GUIDELINE FOR DETERMINING THE APPLICABILITY

OF NITROGEN OXIDES REQUIREMENTS UNDER SECTION 182(f)

December 1993
U.S. Environmental Protection Agency

Office of Air Quality Planning and Standards

Air Quality Management Division

Research Triangle Park, NC 27711
GUIDELINE FOR DETERMINING THE APPLICABILITY

OF NITROGEN OXIDES REQUIREMENTS UNDER SECTION 182(f)

CONTENTS

CHAPTERS

1 INTRODUCTION

1.1 General

1.2 Nitrogen Oxides Supplement to the General Preamble for

Implementation of Title I of the Clean Air Act

1.3 Section 185B Report

1.4 Application of Section 182(f) Requirements

2 ADMINISTRATIVE PROCEDURES

2.1 Processing with the State Implementation Plan (SIP)

Revision

2.2 Petition

3 NET AIR QUALITY BENEFIT

3.1 Demonstration

3.2 Factors

3.3 Geographic Scope

3.4 Scenarios

3.5 Sources

4 CONTRIBUTE TO ATTAINMENT

4.1 Demonstration

4.2 Episodes to Consider

4.3 Geographic Scope

4.4 Applicability to Areas Requesting Redesignation to

Attainment

5 NET OZONE AIR QUALITY BENEFIT

5.1 Demonstration

5.2 Factors

5.3 Attainment/Unclassified Portions

6 EXCESS EMISSIONS REDUCTIONS

6.1 General

6.2 Demonstration

7 MODELING TECHNIQUES

7.1 Photochemical Grid Modeling

7.2 Urban Airshed Model 

7.3 Regional Scale Modeling

7.4 Model Results and SIP Interface

7.5 Other Analytical Techniques
2

8 EMISSIONS ANALYSIS

8.1 General

8.2 Biogenic Volatile Organic Compound (VOC) Emissions

8.3 Years to Analyze

8.4 Scenarios to Compare

8.5 Consistency with the SIP

8.6 New Source Review
CHAPTER 1

INTRODUCTION

1.1 General

The Clean Air Act (CAA), as amended in 1990, includes new

provisions in section 182(f) to control emissions of nitrogen

oxides (NOx) in certain ozone nonattainment areas and ozone

transport regions. Section 182(f) also specifies circumstances

under which the new NOx requirements would be limited or would

not apply. This document describes EPA's preliminary views on

how EPA should interpret section 182(f) and the circumstances

under which EPA would determine that the new NOx requirements

would be limited or would not apply. 

Although this document includes various statements that

States or petitioners must take certain actions, these statements

are guidance made pursuant to EPA's preliminary interpretations,

and thus do not bind the States and the public as a matter of

law. The EPA's interpretation of the section 182(f) provisions

will provide a basis for subsequent EPA approval or disapproval

of requests for exemption from the new NOx requirements. While

this document contains guidance on the interpretation of the

section 182(f) provisions, unique circumstances or as yet

unrecognized issues are likely to cause case-by-case exceptions

to arise. The EPA intends to provide the public with an

opportunity to comment on any exemption requests received by the

Agency. 

1.2 Nitrogen Oxides Supplement to the General Preamble for

Implementation of Title I of the Clean Air Act

The new NOx requirements, which are summarized below, are

described in detail in EPA's Nitrogen Oxides Supplement to the

General Preamble for Implementation of Title I of the Clean Air

Act. This guidance was published in the Federal Register on

November 25, 1992 (57 FR 55620).

Section 182(f) requires States to apply the same

requirements to major stationary sources of NOx as are applied to

major stationary sources of volatile organic compounds (VOC). 

The new NOx requirements are reasonably available control

technology (RACT) and new source review (NSR). These

requirements apply to major stationary sources in certain areas

that are designated nonattainment for the ozone national ambient

air quality standard (NAAQS) and in an ozone transport region. 
2

The RACT requirements are in section 182(b)(2). This

section requires RACT for major NOx stationary sources in ozone

nonattainment areas classified moderate and above as well as in

an ozone transport region. States are required to submit

regulations for RACT by November 15, 1992 and sources are

required to achieve compliance with RACT by May 31, 1995. The

EPA has defined RACT as the lowest emission limitation that a

particular source is capable of meeting by the application of

control technology that is reasonably available considering

technological and economic feasibility (44 FR 53762; September

17, 1979).

The NSR requirements are in section 182(a)(2)(C). This

section requires States to adopt revised NSR regulations in ozone

nonattainment areas classified marginal and above as well as

within an ozone transport region. States are required to submit

regulations for NSR by November 15, 1992. NSR provisions require

major new or modified stationary sources to comply with control

technology that represents the lowest achievable emission rate

and requires the sources to obtain emission offsets.

The RACT and NSR requirements for major sources in

attainment/unclassified portions of the northeast ozone transport

region originate in section 184(b)(2). 

1.3 Section 185B Report

Under section 185B, the Administrator, in conjunction with

the National Academy of Sciences (NAS), conducted a study on the

role of ozone precursors in tropospheric ozone formation. The

section 185B study must examined the role of NOx and VOC

emissions, the extent to which NOx reductions may contribute or

be counterproductive to achieving attainment in different

nonattainment areas, the sensitivity of ozone to the control of

NOx, the availability and extent of controls for NOx, the role of

biogenic VOC emissions, and the basic information required for

air quality models. The EPA announced in the February 26, 1993

Federal Register a 30-day public comment period on the draft

section 185B report. The final report was submitted to Congress

on July 30, 1993. The National Research Council announced the

completion of the December 1991 NAS report, Rethinking the Ozone

Problem in Urban and Regional Air Pollution. The final section

185B report incorporates this NAS report along with a recent EPA

report addressing the availability and extent of NOx controls. 

In addition, the section 185B report also provides EPA

perspectives on key ozone control strategy issues addressed by

the National Research Council, emphasizing the NOx issues as

directed by section 185B. 
3

In making a determination under section 182(f) that the NOx

requirements do not apply, or may be limited, the EPA must

consider the section 185B study. This section 182(f) document

includes consideration of EPA's section 185B report to Congress,

including the December 1991 NAS report.

1.4 Application of Section 182(f) Requirements

Section 182(f)(1) provides that the new NOx requirements

shall not apply if the Administrator determines that any one of

the following tests is met: 

(1) in any area, the net air quality benefits are greater

in the absence of NOx reductions from the sources

concerned; 

(2) in nonattainment areas not within an ozone transport

region, additional NOx reductions would not contribute

to ozone attainment in the area; or 

(3) in nonattainment areas within an ozone transport

region, additional NOx reductions would not produce net

ozone air quality benefits in the transport region.

Further, section 182(f)(2) states that the application of

the new NOx requirements may be limited to the extent necessary

to avoid excess reductions of NOx as determined by applying tests

similar to tests (1)-(3) above. 

