "implementation,

maintenance, and enforcement" of the NAAQS. These SIPs, once approved, establish the general

authority that is needed for implementation of any NAAQS and constitute the infrastructure of the

air quality management program which has been in place since the Act was enacted in 1970. As

previously discussed, the pre-existing PM10 NAAQS will remain in place until States with areas

that are attaining that NAAQS have submitted and EPA has approved a section 110 SIP that

addresses the revised PM NAAQS. Therefore, each State will need to review and revise, as

appropriate, its section 110 SIP for this purpose. For example, an adequate section 110 SIP

should enable the State to develop a PM infrastructure by identifying and/or establishing: 1) the

authority and adequate resources to develop an accurate, complete, and comprehensive inventory; 

2) the authority and resources to develop, deploy, and operate the PM monitoring network; and

3) the authority and resources to perform modeling. It should be noted that EPA believes that

many of the existing section 110 SIPs for currently-attaining PM10 areas may be adequate to meet

many of the new section 110 SIP elements. The EPA is currently in the process of developing

guidance which will more fully address the necessary requirements for an adequate section 110

SIP. This guidance will be completed in the near future. 

Consistent with the Presidential Directive, States will have up to 3 years (July 2000) to

submit their section 110 SIP for the revised PM NAAQS for EPA approval. States are

encouraged to submit these SIPs early in order to have the pre-existing PM10 NAAQS revoked as

expeditiously as possible. Since the goal of retaining the pre-existing PM10 NAAQS while

transitioning from an existing to revised NAAQS is to first, preserve control measures

implemented to date, and second, to ensure that States have the authority and ability to implement

the revised PM NAAQS, EPA believes that, while section 110 could conceivably encompass a

broad range of requirements, including ones that are primarily procedural and administrative in

nature, there are certain fundamental requirements that will be key to the States’ ability to

demonstrate that the section 110 SIP is adequate to implement the revised PM10 and PM2.5

standards. Thus, EPA will, on a case-by-case basis, consider and fully approve those section 110

SIPs that adequately demonstrate that these key requirements have been met, that is, that the

areas in question have adopted all state-implemented measures in the SIP, and have identified

and/or established the authority and ability to develop the infrastructure needed to implement the

revised suite of PM standards. In those instances where a State believes its current section 110

SIP is adequate to provide the authority to implement any PM NAAQS, the Governor, or his/her
16

designee, should submit a letter certifying that the existing section 110 SIP is adequate to

implement the revised PM NAAQS. The EPA will then initiate rulemaking on the adequacy of

the SIP for the purpose of satisfying the necessary requirements of section 110.

Once EPA approves (1) a SIP that has all State-adopted and implemented measures and

(2) the section 110 SIP, EPA will take action to revoke the pre-existing PM10 NAAQS for that

area. When EPA revokes the pre-existing 24-hour PM10 NAAQS in a particular area, the section

107 designation for PM10 for that area will also be revoked. However, the revocation of the area

designations for PM10 will not affect the applicability of the PSD program, including the PM10

increment, which will continue to apply to an area even after the revocation of the existing PM10

designation occurs. EPA will provide guidance on the applicability of conformity requirements

before any revocation of the pre-existing PM10 NAAQS.

a. Designated Nonattainment Areas with an Approved Part D SIP in Place

For those areas designated nonattainment that attained the pre-existing PM10 NAAQS as

of September 16, 1997 and that have already received EPA approval of their part D SIP

embodying all of the measures that were adopted and implemented at the State level, no further

submission or approval pursuant to part D is necessary. As described above, these areas will still

need to satisfy the 40 CFR part 50, section 50.6, requirement to have a section 110 SIP to

implement the revised PM NAAQS approved before EPA will revoke the pre-existing PM10

NAAQS.

b. Designated Nonattainment Areas That Do Not Have an Approved Part D SIP

For those designated nonattainment areas that attained as of September 16, 1997 and do

not have an approved part D SIP in place, all measures that were adopted and implemented at the

State level for the purpose of meeting the pre-existing PM10 standards must be submitted and

approved by EPA. If an area has already submitted a part D SIP embodying all such measures to

EPA, then EPA will take action to approve those measures and incorporate them into the SIP for

the State. In parallel with this action, the Governor, or his/her designee should submit to EPA, a

letter certifying that the measures submitted as part of the part D SIP include all State-level

adopted and implemented measures which resulted in attainment of the pre-existing PM10

NAAQS.

If an area has not yet submitted all State-level adopted and implemented measures for

inclusion in the SIP, then the area needs to submit such measures for EPA approval for inclusion

in the SIP. In parallel with this action, the Governor, or his/her designee should submit to EPA,

a letter certifying that the measures submitted as part of the part D SIP include all State-level

adopted and implemented measures which resulted in attainment of the pre-existing PM10

NAAQS. As stated previously, although the revocation of the existing PM NAAQS is inherent in

the concept of establishing a revised PM NAAQS, EPA has decided, for the purposes of ensuring

that air quality protection is not diminished on the way to meeting the revised PM10 and PM2.5
17

NAAQS, to continue the applicability of the pre-existing PM10 NAAQS for an interim period. 

Inclusion of these measures in the SIP will assure that air quality gains made by the State are

preserved. However, given the narrow, targeted purpose underlying retention of the pre-existing

PM10 standards and the limited, temporary period during which those standards will continue to

apply, EPA does not believe it is appropriate, either as a practical or regulatory matter, to insist

on the submission of measures beyond those already developed and being implemented pursuant

to part D at the State level to address the PM problem. As described above, these areas will still

need to satisfy the 40 CFR part 50, section 50.6, requirement to have a section 110 SIP to

implement the revised PM NAAQS approved before EPA will revoke the pre-existing PM10

NAAQS. 

c. Attainment Areas

For those areas that were redesignated to attainment pursuant to section 107(d)(3)(E) of

the Act and have approved maintenance plans embodying all of the measures that were adopted

and implemented at the State level, no further submission or approval pursuant to part D is

necessary. As described above, these areas will still need to satisfy the 40 CFR part 50, section

50.6, requirement to have a section 110 SIP to implement the revised PM NAAQS approved

before EPA will revoke the pre-existing PM10 NAAQS.

d. Unclassifiable Areas

The PM NAAQS rule provides that, for areas that are currently designated as

unclassifiable, all control measures that were adopted and implemented at the State level for the

purposes of meeting the pre-existing PM10 NAAQS must be submitted and approved by EPA for

inclusion in the SIP. In parallel with this action, the Governor, or his/her designee, should submit

a letter certifying that all measures submitted reflect any and all controls that were adopted and

implemented to meet the pre-existing PM10 NAAQS. As described above, these areas will still

need to satisfy the 40 CFR part 50, section 50.6, requirement to have a section 110 SIP to

implement the revised PM NAAQS approved before EPA will revoke the pre-existing PM10

NAAQS.