Official Release of the January 2011 AP-42 Method for Estimating Re-Entrained Road Dust From Paved Roads

Margo Tsirigotis Oge
February 4, 2011

[Federal Register: February 4, 2011 (Volume 76, Number 24)]
[Rules and Regulations]               
[Page 6328-6330]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr04fe11-8]                         

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 51 and 93

[FRL-9261-6]

 
Official Release of the January 2011 AP-42 Method for Estimating 
Re-Entrained Road Dust From Paved Roads

AGENCY: Environmental Protection Agency (EPA).

ACTION: Announcement of Availability.

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SUMMARY: On January 13, 2011, EPA posted the latest version of the 
method for estimating re-entrained road dust emissions from cars, 
trucks, buses, and

[[Page 6329]]

motorcycles on paved roads. This document approves this method for use 
in PM10 and PM2.5 state air quality 
implementation plans (SIPs) and regional emissions analyses for 
transportation conformity determinations (``regional conformity 
analyses''). This new method is incorporated in Chapter 13 of 
Compilation of Air Pollutant Emission Factors, AP-42, Fifth Edition, 
Volume I, that was published in January 2011.
    Today's action also starts a two-year grace period after which the 
January 2011 AP-42 method is required to be used in regional conformity 
analyses in PM10 nonattainment and maintenance areas and any 
PM2.5 nonattainment and maintenance areas where the EPA 
regional administrator or the state air quality agency determined that 
re-entrained road dust is a significant contributor to the area's 
PM2.5 problem, or if the area has a PM2.5 motor 
vehicle emissions budget that includes re-entrained road dust. This 
document is not relevant to SIP development or regional conformity 
analyses for ozone, carbon monoxide, and nitrogen dioxide nonattainment 
and maintenance areas, or for areas that use EPA-approved locally 
developed road dust methods.

DATES: EPA's approval of the January 2011 AP-42 method for estimating 
re-entrained road dust from paved roads for SIPs and regional 
conformity analyses is effective February 4, 2011. As discussed further 
below, today's approval also starts a two-year conformity grace period 
which ends on February 4, 2013, after which the January 2011 AP-42 
method is required to be used for SIPs and regional conformity 
analyses.

FOR FURTHER INFORMATION CONTACT: For questions about using AP-42 in 
SIPs and transportation conformity, contact David Bizot at 
Bizot.David@epa.gov or (734) 214-4432, or Laura Berry at 
Berry.Laura@epa.gov or (734) 214-4858. For technical questions 
regarding the use of AP-42, contact Ron Myers at Myers.Ron@epa.gov or 
(919) 541-5407.

SUPPLEMENTARY INFORMATION: The official version of the January 2011 
edition of Section 13.2.1 of AP-42, Paved Roads, and supporting 
documentation can be found at: http://www.epa.gov/ttn/chief/ap42/ch13/
index.html.
    The contents of this document are as follows:

I. Background on AP-42 and the January 2011 AP-42 Method
II. SIP Policy for Using AP-42
III. Transportation Conformity Policy for Using AP-42