As described in this document, the "net air quality

benefits" test and the "excess emissions" provision may be

applied in an ozone transport region or outside the transport

region; the "contribute to attainment" test may only be applied

outside of an ozone transport region; and the "net ozone

benefits" test may only be applied within an ozone transport

region. Where any one of the tests is met (even if another test

is failed), the section 182(f) NOx requirements would not apply

or, under the excess reductions provision, a portion of these

requirements would not apply. 
4

CHAPTER 2

ADMINISTRATIVE PROCEDURES

2.1 Processing with the State Implementation Plan (SIP) Revision

A State may, at any time, demonstrate to the Administrator

that the new NOx requirements should not apply. For example, a

State may submit a demonstration under section 182(f) along with,

or as a revision to, the SIP at the time the NOx RACT rules are

due; or a State may choose to submit the section 182(f)

demonstration at a later date along with or as part of a separate

SIP revision. The State's demonstration is not required to be a

SIP revision itself.

 The EPA will approve or disapprove the State's demonstration

when the Administrator approves a plan or plan revision. The EPA

will consider the section 185B report and will base its decision

on the demonstration and supporting information provided by the

State. Such demonstration and information should be in

sufficient detail for EPA to determine that the exemption request

is consistent with the guidance contained in this section 182(f)

document. The EPA encourages the States to consult with the

appropriate EPA Regional Office during the development of the

documentation. This is necessary to ensure that the

documentation provided by the State is likely to be approved and

that any required rules can be adopted in a timely manner. NOx

RACT and/or NSR rules that have been submitted or were previously

approved by EPA would continue to be processed for approval or

continue to be enforced while EPA considered the section 182(f)

demonstration.

2.2 Petition

Section 182(f)(3) provides that a person (including a State)

may petition the Administrator for a NOx exemption at any time

after the final section 185B report is submitted to Congress. 

The petition may be made with respect to any nonattainment area

or any ozone transport region. The EPA must grant or deny a

petition within 6 months after its filing. 

Since an individual petition is likely to affect the SIP

planning process which is primarily a State responsibility, EPA

believes it is reasonable to require the petitioner to provide a

copy of the petition and demonstration to the State or States

which have jurisdiction over the source or sources covered by the

petition at the same time it is submitted to the Administrator

(where a petition under section 182(f)(3) is being submitted by a

person other than the State itself). Where additional States may
5

be affected by the petition, the State receiving the petition

should coordinate with the other States as necessary. In some

cases there may be multiple petitions for a given area. In other

cases a single petition may have multi-State implications. 

Shortly after EPA receives a petition, the Agency will announce

its receipt and availability for public review in the Federal

Register. The EPA will provide the State(s) a 3-month period to

make a recommendation to EPA regarding the petition. This 3-

month period will run concurrently with the 6-month review period

required under section 182(f)(3). The petitioner should submit

the petition and demonstration to the Administrator through the

appropriate EPA Regional Office.

The EPA encourages any petitioner to consult with the State

air quality agency and the appropriate EPA Regional Office during

the development of a section 182(f) demonstration. This is

necessary to ensure that the documentation provided (1) meets EPA

guidance, (2) does not conflict with similar analyses by the

State, and (3) is likely to be accepted by the State and EPA. 

The EPA's decision to grant or deny a petition will include

consideration of the section 185B report and will be based on the

demonstration provided by the petitioner, the State's

recommendation, and the provisions of section 182(f). As noted

above, this document sets forth EPA's preliminary interpretations

of the section 182(f) provisions.

The EPA will provide notice of its final action on a

petition and the rationale for that action in a letter to the

petitioner within the 6 month period. In addition, EPA will

publish a notice describing the petition and EPA's determination

in the Federal Register. If EPA denies a petition, the

petitioner may supplement or revise the original petition at a

later date. Any revised petition would begin a new 6 month

period.

If EPA grants a petition, the section 182(f) NOx

requirements or portions of those requirements, would no longer

apply to those sources or areas, as described in EPA's approval

action. However, States remain free to adopt NOx restrictions

for other reasons. For example, a State may determine that NOx

reductions are needed for purposes of ozone maintenance planning,

ozone attainment in separate downwind nonattainment areas,

visibility protection, PM-10 control strategy, acid deposition

program or other environmental protection. The EPA could approve

certain NOx restrictions in a SIP revision despite granting a

petition under section 182(f), so long as the NOx restrictions

would not interfere with meeting any applicable requirement

concerning attainment and reasonable further progress or any

other applicable requirement of the CAA [see section 110(l)].
6

Section 182(f)(3) states that a person may petition the

Administrator for a determination under section 182(f) at any

time after the final report under section 185B is submitted to

Congress. The final section 185B report was sent to Congress by

the Administrator on July 30, 1993. Section 182(f)(3) also

requires the Administrator to grant or deny such a petition

within 6 months after its filing with EPA.
7

CHAPTER 3

NET AIR QUALITY BENEFIT

3.1 Demonstration

This demonstration applies to specific sources in an ozone

nonattainment area or in an ozone transport region. It must show

that NOx reductions from the sources seeking the exemption would

be counter-productive overall, considering the net air quality

benefits. Congress specified in this "test" for specific sources

a higher hurdle than in the other tests for areawide exemptions: 

the demonstration must show a beneficial impact from the

avoidance of the NOx controls.

The procedure for this test is to first project areawide

baseline conditions that may be expected at the attainment

deadline (section 8.3). Then, analyses are conducted for 2

scenarios (section 3.4): with and without NOx reductions at the

sources concerned. As described in section 8.2, multi-year

analyses may also be conducted.

3.2 Factors

Unlike the tests described in chapters 4 and 5, the CAA does

not limit this test to consideration of ozone impacts. Instead,

this test is based on a broader set of air quality impacts

considered in the CAA. There are many air quality impacts

explicitly addressed in the CAA, both health and welfare related,

that may be directly or indirectly related to NOx emissions. 

These impacts include ozone, nitrogen dioxide, and particulate

matter formation, visibility impairment, acid deposition, air

toxics formation, and nitrogen deposition in nutrient-sensitive

areas. 

Due to the number and variety of impacts, it is generally

impractical or impossible to compare effects quantitatively from

one of these factors to those from another factor or among

several factors. For example, there is no readily available

scale to use to compare nitrogen dioxide impacts with acid

deposition impacts and/or visibility impacts. Thus, in order to

describe a method for determining the "net air quality benefit,"

a distinction must be made regarding which of the many factors

can and should be analyzed.

The EPA has concluded that the factors considered for the

purposes of section 182(f) must be consistent with the

requirements of the CAA. Thus, although "air quality impacts"

could potentially be defined in a very broad manner, EPA has
8

concluded that the air quality impacts considered under section

182(f) must related directly to goals, standards, or mandates

that are explicitly addressed in the CAA. Therefore, the test

for net air quality benefits must assure that a decision to grant

an exemption would not interfere with the achievement of the

specific programs or goals mandated in the CAA.

