Predicted changes in summertime organic aerosol concentrations due to increased temperatures

Changes in summertime organic aerosol (OA) concentrations in the Eastern U.S. are investigated for different temperature change scenarios using the chemical transport model PMCAMx-2008. OA is simulated using the volatility basis set approach, assuming that the primary emissions are semi-volatile and that the intermediate volatile and semi-volatile organic compounds are oxidized in the gas phase, resulting in products with lower volatility. For the basic temperature change scenario where biogenic emissions are kept constant, ground-level OA decreases by −0.3% K⁻¹ on average. Increases in the north (+0.1% K⁻¹) and decreases in the south (−0.5% K⁻¹) are predicted. The effect of the uncertain temperature dependence of the aging rate constant is modest, changing the OA by only 0.1% K⁻¹ over the temperature-independent case. For the more realistic scenario in which biogenic OA precursor emissions are allowed to increase with temperature (up to 10% K⁻¹), however, average OA increases by 4.1% K⁻¹, with even higher increases in southern regions. These results suggest that as temperature increases, complicated changes in production, partitioning and chemical aging will take place. Nevertheless, the change in biogenic emissions and subsequent production of biogenic OA is more than an order of magnitude more important than the changes in the rates of chemical and physical atmospheric processes.