[Federal Register Volume 62, Number 46 (Monday, March 10, 1997)]
[Notices]
[Pages 10849-10852]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-5884]


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ENVIRONMENTAL PROTECTION AGENCY

[AMS-FRL-5699-8]


Air Pollution Control; Motor Vehicle Emission Factors

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notice of public workshop.

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SUMMARY: The Environmental Protection Agency is now in the process of 
developing revision and improvements to the highway vehicle emission 
factor model (the MOBILE model). The current version of the model, 
MOBILE5a, was released for use March 26, 1993. The next version of the 
model, MOBILE6, is tentatively planned for completion early in 1998 and 
release for use in the summer of 1998. This notice announces the first 
public workshop for the purpose of discussing issues raised by the 
pending revisions to the model, and provides the first formal 
opportunity for comment and reaction to the plans for data collection, 
analysis, and proposed model revisions. There will be at least one 
additional MOBILE6 workshop, most probably to be held late this year. 
The workshop will also include a short presentation concerning EPA's 
plans for development of a nonroad mobile source emission inventory 
model.

DATES: The workshop will be held Wednesday, March 19 and Thursday, 
March 20, 1997. The times are from 8:30 am to 5:00 pm March, and 8:30 
am to 3:00 pm March 20. Al times are Eastern Standard Time.

ADDRESSES: The workshop will be held in Powsley Auditorium of the 
Morris Lawrence Building, Washtenaw Community College, 400 East Huron 
River Drive, Ann Arbor, MI 48106. Directions to the workshop can be 
requested from the contact person listed below, or from the EPA 
Technology Transfer Network (TTN) bulletin board system (BBS), or 
through accessing the OMS World Wide Web (WWW) site. Information on how 
to electronically access this and other workshop-related information 
appears immediately below.

FOR FURTHER INFORMATION CONTACT: Ms. Betty Measley, U.S. EPA Office of 
Mobile Sources, Assessment and Modeling Division, Emission Inventory 
Group, 2565 Plymouth Road, Ann Arbor MI 48105. Telephone: (313) 741-
7903; fax (313) 741-7939.

SUPPLEMENTARY INFORMATION: This notice, as well as related information 
concerning the workshop, may be found in the OMS section of the EPA TTN 
BBS. To access this information using the WWW:

http://www.epa.gov/OMSWWW/models.htm
gopher: gopher.epa.gov menus<r-arrow>Offices: Air:OMS
ftp: ftp.epa.gov Chg Dir<r-arrow>pub/gopher/OMS

    For those directly accessing the TTN BBS by modem connection:

TTNBBS Dial-in: (919) 541-5742 [Voice help: (919) 541-5384]
Web access to TTN: http://ttnwww.rtpnc.epa.gov
telnet: ttnbbs.rtpnc.epa.gov (for reading/leaving messages)
ftp: ttnftp.rtpnc.epa.gov Chg Dir<r-arrow>H-Drive/OMS

    Workshop-related files, including a copy of this notice, a map 
showing the location of WCC, and later additional information as 
described in the body of this announcement, will be found at the OMS 
Section, Models & Utilities Subsection
    Under Section 130 of the Clean Air Act Amendments of 1990, EPA is 
required to review, and to revise a necessary, the emission factors 
used to estimate emissions of volatile organic compounds (VOC), carbon 
monoxide (CO), and oxides of nitrogen (NO<INF>X) from area and mobile 
sources. In the case of highway vehicles, emission factors for these 
pollutants as a function of various parameters are estimated using the 
highway vehicle emission factor model, commonly referred to as MOBILE. 
This model, which was first developed in the late 1970s, has been 
revised, updated, and improved periodically since that time to account 
for increasing data and analyses concerning in-use emissions 
performance of highway vehicles, changes in vehicle and emission 
control technology, changes in fuel composition, strengthening of 
applicable emission standards, refinements to applicable test 
procedures, and other items that affect emission levels in use.
    Section 130 of the Act requires that this emission factor review, 
and revision as needed, be performed at least every three years. As 
noted above, the current official version of the model, MOBILE5a, was 
released in March 1993. Since that time, one interim update to the 
model has been developed, MOBILE5a__H, released in November 1995. While 
not involving revision and update to the entire model, this version and 
developed to address specific needs on the part of emission factor 
users. MOBILE5a__H incorporated a number of changes intended to improve 
the ability of modelers, particularly States and local/regional 
governments, in estimating the benefits of various innovative 
inspection and maintenance (I/M) programs and to improve the accuracy 
of modeling situations in which such programs change over time or 
different programs are applied to different subsets of the covered 
fleet.
    The time elapsed since the last complete revision to the model and 
the additional test data and analyses available since that time warrant 
another thorough update and revision to the model. OMS plans 
significant changes not only to the underlying emission factor 
estimates, but to how emissions factors are modeled to account for 
things such as a separation of start and running exhaust emissions, 
roadway facility type, average traffic speeds, and a number of other 
important changes that will affect the input information required to 
use the model as well as the type of information produced by the model. 
Thus, this first MOBILE6 workshop will present an overview of the more 
important model revisions being planned. The tentative agenda for this 
workshop is discussed below. Other aspects of the modeling of highway 
vehicle emission that are not specifically included within the 
following discussion may also be briefly addressed in this workshop; 
however, the agenda discussed below is intended to illustrate the major 
areas of discussion for the workshop.
    The workshop being announced by today's notice will span two days. 
In an effort to facilitate travel plans on the part of attendees, a 
preliminary agenda for the two days is presented below. Note that the 
first day (March 19) is largely devoted to ``technical'' issues 
involved in updating and revising the model, while the second part-day