The primary test should be the effect the exemption would

have on attainment of the primary NAAQS for the criteria

pollutants. The primary NAAQS are set by the Administrator to

assure protection of the public health with an "adequate margin

of safety;" EPA has, thus, concluded that this test should focus

specifically on the effect of an exemption on the numbers of

exceedances of the primary NAAQS. A petitioner should model the

"NOx control" vs. "no NOx control" scenarios to assess the impact

the NOx controls would have on the numbers of exceedances of the

primary NAAQS, as described elsewhere in this document.

Secondary tests, as needed, can extend to the (qualitative

or quantitative) consideration of other air quality impacts that

are explicitly recognized in the CAA. These could include, for

example, the welfare effects which EPA has considered and deemed

necessary to protect against in setting secondary NAAQS for the

criteria pollutants. A petitioner could also consider any other

air quality effects that are explicitly addressed in the CAA

through goals, standards or mandates, for example, visibility or

air toxics emissions.

The CAA requires the NAAQS to be attained as expeditiously

as practicable and the CAA includes deadlines for rule adoption,

submittal of control strategies, and attainment of the primary

national ambient air quality standards (NAAQS). Thus, the

impacts on attainment of the primary NAAQS must be a primary

concern to this net air quality benefit test. In contrast,

impacts on nutrient-sensitive areas is an important environmental

issue that is addressed in the CAA, but does not have the same

detailed set of requirements and deadlines stated in the CAA as

do the NAAQS; thus, it should generally be a secondary concern to

this net air quality benefit test. Further, EPA is not aware of

any conflicts between the section 182(f) exemption and the

requirements of section 407, concerning acid deposition, that

might be considered in this analysis; i.e., granting a section

182(f) exemption would not relieve, conflict with, or otherwise

affect a source's obligation or ability to achieve NOx reductions

consistent with the section 407 requirements. In cases where NOx

reductions from a utility subject to section 407 would be

counterproductive to the net air quality benefit, EPA encourages

the State and utility to use the emission averaging provisions of

section 407 to achieve the required NOx reductions at a location
9

where they are not counterproductive to the net air quality

benefit. If any statutory conflicts are documented, they could

be considered on a case-by-case basis. 

In all cases, the method for consideration of the net

benefits must be related primarily to "air quality" since section

182(f) specifically requires a determination of the "air quality"

benefits. Thus, simpler tests, such as a "net emissions" test,

should not be relied upon since changes in emissions are not

necessarily directly related to changes in air quality. In

general, air quality impacts can be best determined by use of air

quality dispersion models. However, at the present time, there

are no EPA-recommended air quality dispersion models for

simulation of nitrate (particulate) formation or comparison among

ozone, nitrogen dioxide, and/or PM-10 NAAQS impacts in a single

nonattainment area. 

In order to use air quality dispersion modeling whenever

possible and to avoid conflicts with other requirements of the

CAA, the methods described below should be used to determine the

net air quality benefit over an appropriate geographic area (see

section 3.3) which includes the ozone nonattainment areas

encompassing or nearby the sources concerned. These methods

include a primary consideration of the primary NAAQS air quality

benefits and secondary consideration of other air quality

benefits.

Ozone Nonattainment Areas

For areas that are nonattainment only for ozone, the effects

of NOx reductions on ozone concentrations should be quantified

with currently available air quality modeling techniques (see

chapter 7). The net air quality benefit should be based on a

comparison of the geographic area exposed to concentrations above

the ozone NAAQS with and without NOx reductions from the sources

concerned. 

Where Urban Airshed Model (UAM) results are available,

population exposure to concentrations above or near the NAAQS may

be used instead of the geographic area exposure factor. The

Regional Oxidant Model (ROM) results for NOx reduction scenarios

over major emissions/population centers should not be used

quantitatively for population exposure analyses. This is because

ROM results have their largest associated uncertainties in areas

where there is an inhomogeneous mix of emissions from major

sources. Since such areas also tend to have greatest

populations, use of the ROM, by itself, to estimate population

exposure may have considerable associated uncertainty.
10

It is important to note that EPA believes that photochemical

grid models such as UAM and ROM are not sufficient to assess

incremental changes to areawide ozone concentrations from

emissions reductions at a single or group of small sources. 

Emission changes should amount to some significant fraction of

base emissions before modeling results with ROM or UAM can be

interpreted with sufficient confidence that the results are not

lost in the noise of the model and the input data. 

The EPA has reservations with respect to modeling NOx

reductions at a single source or group of sources unless the

modeling includes at least 10% of the domain-wide emissions. 

Thus, this exemption analysis is appropriate for groups of large

emitters or for consideration of entire source categories, rather

than emission reductions at a single or group of small sources. 

However, EPA will consider on a case-by-case basis an analysis

that considers less than a 10% change in the domain-wide

emissions. In such cases, the analysis of a small portion of the

emissions would show only a small difference in ozone

concentration, if any, between the with NOx and without NOx

scenarios, and, therefore, consideration of secondary factors

(described below) is particularly important in order to show a

net air quality benefit.

In some cases, the amount of emission reductions assumed in

the modeling analysis could be very large; thus, there may be

cases where the analysis does not result in any values above the

NAAQS for any pollutant and, thus, there would not be a

comparison of area or population exposed. This could occur even

though the difference in ozone concentration between the two

scenarios is large. In such cases, the petitioner should look to

the factors considered in the secondary test, such as welfare

effects or other air quality effects addressed by the CAA.

Areas Nonattainment for Both Ozone and Nitrogen Dioxide 

For areas that are nonattainment for both ozone and nitrogen

dioxide, NOx reductions clearly are needed to provide for

attainment of the nitrogen dioxide standard, while either NOx or

VOC reductions (or both) might best provide for attainment of the

ozone standard. In such cases EPA would not make a finding of a

net air quality benefit since the CAA requires the NAAQS for

nitrogen dioxide to be met as expeditiously as practicable. 

Areas Nonattainment for Both Ozone and PM-10

For areas that are nonattainment for both ozone and PM-10, a

determination is first needed if the secondary nitrates formed

from NOx emissions contribute significantly to the PM-10 NAAQS
11

violation(s) in the specific nonattainment area. This

significance determination is needed since, especially in the

eastern United States, EPA expects that the nitrate portion of

measured PM-10 will be found to be insignificant in many cases. 

Where sufficient and reliable data exist to determine the nitrate

contribution to ambient PM-10 concentrations, this determination

may be limited to those NOx emissions sources subject to the

section 182(f) requirements. Where the contribution is

insignificant (see below), then the net air quality determination

should be based primarily on the ozone impacts. Where the

contribution is significant, EPA would not make a finding of a

net air quality benefit since the CAA requires the NAAQS for PM10 to be met as expeditiously as practicable. For this purpose,

EPA intends to use its definition of a significant contribution

to a PM-10 nonattainment area which is 1.0 microgram per cubic

meter (nitrate and associated materials) for the annual standard

and 5 micrograms per cubic meter for the 24-hour standard (40 CFR

51.165). 

