PNNL

Abstract

The global source attributions for mass concentration, direct and indirect radiative forcing (DRF and IRF) of sulfate aerosol from sixteen regions/sectors for years 2010-2014 are quantified in this study using the Community Earth System Model (CESM) with a newly implemented sulfur source-tagging technique. Sulfate concentrations are mostly contributed by local emissions in regions with high emissions, while over regions with relatively low SO2 emissions, the near-surface sulfate concentrations are primarily attributed to non-local sources from long-range transport. The export of SO2 and sulfate from Europe contributes 16–20% of near-surface sulfate concentrations over North Africa, Russia/Belarussia/Ukraine (RBU) region and Central Asia. Sources from the Middle East accounts for 15–24% of sulfate over North Africa, Southern Africa and Central Asia in winter and autumn, and 19% over South Asia in spring. Sources in RBU account for 21–42% of sulfate concentrations over Central Asia. East Asia accounts for about 50% of sulfate over Southeast Asia in winter and autumn, 15% over RBU in summer, and 11% over North America in spring. South Asia contributes to 11–24% of sulfate over Southeast Asia in winter and spring. Regional source efficiencies of sulfate concentrations are higher over regions with strong extra-regional transport and dry atmospheric conditions, suggesting that extra-regional contribution, together with lifetime of aerosols, are important in determining the regional air quality. The simulated global total sulfate DRF is –0.42 W m-2, with –0.31 W m-2 contributed by anthropogenic sulfate and–0.11 W m-2 contributed by natural sulfate. In the Southern Hemisphere tropics, dimethyl sulfide (DMS) contributes 17–84% to the total DRF. East Asia has the largest contribution of 20–30% over the Northern Hemisphere mid- and high-latitudes. A 20% perturbation of sulfate and its precursor emissions gives a sulfate incremental IRF of –0.44 W m-2. DMS has the largest contribution, explaining –0.23 W m-2 of the global sulfate incremental IRF. Incremental IRF over regions in the Southern Hemisphere with low background aerosols is more sensitive to emission perturbation than those over the polluted Northern Hemisphere.