U.S. Environmental Protection Agency

April, 2001

Document Released for Public Information

"Soak Length Activity Factors for Diurnal Emissions" 

Report Number   EPA420-R-01-014     (M6.FLT.006)
 
     The Office of Transportation and Air Quality, Assessment and
Standards Division announces the release of "Soak Length Activity
Factors for Diurnal Emissions" for public information.  Also, two
Excel worksheet data and calculation files "EVP_DIU2.XLS" and
"DIURRULE.XLS" are referenced in the report, and should be
viewed in conjunction with the report.  This document
EPA420-R-01-014, also known as M6.FLT.006, and the associated
spreadsheet files are available at the MOBILE6 section of the
OTAQ Web Site (http://www.epa.gov/otaq/m6.htm). 

     Diurnal activity estimates have been derived for use in
MOBILE6.  They were derived primarily from instrumented vehicle
study data collected in Spokane, Atlanta and Baltimore. These
activity estimates will be used to properly distribute the
diurnal evaporative emissions in MOBILE6 between the hours of the
day, and within a given hour.  The report also discusses the
various types of diurnals.  These include interrupted diurnals,
full diurnals andmulti-day diurnals.  The rules which are used to
determine which type of diurnal is present as a function of time
of day and the length of the diurnal soak period are also
discussed.  

     This report was originally released (as a draft) in
February, 1998 under the title, "Soak Length Activity Factors for
Diurnal Emissions".  It was revised and finalized in April, 2001.
This final revision incorporates suggestions and comments
received from stakeholders during the 60-day review period and
from peer reviewers.