Simulation and analysis of secondary organic aerosol dynamics in the South Coast Air Basin of California

摘要

The dynamics of secondary organic aerosol (SOA) formation are analyzed using a species-resolved SOA model for the South Coast Air Basin of California (SoCAB). Updated versions of the Caltech Atmospheric Chemistry Mechanism (CACM) and the Model to Predict the Multiphase Partitioning of Organics (MPMPO) are integrated with the CIT airshed model. The simulations are performed using input data from the 8–9 September 1993 episode. Results show that urban areas with major volatile organic compound (VOC) emission sites experience peaks in SOA levels during morning hours. Downwind locations, such as Azusa and Claremont, experience sustained levels of high SOA concentrations in comparison with coastal areas such as central Los Angeles and Long Beach. Concentrations of condensible organics are higher in inland locations compared to those in coastal locations because of high oxidation capacity and transport of pollutants. Furthermore, SOA constitutes up to 30% of simulated organic particulate matter at inland locations, with maximum contributions occurring during afternoon hours. Anthropogenic sources contribute over 90% of simulated SOA at most locations in the basin. Oxidation products of aromatic compounds from anthropogenic sources constitute over 70% of total simulated SOA. Sensitivity runs indicate strong dependence of SOA on VOC emissions and temperature. Overall, model predictions are in qualitative agreement with recent observations in the SoCAB.