Areas Nonattainment for Ozone and Carbon Monoxide, Lead or

Sulfur Dioxide

For carbon monoxide, lead, and sulfur dioxide, EPA is not

aware of any significant impacts from NOx reductions. Therefore,

the net air quality benefits determination should be primarily

based on the ozone modeling analysis described above for areas

nonattainment for only ozone.

As noted above, equal consideration of all NOx impacts is

generally impractical in this net air quality benefit test

because of the lack of scales to compare the impacts among the

various factors. Nevertheless, additional factors explicitly

addressed in the CAA such as those listed below must be

considered at least on a qualitative basis in addition to any

information developed from the NAAQS analyses. Consideration of

the factors below is especially important in cases where the

analyses on the NAAQS pollutants cannot clearly determine the net

air quality benefit. In any case, EPA believes the amended CAA

places a substantial burden on the applicant to provide a clear

showing that NOx reductions would be counterproductive overall,

considering the net air quality benefits. Additional factors to

determine net air quality benefit may include but are not limited

to:

1. Effects associated with long-term exposures to plants,

animals, and materials.

2. Visibility impairment, long-term and episodic acid

deposition, air toxics, and deposition of nitrogen in
12

nutrient-sensitive watersheds.

3.3 Geographic Scope

In contrast to the other section 182(f) tests, the net air

quality benefit test is not specifically limited to an ozone

nonattainment area or ozone transport region and may be directed

at a specific set of sources. Thus, a very broad geographic area

should be considered. The area may, in some cases, extend beyond

an ozone nonattainment area or ozone transport region. In

addition, the area must not be so small that downwind impacts

from NOx emissions are not fully considered. Sufficient area is

needed to allow for completion and consideration of the various

chemical transformations of NOx and interaction with other

pollutants. At a minimum, the geographic area should include the

ozone nonattainment area(s) encompassing or nearby the sources

concerned. For example, petitioning sources located in

attainment portions of the ozone transport region should analyze

their impact on nearby nonattainment areas and should consider

other factors, such as visibility impacts throughout the

surrounding area.

3.4 Scenarios

Section 182(f) states, for this test, that EPA must

determine that the net air quality benefits are greater in "the

absence of reductions of oxides of nitrogen from the sources

concerned." The procedure for this test is to first project

areawide baseline emissions that may be expected at the

attainment deadline (see sections 3.3 and 8.3). (As described in

section 8.3, multi-year analyses may also be conducted.) Second,

the projected baseline emissions are held constant, except for

the subject individual sources. Then, the air quality analyses

are conducted for these two scenarios: 

1. the projected baseline emissions of VOC and NOx

(without NOx reductions from the sources concerned) and

2. the projected baseline emissions of VOC and NOx

emissions including NOx reductions at all emission

sources subject to the NOx NSR and RACT provisions of

section 182(f).

With respect to new major sources, the two scenarios should

take into account application of the section 182(f) NSR

requirements as described in section 8.5.

3.5 Sources
13

For this net air quality benefit test, the CAA refers to

"reductions of oxides of nitrogen from the sources concerned." 

For purposes of this analysis, "the sources concerned" are

defined as the sources that would be exempted from the section

182(f) NOx requirements by the petition or State request. The

sources concerned may be identified in any of the following ways: 

(1) specific individual sources, (2) one or more source

categories, or (3) a geographic area containing a group of

sources. As described in section 3.4, the sources concerned must

be analyzed together with other NOx and VOC sources in the area;

these other NOx sources should take into account application of

the section 182(f) RACT and NSR requirements (as part of the

areawide baseline conditions expected at the attainment deadline

year) since those NOx reductions are not the subject of the

exemption request.
14

CHAPTER 4

CONTRIBUTE TO ATTAINMENT

4.1 Demonstration

This demonstration applies only to ozone nonattainment areas

that are not within an ozone transport region. The demonstration

must show that additional NOx reductions would not contribute to

ozone attainment in the area. 

The procedure for this test is to utilize a photochemical

grid model (see chapter 7) to simulate several episode cases over

the nonattainment area under conditions that may be expected at

the attainment deadline (see section 8.2) considering three

emission reduction scenarios (see section 8.3): (1) substantial

VOC reductions; (2) substantial NOx reductions; and (3) both the

VOC and NOx reductions. If the areawide predicted maximum 1-hour

ozone concentration for each day modeled under scenario (1) is

less than or equal to that from scenarios (2) and (3) for the

same day, then the test is passed and the section 182(f)

requirements would not apply.

4.2 Episodes to Consider

In most ozone nonattainment areas it is likely that portions

of the area would benefit from NOx reductions and other portions

would not for each modeled day. The EPA believes it is

appropriate to focus this analysis on the areawide maximum 1-hour

predicted ozone concentration since this value is critical to the

attainment demonstration. In contrast, it should not be

necessary to examine the maximum 1-hour ozone concentrations at

each point modeled in the area since these points are not

necessarily important to development of the attainment

demonstration and since this is the only one of the section

182(f) tests which is not keyed to net benefits.

In certain ozone nonattainment areas it is possible

that NOx emission reductions may help to reduce the areawide

maximum predicted ozone concentration under some meteorological

conditions but not under others. The phrase "would not

contribute to attainment" could be interpreted to mean that NOx

emission reductions would not help reduce (1) any areawide

maximum 1-hour predicted ozone concentration, (2) the majority of

areawide maximum 1-hour predicted ozone concentrations, or

(3) the most severe areawide maximum 1-hour predicted ozone

concentration. 

The EPA believes that the "majority" option is not
15

appropriate since this is the only one of the section 182(f)

tests which is not keyed to net benefits. Furthermore, (1) an

area may need to demonstrate attainment under multiple

meteorological conditions, (2) generally a small number of

episodes will be modeled and (3) the NAAQS is based on multiple

exceedances rather than a single, most severe value. For the

above reasons, EPA believes this determination should be based on

each areawide maximum 1-hour predicted ozone concentration

modeled in accordance with this guidance (chapter 7). Thus, all

of the areawide maximum 1-hour predicted ozone concentrations

modeled must be greater with NOx reductions at the sources

concerned than without the reductions, or no exemption would be

granted. An area is not required to model all past exceedances;

only those episodes selected for modeling in accordance with EPA

guidance (chapter 7) need to be considered. 

4.3 Geographic Scope

This demonstration focuses on attainment of the ozone NAAQS 

"in the area." The EPA interprets this to mean, at a minimum, in

the nonattainment area. In contrast to the provision for

transport regions, which is likely to consider several attainment

and nonattainment areas in the section 182(f) analysis, this

demonstration is limited to consideration of the effects in a

single nonattainment area due to NOx emissions reductions from

sources in the same nonattainment area. However, since the

effects of an attainment strategy may extend beyond the

designated nonattainment area and since photochemical grid

modeling is necessary for this demonstration and is likely to use

a modeling domain larger than the nonattainment area, EPA

encourages States/petitioners to include consideration of the

entire modeling domain.

