The range of data on which the Complex Model was based limits the range within which the model will exhibit appropriate accuracy. The E200 range in the database was 33 to 66 vol%; extrapolation widened this range to 30 to 70 vol% for the Complex Model. Likewise the E300 database range of 72 to 94 vol% was widened through extrapolation to 70 to 100 vol% in the Complex Model.

The Agency believes that these extrapolations maximize the utility of the Complex Model without unduly compromising its accuracy. Further widening of the limits on distillation would dramatically increase the likelihood that Complex Model emission estimates would be fictitious. In addition, the regulations contain provisions for widening the valid range limits on any fuel parameter through vehicle testing. See §80.48. (11/10/97)

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)