[Federal Register Volume 69, Number 97 (Wednesday, May 19, 2004)]
[Rules and Regulations]
[Pages 28830-28832]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-11340]



[[Page 28830]]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 51

[FRL-7663-6]


Official Release of the MOBILE6.2 Motor Vehicle Emissions Factor 
Model and the December 2003 AP-42 Methods for Re-Entrained Road Dust

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notice of availability.

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SUMMARY: EPA is approving and announcing the availability of the 
MOBILE6.2 motor vehicle emissions factor model for official use in 
particulate matter (PM10 and PM2.5) SIPs and 
transportation conformity determinations outside of California. 
MOBILE6.2 is an update to MOBILE6 which adds the capability to estimate 
direct exhaust and brake and tire wear particulate matter emission 
factors for PM10 and PM2.5, and exhaust emission 
factors for particulate precursors to the MOBILE6 model. MOBILE6.2 is a 
substantial improvement over previous methods for estimating PM 
emissions and incorporates EPA's most current estimates of PM emissions 
for use by state and local governments to meet Clean Air Act 
requirements.
    EPA is also approving and announcing the availability of new 
methods for the estimation of re-entrained road dust emissions from 
cars, trucks, buses, and motorcycles on paved and unpaved roads for 
PM10 and PM2.5 state implementation plans (SIPs) 
and transportation conformity analyses. These new methods are 
incorporated in the December 2003 edition of Chapter 13 of Compilation 
of Air Pollutant Emission Factors, AP-42, Fifth Edition, Volume I: 
Stationary Point and Area Sources.
    Today's action also starts time periods after which MOBILE6.2 and 
the December 2003 AP-42 methods are required to be used in new 
transportation conformity analyses for PM10 emissions.
    EPA strongly encourages areas to use the interagency consultation 
process to examine how MOBILE6.2 and the December 2003 AP-42 methods 
will affect future transportation conformity analyses, so, if 
necessary, PM10 SIPs and motor vehicle emissions budgets can 
be revised with MOBILE6.2 and AP-42 or transportation plans and 
programs can be revised as appropriate prior to the end of the 
conformity grace period.

DATES: EPA's approval of the MOBILE6.2 emissions factor model and 
December 2003 AP-42 methods for re-entrained road dust is effective May 
19, 2004. See below for further information regarding how today's 
approval starts time periods after which MOBILE6.2 and the December 
2003 AP-42 methods are required in new transportation conformity 
analyses and certain SIP and motor vehicle emissions budget revisions.

FOR FURTHER INFORMATION CONTACT: If you have questions on this notice, 
please send an e-mail to EPA at [email protected] or contact EPA at (734) 
214-4636 for technical model questions about MOBILE6.2. Please send an 
e-mail to EPA at [email protected] or contact EPA at (919) 541-1000 
for technical questions about the December 2003 AP-42 methods.

SUPPLEMENTARY INFORMATION:

Availability of Models and Support Materials

    Copies of the official version of the MOBILE6.2 model are available 
on EPA's MOBILE Web site, http://www.epa.gov/otaq/m6.htm. The MOBILE 
Web site also contains the following support materials for implementing 
the new model: a detailed MOBILE6.2 User's Guide; EPA's ``Policy 
Guidance on the Use of MOBILE6.2 and the December 2003 AP-42 Method for 
Re-Entrained Road Dust for SIP Development and Transportation 
Conformity''; EPA's ``Technical Guidance on the Use of MOBILE6.2 for 
Emission Inventory Preparation''; and a list of Frequently Asked 
Questions about MOBILE6.2. EPA will continue to update this Web site in 
the future as other MOBILE6.2 support materials are developed.
    Individuals who wish to receive EPA announcements related to the 
MOBILE model should subscribe to the EPA-MOBILENEWS e-mail listserver. 
To subscribe to the EPA-MOBILENEWS listserver, write the following in 
the body of the e-mail message:
    subscribe EPA-MOBILENEWS FIRSTNAME LASTNAME where FIRSTNAME and 
LASTNAME is your name (for example: John Smith) and send the e-mail to 
the EPA Listserver at [email protected].
    Your e-mail address will then be added to the list of subscribers 
and a confirmation message will be sent to your e-mail address. 
Whenever a message is posted to the EPA-MOBILENEWS listserver by the 
listserver owner (the Assessment and Standards Division of the EPA 
Office of Transportation and Air Quality), a copy of that message will 
be sent to every person who has subscribed.
    You can remove yourself from the list by sending another message to 
the listserver address. This message must be sent from the same e-mail 
address that you used to subscribe, and should contain the message: 
unsubscribe EPA-MOBILENEWS.
    Copies of the official version of the December 2003 edition of 
Sections 13.2.1 and 13.2.2 of AP-42 can be found at www.epa.gov/ttn/chief/ap42/ch13/index.html. In the rest of this document, unless 
otherwise indicated, ``AP-42'' refers to the December 2003 edition of 
Sections 13.2.1 and 13.2.2 of AP-42.