States should consider imposition of the NOx requirements if

needed to avoid adverse impacts in downwind areas, either intraor inter-State. States need to consider such impacts since they

are ultimately responsible for achieving attainment in all

portions of their State (see generally section 110) and for

ensuring that emissions originating in their State do not

contribute significantly to nonattainment in, or interfere with

maintenance by, any other State [see section 110(a)(2)(D)(i)(I)].

4.4 Applicability to Areas Requesting Redesignation to

Attainment

In some cases, an ozone nonattainment area might attain the

ozone standard, as demonstrated by 3 years of adequate monitoring

data, without having implemented the section 182(f) NOx

provisions over that 3-year period. Where the State submits a
16

request for redesignation to attainment along with necessary

supporting documentation and where NOx RACT and NSR requirements

were not implemented over that 3-year period, it is clear that

the section 182(f) language is met since "additional reductions

of oxides of nitrogen would not contribute to attainment." That

is, since attainment has already occurred, additional NOx

reductions could not improve the area's attainment status and,

therefore, the section 182(f) demonstration could be approved. 

Additional guidance on this subject is contained in a September

17, 1993 memorandum from Michael Shapiro to the EPA Regional

Offices regarding requests for redesignation to attainment.

The section 182(f) demonstration would not be approved if

there is evidence, such as photochemical grid modeling, showing

that the NOx exemption would interfere with attainment or

maintenance in downwind areas. As noted above, section 110

prohibits such impacts.
17

CHAPTER 5

NET OZONE AIR QUALITY BENEFIT

5.1 Demonstration

This demonstration applies in an ozone transport region. It

must show that additional NOx reductions would not produce net

ozone benefits in the transport region. In this test the net

benefit must be demonstrated on a regionwide basis. Regionwide

includes all portions of the ozone transport region in which

impacts from NOx emissions from the area seeking the exemption

can be determined by the photochemical grid model.

The procedure for this test is to utilize a photochemical

grid model (see chapter 7) to simulate conditions that may be

expected at the attainment deadline (see section 8.3) considering

three emission reduction scenarios (section 8.4): (1)

substantial (se section 8.4) VOC reductions; (2) substantial NOx

reductions; and (3) both the VOC and NOx reductions. The net

ozone benefit may be determined by comparing the ozone

concentrations modeled in scenario (1) with results modeled from

scenarios (2) and (3). If the exposure to ozone concentrations

from scenario (1) is less than or equal to the exposure to ozone

concentrations from scenarios (2) and (3), then the section

182(f) net ozone benefits demonstration could be approved. As

described in section 8.3, multi-year analyses may also be

conducted.

5.2 Factors

The ozone NAAQS is set at 0.12 parts per million (ppm). In

defining "net ozone benefit," however, EPA recognized that

various forms of expression could be considered with respect to

ozone impacts. These forms include the 1-hour 0.12 ppm NAAQS, a

1-hour value less than 0.12 ppm, an 8-hour value set lower than

0.12 ppm, and a seasonal value set lower than the 0.12 ppm value. 

However, ozone concentrations with different averaging periods

and values cannot readily be compared to each other. For

example, it is difficult to compare a set of 1-hour ozone peak

concentrations above 0.12 ppm against a set of 8-hour ozone peak

concentrations above 0.06 and determine which results are more

beneficial. 

The EPA believes it is reasonable to focus the net ozone

benefits test on the 1-hour 0.12 ppm ozone NAAQS, where possible

for the following reasons: (1) the 0.12 ppm ozone NAAQS has been

set by the Administrator as the level necessary to protect the

most sensitive individuals from adverse health effects with an
18

"adequate margin of safety;" (2) ozone concentrations with

different averaging periods and values cannot readily be compared

to each other, (3) the purpose of the various section 182

provisions is primarily to attain the ozone NAAQS, and (4) it is

important for this guidance document to avoid any conflicts (as

noted in chapter 3) with the section 182 requirements. 

Therefore, the averaging time to be used should be the one-hour

daily maximum ozone concentration and the analysis should focus

on values above the 0.12 ppm NAAQS level. Specifically, the net

ozone benefits test focuses on the total geographic area exposed

to ozone concentrations above the 0.12 ppm NAAQS level.

Where Urban Airshed Model (UAM) results are available,

population exposure to concentrations above or near the ozone

NAAQS may be used, instead of the geographic area exposure

factor. The Regional Oxidant Model (ROM) results for NOx

reduction scenarios over major emissions/population centers

should not be used quantitatively for population exposure

analyses. This is because ROM results have their largest

associated uncertainties in areas where there is an inhomogeneous

mix of emissions from major sources. Since such areas also tend

to have greatest populations, use of the ROM, by itself, to

estimate population exposure may have considerable associated

uncertainty.

Depending on the amount of NOx and VOC reductions selected

for each scenario, the model results in some cases might show all

scenarios to be below the 0.12 ppm ozone NAAQS level. In such

cases some might argue that there is no ozone benefit and, thus,

the NOx requirements should not apply. The EPA does not agree

with such an interpretation because the CAA specifies "net ozone"

rather than "ozone attainment" for this test. In fact, a "net"

ozone test is necessary to integrate the benefits and disbenefits

of NOx reductions that are likely to vary from grid to grid in a

given analysis area. That is, NOx reductions may reduce hourly

ozone concentrations in some locations and increase hourly ozone

concentrations in other locations within the same modeling

domain. Therefore, a broader factor is needed than the areawide

0.12 ppm where the modeled scenarios show all values below the

ozone NAAQS. 

Consideration of ozone air quality impacts other than the

primary NAAQS values is appropriate as a secondary factor. Thus,

values such as the following are appropriate for consideration

where no conclusion can be drawn through the above analysis based

on the ozone NAAQS values: effects associated with long-term

exposures to ecosystems, crops, animals, and materials.

5.3 Attainment/Unclassified Portions
19

The section 182(f)(1)(B) demonstration explicitly refers to

nonattainment areas within an ozone transport region. The CAA

does not clearly state whether or not portions of ozone transport

regions that are attainment/unclassified can make the net ozone

benefit demonstration. The section 182(f)(1) net air quality

benefit test is available to any area; however, as noted

previously it is a higher hurdle. Thus, while a severely

polluted area might be able to demonstrate that NOx reductions do

not apply because the "net ozone benefits" test is satisfied, the

CAA could be interpreted to require NOx reductions in the

surrounding attainment area because that area cannot meet the

same test. It is unlikely that Congress intended such a result.

