U.S. Environmental Protection Agency

April 2001

Document Released for Public Information

"Modeling Hourly Diurnal and Interrupted Diurnal Emissions Based on 
Real-Time Diurnal Data"

Report Number   EPA420-R-01-019     (M6.EVP.002)
 
	The Office of Transportation and Air Quality, Assessment and 
Standards Division announces the release of "Modeling Hourly Diurnal 
and Interrupted Diurnal Emissions Based on Real-Time Diurnal Data" for 
public information.  This document EPA420-R-01-019, also known as 
M6.EVP.002, is available at the MOBILE6 section of the OTAQ Web Site 
(http://www.epa.gov/otaq/m6.htm).

	Evaporative emissions due to changes in ambient temperature 
are an important source of hydrocarbons.  These full-day diurnal 
emissions are described as daily averages in a parallel report 
(M6.EVP.001).  This report presents the method used in MOBILE6 for 
distributing these full-day emissions among the 24 hours of the day. 

	This document reports both on the methodology used to analyze 
the data from real-time diurnal (RTD) tests on 270 vehicles and on the 
results obtained from those analyses.  The purpose of the analysis was 
to develop a model of the hourly diurnal emissions of the in-use fleet 
to be used in MOBILE6.

	This report was originally released (as a draft) in May 1998, 
and then revised (and re-released) in July 1999.  This current version 
is the final revision of the July 1999 draft (of M6.EVP.002).  This 
final revision incorporates suggestions and comments received from 
stakeholders during the 60-day review period and from peer reviewers.