[[Page 10850]]

(March 20) is focused more on ``user changes,'' meaning those revisions 
planned that will affect the input data requirements and file structure 
and output changes. Many attendees will likely want to be present for 
both sessions, however, some may find that they can limit their 
attendance to one or the other days based on their specific interests 
and needs.

Topics To Be Discussed on March 19

    The first day of the workshop is planned to include presentations 
on the new facility-specific speed correction cycles, start emissions 
and separation of start from running exhaust emissions, technology 
fractions for future model years, the findings of the in-use 
deterioration team, effects of fuel oxygenates and sulfur content on 
emissions, ``real-time'' diurnal evaporative emissions, and revisions 
to the modeling of emissions from heavy-duty vehicles. Each 
presentation will be followed by a short discussion/question and answer 
period, and there should be some time left at the end of the day for 
more general open discussion of the material that has been presented.

New Facility-Specific Driving Cycles

    One area of concern with respect to the accuracy of modeled 
emission factors has been the methods used to correct emission 
estimates based on the Federal Test Procedure (FTP), intended to 
represent overall urban area driving and with an average speed of 19.6 
mph, for other average speeds. EPA is designing a plan for a much 
different approach to this issue that we hope to include in MOBILE6, 
which should both improve the accuracy of emission estimates over the 
range of travel speeds of interest and improve the integration of 
emission factor modeling with transportation planning and modeling. 
This would represent a major departure from the approach taken in 
previous versions of the model, and will result in significant changes 
to both the input data requirements and output emission factor 
estimates relative to earlier versions.

Start Emissions and Separation of Start From Running Emissions

    MOBILE has used operating mode fractions (describing the portion of 
overall vehicle miles travelled (VMT) by vehicles in cold-start, hot-
start, or stabilized operation) as an input to provide exhaust emission 
factors in grams per mile that include start emissions. Based on the 
needs of the air quality and transportation planning communities and 
the availability of data suitable for this type of analysis, EPA is 
proposing to make two major changes in this area: Provision of start 
emissions (in grams per vehicle per start) and stabilized running 
exhaust emissions (in grams per mile) at the option of the model user, 
and basing start emission estimates on time that a vehicle has been off 
(rather than simply ``cold'' and ``hot'' starts, start emissions will 
be modeled as a function of time that vehicles have been off, or ``soak 
time'').

Technology Fractions

    Emissions from highway vehicles are estimated on a fleetwide basis 
using information on the fractions of each model years' fleet that use 
different technologies (e.g., fuel delivery systems, catalytic 
converter type). Projecting future year emission requires that 
projections of future technology fractions by model year be included in 
the MOBILE model. A contractor working for EPA has developed such 
estimates for future years, which will be presented and discussed.

In-Use Deterioration Team Findings

    A team within OMS has spent considerable effort reexamining the 
extent of and causes of in-use deterioration, or the increase in 
emissions over time as vehicles accumulate mileage and components, 
including emission control components, age and degrade in performance. 
The team has worked in cooperation with the In-Use Deterioration Work 
Group of the Mobile Source Technical Advisory Subcommittee (a 
subcommittee to the Clean Air Advisory Committee established under the 
Federal Advisory Committee Act). All available data on in-use emissions 
performance over time have been used in an attempt to better quantify 
the extent of in-use emissions deterioration. An overview of the 
findings of the team to date, and some of the potential implications 
for the modeling of in-use deterioration of emissions in MOBILE6, will 
be presented and discussed at this workshop.

