EPA's Proposal for MOBILE6
            Emission Control Technology Distribution

                         March 14, 1997


Abstract

     In its highway vehicle emission factor model (MOBILE5), EPA
stratifies the in-use fleet into emission control technology
groups that have similar in-use emission characteristics.  The
four (4) technology groups used in the MOBILE5 model to determine
basic emission rates were:

    open-loop
    carbureted (CARB) closed-loop
    throttle body fuel injection (TBI) closed-loop
    port fuel injection (PFI) closed-loop
  
The basic emission rates for each of these groups are determined
by model year groupings and are weighted together by sales
information or predicted market share to represent the in-use
fleet emissions for a given calendar year.  With the current
revision to the MOBILE model, EPA plans to update the appropriate
technology groupings, as well as the estimate of the market share
of each group for the historical period and the forecast period.


Summary of Proposal

  The primary goals are to determine:

     What the significant technologies impacting emissions are.

     Other factors (emission standards, model year, etc.) which will
     affect this analysis.
  
A major barrier to this analysis will be the fact that many
useful datasets do not have an adequate emission control
technology description.  Another problem is that data collected
in I/M areas will not necessarily be representative of non-I/M
areas.


Supporting Data

     As a first step toward determining the significant
technologies, EPA directed its contractor (E.H. Pechan and
Associates, Inc.) to:

  Identify the technology groups that (will) have similar in-use
  emission characteristics for both the historical (1990-1996)
  period and the future from 1996 to 2020.

  Estimate the distributions of these groupings for each year over
  the historical period from available sales data.

  Forecast the technology distributions for future model years. 
  
Pechan's subcontractor (Energy and Environmental Analysis, Inc.)
has delivered its report, and EPA is currently reviewing that
report.  The report recommends that, for the 1990 and later model
year vehicles, the following ten (10) technology groupings for
consideration:

    PFI/3CL
    PFI/3CL/EGR
    PFI/3CL/AIR/EGR
    PFI/3CL+OXID/AIR/EGR
    TBI/3CL
    TBI/3CL/EGR
    TBI/3CL/AIR/EGR
    TBI/3CL+OXID/AIR/EGR
    TBI/3CL+OXID/AIR/EGR
    Other
  
Where  3CL: Three-Way (oxidation & reduction) Catalyst with
            electronic Closed-Loop fuel control
       +OXID: Additional oxidation-only catalyst 
       AIR: Supplemental air injection system
       EGR: Exhaust Gas Recirculation system


Methodology

     We plan to use EPA's Emission Factor (EF) database to
determine the impacts of the above technology groupings on
emissions.  Where information on the technology type of the
individual test vehicles is scarce, we will find what we can from
the Certification databases. Since technology has different
effects on each pollutant, the analysis will be done separately
for each pollutant.  The following five (5) model year groupings
for LDGV were chosen:  

          o  Pre-1981
          o  1981-1982
          o  1983-1985
          o  1986-1993
          o  1994+

Pre-1981 model years will *not* be analyzed by technology.  They
will be separated only by emission standards.  The 1994 and newer
model years contain some Tier 1 standard vehicles.  The 1981 and
1982 model years contain CO waiver vehicles which will be treated
separately.  The split for the 1986-1993 model years was chosen
to reflect the split used by the In-Use Deterioration team.

     The analysis will be done initially in Log-space to reduce
the effects of high emitters on sample averages.  Additional
analysis may be necessary in normal space accounting more
specifically for high emitters.