I. What Is MOBILE6.2 and How Is It Different From MOBILE6?

    MOBILE is an EPA emissions factor model for estimating pollution 
from on-road motor vehicles in states outside of California. The model 
accounts for the emission impacts of factors such as changes in vehicle 
emission standards, changes in vehicle populations and activity, and 
variation in local conditions such as temperature, humidity, fuel 
quality, and air quality programs.
    MOBILE is used to calculate current and future inventories of motor 
vehicle emissions at the national and local level. These inventories 
are used to make decisions about air pollution policies and programs at 
the local, state and national level. Inventories based on MOBILE are 
also used to meet the federal Clean Air Act's state implementation plan 
(SIP) and transportation conformity requirements.
    The previous version of MOBILE, known as MOBILE6, calculated 
emissions of volatile organic compounds (VOCs), nitrogen oxides 
(NOX) and carbon monoxide (CO) from passenger cars, 
motorcycles, buses, and light-duty and heavy-duty trucks. MOBILE6.2 is 
an update to MOBILE6 which adds the capability to estimate direct 
particulate matter (PM) emission factors for PM10 and 
PM2.5, and emission factors for particulate precursors, to 
the original MOBILE6 model. In other words, MOBILE6.2 allows the 
estimation of emission factors for HC (and air toxics), NOX, 
CO, gaseous SO2, ammonia, and direct PM from vehicle exhaust 
and brake and tire wear. MOBILE6.2 also corrects some minor coding 
errors in the portion of the model code that estimates HC, 
NOX, and CO emission factors, and it adds the capability of 
entering hourly relative humidity values. MOBILE6.2 also incorporates 
some revisions to CO emission factors for cars and light-duty trucks 
that meet national low emission vehicle (NLEV), low emission vehicle 
(LEV), and Tier 2 vehicle standards.

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Functionally, MOBILE6.2 now replaces MOBILE6 as the highway vehicle 
emission factor model that EPA will maintain and support.

II. What Is the Impact of MOBILE6.2 on Ozone and CO SIPs and Conformity 
Determinations?

    Although MOBILE6.2 includes some corrections and enhancements to 
parts of the model that estimate emissions of HC, NOX, and 
CO, the impact of these changes is generally small. Even though 
MOBILE6.2 is very similar to MOBILE6 for these pollutants, states and 
local agencies outside of California should use MOBILE6.2 for future 
HC, NOX, and CO SIPs and conformity analyses in order to 
take full advantage of the improvements incorporated in this version. 
SIPs and conformity analyses already in progress with MOBILE6 can be 
completed using MOBILE6 as determined through the interagency 
consultation process. Because the changes in HC, NOX, and CO 
emissions in MOBILE6.2 are generally very small, the release of 
MOBILE6.2 does not start a new grace period before MOBILE6.2 is 
required to be used for all new transportation conformity analyses in 
ozone or CO nonattainment or maintenance areas and it does not trigger 
the need for any new ozone or CO SIP revisions.

III. What Are the December 2003 AP-42 Methods?

    Motor vehicle emissions inventories for PM are comprised of four 
components: exhaust emissions, emissions from brake wear, emissions 
from tire wear, and re-entrained road dust. MOBILE6.2 does not include 
the capability of estimating the emissions of re-entrained road dust as 
the result of motor vehicle activity. EPA has developed separate 
revised AP-42 methodologies for estimating re-entrained road dust from 
paved and unpaved roads. These new methods for estimating road dust 
emission factors for paved and unpaved roads are being incorporated in 
EPA's document AP-42. These new AP-42 methodologies (AP-42, Sections 
13.2.1, Paved Roads and 13.2.2, Unpaved Roads, each dated December 
2003) replace previous methods for estimating re-entrained road dust 
emissions for these categories with some limitations. AP-42 is the 
approved method only for situations for which silt loading, mean 
vehicle weight, and mean vehicle speed fall within ranges given in AP-
42 section 13.2.1.3 and with reasonably free-flowing traffic. For other 
conditions, areas may use an appropriate method approved by EPA on a 
case-by-case basis. In some areas, alternate methods may be more 
appropriate than AP-42 given specific local conditions even within the 
parameters given in AP-42 section 13.2.1.3. State and local agencies 
should consult with EPA for approval of alternative approaches. This 
policy is described in more detail in the document ``Policy Guidance on 
the Use of MOBILE6.2 and the December 2003 AP-42 Method for Re-
Entrained Road Dust for SIP Development and Transportation Conformity'' 
(available at http://www.epa.gov/otaq/models/mobile6/mobil6.2_letter.pdf). The following discussion of the use of AP-42 in SIPs and 
conformity determinations also applies to approved alternatives to AP-
42.

