Decadal trend and interannual variation of outflow of aerosols from East Asia: Roles of variations in meteorological parameters and emissions

We apply a global three-dimensional Goddard Earth Observing System (GEOS) chemical transport model (GEOS-Chem) to quantify the decadal trend and interannual variation of aerosol outflow from East Asia. Simulations of aerosols are performed for years 1986–2006, driven by the NASA/GEOS-4 assimilated meteorological fields. The impacts of variations in meteorological parameters and emissions are imposed separately and together by numerical experiments. With variations in both meteorological parameters and anthropogenic emissions, simulated annual outflow of PM2.5 (sum of sulfate, nitrate, ammonium, black carbon, and organic carbon) from East Asia increased by 6.0 Tg (or 53%) over years 1986–2006, in which the outflow fluxes of sulfate, nitrate, and ammonium aerosols had the largest contributions with decadal trends of +1.2, +0.8, and +0.7 Tg decade−1, respectively. Simulated outflow fluxes of aerosols also exhibited large interannual variations; the absolute percent departure from the mean (APDM) values of the annual outflow fluxes of sulfate, nitrate, ammonium, black carbon, organic carbon, and PM2.5 were 5.9%, 7.9%, 5.4%, 5.8%, 4.2%, and 5.2%, respectively, as variations in both meteorological parameters and anthropogenic emissions were considered. Model sensitivity studies show that, for outflow fluxes of aerosols from East Asia, the decadal trends were driven by variations in anthropogenic emissions whereas the interannual variations were dominated by variations in meteorological parameters. The increases in anthropogenic emissions alone explained about 86% of the decadal trend in outflow of PM2.5. Although variations in meteorological parameters can influence the interannual variations in aerosol outflow by changing both aerosol concentrations over East Asia and zonal winds, the latter is identified to be the key factor because of the high positive correlation coefficient between the annual outflow flux of PM2.5 and zonal wind at 700 hPa (the altitude with the maximum outflow fluxes) for years 1986–2006.