Transportation Conformity Rule Amendments for the New PM2.5, 24280-24292 [05-9086]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 70, Number 87 (Friday, May 6, 2005)]
[Rules and Regulations]
[Pages 24280-24292]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 05-9086]



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Part VI





Environmental Protection Agency





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40 CFR Part 93



Transportation Conformity Rule Amendments for the New PM2.5 
National Ambient Air Quality Standard: PM2.5 Precursors; 
Final Rule

Federal Register / Vol. 70, No. 87 / Friday, May 6, 2005 / Rules and 
Regulations

[[Page 24280]]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 93

[Docket No. OAR-2003-0049; FRL-7908-3]
RIN 2060-AN03


Transportation Conformity Rule Amendments for the New PM2.5 
National Ambient Air Quality Standard: PM2.5 Precursors

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: This final rule adds the following transportation-related 
PM2.5 precursors to the transportation conformity 
regulations: nitrogen oxides (NOX), volatile organic 
compounds (VOCs), sulfur oxides (SOX), and ammonia 
(NH3). The final rule specifies when each of these 
precursors must be considered in conformity determinations in 
PM2.5 nonattainment and maintenance areas before and after 
PM2.5 state air quality implementation plans (SIPs) are 
submitted. Today's action also makes a technical correction to a cross-
reference of the U.S. Department of Transportation's (DOT) planning 
regulations in the public consultation procedures of the conformity 
rule. The Clean Air Act requires federally supported highway and 
transit projects to be consistent with (``conform to'') the purpose of 
a SIP. EPA has consulted with DOT on the development of this final rule 
and DOT concurs with its content.

EFFECTIVE DATE: June 6, 2005.

ADDRESSES: Materials relevant to this rulemaking are in Public Docket 
I.D. No. OAR-2003-0049 located at the Air Docket, Environmental 
Protection Agency, Mailcode: 6102T, 1200 Pennsylvania Ave., NW., 
Washington, DC 20460; phone: 202-566-1742. For more information about 
accessing information from the docket, see Section I.B. of the 
SUPPLEMENTARY INFORMATION section.

FOR FURTHER INFORMATION CONTACT: Rudy Kapichak, State Measures and 
Conformity Group, Transportation and Regional Programs Division, U.S. 
Environmental Protection Agency, 2000 Traverwood Road, Ann Arbor, MI 
48105, e-mail address: kapichak.rudolph@epa.gov, telephone number: 
(734) 214-4574, fax number 734-214-4052; or Angela Spickard, State 
Measures and Conformity Group, Transportation and Regional Programs 
Division, U.S. Environmental Protection Agency, 2000 Traverwood Road, 
Ann Arbor, MI 48105, e-mail address: spickard.angela@epa.gov, telephone 
number: (734) 214-4283, fax number 734-214-4052.

SUPPLEMENTARY INFORMATION: The contents of this preamble are listed in 
the following outline:

I. General Information
II. Background
III. PM2.5 Precursors
IV. Technical Correction to Public Consultation Procedures
V. How Does Today's Final Rule Affect Conformity SIPs?
VI. Statutory and Executive Order Reviews

I. General Information

A. Does This Action Apply to Me?

    Entities potentially regulated by the conformity rule are those 
that adopt, approve, or fund transportation plans, programs, or 
projects under title 23 U.S.C. or title 49 U.S.C. Regulated categories 
and entities affected by today's action include:

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                Category                  Examples of regulated entities
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Local government.......................  Local transportation and air
                                          quality agencies, including
                                          metropolitan planning
                                          organizations (MPOs).
State government.......................  State transportation and air
                                          quality agencies.
Federal Government.....................  Department of Transportation
                                          (Federal Highway
                                          Administration (FHWA) and
                                          Federal Transit Administration
                                          (FTA)).
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    This table is not intended to be exhaustive, but rather provides a 
guide for readers regarding entities likely to be affected by this 
final rule. This table lists the types of entities of which EPA is 
aware that potentially could be regulated by the conformity rule. Other 
types of entities not listed in the table could also be regulated. To 
determine whether your organization is regulated by this action, you 
should carefully examine the applicability requirements in Sec.  93.102 
of the transportation conformity rule. If you have questions regarding 
the applicability of this action to a particular entity, consult the 
persons listed in the preceding FOR FURTHER INFORMATION CONTACT 
section.

B. How Can I Get Copies of This Document?

    1. Docket. Materials relevant to this rulemaking are in Public 
Docket I.D. No. OAR-2003-0049. The official public docket consists of 
the documents specifically referenced in this action, any public 
comments received, and other information related to this action. 
Although a part of the official docket, the public docket does not 
include Confidential Business Information (CBI) or other information 
whose disclosure is restricted by statute. The official public docket 
is the collection of materials that is available for public viewing at 
the Air Docket in the EPA Docket Center, (EPA/DC) EPA West, Room B102, 
1301 Constitution Ave., NW., Washington, DC. The Docket telephone 
number is (202) 566-1742. The EPA Docket Center Public Reading Room is 
open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding 
legal holidays. The telephone number for the Public Reading Room is 
(202) 566-1744. You may have to pay a reasonable fee for copying docket 
materials.
    2. Electronic Access. You may access this Federal Register document 
electronically through EPA's Transportation Conformity Web site at 
https://www.epa.gov/otaq/transp/traqconf.htm. You may also access this 
document electronically under the Federal Register listings at https://
www.epa.gov/fedrgstr/.
    An electronic version of the public docket is available through 
EPA's electronic public docket and comment system, EPA Dockets. You may 
use EPA Dockets at https://www.epa.gov/edocket/ to view public comments, 
access the index listing of the contents of the official public docket, 
and to access those documents in the public docket that are available 
electronically. Although not all docket materials may be available 
electronically, you may still access any of the publicly available 
docket materials through the docket facility identified in Section 
I.B.1. Once in the EPA electronic docket system, select ``search,'' 
then key in the appropriate docket identification number.

