Environ. Sci. Technol. 1993, 27, 1454-1454
SIR Venturini raises a valid point that when assessing the impacts of fuel modifications upon vehicle emissions, the basis for comparison must be clearly understood. Our study was designed to demonstrate the benefits of replacing one commercial gasoline with another, not to investigate the effects of varying particular fuel properties using a set of experimental fuels. The reformulated gasoline we used was never intended to represent California Phase 2 gasoline. Hence, our results should not be used directly to estimate emissions benefits which may result when Phase 2 gasoline enters the marketplace in 1996. By the same token, the Auto/Oil(2) and ARC0 (3) studies cited by Venturini should not be used to project the benefits from Phase 2 gasoline either, since the basis for comparison in both studies was a nationwide-average gasoline which is not representative of the California fuels to be replaced by Phase 2 gasoline. Our failure to detect differences in reactivity was also attributed by Venturini to our selection of test fuels, with the implication that Phase 2 gasoline would produce a significant reactivity benefit. However, as was emphasized in our paper, various fuel modifications result in offsetting reactivity changes. For instance, addition of MTBE (which in itself has low reactivity) increases emissions of form-
1454 Environ. Sci. Technoi., Vol. 27, No. 7, 1993
aldehyde and isobutylene (which have high reactivity). Due to such offsets, we believe that Phase 2 gasoline will offer only modest reactivity benefits. Apparently, the California Air Resources Board now believes this alsosince they recently adopted areactivity adjustment factor (RAF) of 0.98 for transitional low emission vehicles (TLEVs) operating on Phase 2 gasoline (1). (A RAF of 0.98 indicates a 2% reactivity benefit for Phase 2 gasoline versus industry-average gasoline.) Literature Cited (1) CARB Board Hearing, Jan 14, 1993. (2) Hochhauser, A. M.; Benson, J. D.; Burns, V.; Gorse, R. A.; Koehl, W. J.; Painter, L. J.; Rippon, B. H.; Reuter, R. M.; Rutherford, J. A. SAE Tech. Pap. Ser. 1991,No. 912322. (3) Clossey, T. J.; DeJovine, J. M.; McHugh, K. J.; Paulson, D. A.; Rapp, L. A.; Segal, J. S.; Sullivan, B. K.; Townsend, D. J. SAE Tech. Pap. Ser. 1992, No. 920798.
S. Kent Hoekman
Chevron Research and Technology Company 100 Chevron Way Richmond, California 94802-0627
0013-936X/93/0927-1454$04.00/0
0 1993 American Chemlcal Society
