Novel pathways to form secondary organic aerosols: Glyoxal SOA in WRF/Chem

Current approaches to simulate secondary organic aerosols (SOA) in regional and global numerical models are based on parameterizations of the oxidation of precursor gases in the gas-phase and subsequent partitioning into particles. Recent findings suggest however that formation in the aqueous-phase of aerosols might contribute substantially to ambient SOA load. In this work we investigate the contribution of glyoxal to SOA through chemical processes associated with aerosols. Both a very simple and a more explicit mechanism of SOA formation from glyoxal was included in the regional chemistry transport model WRF/Chem. We simulated the first 2 weeks of June 2010 over the domain of California to make use of the extensive dataset collected during the CARES/CalNex field campaigns to evaluate our simulations. Contributions to total SOA mass were found to range from 1 to 15 % in the LA basin, and <1 to 9 % in the isoprene-rich eastern slopes of the Central Valley. We find that the simple approach previously used in box as well as global modeling studies gives the highest contributions. A combination of reversible partitioning and volume pathways can provide comparable amounts only if partitioning of glyoxal into the aerosol liquid-phase is instantaneous.