II. Background

A. What Is Transportation Conformity?

    Transportation conformity is required under Clean Air Act section 
176(c) (42 U.S.C. 7506(c)) to ensure that federally

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supported highway and transit project activities are consistent with 
(``conform to'') the purpose of the state air quality implementation 
plan (SIP). Conformity currently applies to areas that are designated 
nonattainment, and those redesignated to attainment after 1990 
(``maintenance areas'' with plans developed under Clean Air Act section 
175A) for the following transportation-related criteria pollutants: 
ozone, particulate matter (PM2.5 and PM10),\1\ 
carbon monoxide (CO), and nitrogen dioxide (NO2). Conformity 
to the purpose of the SIP means that transportation activities will not 
cause new air quality violations, worsen existing violations, or delay 
timely attainment of the relevant national ambient air quality 
standards (NAAQS or ``standards'').
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    \1\ Section 93.102(b)(1) of the conformity rule defines 
PM2.5 and PM10 as particles with an 
aerodynamic diameter less than or equal to a nominal 2.5 and 10 
micrometers, respectively.
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B. What Is the History of the Transportation Conformity Rule?

    EPA's transportation conformity rule establishes the criteria and 
procedures for determining whether transportation activities conform to 
the SIP. EPA first promulgated the transportation conformity rule on 
November 24, 1993, (58 FR 62188) and subsequently published a 
comprehensive set of amendments on August 15, 1997, (62 FR 43780) that 
clarified and streamlined language from the 1993 rule. EPA has made 
other smaller amendments to the rule both before and after the 1997 
amendments.
    On July 1, 2004, EPA published a final rule (69 FR 4004) that 
amended the conformity rule to accomplish three objectives. The final 
rule:
     Provided conformity procedures for state and local 
agencies under the new ozone and PM2.5 air quality 
standards;
     Incorporated existing EPA and U.S. Department of 
Transportation (DOT) federal guidance into the conformity rule 
consistent with a March 2, 1999, U.S. Court of Appeals decision; and
     Streamlined and improved the conformity rule.

The July 1, 2004, final conformity rule incorporated most of the 
provisions from the November 5, 2003, proposal for conformity under the 
new ozone and PM2.5 standards (68 FR 62690). EPA is 
conducting its conformity rulemakings for the new standards in the 
context of EPA's broader strategies for implementing the new ozone and 
PM2.5 standards.
    The July 2004 final rule also incorporated all of the amendments 
resulting from a separate June 30, 2003, proposal (68 FR 38974). This 
proposal addressed the March 2, 1999, court ruling by the U.S. Court of 
Appeals for the District of Columbia Circuit (Environmental Defense 
Fund v. EPA, et al., 167 F. 3d 641, D.C. Cir. 1999), and incorporated 
existing federal guidance consistent with the court decision.
    Most recently, on December 13, 2004, EPA published in the Federal 
Register a supplemental notice of proposed rulemaking to the November 
5, 2003, new standards conformity proposal entitled, ``Options for 
PM2.5 and PM10 Hot-Spot Analyses in the 
Transportation Conformity Rule Amendments for the New PM2.5 
and Existing PM10 National Ambient Air Quality Standards'' 
(69 FR 72140). In response to substantial comments received on the 
November 2003 proposal, EPA, in consultation with DOT, proposed 
additional options for PM2.5 and PM10 hot-spot 
requirements and requested comment on them as well as on the options 
presented in the November 2003 proposal. Subsequently, EPA extended the 
public comment period for this supplemental proposal, to January 27, 
2005. EPA has not yet taken final action on the December 13, 2004 
supplemental proposal. We are currently reviewing the public comments 
received on the supplemental proposal and will be issuing a final rule 
in the near future.

C. Why Are We Issuing This Final Rule?

    In the November 5, 2003, proposal, EPA proposed options for 
addressing PM2.5 precursors in the conformity process. 
However, EPA did not finalize PM2.5 precursor requirements 
in the subsequent July 1, 2004, final rule because EPA had not proposed 
a broader PM2.5 implementation rule to seek comment on 
options for addressing PM2.5 precursors in the New Source 
Review program and in SIP planning activities such as reasonable 
further progress plans, attainment demonstrations, reasonably available 
control technology (RACT) requirements, and reasonably available 
control measures (RACM) analyses. At that time, EPA believed that it 
would have been inappropriate to select a final option for precursors 
in transportation conformity determinations prior to the development of 
the precursor options in the broader PM2.5 implementation 
rule proposal. While EPA has not yet proposed the PM2.5 
implementation strategy, EPA has moved ahead with PM2.5 
designations and this action has caused us to re-evaluate the need to 
defer finalization of the PM2.5 precursor requirements for 
transportation conformity until the implementation rule is proposed. 
Our re-evaluation is based on the fact that the one-year conformity 
grace period began on April 5, 2005, the effective date of the 
designations. EPA believes that it is crucial that PM2.5 
nonattainment areas be aware of the requirements for PM2.5 
precursors at the beginning of the one-year grace period in order to 
facilitate completion of all necessary work to determine conformity by 
the end of the grace period for all applicable precursors. Therefore, 
EPA has decided to finalize the transportation conformity requirements 
for PM2.5 precursors in advance of proposing the 
PM2.5 implementation rule. Although the implementation rule 
has not yet been proposed, on-going consideration of issues related to 
precursors in the implementation rule have been coordinated with 
development of this final rule.
    EPA's implementation strategy for the PM2.5 standard 
will include options for addressing PM2.5 precursors in 
other air quality planning programs (e.g., New Source Review for 
stationary sources). The public will have the opportunity to comment on 
these options during the comment period for that rulemaking once it is 
published in Federal Register.
    In today's final rule, EPA addresses all public comments on the 
PM2.5 precursor options included in the November 2003 
conformity proposal that were received during the comment period for 
that rulemaking. The comment period for the November 2003 conformity 
proposal ended on December 22, 2003.
    Today's final rule should not be interpreted as prejudging our 
decision on the PM2.5 precursor requirements that will soon 
be proposed in the PM2.5 implementation rulemaking. Our 
final rule for the implementation proposal will reflect how 
PM2.5 precursors should best be considered in other air 
quality planning programs and the comments received on that proposal. 
While EPA's final decisions on PM2.5 precursors must be 
legally consistent, EPA could take differing positions with respect to 
various precursors in other programs as appropriate to the programmatic 
needs, legal requirements and pollution sources relevant to the 
differing programs.
    EPA notes, however, that if in the future we change our legal 
rationale for considering PM2.5 precursors among the various 
air quality planning programs from the positions currently under 
consideration as a result of comments received on the PM2.5 
implementation strategy proposal, such changes could necessitate a 
subsequent revision to the transportation conformity rule. In the

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case where an amendment to the conformity regulations is needed to 
reflect an alternative approach to considering PM2.5 
precursors, EPA would conduct such a revision through full public 
notice and comment rulemaking.
    DOT is our federal partner in implementing the transportation 
conformity regulations. We have consulted DOT in developing this final 
rule and DOT concurs with its content.

