Evaluation of a revised emission inventory in the Metropolitan Area of Sao Paulo, Brazil, based on a photochemical model approach

摘要

Photochemical air pollution has become an important problem in the Metropolitan Area of Sao Paulo (MASP) over the past years. Approximately, 90% of the ozone precursors are emitted to the atmosphere by vehicular fleet. The estimation of precursors emissions, especially those from motor vehicles, is a rather complex task and it represents the major source of uncertainty. Ethanol represents about 32% of the fuel used in the light fleet vehicles. In this study, a validation of the nonmethane organic gases (NMOG) and NO_x official emissions has been performed, using an observation-based approach. The NO_x/CO and NMOG/CO ratios were calculated from early-morning (0700 to 0800) ambient measurements taken in July and August, 1999. This approach assumes that early morning ambient concentrations of CO, NO_x and NMOG are dominated by motor vehicle emissions. From these ratios and on the assumption that the official inventory of CO emissions is reasonably correct, on-road motor vehicle emissions seem to be significantly overestimated and NMOG emissions slightly underestimated. A photochemical model was applied to an episode air pollution period in the Sao Paulo area (August 9-12, 1999), using the revised motor vehicle emission inventory and meteorology fields obtained from the CALMET model. Ozone concentrations predicted by the CIT airshed model match observations more closely when the revised inventory is used instead of official emission estimates.