I. Background on AP-42 and the January 2011 AP-42 Method

    Motor vehicle emissions inventories for PM10 and 
PM2.5 are comprised of four components: Exhaust emissions, 
emissions from brake wear, emissions from tire wear, and re-entrained 
road dust. EPA's methodologies for estimating PM emissions from re-
entrained road dust are found in AP-42, the Agency's compilation of 
data and methods for estimating average emission rates from a variety 
of activities and sources from various sectors. The sections of AP-42 
that address re-entrained road dust emissions are: Section 13.2.1 
(Paved Roads) and Section 13.2.2 (Unpaved Roads). State and local 
agencies currently use the latest versions of these sections of AP-42 
for calculating re-entrained road dust in PM SIP development and 
regional conformity analyses, as applicable, unless EPA has approved an 
alternate method.
    In today's document, EPA is approving, for SIPs and regional 
emissions analyses, the January 2011 edition of Section 13.2.1 of AP-42 
that reflects a new methodology for calculating re-entrained road dust 
from paved roads.\1\ The January 2011 AP-42 method did not change the 
methods for calculating road dust from unpaved roads (Section 13.2.2), 
last updated in November 2006,\2\ nor affect EPA's previous approvals 
of other emissions models.\3\
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    \1\ When completing project-level PM hot-spot analyses for 
transportation conformity purposes, either AP-42 or alternative 
local methods can be used. For more details, see EPA's 
``Transportation Conformity Guidance for Quantitative Hot-spot 
Analyses in PM2.5 and PM10 Nonattainment and 
Maintenance Areas'' (EPA-420-B-10-040, December 2010).
    \2\ For estimating road dust from unpaved roads, the November 
2006 update to Section 13.2.2 of AP-42 remains in effect. See 
``Policy Guidance on the Use of the November 1, 2006, Update to AP-
42 for Re-entrained Road Dust for SIP Development and Transportation 
Conformity'' at: http://www.epa.gov/otaq/stateresources/transconf/
policy/420b07055.pdf. This document supersedes the portions of this 
guidance that cover estimating dust from paved roads.
    \3\ Such as EPA's approvals of the MOVES2010 emissions model for 
SIPs and regional conformity purposes (75 FR 9411) and of the 
MOVES2010a and EMFAC models for transportation conformity hot-spot 
analyses (75 FR 79370).
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    The January 2011 AP-42 method includes revisions of the equation 
used to predict PM emissions, an extension of the applicable range of 
speeds down to 1 mph from the previous 10 mph, and the incorporation of 
an improved methodology for characterizing silt loading. These 
revisions were based on additional data from tests that were conducted 
on roads with slow moving and stop-and-go traffic, as well as public 
comments received on the draft revision. Please see EPA's AP-42 Web 
site for technical supporting documentation that provides additional 
detail regarding the revisions and the revision process.\4\
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    \4\ See http://www.epa.gov/ttn/chief/ap42/ch13/index.html.
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    It is estimated that PM10 emissions predicted by the 
January 2011 AP-42 method will be, on average, 40% less than the 
emissions for paved roads predicted by the November 2006 update. 
However, some silt loading and average vehicle weight conditions could 
result in different reduction levels and in some cases greater 
estimated emissions. PM2.5 emissions from paved roads 
predicted by the January 2011 AP-42 method will be generally greater 
than the emissions predicted by the November 2006 update. However, some 
silt loading and average vehicle weight conditions could result in 
lower estimated emissions.
    EPA notes that the January 2011 AP-42 method is approved 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 
should use, or continue to use, an alternate method approved by EPA on 
a case-by-case basis for use in SIPs or regional conformity analyses. 
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 alternate road dust methods.

II. SIP Policy for Using AP-42

    In general, states should use the January 2011 AP-42 method for 
PM10 and PM2.5 SIPs that are currently under 
development and future PM SIP revisions, unless EPA has approved an 
alternate method. The Clean Air Act (CAA) requires that SIP inventories 
and control measures be based on the most current information and 
applicable models that are available when a SIP is developed.\5\ States 
should use the January 2011 AP-42 method where PM SIP development is in 
its initial stages or hasn't progressed far enough along that switching 
to this method would create a significant adverse impact on state and 
local resources.
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    \5\ See CAA section 172(c)(3) and 40 CFR 51.112(a)(1).
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    Although the January 2011 AP-42 method should be used in 
PM10 and PM2.5 SIP development as expeditiously

[[Page 6330]]

as possible, EPA also recognizes the time and effort that states have 
already undertaken in SIP development using previous AP-42 methods. PM 
SIPs that EPA has already approved are not required to be revised 
solely based on the existence of the January 2011 AP-42 method. States 
that have already submitted PM SIPs or will submit PM SIPs shortly 
after today's approval are not required to revise these SIPs based on 
the recent availability of the January 2011 AP-42 method. States can 
choose to use the January 2011 AP-42 method in these PM SIPs, for 
example, if it is determined that it is appropriate to update motor 
vehicle emissions budgets (``budgets'') with the new method for future 
transportation conformity determinations. However, EPA does not believe 
that a state's use of a previous AP-42 method should be an obstacle to 
EPA approval for PM 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 a previous method). It would be 
unreasonable in such cases to require states to revise these PM SIPs 
with the January 2011 AP-42 method since significant work has already 
occurred and EPA intends to act on these SIPs in a timely manner.
    If you have questions about which road dust method should be used 
in your SIP, please consult with your EPA Regional Office.