D. How Does This Final Rule Affect the One-Year Conformity Grace 
Period?

    As explained in the July 1, 2004, final rule that addresses the 
conformity requirements for the 8-hour ozone and PM2.5 
standards (69 FR 40004), conformity applies one year after the 
effective date of EPA's initial nonattainment designation for a given 
pollutant and standard. On January 5, 2005 (70 FR 943), EPA designated 
areas as attainment and nonattainment for the PM2.5 air 
quality standard. These designations became effective on April 5, 2005, 
90 days after EPA's published action in the Federal Register. 
Therefore, conformity for the PM2.5 standard will apply on 
April 5, 2006.
    Today's final rule does not change the one-year conformity grace 
period for any area recently designated nonattainment for the 
PM2.5 standard. On April 5, 2006, metropolitan 
PM2.5 nonattainment areas must have in place a 
transportation plan and transportation improvement program (TIP) that 
conforms in accordance with the PM2.5 precursor requirements 
finalized by today's action and the requirements previously finalized 
by the July 1, 2004, rulemaking. See the July 1, 2004, final rule (69 
FR 40008 through 40014) for more information on the implementation of 
the one-year conformity grace period in newly designated 
PM2.5 nonattainment areas.

III. PM2.5 Precursors

A. Description of the Final Rule

    Today's final rule identifies four transportation-related 
PM2.5 precursors--nitrogen oxides (NOX), volatile 
organic compounds (VOCs), sulfur oxides (SOX), and ammonia 
(NH3)--for consideration in the conformity process in 
PM2.5 nonattainment and maintenance areas. Once a 
PM2.5 SIP is submitted, a regional emissions analysis would 
be required for a given precursor if the SIP establishes an adequate or 
approved budget for that particular precursor.
    The November 5, 2003, notice of proposed rulemaking contained two 
options for addressing PM2.5 precursors in conformity 
determinations made before a SIP is submitted and emissions budgets are 
found adequate or approved. EPA is finalizing a modified version of the 
proposed options in this final rule. Specifically, a regional emissions 
analysis is required for NOX as a PM2.5 precursor 
in all PM2.5 nonattainment areas, unless the head of the 
state air agency and the EPA Regional Administrator make a finding that 
NOX is not a significant contributor to the PM2.5 
air quality problem in a given area. Regional emissions analyses are 
not required for VOC, SOX or ammonia before an adequate or 
approved SIP budget for such precursors is established, unless the head 
of the state air agency or EPA Regional Administrator makes a finding 
that on-road emissions of any of these precursors is a significant 
contributor. Prior to EPA finding the budgets from the submitted 
PM2.5 SIP adequate or approving the PM2.5 SIP, 
the MPO and DOT will document in their conformity determinations that a 
regional emissions analysis has not been conducted for NOX 
when EPA and the state air agency have determined NOX to be 
insignificant. The regulatory text for this final rule can be found in 
Sec. Sec.  93.102(b)(2)(iv) and (v) and 93.119(f)(9) and (10).
    A state air agency and/or EPA finding of significance or 
insignificance (a ``significance finding'') for a PM2.5 
precursor will be based on criteria similar to the general criteria for 
insignificance of motor vehicle emissions in Sec.  93.109(k) of the 
conformity rule. Specifically, the following criteria will be 
considered in making significance or insignificance findings for 
PM2.5 precursors: The contribution of on-road emissions of 
the precursor to the total 2002 baseline SIP inventory; the current 
state of air quality for the area; the results of speciation monitoring 
for the area; the likelihood that future motor vehicle control measures 
will be implemented for a given precursor; and projections of future 
on-road emissions of the precursor. Determining the significance or 
insignificance of motor vehicle emissions in a given area will be 
conducted on a case-by-case basis.
    Significance and insignificance findings will be made only after 
discussions among the interagency consultation partners for the 
PM2.5 nonattainment area. These discussions should include a 
review of the available data being considered to support the 
significance finding. Interagency consultation also ensures that all of 
the relevant agencies are aware that such a finding is being 
considered. It is important to provide transportation agencies with 
adequate notice of which, if any, precursors they may need to address 
in conformity analyses. A significance finding will be made through a 
letter from the state air agency or EPA regional office to the relevant 
state and local air quality and transportation agencies, MPO(s), DOT 
and EPA (in the case of a state air agency finding). An insignificance 
finding will be made through either letters from the state air agency 
and the EPA regional office or a letter co-signed by the state air 
agency and the EPA regional office to the relevant state and local air 
quality and transportation agencies, MPO(s) and DOT.
    EPA notes that any significance or insignificance finding made 
prior to EPA's adequacy finding for budgets in a SIP, or EPA's approval 
of the SIP, should not be viewed as the ultimate determination of the 
significance of precursor emissions in a given area. State and local 
agencies may find through the SIP development process that emissions of 
one or more precursors are significant, even if a precursor had 
previously been considered insignificant. In such a case, the 
PM2.5 SIP would establish a motor vehicle emissions budget 
for that precursor and a regional emissions analysis for that precursor 
would be included in subsequent conformity determinations. 
Alternatively, state and local agencies may find through the SIP 
development process that emissions of one or more precursors are 
insignificant even if a precursor had previously been considered 
significant. In such a case, the PM2.5 SIP would not 
establish a motor vehicle emissions budget for that precursor and a 
regional emissions analysis for that precursor would not be necessary 
in subsequent conformity determinations.
    To calculate emission factors for PM2.5 precursors, 
areas must use the latest EPA-approved motor vehicle emissions factor 
model (currently MOBILE6.2 for all states except California). 
PM2.5 nonattainment and maintenance areas in California must 
use EMFAC2002 or a more recently EPA-approved model. It should be noted 
that EMFAC2002 does not calculate emissions factors for ammonia. 
However, EPA understands that California is developing a methodology 
for estimating ammonia emissions from on-road vehicles. It is 
anticipated that this methodology will be completed prior to the end of 
the one-year conformity grace period. However, as a practical matter, 
conformity for ammonia would not be required in California until there 
is an acceptable method for estimating such

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emissions, because a method would be needed to estimate current or 
future ammonia emissions for either a significance finding or SIP motor 
vehicle emissions budget.

