U.S. Environmental Protection Agency

May 3, 1999

Document Released for Public Information

Update of Heavy-Duty Emission Levels (Model Years 1988-2004+) 
for Use in MOBILE6


Report Number EPA420-R-99-010  (M6.HDE.001)
 
The Office of Mobile Sources, Assessment and Modeling Division
announces the release of "Update of Heavy-Duty Emission Levels
(Model Years 1988-2004+)for Use in MOBILE6" for public
information.  This document EPA420-R99-010, also known as
M6.HDE.001,is available at the MOBILE6 section of the OMS Web
Site/(http://www.epa.gov/oms/m6.htm

For MOBILE6, EPA intends to update the estimates of heavy-duty
engine emission factors currently contained in MOBILE5b.  To
accomplish this, EPA plans to follow the same method employed in
previous versions of the MOBILE model, using updated inputs. 
Succinctly, the methodology entails determination of a gram per
mile (g/mi) emission factor by multiplying a work-specific
emission level (in units of grams per horsepower-hour (g/bhp-hr))
by a conversion factor which converts work units into mileage
units (bhp-hr/mi).

Emission Factor (g/mi) = Work-Specific Emission Level (g/bhp-hr)
* Conversion Factor (bhp-hr/mi)


     EPA defines heavy-duty vehicles as those vehicles exceeding
8,500 lbs. gross vehicle weight (GVW). This broad class of
vehicles is divided into those requiring gasoline or diesel
fuels, and is further subdivided into more specific classes based
on GVW categories.  EPA uses this more detailed subdivision
scheme to account for different characteristics and uses of the
engines included in each GVW class.
 
This document describes the emission levels to be used in
MOBILE6.  Itis being released and posted in April, 1999.  It is
the revised and final version of a document originally posted for
stakeholder review and comment in October, 1997.

Thank you for your continuing interest in the development of
MOBILE6. 

Sincerely,

Emission Inventory Group, 
Assessment and Modeling Division, 
US EPA, Office of Mobile Sources