Fuel Sulfur and Oxygenate Content Effects

    EPA has known for some time that other aspects of fuel (gasoline) 
composition, beyond volatility as measured by Reid vapor pressure 
(RVP), have an impact on emissions. MOBILE5a included the ability for 
the modeler to specify the effects of RVP, and of oxygenate type (i.e., 
alcohol or ether blends) and content (% by wgt), on emissions. At this 
workshop, information on revising and improving the modeling of 
oxygenate type of content on emissions, and on the impacts of sulfur on 
emissions, will be presented and discussed.

Onboard Diagnostic System Effects

    With the introduction of second generation onboard diagnostic 
systems (OBD-II) to the light-duty fleet, EPA needs to develop methods 
of modeling the impact of these systems on reducing in-use 
deterioration of both exhaust and evaporative emissions, in both 
inspection/maintenance (I/M) program areas and non-I/M areas. Proposed 
approaches to including such effects on MOBILE6, based on part on 
previous work by the California Air Resources Board and recommendations 
made by the Modeling Work Group of the Mobile Source Technical Advisory 
Subcommittee, will be presented and discussed.

Heavy-Duty Vehicle Emission Estimates

    The estimation of in-use emissions from heavy-duty vehicles is 
complicated by the fact that such engines are regulated on a mass/work 
basis (grams per brake horsepower-hour), while users of emission 
factors generally need emissions on a mass/activity basis (i.e., grams 
per mile). This necessitates the use of conversion factors to adjust g/
bhp-hr emissions to g/mi. These conversion factors will be updated for 
MOBILE6. In addition, plans are to expand the number of vehicle 
categories for which specific emission factors are estimated by the 
model, replacing ``heavy-duty gas vehicle'' and ``heavy-duty diesel 
vehicle'' emission factors with estimates specific to a number of 
subcategories (e.g., by GVW class, with buses treated separately), 
EPA's plans for revisions in these areas will be presented and 
discussed.

Fleet Characteristics

    In order to model emission factors for the entire in-use fleet of 
highway vehicles, information on the total numbers of vehicles by 
vehicle type, the registration distributions by age of each vehicle 
type, and the annual mileage accumulation rates by age of each vehicle 
type are required. Wile modelers often substitute locality-specific 
data for the national data that is included in MOBILE, particularly for 
registration distributions by age, it is still important for national 
modeling and estimation of the impact of new rules, standards, and test 
procedures to update these types of information periodically. EPA has 
retained a contractor to develop more recent information on fleet 
characteristics, including detailed information on the various 
subclasses of heavy-duty gas and diesel vehicles, and buses, for use in 
MOBILE6. A progress

[[Page 10851]]

report on results to date and plans for incorporating such data into 
MOBILE6 will be presented and discussed.

Real-Time Diurnal Emissions

    For gasoline-fueled vehicle types, non-exhaust emissions are a 
significant portion of total emissions of volatile organic compounds 
(VOC). Non-exhaust, or evaporative, emissions consist of diurnal 
emissions, hot soak (trip-end) emissions, refueling emissions, and 
running and resting losses. Diurnal emissions, generated during times 
that a vehicle is not being driven and ambient temperatures are 
increasing, have in the past been based on data obtained during one-
hour forced heat builds, with the temperature increase representative 
of an entire eight-hour period being performed over one hour. More 
recent testing has shown that if the emissions are measured over longer 
periods of time, more representative of the rate and duration of 
temperature increases actually experienced by in-use vehicles, the 
results are not the same. To improve the accuracy of diurnal emissions 
estimates, and to provide users with the ability to better model 
emissions over shorter periods of time than full days (e.g., airshed 
models typically require emissions on an hour-by-hour basis), MOBILE6 
will incorporate so-called ``real time'' diurnal emissions estimates 
and means of estimating such emissions over shorter time periods and 
lesser temperature increases characteristic of such shorter times. 
Plans for implementing this approach in MOBILE6 will be presented and 
discussed.

Liquids Leaks, Trip Characteristics

    Plans are for the new version of the model to have means of 
explicitly accounting for, and estimating emissions due to evaporation 
of, liquid leaks of fuel. Modeling liquid leaks explicitly in MOBILE 
would have an impact on estimates for other nontailpipe emission 
factors (diurnals, hot soaks, running and resting losses), as the 
presumption is that liquid leaks, if and when encountered, have been 
included within these other emission source categories. All of these 
evaporative emission estimates are affected by trip characteristics, or 
travel patterns, such as average number of trips per day, miles per 
day, miles per trip, and so forth. EPA plans to have updated these trip 
characteristics in MOBILE6 on the basis of analysis of data obtained 
from instrumented vehicles.
    These are the main areas in which presentations are planned for the 
first day of the workshop. Results of test programs and data analyses 
will be presented where available, and in all subject areas plans for 
additional work and proposed revisions to the model's treatment of each 
area will be discussed.