B. Rationale for This Final Rule

    Section 176(c)(1)(B) of the Clean Air Act requires that federal 
funding and approval be given only to transportation activities that 
are consistent with state and local air quality goals. To fulfill this 
requirement with respect to PM2.5, EPA is requiring that 
transportation conformity determinations consider PM2.5 
precursors if they are significant contributors to an area's 
PM2.5 air quality problem.
    Today's final rule incorporates NOX, VOCs, 
SOX, and ammonia as possible transportation-related 
PM2.5 precursors because all of these precursors are emitted 
from on-road motor vehicles. Based on data collected from monitoring 
sites in the national speciation trends network,\2\ secondary particles 
from precursors commonly account for over half of the total fine 
particle mass from all emissions sources measured at these sites. 
Therefore, we expect that areas may need to address on-road emissions 
of relevant precursors (i.e., NOX, VOC, SOX and 
ammonia) in their SIPs and in conformity.
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    \2\ The speciation trends network consists of over 50 monitoring 
sites in urban areas and provides nationally consistent data on 
PM2.5 constituents by type (i.e., ``speciated'') 
including nitrates, elemental carbon, organic carbon and sulfates.
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    The final rule allows for the consideration of the four precursors 
in conformity prior to PM2.5 SIPs when such precursors are 
significant: NOX is considered significant in the absence of 
a finding; VOCs, SOX and ammonia must be found significant 
to be included. In finalizing this rule EPA attempted to strike a 
balance between: (1) Expeditiously addressing transportation-related 
emissions that could exacerbate the PM2.5 air quality 
problem before a SIP is established, and (2) targeting conformity 
requirements in PM2.5 areas in an efficient and reasonable 
manner.
    EPA based its decision on a number of factors. For example, EPA 
considered the environmentally conservative nature of requiring 
conformity determinations for all four precursors prior to the 
submission of a SIP unless a finding is made that on-road emissions of 
a precursor or precursors is insignificant, rather than only for 
NOX. Requiring that all four precursors be addressed in 
conformity prior to the submission of a SIP may be a more 
environmentally protective approach to meeting the Clean Air Act's 
conformity requirements because any significant precursors would 
automatically be addressed without the need for a significance finding 
to be made by the state air agency or the EPA regional office. On the 
other hand, requiring significance findings for the precursors VOCs, 
SOX and ammonia better accounts for regional variability in 
air quality and better targets resources to the precursors that are 
most important in an individual area. Also, requiring significance 
findings for these three precursors could help areas avoid adopting on-
road control measures to address a particular precursor before a SIP is 
submitted that ultimately prove to be unnecessary after a SIP is 
developed, if emissions of the targeted precursor are ultimately found 
to be insignificant. In addition, EPA also considered with respect to 
each precursor the chemistry of secondary particle formation, the 
results of speciated air quality monitoring and on-road emissions 
inventory data. In addition to the information provided below, the 
November 2003 notice of proposed rulemaking contains a more detailed 
discussion of speciated air quality data and on-road emissions data (68 
FR 62706 through 62708). Please refer to the notice of proposed 
rulemaking for additional details.
    Sulfur dioxide. While speciated air quality data show that sulfate 
is a relatively significant component (e.g., ranging from nine to 40 
percent) of PM2.5 mass in all regions of the country, 
emissions inventory data and projections show that on-road emissions of 
SOX constitute a ``de minimis'' (i.e., extremely small) 
portion of total SOX emissions. Emissions inventory data for 
1999 for the 372 potential PM2.5 nonattainment counties for 
PM2.5 (based on 1999-2001 air quality data) show that on-
road sources were responsible for only two percent of total 
SOX emissions. By comparison, fuel combustion sources (e.g., 
electric utility and industrial combustion of coal and oil) contributed 
approximately 88 percent of the SOX emissions in 1999 in 
these same counties.
    Furthermore, EPA has already adopted two regulations that will 
greatly reduce emissions of SOX from on-road sources by the 
time such regulations are both in full effect in 2009. First, in 2004 
the low sulfur gasoline program began to be phased in and will be fully 
effective in 2007 (February 10, 2000, 65 FR 6697). This regulation will 
reduce the sulfur content of gasoline by approximately 90 percent when 
fully effective.\3\ Second, in 2006 the low sulfur diesel program will 
begin to be phased in and will be fully effective by 2009 (January 18, 
2001, 66 FR 5001). This regulation will reduce the sulfur content of 
diesel fuel by approximately 97 percent nationally when fully 
effective.
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    \3\ In addition, California has adopted its own rule which 
addresses the sulfur content of gasoline in that State. California's 
regulation is similar in stringency to the Federal regulation.
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    Projections of on-road emissions of SO2 in 2020 indicate 
that on-road sources will be responsible for less than one percent of 
the total SO2 emissions in 2020 in the 372 potential 
PM2.5 nonattainment counties (based on 1999-2001 air quality 
data).\4\ These projections confirm that the implementation of the fuel 
regulations discussed above will ensure that as a general matter 
SO2 emissions from on-road sources remain at insignificant 
levels in all areas. Therefore, states are not required to include 
SOX in conformity determinations prior to submission of a 
SIP unless the state air agency or EPA regional office makes a finding 
that on-road emissions of SOX are a significant contributor 
to an area's PM2.5 problem. If a state determines through 
its SIP development process that on-road emissions of SOX 
are significant and the SIP includes an adequate or approved emissions 
budget for SOX, then future conformity determinations will 
be required to include a regional emissions analysis for 
SOX.
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    \4\ EPA 420-R-00-020, October 2002, ``Procedures for Developing 
Base Year and Future Year Mass and Modeling Inventories for the 
Heavy-Duty Engine and Vehicle Standards and Highway Diesel Fuel 
(HDD) Rulemaking.''
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    Nitrogen oxides. Based on a review of speciated monitoring data 
analyses, nitrate concentrations vary significantly across the country. 
For example, in some southeastern locations, annual average nitrate 
levels range from six to eight percent of total PM2.5 mass, 
whereas nitrate comprises 40 percent or more of PM2.5 mass 
in certain California locations. Nitrate formation is favored by the 
availability of ammonia, low temperatures, and high relative humidity. 
Nitrate formation also depends upon the amount of nearby SO2 
emissions because ammonia reacts preferentially with SO2 
over NOX (i.e., ammonia first reacts to form ammonium 
sulfate and then reacts to form ammonium nitrate).
    The sources of NOX are numerous and widespread, 
including motor vehicles, power plants, and many other combustion 
activities. We believe these source categories and the potential for 
significant impacts on air quality exist in many nonattainment areas. 
The analysis of speciated air quality data

