| The accuracy of atmospheric chemical transport models (CTMs) hinges on sufficient representation of emissions and pollutant reactivity. The simulation of fine particulate matter, especially its organic components, remains a major challenge due to incomplete understanding of the corresponding complex atmospheric processes. Primary organic aerosol (POA) is emitted in the aerosol phase, while secondary OA (SOA) is emitted in the gas phase, reacts, and condenses on preexisting particles. The CTM PMCAMx employs the volatility basis set to describe OA behavior, including semi-volatile primary emissions and continued chemical aging of anthropogenic organic compounds. This tool is used to study the pollutant response to climate change in the Eastern United States, to develop observation-based methods to determine SOA levels, and to quantify the contributions of various SOA precursors.;Ground-level summertime OA is predicted to decrease by 1.5% on average in response to a 5 K temperature increase, assuming constant emissions. When biogenic OA precursor emissions are increased with temperature, average OA is much more affected, increasing by 20.5%. In a more realistic scenario with variable present and future (based on the IPCC A2 scenario) meteorology and meteorologically-sensitive biogenic emissions, PM2.5 increases by 9% on average by 2050, but the change is spatially variable even in sign. Sulfate and organic aerosol are responsible for most of the aerosol change, respectively increasing by 11% and 12% on average. Variability is driven concurrently by changes in temperature, wind speed, rainfall, and relative humidity, with no single dominant meteorological factor.;PMCAMx is also used as a diagnostic tool to evaluate the elemental carbon (EC) tracer method, which separates total OA into its primary and secondary components. The method is applied to "pseudo-observations" generated by PMCAMx and then compared to internally calculated POA and SOA. This evaluation shows that, with an appropriate organic to elemental carbon ratio, the method is able to provide daily-averaged estimates of the sum of fresh primary OA, SOA from the oxidation of evaporated POA and intermediate volatility compounds, and background OA.;Finally, the SOA formation yields in the Eastern US are analyzed. Gasphase biogenic and aromatic emissions are the dominant SOA precursors. All yields are corrected to appropriately account for SOA density and then updated with recent smog chamber studies. These changes led to a slight improvement in PMCAMx performance over the domain. |
