Modeling the Formation and Evolution of Secondary Organic Aerosol during CalNex 2010.

摘要

Field studies in polluted areas over the last decade have observed large formation of secondary organic aerosol (SOA) that is often poorly captured by models. Four parameterizations for urban secondary organic aerosol (SOA), frequently used in 3D models, are evaluated using a box model representing the Los Angeles Region during the CalNex 2010 field campaign. The model SOA formed only from the oxidation of VOCs (V-SOA) is insufficient to explain the observed SOA, even with parameterizations with multi-generation oxidation that produce much higher yields than have been observed in chamber experiments, or with increased yields to their upper limit estimates accounting for recently reported losses of vapors to chamber walls. The Community Multiscale Air Quality (WRF-CMAQ) model (v.5.0.1) underestimates the observed SOA mass by a factor of 25, which is consistent with many previous model-measurement comparisons for pre-2007 anthropogenic SOA modules in urban areas. Including SOA from primary semi-volatile and intermediate volatility organic compounds (P-S/IVOCs) improves model/measurement agreement for mass concentration. The results from 3 parameterizations show large differences and are not well constrained, underscoring the current uncertainties in this area. Our results strongly suggest that other precursors besides VOCs, such as P-S/IVOCs, are needed to explain the observed SOA concentrations in Pasadena. All the recent parameterizations over-predict urban SOA formation at long photochemical ages (~3 days). Reducing IVOC emissions by one-half in the model to better match recent IVOC measurements improves SOA predictions at these long photochemical ages.