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and the discussion of emission inventory data in the November 2003 
transportation conformity notice of proposed rulemaking provide an 
appropriate basis for deciding that states must include NOX 
in conformity determinations made before SIPs are submitted and 
emissions budgets are found adequate or approved, unless the state air 
agency and the EPA regional office find that on-road emissions of 
NOX are not a significant contributor to the area's 
PM2.5 problem.
    EPA believes that requiring both the state air agency and the EPA 
regional office make an insignificance finding for NOX is 
warranted because in this rulemaking EPA has initially determined that 
NOX is a significant precursor for all PM2.5 
nonattainment areas. Additionally, all other insignificance findings 
require both state air agency and EPA regional office action because 
they are made through either a motor vehicle emission budget adequacy 
finding or a SIP approval as required by Sec.  93.109(k) of the 
conformity regulation. Therefore, based on the reasons stated above, 
EPA believes that it is necessary that both the state air agency and 
the EPA regional office make a finding that on-road emissions of 
NOX are an insignificant contributor to an area's 
PM2.5 air quality problem prior to the submission of a SIP. 
A finding made by both agencies provides assurance that on-road 
emissions of NOX are in fact insignificant contributors to 
an area's PM2.5 air quality problem and therefore may be 
omitted from conformity determinations prior to the submission of a SIP 
for the area. After a PM2.5 SIP is submitted, conformity 
determinations will be required for on-road emissions of NOX 
if the SIP includes emissions budgets that are found adequate or are 
approved.
    Volatile Organic Compounds. In 2003, EPA estimates that on-road 
motor vehicles accounted for 28 percent of total VOCs nationwide. 
Carbonaceous particles, which result, in part, from reactions involving 
VOCs, account for 25-70% of constructed fine particle mass measured at 
specific Speciation Trends Network sites. The highest percentages of 
carbonaceous particles tend to be in the western United States, while 
the lowest percentages tend to be in the eastern United States.
    Although research clearly indicates that VOCs can contribute to the 
formation of carbonaceous secondary PM2.5 compounds, the 
current science is still incomplete in its understanding of the 
fraction of particulate organic compounds that began as VOCs. A major 
reason for this existing deficiency is the varying degrees of 
volatility of organic compounds, as well as our inability to model 
collectively the reactivity of these different groups of compounds. For 
example, there are highly reactive volatile compounds with six or fewer 
carbon atoms that indirectly contribute to PM formation through 
reaction with oxidizing compounds such as the hydroxyl radical and 
ozone. There are also semi-volatile compounds with between seven and 24 
carbon atoms that can exist in particle form and can readily be 
oxidized to form other low volatility compounds. Finally, high 
molecular weight organic compounds (with 25 carbon atoms or more and 
low vapor pressure) are emitted directly as primary organic particles 
and exist primarily in the condensed phase at ambient temperatures. For 
this reason, these high molecular weight organic compounds are 
generally considered to be primary particles and not VOCs. The relative 
importance of each of these groups of organic compounds in the 
formation of organic particles varies from area to area. In addition, 
the contribution of on-road source emissions to each of these three 
groups of organic compounds may also vary from area to area.
    Current scientific and technical information clearly shows that 
carbonaceous material is a significant fraction of total 
PM2.5 mass in most areas, and that certain aromatic VOC 
emissions such as toluene, xylene, and trimethyl-benzene are precursors 
to the formation of secondary PM2.5 (secondary organic 
aerosols). However, while significant progress has been made in 
understanding the role of gaseous organic material in the formation of 
organic PM, this relationship is complex and requires further research 
and technical tools to determine the extent of the contribution of 
specific VOC compounds to organic PM mass, prior to EPA being able to 
determine the extent of the contribution of VOCs to nonattainment 
problems in all PM2.5 areas.
    Additional research is also needed to determine the sources of VOC 
emissions that contribute most to PM2.5 air quality issues. 
For example, analysis of air quality samples collected in Pittsburgh, 
Pennsylvania from 1998 through 2003 indicate that approximately half of 
the secondary organic aerosol in Pittsburgh may be attributable to 
biogenic sources (e.g., trees) as opposed to anthropogenic sources 
(i.e., man-made sources such as power plants and motor vehicles). 
Similarly, analysis of air quality samples collected in Atlanta, 
Georgia from 1998 through 2003 indicate that as much as 80 percent of 
the secondary organic aerosol may be attributable to biogenic sources. 
These data \5\ are significant because biogenic emissions cannot be 
controlled. In addition, EPA believes that in some PM2.5 
nonattainment areas, particularly during seasons with high 
photochemical activity, a significant amount of the secondary organic 
aerosol may be due to biogenic emissions as opposed to anthropogenic 
emissions of VOCs, as evidenced by the data from Pittsburgh and 
Atlanta.
---------------------------------------------------------------------------

    \5\ Data from the PM Supersites Program documented in a 
September 2004 summary response entitled, ``Policy Relevant Science 
Questions Regarding PM--Precursors,'' Prepared by Spyros Pandis, 
CMU; David Allen, University of Texas at Austin; Armistead (Ted) 
Russell, Georgia Institute of Technology; and Paul A. Solomon, U.S. 
EPA, ORD. This document can be found in the docket for today's 
rulemaking.
---------------------------------------------------------------------------

    EPA acknowledges that analytical tools are evolving to enable areas 
to adequately model the contribution of VOCs to PM2.5 
formation. Researchers in the field anticipate that within the next 
five years the ability of models to simulate various components of 
PM2.5 will improve greatly, as will their ability to 
estimate the effectiveness of various control measures. These model 
improvements are particularly significant for secondary organic 
aerosols and biogenic and anthropogenic emissions of VOCs. However, 
until such model improvements are made and our understanding of VOC 
secondary particle formation improves, EPA believes it is not 
appropriate to require regional conformity analyses for VOCs in 
PM2.5 nonattainment areas prior to the submission of a 
PM2.5 SIP and emissions budgets for VOCs being found 
adequate or approved, unless the state air agency or EPA regional 
office finds that VOCs are a significant contributor to an area's 
PM2.5 problem. If a state determines through its SIP 
development process that on-road emissions of VOCs are significant and 
the SIP includes an adequate or approved emissions budget for VOCs, 
then future conformity determinations will be required to include a 
regional emissions analysis for VOCs.
    Ammonia. We believe a case-by-case approach is also appropriate for 
ammonia because there is sufficient uncertainty about emissions 
inventories and about the potential efficacy of control measures from 
location to location. Reductions of ammonia may be effective primarily 
in areas where nitric acid is in abundance and ammonia is the limiting 
factor to ammonium nitrate formation (ammonium nitrate is a type of

[[Page 24285]]

particulate matter). Although ammonia reductions may be appropriate in 
selected locations, in other locations such reductions may lead to 
increased atmospheric acidity, exacerbating acidic deposition problems. 
In other words, states should evaluate the benefits of including 
ammonia in conformity determinations prior to the submission of SIPs 
and emissions budgets being found adequate or approved. Therefore, 
states are not required to include ammonia in conformity determinations 
prior to submission of a SIP unless the state air agency or EPA 
regional office makes a finding that on-road emissions of ammonia are a 
significant contributor to an area's PM2.5 problem. If a 
state determines through its SIP development process that on-road 
emissions of ammonia are significant and the SIP includes an adequate 
or approved emissions budget for ammonia, then future conformity 
determinations will be required to include a regional emissions 
analysis for ammonia.

