Effects of aromatics, MTBE, olefins, and T90 on urban air quality year 2005/2010

Subject to the limitations described in the Discussion, changing fuel composition changes the light-duty vehicle contribution to ozone. By the year 2005/2010, light-duty vehicles will contribute only 5 to 9% of the peak ozone in the three cities studied, because large reductions in automotive emissions are projected due to regulations now in place. For the reformulated gasolines studied, the contribution of light-duty vehicles to peak ozone can be reduced up to 26%. Reducing gasoline olefin content reduces ozone formation, due to its impact on evaporative, running-loss, and refueling and storage emissions. Lowering gasoline boiling range also reduces ozone formation by lowering the reactivity of exhaust emissions. Reducing aromatic content or adding MTBE had no clear effect on ozone formation. The emissions inventories used in the air quality modeling contain significant uncertainties. In particular, recent studies have suggested that emissions models may significantly underestimate hydrocarbon and CO emissions from today's vehicle fleet. If this is the case, the predicted ozone reductions due to reformulated gasoline reported here may be underestimated