The regulations state that gasolines with RVP equal to or less than the RVP required under 40 CFR 80.27 (Summer Gasoline) shall use the applicable Summer Complex Model under 80.45 and the Winter Model for RVP's greater than that required under 40 CFR 80.2

Section 80.101(g)(5) and (6) state that the emissions performance of gasoline with an RVP that is equal to or less than that required under § 80.27 must be determined using the appropriate summer complex model and that the emissions performance of gasoline with a higher RVP must be determined using the winter complex model.

The intent of the regulations was to clearly distinguish summer and winter gasoline for the purposes of determining compliance. Although the regulations establish a criterion based on actual RVP levels, it also is intended that gasoline which is produced for use outside the high ozone period (May 1 through September 15 for most of the country, and April 1 through October 30 in California), or is not intended to blend down storage tanks in preparation for the high ozone period, should be evaluated using the winter complex model.

For example, gasoline produced beginning at the end of the ozone control period for distribution over the winter months should be evaluated using the winter complex model regardless of the actual RVP of this gasoline. In the situations described in the question, 7.8 psi gasoline should be considered summer gasoline unless it is produced for use clearly outside the high ozone period, and 9.0 psi gasoline produced in California for winter use in Arizona should be considered winter gasoline.(8/29/94)

This question and answer was posted at Consolidated List of Reformulated Gasoline and Anti-Dumping Questions and Answers: July 1, 1994 through November 10, 1997 (PDF)(333 pp, 18.17 MB, EPA420-R-03-009, July 2003, About PDF)