C. Response to Comments

1. Required Precursors

    Two comments received on the November 5, 2003, proposed rulemaking 
indicated support for identifying NOX, VOCs, SOX 
and ammonia as potential transportation-related PM2.5 
precursors. No commenters were opposed to identifying all of these as 
potential precursors.
    EPA received a number of comments on the proposed options for 
addressing precursors during the period before PM2.5 SIPs 
are submitted and emissions budgets are found adequate or approved. The 
majority of commenters supported option 2 included in the November 2003 
proposal. Option 2 would have required significance findings for any of 
the four precursors to be analyzed in conformity determinations prior 
to EPA finding emissions budgets in a PM2.5 SIP adequate or 
EPA's approval of that SIP. Some commenters that supported option 2 
believed that limited resources would be best used by determining which 
precursors contribute significantly to an area's air quality problem 
before conformity for those precursors was required. A number of 
commenters also supported the proposed option 1. Option 1 would have 
required NOX and VOCs to be analyzed in conformity 
determinations prior to the submission of PM2.5 SIPs unless 
one or both precursors was determined to be insignificant. This option 
also would not have required SOX or ammonia to be analyzed 
for conformity prior to a submitted SIP unless one or both precursors 
was found significant. Two supporters of option 1 believed sufficient 
air quality data exists for their areas to support requiring analysis 
of NOX and VOCs in conformity determinations prior to the 
submission of a PM2.5 SIP.
    One commenter recommended that to properly implement the Clean Air 
Act in all PM2.5 areas, conformity determinations should be 
required for all four precursors prior to the submission of a 
PM2.5 SIP unless a precursor was found to be insignificant. 
This commenter believed that it would be unreasonable to allow an area 
to opt out of conducting an analysis by default for a precursor that 
could be responsible for a large portion of PM2.5. 
Additionally, two commenters indicated that SOX should be 
addressed in conformity determinations prior to submission of a 
PM2.5 SIP unless it is found to be insignificant. One 
commenter stated that ammonia should be included in conformity 
determinations as soon as modeling and analysis tools are available. 
Another commenter opined that the only pollutant that should require a 
significance finding prior to the submission of a PM2.5 SIP 
is ammonia.
    EPA considered all of these comments along with a number of other 
factors including, speciated air quality data, emissions inventory 
information, and the state of the scientific understanding of the 
formation of secondary particles. We based today's decision on all of 
these factors as described above in section III.B.
    Several commenters believed that SIP budgets for one or more of the 
PM2.5 precursors should be established before conformity is 
required for those precursors. Specifically, two commenters believed 
that SOX and ammonia should be evaluated for significance 
and have SIP budgets before conformity is required. Three other 
commenters believed that conformity determinations should not be 
required for any PM2.5 precursors prior to the submission of 
a SIP and emissions budgets being found adequate or approved. One of 
these commenters stated that Sec. Sec.  93.102(b)(2)(iii)-(v) and 
93.102(b)(3) should refer to budgets because conformity should only be 
required if there is an explicit motor vehicle emissions budget that is 
intended to be a ceiling on future emissions.
    EPA disagrees with these commenters. Clean Air Act section 
176(c)(6) requires that conformity apply in new nonattainment areas one 
year after the effective date of the nonattainment designation, even 
prior to the submission of SIPs establishing budgets for a particular 
pollutant or precursor. Clean Air Act section 176(c)(4) provides EPA 
with the authority to establish conformity tests that will ensure that 
transportation plans, TIPs and projects do not result in new violations 
of an air quality standard, increase the frequency or severity of an 
existing violation, or delay timely attainment of a standard during the 
period before a SIP is submitted. While the contribution of mobile 
sources to PM2.5 nonattainment problems is likely to vary 
from area to area, on-road emissions of at least NOX, and 
perhaps other precursors, are likely to make a significant contribution 
to PM2.5 problems in most areas. Therefore, EPA believes it 
is both required by the Clean Air Act and necessary to protect public 
health for PM2.5 areas to begin considering the role of on-
road emissions of PM2.5 precursors in their PM2.5 
air quality problems, and to demonstrate conformity for those 
precursors that make a significant contribution to their air quality 
problems once conformity applies for PM2.5. Before adequate 
or approved SIP budgets are established, PM2.5 areas must 
use one of the interim emissions tests in Sec.  93.119 to fulfill this 
statutory requirement.
    One commenter opined that requiring conformity for additional 
precursors results in additional burden. The commenter stated that any 
additional pollutant or precursor that has to be included in a 
conformity determination leads to additional modeling runs, additional 
documentation of results, additional explanation to the public and 
regional decision makers and an additional opportunity for a conformity 
lapse. This commenter believed that EPA should not minimize these 
resource requirements or use this argument to support the inclusion of 
PM2.5 precursors in conformity determinations prior to a SIP 
submission.
    EPA understands the commenter's concerns and has attempted to 
structure requirements for PM2.5 precursors so that human 
health and air quality are protected while targeting regional emissions 
analyses to only those precursors whose on-road emissions make a 
significant contribution to an area's PM2.5 air quality 
problem. However, EPA continues to believe as stated in the November 
2003 proposal that including PM2.5 precursors in 
PM2.5 regional emissions analyses prior to the submission of 
a SIP should not result in any additional transportation or emissions 
modeling because PM2.5 areas will already be producing VMT 
and