Topics To Be Discussed on March 20

    As noted above, the focus of the presentations and discussion on 
the second day of the workshop will be more toward changes that impact 
the input data requirements and file structure and on proposed output 
changes. The second day will also include a presentation concerning 
EPA's plans for development of a nonroad emission inventory model.

Inspection/Maintenance (I/M) Programs and Credits

    One of the more important aspects of the model from the perspective 
of many States and local/regional entities is the modeling of the 
benefits of various types of periodic I/M programs. MOBILE5a__H was 
released in 1995 to provide an interim tool for use in modeling certain 
types of tests and combinations of programs that could not be modeled 
adequately using MOBILE5a. The increasing variety of test types (e.g., 
idle tests, IM240 tests, use of remote sensing devices in conjunction 
with other I/M programs, the ASM and BAR90 tests), the tendency toward 
greater use of multiple sets of cutpoints (based, for example, on age 
of vehicle at time of test), and the frequency with which a given area 
is using more than one type of I/M program, whether simultaneously or 
sequentially, all suggest that there is a need for changes in how the 
emission benefits resulting from such programs are estimated and 
reflected in MOBILE emission factors. In MOBILE6, EPA is considering 
significant changes to the means by which credits for I/M programs are 
modeled. EPA will present proposals for changes in the modeling of I/M 
programs for discussion and comment.

Input/Output Structure Changes

    In past updates to the MOBILE model, EPA has made a strong effort 
to maintain upward compatibility of input data files used to run the 
model. That is, a MOBILE4.1 input file, for example, can be used to run 
MOBILE5a, although some features of MOBILE5a have no corresponding 
feature in MOBILE4.1. This has been accomplished through adding new 
options as either (i) additional permitted values assigned to existing 
control flags, or (ii) additional optional variables appended to the 
end (right side) of existing input file lines, set up so that if they 
are missing (as would be the case if an input file for an older MOBILE 
version not having that feature) this in interpreted as ``new option 
not to be included in modeling.'' The extent of changes planned and 
proposed for MOBILE6 are such that it wil not longer be possible to 
maintain this ``upward compatibility'' of input files. The output files 
are also likely to change significantly.
    Because this is likely to be of great interest of State and local/
regional modelers in particular, EPA will devote one presentation to 
specifically outlining all of the input and output changes implied by 
the model revisions noted above, as well as others not the subject of 
specific presentations at this workshop. This information is still in 
the proposal stage, and the input of and reaction from modelers at and 
after the workshop will assist in determining the precise nature of 
these changes in MOBILE6.

Nonroad Model--Overview of Plans

    The final presentation at the workshop will not be directly related 
to MOBILE6, but instead will present an overview of EPA's plans for the 
development of a nonroad mobile source emission inventory (as versus 
emission factor) model. Current nonroad inventory development practices 
are based on EPA's Nonroad Engine and Vehicle Emissions Study (NEVES), 
done under the 1990 Clean Air Act Amendment requirements, and 
``Procedures for Emission Inventory Preparation, Volume IV: Mobile 
Sources (EPA-450/4-81-026d (revised), 1992). In consideration of the 
increased recognition of the importance of emissions from nonroad 
sources in terms of overall emissions and air quality, and the 
considerable practical difficulty of implmenting the current guidance, 
EPA is planning to develop a SIP-related nonroad emissions inventory 
model to meet the needs of the modeling audidence. EPA will present its 
plans and proposals for development of a nonroad mobile source emission 
inventory model, and will be especially interested in input from 
workshop attendees as to their needs and preferences for such a model. 
Specifically, EPA would lke to know the types of locality-specific 
input data (e.g., equipment populations) that users of such a model 
would anticipate developing and using in order to customize nonroad 
emission inventories for the geographic domain of interest. Such 
information obtained at the workshop will assist EPA in determining the 
best approaches to use

[[Page 10852]]

in a nonroad emission inventory model to maximize its utility.

Additional Information

    To the extent possible, EPA will post material at the TTN BBS site 
described under For further information contact above in advance of the 
workshop. Those planning to attend, and those interested in following 
the progress of workshop planning more closely, should periodically 
visit the workshop information site. For example, some of the 
presentation materials that will be used at the workshop will be posted 
in advance to facilitate discussion and comment at the workshop.

    Dated: February 28, 1997.
Mary D. Nichols,
Assistant Administrator for Air and Radiation.
[FR Doc. 97-5884 Filed 3-7-97; 8:45 am]
BILLING CODE 6560-50-M