Urban ozone air quality impact of emissions from vehicles using reformulated gasolines and M85

The urban ozone air quality impact of exhaust emissions from vehicles using reformulated gasolines and flexible/variable-fuel vehicles using M85 has been studied using emissions data from the Auto/Oil Air Quality Improvement Research Program and a single-cell trajectory air quality model with two different chemical mechanisms (the updated version of Carbon-Bond-IV (CB4) and the LCC mechanism). Peak ozone concentrations are predicted for each fuel for all combinations of the following ambient conditions: low and high atmospheric dilution or mixing height, four NMOG/NO x ratios, two each of the initial NMOG concentration, the vehicular contribution to the ambient air, and the NMOG composition of the initial ambient mixture. The ozone impact of a fuel dependent strongly on the atmospheric dilution and NMOG/NO x ratio of an area. The differences in ozone impact among fuels are limited under the condition of high atmospheric dilution and a high NMOG/NO x ratio. The ozone-forming potentials (OFPs) for the exhaust emissions based on the maximum incremental reactivities (MIRs) for various fuels are generally well correlated with model-calculated peak ozone levels at a low NMOG/NO x ratio. These OFPs can serve to separate out fuels with rather different reactivities, but not fuels with comparable reactivities. Model-calculated ozone levels for various fuels based on CB4 and LCC mechanisms are relatively well correlated at low NMOG/NO x ratios, but much less so at higher ratios. Fuels with a high aromatic content, including high-toluene fuels, tend to be ranked more favorably by CB4 than by LCC. On the other hand, M85 is ranked more favorably by LCC than by CB4. Fuels with a low 90% boiling point and a low content of aromatics and olefins are generally less reactive. M85 would be an attractive fuel if the formaldehyde emissions could be curtailed significantly.