Over the past five decades, the North Atlantic and North Pacific oceans have warmed a greater amount and at a greater rate in the summer than the winter. One contribution to this warming is the reduction of ‘radiative shielding’ sulfur dioxide emissions from North America in the wake of the EPA’s clean air act. To investigate the seasonality in SO2 emissions, presence, and radiative forcing, simulations of varying anthropogenic sulfur dioxide emissions in the Community Earth System Model were conducted.

Model simulations were motivated by analysis of historical global SO2 emissions. Four CESM simulations were run in which emissions outside of the eastern United States were set to 2000 levels, and U.S. sulfur dioxide emissions were set at 1850, 1970, 2000, and 2010 levels, thus capturing a wide range of sulfate presence. Despite largely constant SO2 emissions over the seasonal cycle, anthropogenic SO4 and SO4 radiative forcing show strong seasonality over mid-latitude oceans. Analysis into the physical and chemical causes of these seasonal SO4 patterns shows greater aqueous production of SO4 through cloud droplets, although wet deposition rapidly removes SO4 in all seasons. Interstitial production shows strong seasonality due to OH photochemistry and is largely removed via dry deposition, a slower process that appears to affect downstream seasonality.

By better understanding the emission, chemical production, and removal of sulfate aerosols, this study aims to better understand historical climate variability and change and the complex mechanism in which aerosols interact and feedback at global and regional scales. Ultimately, this research aids in improving predictive climate models and informs policy decisions aimed at mitigating climate change.