An alternative reading of the CAA can be found through

section 184(b)(2). This provision states that the attainment/

unclassified portions of the transport region must meet "the

requirements which would be applicable to major stationary

sources if the area were classified as a moderate nonattainment

area." Thus, the CAA could be interpreted to provide the same

section 182(f)(1)(B) demonstration process for these attainment/

unclassified areas, since they should be treated as moderate

nonattainment areas for the purpose of applying the section

182(f) requirements and moderate nonattainment areas in the

transport region are eligible to meet the "net ozone benefits"

test.

Even without that language, EPA would be inclined to allow

an attainment/unclassified area in a transport region to satisfy

the "net ozone benefits" test. It would be absurd, and therefore

it is unlikely that Congress intended to apply more stringent

requirements in the attainment/unclassified portions of the

transport region than would apply to the more severely polluted

portions. Congress apparently did not intend any lesser

requirements to apply in the attainment/unclassified portions of

the transport region. The EPA believes that it is appropriate to

extend the section 182(f) provision beyond the boundaries of a

nonattainment area into adjacent attainment/unclassified areas

which are part of the same section 182(f) demonstration. Thus,

where a State/petitioner demonstrates that NOx reductions would

not produce net ozone benefits in the transport region, then the

section 182(f) NOx requirements would not apply to those sources

or areas as described in EPA's approval action. Such a

demonstration must include all portions of the ozone transport

region in which impacts from NOx emissions from the area seeking

the exemption can be determined by the photochemical grid model.
20

CHAPTER 6

EXCESS EMISSIONS REDUCTIONS

6.1 General

Section 182(f)(2) provides the flexibility to limit the

scope of the NOx NSR and RACT requirements. Application of the

NOx NSR and/or RACT requirements can be limited to the extent

that any portion of those reductions are demonstrated to result

in "excess reductions." The tests for demonstrating excess

reductions are generally the same as in section 182(f)(1): net

air quality benefit, contribute to attainment and net ozone

benefit. However, in this case, the demonstration must show that

a portion of the otherwise required NOx reductions are either

counterproductive to the net air quality, do not contribute to

attainment, or do not provide a net ozone benefit [depending on

the section 182(f) test applied].

As described below, for the contribute to attainment or net

ozone tests, the excess reductions test must show that certain

NOx reductions are in excess of the reductions specified in

either the attainment demonstration required by section 182 and

contained in the approved SIP or an attainment demonstration

adopted by the State to meet the section 182 attainment

demonstration requirement and submitted to EPA for approval. The

excess emission reductions may be described, for example, as (1)

an areawide across-the-board tonnage reduction; (2) emissions

attributed to specific sources; or (3) emissions from a

geographic portion of the nonattainment or transport area.

6.2 Demonstration

The "contribute to attainment" and "net ozone benefit" tests

described in chapters 4 and 5 both require an areawide or

regional analysis. In such areawide/regional analyses, NOx

emission reductions at a large number of sources are considered. 

These analyses are appropriate to determine in a directional

manner whether or not NOx reductions are expected to be

beneficial with respect to the air quality in the area/region. 

The analyses described in chapters 4 and 5 may be less precise

than an attainment demonstration required under section 182(c).

The EPA believes that the excess reductions provision

requires a more precise analysis; specifically an analysis which

is based on the attainment demonstration. That is, the excess

reductions provision must be more than a directional finding on

an areawide basis. Under the excess reductions provision, an

analysis is needed to show that a specific portion of the total
21

areawide NOx emissions is not beneficial under one of the three

tests. Thus, individual or groups of sources may petition to

show that, while NOx reductions may be beneficial directionally

in the area, NOx reductions from their specific sources are not

beneficial and, thus, should be exempt from the NOx requirements.

Without providing some constraints in this guidance

document, the excess reductions provisions could undermine the

section 182(f) requirements, since each individual emission

source could theoretically petition for an exemption with the

argument that their small contribution to the overall ozone

problem is inconsequential. Such a petition might be considered

consistent with the analyses required in chapters 4 and 5, since

an exemption may be granted where the modeled NOx reductions show

no impact on ozone concentrations. Certainly, if EPA allowed

very small amounts of NOx reductions to be modeled individually,

this interpretation would create a significant loophole. 

Congress would not have intended, and therefore EPA does not

accept the argument, that the owner/operator of one car or one

small boiler can be excused from the CAA requirements because

their emissions, viewed alone, are small. Considered together

with other small contributions, the emissions may be important to

attainment. That is, emissions from one car or one commercial

boiler would not change the areawide ozone concentration, yet

together with other cars or boilers, they may be critical to the

area's attainment strategy. Furthermore, as previously

described in this document, ozone air quality models should not

be applied solely to determine the incremental effect of small

sources as such emissions could be lost in the noise of the air

quality model and emissions inventory uncertainties when

considered alone. 

For the above reasons, EPA has determined that the excess

reductions demonstration for the "contribute to attainment" or

"net ozone benefits" tests must be tied to the area's SIP

attainment demonstration. Thus, this test must show that the

excess reductions are reductions in excess of those specified in

the attainment demonstration required by section 182 and either

contained in the approved SIP or as adopted by the State to meet

the section 182 attainment demonstration requirement and

submitted to EPA for approval. This tie to the attainment

demonstration assures that an excess reductions petition would

not arbitrarily be based on small emissions and would not

undermine the State's control strategy. 

In contrast, the "net air quality benefit" test discussed in

chapter 3 is intended to address an individual or small number of

sources and already has an adequate constraint. The net air

quality benefit test requires a showing that NOx reductions

specifically from the sources concerned are counterproductive. 
22

The net air quality benefit test imposes a higher hurdle than the

other two tests and EPA believes this higher hurdle is adequate

for purposes of the excess emissions test as well.
23

CHAPTER 7

MODELING TECHNIQUES

7.1 Photochemical Grid Modeling

As described in chapters 3-6, photochemical grid modeling is

generally needed to document cases where NOx reductions are

counterproductive to net air quality (chapter 3), do not

contribute to attainment (chapter 4), do not show a net ozone

benefit (chapter 5), or include excess reductions (chapter 6). 

As described below, the Urban Airshed Model (UAM) or, in an ozone

transport region, the Regional Oxidant Model (ROM) are acceptable

models for these purposes. 

The EPA investigated the feasibility and acceptability of

applying relatively inexpensive screening techniques to evaluate

if NOx control measures are likely to be beneficial with respect

to attainment of the ozone NAAQS (Langstaff and Scheffe, 1991). 

However, EPA determined that, as a technical matter,

photochemical grid modeling is the only reliable tool to justify

an areawide exemption from the NOx requirements.

The EPA's reliance on photochemical grid models is supported

by the recently published findings of the NAS on tropospheric

ozone (December 1991). The NAS report concluded that threedimensional or grid-based ozone air quality models are currently

the best available models for representing the chemical and

physical processes of ozone formation. The report provides a

list of such models (Table 10-1), including UAM and ROM. The NAS

report also states that "ROM is the only regional model available

for assessment of control strategies for urban and rural ozone in

the eastern United States" (page 365).