[[Page 24286]]

emissions estimates for direct PM2.5 (68 FR 62706). The same 
VMT estimates would be used in calculating emissions of any and all 
precursors. Additionally, emission factors for the relevant precursors 
would generally be produced in the same model runs as the emission 
factors for direct PM2.5. EPA recognizes that there would be 
some small increase in burden in documenting these results and in 
discussing these precursors with regional decision makers and the 
public, but we believe this small increase is merited if a precursor is 
a significant contributor to an area's air quality problem.
    EPA also recognizes that it is possible that an area could lapse 
because it may not be able to demonstrate conformity for one or more of 
the PM2.5 precursors. EPA and DOT always attempt to work 
with areas that are experiencing problems demonstrating conformity in 
order to resolve problems before a lapse occurs. However, the Clean Air 
Act's conformity requirements are intended to ensure that the use of 
Federal transportation funds does not cause new air quality problems, 
make existing problems worse, or delay meeting a Clean Air Act 
requirement such as attainment. Therefore, if one or more precursors is 
a significant contributor to an area's air quality problem, the 
inability to demonstrate conformity for such precursors would be 
consistent with the Clean Air Act's intended purpose of the conformity 
process. In other words, if conformity cannot be demonstrated for a 
significant precursor, Federal transportation funds could not be spent 
on transportation activities that potentially would cause a new air 
quality problem, worsen an existing problem, or delay attainment or 
other emission reduction milestone. The inability to demonstrate 
conformity would indicate that further action is needed before Federal 
transportation funding and approvals can occur so that ultimately both 
transportation and air quality goals are achieved.

2. Significance Findings

    A number of commenters expressed support for significance findings 
to be made by either the state air agency or the EPA regional office 
before a PM2.5 SIP is submitted. However, commenters also 
suggested different options for making significance findings. Thirteen 
commenters stated that both the state air agency and the EPA regional 
office should make the finding, while two commenters stated that the 
finding should be made through an area's interagency consultation 
process. Another commenter recommended that only the state should have 
the ability to make significance findings.
    EPA is making one change with regard to insignificance findings. 
EPA has determined that insignificance findings for NOX 
should be made by both the state air agency and the EPA regional 
office. EPA believes that requiring both the state air agency and the 
EPA regional office to make an insignificance finding for 
NOX is appropriate because, as stated above in this 
rulemaking, EPA has initially determined that NOX is a 
significant precursor for all PM2.5 nonattainment areas. 
Additionally, all other insignificance findings made within the 
transportation conformity and SIP processes require both state air 
agency and EPA regional office action because they are made through 
either a motor vehicle emission budget adequacy finding or a SIP 
approval as required by Sec.  93.109(k) of the conformity regulation. 
Therefore, EPA believes that it is necessary that both the state air 
agency and the EPA regional office make a finding that on-road 
emissions of NOX are an insignificant contributor to an 
area's PM2.5 air quality problem prior to the submission of 
a SIP. A finding made by both agencies provides assurance that on-road 
emissions of NOX are in fact insignificant contributors to 
an area's PM2.5 air quality problem and therefore may be 
omitted from conformity determinations prior to the submission of a SIP 
for the area.
    Finally, EPA believes that an insignificance finding for 
NOX should be made by both the state air agency and the EPA 
regional office because NOX is the only pollutant/precursor 
for which a regional analysis is not required if a finding is made. 
That is, the conformity rule allows NOX to be found 
insignificant before a SIP is submitted and therefore not be included 
in subsequent conformity determinations. For all other PM2.5 
and PM10 pollutants/precursors covered by the conformity 
rule (i.e., VOCs, SOX and ammonia as PM2.5 
precursors; NOX and VOCs as PM10 precursors and 
road dust as a contributor to PM2.5 air quality problems) 
either the state air agency or the EPA regional office can decide if 
emissions are significant and therefore should be included in 
conformity determinations prior to the submission of a SIP and 
emissions budgets being found adequate or approved. However, a finding 
for NOX (in this case, a finding of insignificance) would 
lead to a less environmentally conservative result where NOX 
would no longer be considered in conformity determinations.
    In contrast, consistent with the rule's requirements for 
significance findings for other precursor emissions and the November 5, 
2003, proposal, today's action specifies that significance findings for 
VOCs, SOX and ammonia as PM2.5 precursors can be 
made by either the state air agency or the EPA regional office. We 
believe that changes to the procedures for finding VOCs, SOX 
and ammonia precursor emissions significant in response to comments are 
unnecessary because such findings would result in the inclusion of one 
or more precursors in conformity which would be more environmentally 
protective. Furthermore, allowing significance findings for VOCs, 
SOX and ammonia to be made by either the state air agency or 
the EPA regional office acknowledges the state's authority as well as 
EPA's role in ensuring national consistency in such decisions. The 
language used in the final rule for these three PM2.5 
precursors is consistent with how such findings have been made for 
PM10 precursors, since the original 1993 conformity rule. 
Today's final rule for these three precursors is also consistent with 
how such findings are to be made for PM2.5 road dust. The 
road dust requirements were finalized in the July 1, 2004, final rule. 
EPA believes that maintaining consistency in cases where precursors are 
determined to be significant will facilitate implementation of the 
conformity rules with no adverse impacts, in light of the role 
interagency consultation will play as explained above.
    One commenter, who favored including all precursors in conformity 
determinations prior to the submission of a SIP, stated that a 
precursor could be found to be insignificant if current on-road 
emissions are less than five percent of total PM2.5 and no 
increases are expected on a percentage basis during the period covered 
by the SIP or the conformity determination for the area. EPA disagrees 
with this suggested approach. Merely using a percentage level as a 
basis for a significance or insignificance finding ignores many other 
aspects of an area's nonattainment problem. Rather, EPA believes that a 
combination of the criteria for insignificance findings contained in 
Sec.  93.109(k) of the conformity rule and the discussion of 
insignificance and significance findings as they apply to 
PM2.5 precursors contained in this notice provide the 
appropriate basis for deciding whether or not a PM2.5 
precursor is significant or insignificant in a given area. Discussion 
of EPA's rationale for establishing criteria for significance and 
insignificance findings