IV. PM10 SIP Policy for MOBILE6.2 and AP-42

    EPA has articulated its policy regarding the use of MOBILE6.2 and 
AP-42 in PM10 SIP development in its ``Policy Guidance on 
the Use of MOBILE6.2 and the December 2003 AP-42 Method for Re-
Entrained Road Dust for SIP Development and Transportation 
Conformity.'' Today's action highlights certain aspects of the 
guidance, but state and local governments should refer to the guidance 
for more detailed information on how and when to use MOBILE6.2 and AP-
42 in attainment and maintenance PM10 SIPs, inventory 
updates, and other PM10 SIP submission requirements. See 
Availability of Related SIP Policies to obtain the MOBILE6.2 and AP-42 
policy guidance.
    PM10 SIPs that EPA has already approved are not 
typically required to be revised now that EPA has approved MOBILE6.2 
and AP-42. Although MOBILE6.2 and AP-42 should be used in new 
PM10 SIP development as expeditiously as possible, EPA also 
recognizes the time and level of effort that States have already 
undertaken in PM10 SIP development with previous models or 
methods. States that have already submitted PM10 SIPs or 
will submit PM10 SIPs shortly after EPA's approval of 
MOBILE6.2 and AP-42 are not required to revise these SIPs simply 
because a new motor vehicle emissions model is now available. States 
can choose to use MOBILE6.2 in these SIPs, for example, if it is 
determined that future conformity determinations would be ensured 
through such a SIP revision. However, EPA does not believe that a 
State's use of an earlier model such as PART5 should be an obstacle to 
EPA approval for SIPs that have been or will soon be submitted, 
assuming that such SIPs are otherwise approvable and significant SIP 
work has already occurred (e.g., attainment modeling for an attainment 
SIP has already been completed with an earlier model). It would be 
unreasonable to require States to revise these SIPs with MOBILE6.2 and 
AP-42 since significant work has already occurred, and EPA intends to 
act on these SIPs in a timely manner.
    States should use MOBILE6.2 and AP-42 where PM10 SIP 
development is in its initial stages or hasn't progressed far enough 
along that switching to MOBILE6.2 and AP-42 would create a 
significantly adverse impact on State resources. For example, 
PM10 SIPs that will be submitted late in 2004 should be 
based on MOBILE6.2 and AP-42 since there is adequate time to 
incorporate the new model's results. MOBILE6.2 and AP-42 should be 
incorporated into these SIPs since emissions estimates in these models 
are based on the best information currently available, as required by 
Clean Air Act section 172(c)(3) and 40 CFR 51.112(a)(1).

V. PM10 Transportation Conformity Policy for MOBILE6.2 and 
AP-42

    Transportation conformity is a Clean Air Act requirement to ensure 
that federally supported highway and transit activities are consistent 
with (``conform to'') the SIP. Conformity to a SIP means that a 
transportation activity will not cause or contribute to new air 
pollution violations; worsen existing violations; or delay timely 
attainment of federal air quality standards.
    The transportation conformity rule (40 CFR part 93) requires that 
conformity analyses be based on the latest motor vehicle emissions 
model approved by EPA. Section 176(c)(1) of the Clean Air Act states 
that ``. * * * [t]he determination of conformity shall be based on the 
most recent estimates of emissions, and such estimates shall be 
determined from the most recent population, employment, travel, and 
congestion estimates * * *.'' When we approve new emissions models such 
as MOBILE6.2 and AP-42, a grace period is established before the models 
are required for conformity analyses. The conformity rule provides for 
a grace period for new emissions models of between 3-24 months.
    EPA articulated its intentions for establishing the length of a 
conformity grace period in the preamble to the 1993 transportation 
conformity rule (58 FR 62211):

    ``EPA and [the Department of Transportation (DOT)] will consider 
extending the grace period if the effects of the new emissions model 
are so significant that previous SIP demonstrations of what emission 
levels are consistent with attainment would be substantially 
affected. In such cases, States should have an

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opportunity to revise their SIPs before MPOs must use the model's 
new emissions factors.''