The 1990 CAA requires the use of gridded models in many

ozone nonattainment areas. In 1990, EPA released an updated

version of the UAM, reflecting numerous advances in

photochemistry and numerical solution techniques which emerged

during the 1980s. An extensive multi-volume UAM User's Manual

was prepared to facilitate operation of the UAM. Guidance on

regulatory application of the UAM was completed in July 1991. 

Several efforts are underway to improve pre- and post-processing

UAM capabilities and train the States in applying the model.

The EPA encourages applications of advanced modeling methods

where they are found to be more appropriate. Such methods may be

acceptable on a case-by-case basis after (1) preparation of a

modeling protocol, (2) proper testing and evaluation, and (3)

approval by the appropriate EPA Regional Office.
24

Less sophisticated models, such as EKMA, lack the detailed

treatment/consideration of physical orientation of NOx sources

and dispersion of their plumes. Further, since trajectory models

only address a limited number of trajectories, they cannot assess

whether NOx control contributes to attainment at all locations in

an ozone nonattainment area. Therefore, such models are

insufficient and not acceptable for the section 182(f)

demonstration.

7.2 Urban Airshed Model

UAM results are acceptable for the purpose of the section

182(f) demonstrations. Application of UAM should be consistent

with techniques specified in the EPA "Guideline on Air Quality

Models (Revised)." Further, application of UAM should also be

consistent with procedures contained in the EPA "Guideline for

Regulatory Application of the Urban Airshed Model" (July 1991). 

Thus, episode selection for the section 182(f) demonstration

should be consistent with the UAM guidance for SIP attainment

demonstrations. An assessment of the model's performance and a

copy of the modeling protocol should be included in the analysis

for informational purposes.

7.3 Regional Scale Modeling

In an ozone transport region, the net ozone benefits test

should be met by use of regional scale modeling. Regional scale

modeling is needed since the section 182(f) language explicitly

refers to net ozone benefits "in such region." Regionwide or

regional scale modeling includes all portions of the ozone

transport region in which impacts from NOx emissions from the

area seeking the exemption can be determined by the photochemical

grid model. Prior to the availability of ROM and/or UAM results

supporting the section 182(c) attainment demonstrations, the

EPA's "Regional Ozone Modeling for Northeast Transport" study

(June 1991) is an acceptable basis for this demonstration. When

more recent ROM and/or UAM regionwide studies for the Northeast

Ozone Transport Region have been completed and are available,

they must be used for any section 182(f) demonstration.

Where UAM studies have been completed and are available, ROM

results are acceptable for evaluating effects outside of the UAM

modeling domains established pursuant to attainment demonstration

requirements for section 182. Thus, ROM results are acceptable

for evaluating effects in portions of a transport region outside

of the UAM modeling domain for the purpose of a section 182(f)

demonstration. It is not appropriate, however, to use ROM to

assess the effects in an individual city outside of any UAM

domain. ROM is most suitable for assessing composite impacts
25

over large areas (which may include individual cities) where UAM

results are unavailable. Results of available ROM applications

are archived on the EPA's Gridded Model Information Support

System (GMISS).

7.4 Model Results and SIP Interface

Where a petition for an exemption [section 182(f)(1)] or

excess reductions determination [section 182(f)(2)] is granted by

EPA prior to adoption and submittal of the State's rules, the

State may simply choose not to submit the NOx rules. If a

petition is granted after submittal of the NOx rules, but prior

to EPA approval, the State may choose to withdraw the rules and

preclude further EPA action. In a case where a petition is

granted ("exempted area") after EPA approves of the NOx rules,

the SIP would need to be modified through a SIP revision to

rescind the NOx rules provided such rescission would not

interfere with attainment or reasonable further progress

[section 110(l)].

Following application of a photochemical grid model that is

required for serious and above areas to support the attainment

demonstrations due by November 1994, a State must select and

adopt a control strategy that provides for attainment as

expeditiously as practicable, but no later than the date

prescribed in section 181. This decision must be addressed by a

State whether or not an area was exempted from the November 1992

submittal of NOx RACT and/or NSR rules and may result in revision

of the previously adopted rules. In some instances the NOx RACT

and NSR requirements already adopted may need to be supplemented

with additional or more advanced NOx controls in order for the

area to attain the NAAQS.

In other cases, an area initially exempted may choose, based

on the new photochemical grid modeling results, to adopt certain

NOx reduction rules in order to attain and/or meet reasonable

further progress requirements through NOx substitution. The area

would be removed from "exempt" status since NOx reductions were

subsequently found to be beneficial in their ozone attainment

plan. Consequently, the area would have to adopt the NOx RACT

and NSR rules except to the extent modeling shows that the

controls beyond those chosen are "excess reductions" (chapter 6)

or are counterproductive to the net air quality (chapter 3). 

Credit for NOx substitution would be granted only if in

accordance with the EPA guidance. In any event, these changes

must be submitted as a SIP revision and must provide for

attainment as expeditiously as practicable and meet reasonable

further progress requirements.
26

Alternatively, for an area that adopted the NOx RACT and NSR

rules as required by section 182 (i.e., not exempt), a State may

choose to revise some or all of those rules to require less NOx

stationary source controls. This action would be based on the

application of a photochemical grid model showing that the

subject NOx controls result in excess emission reductions, as

determined using the section 182(f) tests set forth at the

beginning of this section. The revisions must be submitted as a

SIP revision and the SIP must demonstrate attainment as

expeditiously as practicable.

7.5 Other Analytical Techniques

Guidelines on analytical techniques for assessing other air

quality impact factors, such as acid deposition, population

exposure or visibility, are not readily available. Therefore,

EPA encourages petitioners to consult with the State and EPA

Regional Office to agree on an acceptable methodology on a caseby-case basis.
27

CHAPTER 8

EMISSIONS ANALYSIS

8.1 General

As described in chapters 3-6, photochemical grid modeling is

needed to document cases where NOx reductions are

counterproductive to net air quality (chapter 3), do not

contribute to attainment (chapter 4), do not show a net ozone

benefit (chapter 5), or include excess reductions (chapter 6). 

Application of these models requires the use of a representative

emissions inventory. This chapter describes the emission

inventory requirements for the various section 182(f)

demonstrations.

8.2 Biogenic Volatile Organic Compound (VOC) Emissions

The NAS report states that, in some cases, "without control

of NOx emissions, this VOC background should be able to generate

ozone concentrations that exceed the NAAQS concentration of 120

ppb" (page 244). Biogenic emissions can influence both the

nature (i.e., VOC or NOx) and extent of required emissions

controls. Therefore, inclusion of biogenic emissions are

necessary inputs to model applications which assess the roles of

VOC and NOx in ozone formation for purposes of section 182(f). 

In estimating biogenic emissions, the most recent version of the

Biogenic Emissions Inventory System (BEIS) (available through the

EPA Regional Offices) should be used.

