Modeling the Formation and Evolution of Secondary Organic Aerosols (SOA) During the GoAmazon2014/5 Campaign

Latest laboratory and field measurements have identified several pathways by which anthropogenic emissions influence the formation and evolution of SOA particles in the atmosphere. In this study, we will perform coupled chemistry-cloud-meteorology simulations using the Weather Research and Forecasting model (WRF-Chem) at a horizontal grid spacing of 2 km. In conjunction with other GoAmazon2014/5 analyses, we expect that these simulations will provide a better understanding of how anthropogenic emissions related to the Manaus, Brazil urban plume interact with biogenic emissions within the Amazon rainforest. Preliminary simulations using WRF-Chem clearly show the Manaus plume mixing with the regional background, and the simulated SOA is dominated by biogenics during the wet season. The extensive ground-based and aircraft measurements of gas and particle-phase chemical composition collected during GoAmazon2014/5 will be used to evaluate model predictions. We will explore new model parameterizations of SOA within WRF-Chem and investigate the relative role of gas-phase chemistry and aqueous phase SOA formation (using the modified volatility basis-set approach (VBS) previously evaluated in both regional and global models), and volatility of SOA particles. For example, our preliminary simulations, which treat SOA as a non-volatile semi-solid increase simulated SOA loadings by a factor of 3 compared to its traditional semi-volatile treatment, and agree better with measurements at the T2 site. This study will provide useful insights about what model processes and parameters are most important for simulating SOA in this region. This study will also provide a better understanding of the chemistry of SOA and source contribution of anthropogenic/biomass/biogenic sources on simulated SOA.