[[Page 24287]]

can be found in the preamble to the July 1, 2004, final rule (69 FR 
40061 through 40063). Therefore, EPA is not adopting the criteria 
suggested by the commenter.
    One commenter believed that if all precursors were considered in 
conformity prior to a SIP submission it could be presumed that these 
precursors will ultimately be included in the SIP for the area. In such 
a case, the commenter believed it would be difficult to justify not 
including the precursors in the SIP for the area if the state 
presumptively includes all of them in the first conformity 
determination. As previously stated, under today's final rule any 
significance finding made prior to EPA's adequacy finding for budgets 
in a SIP, or EPA's approval of the SIP, should not be viewed as the 
ultimate determination of the significance of precursor emissions in a 
given area. State and local agencies may find through the SIP 
development process that emissions of one or more precursors are 
significant, even if a precursor had previously been considered 
insignificant. In such a case, the PM2.5 SIP would establish 
a motor vehicle emissions budget for that precursor and a regional 
emissions analysis for that precursor would be included in subsequent 
conformity determinations. Similarly, state and local agencies may find 
that a precursor is insignificant when preparing the SIP, even if 
previously found significant prior to the SIP's preparation.
    One commenter stated that the insignificance policy should be 
applied to precursor emissions in PM2.5 nonattainment and 
maintenance areas for a variety of reasons such as the need for 
additional information on the nature and cause of an area's 
PM2.5 problem, speciation of PM2.5 and 
availability of PM2.5 control measures. EPA agrees with this 
commenter. Today's final rule allows nonattainment areas to make 
findings on the significance of each of the four precursors to their 
PM2.5 air quality problem during the period before a SIP is 
submitted and budgets are found adequate as described above. The 
insignificance policy also generally applies after a SIP is submitted, 
via the decisions about precursors that are determined in the SIP.
    One commenter requested additional guidance on significance and 
insignificance findings. EPA does not believe that additional guidance 
on significance and insignificance findings is necessary at this time. 
EPA has described the criteria to be considered and the process to be 
used in making these findings in Sec.  93.109(k) of the conformity rule 
and in today's preamble. Additional discussion and details on 
insignificance findings can be found in the preamble to the July 1, 
2004, final rule (69 FR 40061 through 40063).

3. Precursors in SIPs

    One commenter stated that after PM2.5 SIPs are 
submitted, areas should consider all four precursors in conformity 
determinations unless the SIP clearly states that one or more 
precursors are insignificant. EPA is not making any changes in response 
to this comment. EPA does not believe that it is necessary for a SIP to 
explicitly state that a precursor is insignificant. Instead, EPA 
believes that states will consider the on-road contribution of all four 
precursors to the PM2.5 problem as they develop their SIPs. 
If through the SIP process a state concludes that on-road emissions of 
one or more precursors needs to be addressed in order to attain the 
PM2.5 standard as expeditiously as practicable, then EPA 
expects that the state will include an emissions budget in the SIP for 
each of the relevant precursors. A conformity determination will then 
be required for each precursor for which there is a budget, after the 
emissions budgets are found adequate or approved. In making a decision 
about each precursor, states should consider the insignificance 
criteria contained in Sec.  93.109(k) of the conformity rule and the 
current state of the science concerning the precursor's role in the 
formation of PM2.5. Once SIPs are submitted and found 
adequate or approved the conformity rule requires that conformity be 
assessed against the budgets in the applicable SIP. Conformity 
determinations must then address all precursors for which the SIP 
establishes a budget, and need not address any possible precursor for 
which the state has not established a budget because the emissions of 
that precursor are insignificant.
    EPA notes that, if inventory and modeling analyses demonstrating 
reasonable further progress, attainment or maintenance indicate a level 
of emissions of a precursor that must be maintained to demonstrate 
compliance with the applicable requirement, then that level of 
emissions should be clearly identified in the SIP as a motor vehicle 
emissions budget for transportation conformity purposes consistent with 
Sec.  93.118(e) even if the SIP does not establish particular controls 
for the given precursor. If the state fails to identify such a level of 
emissions as a motor vehicle emissions budget, EPA will find the 
submitted SIP budgets inadequate because the SIP fails to clearly 
identify the motor vehicle emissions budget as required by conformity 
rule Sec.  93.118(e)(4)(iii).
    Several commenters raised concerns about SIP development and 
regional emissions analyses in areas that are nonattainment for both 8-
hour ozone and PM2.5. One of these commenters asked if 
NOX and VOC conformity analyses would be the same for both 
pollutants in these areas. Another commenter asked if NOX 
and VOC budgets would be the same for 8-hour ozone and PM2.5 
SIPs in these areas.
    EPA does not expect that either regional emissions analyses or 
budgets for NOX and VOCs will be the same for 8-hour ozone 
and PM2.5 standards in areas that are nonattainment for both 
pollutants, for several reasons. First, it is likely that most areas 
will have different attainment dates for each of the two pollutants, 
which means that it is likely that analyses and budgets will be 
required for different years. Second, it is possible that in many cases 
the boundaries of the nonattainment area for each pollutant may be 
different. For example, the 8-hour ozone nonattainment area may contain 
more counties than the PM2.5 nonattainment area or vice 
versa. Finally, VOC and NOX regional emissions analyses and 
budgets for 8-hour ozone and PM2.5 areas will most likely be 
developed using different meteorological conditions and, in some areas, 
different travel patterns. For example, because in most areas, ozone is 
a summertime pollutant, NOX and VOC regional emissions and 
budgets in 8-hour ozone areas would be calculated using meteorological 
and travel data for a ``typical'' summer day. In contrast, 
NOX and VOC regional emissions and budgets for 
PM2.5 areas may be established using annual averages for 
meteorological and traffic conditions, rather than conditions for only 
a particular season, because most PM2.5 nonattainment areas 
are violating the annual PM2.5 standard instead of the 24-
hour standard.
    One commenter stated that there was an error in the proposed option 
1 language in Sec.  93.102(b)(iv) of the November 2003 rulemaking. 
Specifically, the commenter suggested that the proposed language 
appeared to require conformity determinations for NOX and 
VOCs if a submitted SIP does not contain emissions budgets for 
NOX and VOCs. EPA disagrees; the language as proposed for 
NOX and VOCs is correct and we are retaining that language 
for NOX in today's final rule. We believe that the commenter 
misunderstood the proposal. The language in Sec.  93.102(b)(iv) that is 
finalized today requires that conformity

[[Page 24288]]

determinations be made for NOX unless: (1) During the period 
before a SIP is submitted and budgets are found adequate or approved 
the state air agency and EPA regional office make a finding that on-
road emissions of NOX are not significant contributors to an 
area's air quality problem; and/or (2) the area's SIP does not 
establish an emissions budget for on-road emissions of NOX. 
In other words, if the SIP includes an adequate or approved emissions 
budget for NOX, then NOX must be analyzed in 
conformity determinations in PM2.5 nonattainment areas. In 
contrast, if the SIP does not contain a budget for NOX and 
instead concludes that emissions of NOX could rise to any 
reasonably foreseeable level withou