8.3 Years to Analyze

In general, the purpose of the section 182(f) requirements

for NOx is related to attainment of the ozone standard. This

suggests an analysis that is focussed on the time that attainment

of that standard is required. In addition, other sections of the

CAA require moderate and above ozone nonattainment areas to

develop modeling analyses which demonstrate attainment by the

appropriate statutory deadline; to the extent that such modeling

analyses are already underway, they could be useful for the

section 182(f) demonstration also. 

Considering these points, EPA believes that the 182(f)

demonstrations should, at a minimum, reflect conditions expected

at the time the subject area is required to attain the ozone

standard. For example, in a serious ozone nonattainment area,

the year would be 1999. As described in section 8.5, the

conditions should also be consistent with assumptions contained

in the SIP. Thus, base year emissions would be projected to the
28

year reflecting the attainment deadline and would include growth

in VOC and NOx emissions as well as CAA-mandated VOC emission

reductions. Specific emission scenarios with and without NOx

reductions would be built upon this projected emissions baseline

as described elsewhere in this document. In addition, as

described later in this section, multi-year analyses may also be

conducted.

In an ozone transport region, a section 182(f) demonstration

would likely cover an area which includes ozone nonattainment

areas of more than one classification, and thus more than one

attainment deadline. For example, a metropolitan area may have a

higher classification than a nearby rural nonattainment area. 

For these areas, it is possible that NOx reductions may be

beneficial to attainment in the near term with respect to the

rural nonattainment area (and lesser classification deadline)

but, at the same time or in a longer timeframe, NOx reductions

might be shown to be not beneficial when considering the area as

a whole (since NOx reductions are generally expected to be more

beneficial in rural areas). In order to determine whether the

NOx reduction requirements should apply, EPA believes that, at a

minimum, the section 182(f) demonstration should reflect

conditions expected at the latest attainment deadline for the

area as a whole. In addition, States should consider imposition

of the NOx requirements if needed to avoid adverse impacts in

downwind areas, either intra- or inter-State. States need to

consider such impacts since they are ultimately responsible to

provide for attainment in all portions of their State and must

not contribute significantly to nonattainment in, or interfere

with maintenance by, any other State.

Alternatively, the State/petitioner may include a multi-year

analysis in its section 182(f) demonstration. This is

appropriate for areas demonstrating either a net air quality

benefit or a net ozone benefit. In these demonstrations, the

analysis may include periodic assessments of the effects of NOx

reductions and integrate those effects to arrive at a finding on

whether or not NOx reductions are beneficial. For example, an

area may develop geographic area exposure analyses for each year

or for every third year up to the attainment year and assess the

overall impact of NOx reductions from that information.

8.4 Scenarios to Compare

For the contribute to attainment and net ozone benefit

tests, the projected emissions should, at a minimum, consider

three scenarios which vary emission reductions from anthropogenic

sources: (1) substantial VOC reductions; (2) similar NOx

reductions; and (3) both the VOC and NOx reductions. Total
29

emissions to model include both anthropogenic and biogenic

emissions.

In contrast to the net air quality demonstration (chapter 3)

which focuses on the scenario "in the absence of reductions of

oxides of nitrogen from the sources concerned," the contribute to

attainment and net ozone benefit demonstrations concern an

unspecified "additional reductions" of NOx. Thus, while the net

air quality benefit test must focus on NOx reductions due to NSR

and RACT, the other demonstrations may more broadly consider NOx

reductions, including reductions that employ advanced control

technology (i.e., beyond RACT). The application of the VOC and

NOx reductions should be as source category specific as possible,

rather than across-the-board, in order for the results to be most

useful.

In the first scenario the demonstration should use the VOC

reductions needed to attain (demonstrated by EKMA or UAM

analyses). Alternatively, if the attainment demonstration has

not been completed, the demonstration may use some other

substantial VOC reduction. Reductions associated with attainment

are appropriate for the reasons described above. In any case,

the VOC reductions should be substantial and documented as

reasonable to expect for the area due to the CAA requirements. 

For example, a minimum of a 40% anthropogenic VOC reduction

areawide from the 1990 emission inventory may be reasonable to

expect for serious areas, considering motor vehicle emission

controls, inspection/maintenance, reasonable further progress and

other CAA requirements. 

In the second scenario, NOx reductions should be modeled

without any VOC reductions above the attainment year baseline. 

The level of NOx reductions should reflect the same percent

reduction of anthropogenic VOC emissions in scenario (1) above. 

It is important to model this case since NOx reductions, instead

of additional VOC reductions, may show a clearer benefit.

In the third scenario, a similar level of NOx reductions

would be modeled along with the level of VOC reductions chosen. 

That is, if a 40% VOC reduction is chosen in scenario (1), then

the model for scenario (3) would simulate a 40% VOC reduction and

approximately a 40% NOx reduction. It would be inappropriate to

select a high level of VOC reductions and a low level of NOx

reductions since this could artificially favor a finding that NOx

reductions are not beneficial; the two levels should be similar. 

8.5 Consistency with the SIP

Any section 182(f) demonstration must include a showing that

the exemption request uses assumptions that are consistent with
30

requirements of the SIP and the CAA. It is possible that a

petition could demonstrate that, under some circumstances, NOx

reductions are not needed to attain the ozone standard. However,

unless the State actually adopts those particular circumstances

into its SIP, there is no assurance that the petition's analysis

is valid. That is, if the assumptions contained in the

petitioner's demonstration are not valid, the conclusions are

similarly not valid and EPA would not approve the petition. The

section 182(f) petition process should not undermine the State's

implementation plan. The petition should reflect measures

consistent with mandatory CAA requirements, federally-approved

SIP requirements, and recent SIP revisions adopted by the State

and submitted to EPA for approval. The EPA encourages

petitioners to coordinate these analyses with the appropriate

State(s) as they are being developed.

8.6 New Source Review

The section 182(f) exemption provisions center on the effect

on ozone concentrations due to NOx emission reductions. With

respect to RACT, which involves emissions reductions from

existing sources, this is a perfect fit. In the case of new or

modified sources, however, other factors should be considered. 

Even after the application of on-site controls appropriate for a

major new or modified source, the source will, considered alone,

result in major increases in NOx emissions. However, the NSR

offset provisions would require the new source to obtain emission

reductions from other sources so as offset any emissions increase

associated with the new source.

To take into account the full impact of the NSR program, the

term "NOx reductions" must be carefully interpreted. When

considering the air quality impacts in chapters 3-6 of this

document "with NOx reductions" or with "substantial NOx

reductions," the analysis should reflect a zero emissions

increase from stationary sources after November 15, 1992 due to

the NSR offset requirement; when considering the "without" NOx

reductions scenarios, the analysis should include NOx emission

increases after November 15, 1992 due to new or modified

stationary sources of NOx, many of which would be subject to the

best available control technology requirement through the

prevention of significant deterioration program, but not to

offsets.