III. Transportation Conformity Policy for Using AP-42

    Transportation conformity is a CAA requirement to ensure that 
federally supported highway and transit activities are consistent with 
the SIP. Conformity to a SIP means that a transportation activity will 
not cause or contribute to new air quality violations, worsen existing 
violations, or delay timely attainment of the national ambient air 
quality standards (NAAQS) or any interim milestone. EPA's 
transportation conformity regulations (40 CFR 51.390 and 40 CFR part 
93, subpart A) describe how federally funded and approved highway and 
transit projects meet these statutory requirements.
    CAA section 176(c)(1) 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 * * *.'' The 
transportation conformity rule (40 CFR 93.111) requires that conformity 
analyses be based on the latest motor vehicle emissions model approved 
by EPA. The conformity rule states that EPA will consult with the DOT 
to establish a grace period following specification of any new 
emissions model. The conformity rule further provides for a grace 
period for new emissions models of between 3-24 months, to be 
established by notification in the Federal Register (40 CFR 
93.111(b)(1)).
    In consultation with DOT, EPA must consider various factors when 
establishing a grace period for conformity determinations, including 
the degree of change in emissions models and the effects of the new 
model on the transportation planning process (40 CFR 93.111(b)(2)).
    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 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 opportunity to revise their SIPs before MPOs 
(metropolitan planning organizations) must use the model's new 
emissions factors.

As stated in Section I of today's document, the January 2011 AP-42 
method may result in PM10 emissions from paved roads being 
reduced as compared to the previous method, but results can vary from 
area to area. In general, PM2.5 emissions from paved roads 
could increase as compared to the previous method, which could affect 
those PM2.5 areas where road dust emissions are included in 
the PM2.5 SIP budget and are based on a previous AP-42 
method. In these limited number of PM2.5 areas and possibly 
some PM10 areas, state and local agencies may need 
additional time to consider whether additional revisions during the 
grace period are necessary to ensure future conformity determinations.
    Upon consideration of all of these factors, EPA is establishing a 
two-year conformity grace period that begins today and ends on February 
4, 2013. At the end of the grace period, the January 2011 AP-42 method 
will be required for regional conformity analyses in PM10 
nonattainment and maintenance areas and any PM2.5 
nonattainment and maintenance areas where re-entrained road dust is a 
significant contributor to the area's PM2.5 problem, or if 
the area has a PM2.5 motor vehicle emissions budget that 
includes re-entrained road dust.\6\ The following discussion about the 
conformity grace period is not relevant for those PM10 and 
PM2.5 areas that are completing conformity determinations 
based on approved alternate road dust methods.
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    \6\ See 40 CFR 93.102(b)(3) for when re-entrained road dust is 
included in regional emissions analyses.
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    During the conformity grace period, affected areas should use the 
interagency consultation process to examine how the January 2011 AP-42 
method will impact their future transportation plan and TIP conformity 
determinations and any regional emissions analyses. Areas should 
consider whether their PM10 and/or PM2.5 SIP(s) 
and budget(s) should be revised with the January 2011 AP-42 method, or 
if transportation plans and TIPs should be revised before the end of 
the conformity grace period in order to assist areas in continuing to 
meet transportation conformity requirements after the grace period 
ends.
    Regional conformity analyses that are started during the grace 
period can use either the January 2011 AP-42 method or the previous 
method. When the grace period ends on February 4, 2013, the January 
2011 AP-42 method will become the only approved method for estimating 
re-entrained road dust. The grace period for new regional emissions 
analyses would be shorter if a PM area revised its SIP and budgets with 
the January 2011 AP-42 method and such budgets became applicable prior 
to the end of the two-year conformity grace period.
    The conformity rule provides some flexibility for regional 
emissions analyses that are started before the end of the grace period. 
Analyses that begin before or during the grace period may continue to 
rely on the previous AP-42 method. 40 CFR 93.111(c). The interagency 
consultation process should be used if it is unclear if an analysis 
based on a previous method was begun before the end of the grace 
period. If you have questions about which AP-42 method should be used 
in your conformity determination, consult with your EPA Regional 
Office.

    Dated: January 28, 2011.
Margo Tsirigotis Oge,
Director, Office of Transportation and Air Quality.
[FR Doc. 2011-2422 Filed 2-3-11; 8:45 am]
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