In consultation with the DOT, EPA considers many factors in 
establishing the length of the grace period, including the degree of 
change in emissions models and the effects of the new model on the 
transportation planning process (40 CFR 93.111).
    Upon consideration of all of these factors, EPA is establishing a 
2-year grace period, which begins today and ends on May 19, 2006, 
before MOBILE6.2 and AP-42 are required for new PM10 
conformity analyses in most cases. During this grace period, areas 
should use the interagency consultation process to examine how 
MOBILE6.2 and AP-42 will affect their future conformity determinations.
    However, the grace period will be shorter than 2 years for 
PM10 if an area revises its SIP and budgets with MOBILE6.2 
and AP-42 and such budgets become applicable for conformity purposes 
prior to the end of the 2-year grace period. For example, if an area 
revises a previously submitted (but not approved) PART5-based 
PM10 SIP with MOBILE6.2 and AP-42 and EPA finds the revised 
budgets adequate for conformity, such budgets would apply for 
conformity on the effective date of the Federal Register notice 
announcing EPA's adequacy finding.
    During the grace period, areas can use earlier models such as PART5 
for PM10 conformity determinations or choose to use 
MOBILE6.2 and AP-42 on a faster time frame. When the grace period ends 
on May 19, 2006, MOBILE6.2 will become the only approved motor vehicle 
emissions model for new PM10 transportation conformity 
analyses outside of California and AP-42 will become the approved 
method for estimating re-entrained road dust unless an alternate method 
is approved as described in section III above. In general, this means 
that all new PM10 conformity analyses started after the end 
of the 2-year grace period must be based on MOBILE6.2 and AP-42, even 
if the SIP is based on PART5. As discussed above, the grace period for 
new conformity analyses would be shorter for PM10 if an area 
revised its SIP and budgets with MOBILE6.2 and AP-42 and such budgets 
became applicable for conformity purposes prior to the end of the 2-
year grace period. EPA strongly encourages areas to use the 
consultation process to examine how MOBILE6.2 and AP-42 will affect 
future conformity determinations, so, if necessary, PM10 
SIPs and budgets can be revised with MOBILE6.2 and AP-42 or 
transportation plans and programs can be revised as appropriate prior 
to the end of the grace period.
    Finally, the conformity rule provides some flexibility for analyses 
that are started before or during the grace period. Regional conformity 
analyses that began before the end of the grace period may continue to 
rely on earlier models such as PART5. Conformity determinations for 
transportation projects may also be based on an earlier model if the 
regional analysis was begun before the end of the grace period, and if 
the final environmental document for the project is issued no more than 
three years after the issuance of the draft environmental document (see 
40 CFR 93.111(c)). The interagency consultation process should be used 
if it is unclear whether an analysis based on an earlier model was 
begun before the end of the grace period.
    The release of MOBILE6.2 and AP-42 does not trigger the need for 
quantitative conformity hot-spot modeling to estimate concentrations of 
PM10 at this time. However, qualitative hot spot analyses 
are still required in PM10 nonattainment and maintenance 
areas.

VI. PM2.5 SIP and Transportation Conformity Policy for 
MOBILE6.2 and AP-42

    EPA has not yet finalized implementation policy for the 
PM2.5 National Ambient Air Quality Standards (NAAQS). 
However, when that policy is finalized and PM2.5 
nonattainment areas have been designated, MOBILE6.2 (except in 
California) and AP-42 (except in areas where another dust methodology 
has been approved) will be the approved models for estimating motor 
vehicle exhaust, brake and tire wear, and re-entrained road dust 
emissions in PM2.5 SIPs and conformity determinations, until 
they are replaced by newer models or methods. No PM2.5 SIPs 
have previously been done using other models and therefore, the release 
of MOBILE6.2 and AP-42 does not constitute a change in models which 
might result in inconsistencies between the SIP and transportation 
analyses. As a result, there is no need for a PM2.5 
conformity grace period for MOBILE6.2 and AP-42. MOBILE6.2 (except in 
California) and AP-42 (except in areas where another dust methodology 
has been approved) must be used in all PM2.5 conformity 
analyses, until they are replaced by newer approved methods or models.

    Dated: May 11, 2004.
Margo Tsirigotis Oge,
Director, Office of Transportation and Air Quality.
[FR Doc. 04-11340 Filed 5-18-04; 8:45 am]
BILLING CODE 6560-50-P