U.S. Environmental Protection Agency


       Document Released for Stakeholder Review and Comment

    Modeling Hourly Diurnal and Interrupted Diurnal Emissions
                     Based on Real-time Data 

                  Report Number EPA420-P-99-027
                            M6.EVP.002

     Evaporative emissions due to changes in ambient temperature
are an important source of hydrocarbons.  These diurnal emissions
were described as daily averages in an earlier report
(M6.EVP.001).  The current report proposes a model for
distributing these emissions among the hours of the day.  This
document reports on both the methodology used to analyze data
from real-time diurnal (RTD) tests on 270 vehicles and the
results from those analyses.  Since this draft report is a
proposal, its analyses and conclusions may change to reflect
comments, suggestions, and new data.


     An earlier draft of this document was released and posted on
May 21, 1998 for stakeholder review. Comments were accepted for
sixty (60) days, ending July 18, 1998.  In response to those
comments, we made substantial revisions to both our methodology
and to this document.