We analyze the effect of varying East Asian (EA) sulfur emissions on sulfateconcentrations in the Northern Hemisphere, using a global coupledoxidant-aerosol model (MOZART-2). We conduct a base and five sensitivitysimulations, in which sulfur emissions from each continent are tagged, toestablish the source-receptor (S-R) relationship between EA sulfur emissionsand sulfate concentrations over source and downwind regions. We find thatfrom west to east across the North Pacific, EA sulfate contributesapproximately 80%–20% of sulfate at the surface, but at least 50%at 500 hPa. Surface sulfate concentrations are dominated by localanthropogenic sources. Of the sulfate produced from sources other than localanthropogenic emissions (defined here as "background" sulfate), EA sourcesaccount for approximately 30%–50% (over the Western US) and10%–20% (over the Eastern US). The surface concentrations of sulfatefrom EA sources over the Western US are highest in MAM (up to 0.15 μg/m),and lowest in DJF (less than 0.06 μg/m). Reducing EASO emissions will significantly decrease the spatial extent of the EAsulfate influence (represented by the areas where at least 0.1 μg mof sulfate originates from EA) over the North Pacificboth at the surface and at 500 hPa in all seasons, but the extent ofinfluence is insensitive to emission increases, particularly in DJF and JJA.We find that EA sulfate concentrations over most downwind regions respondnearly linearly to changes in EA SO emissions, but sulfateconcentrations over the EA source region increase more slowly than SOemissions, particularly at the surface and in winter, due to limitedavailability of oxidants (in particular of HO, which oxidizesSO to sulfate in the aqueous phase). We find that similar estimates ofthe S-R relationship for trans-Pacific transport of EA sulfate would beobtained using either sensitivity (i.e., varying emissions from a region toexamine the effects on downwind concentrations) or tagging techniques. Ourfindings suggest that future changes in EA sulfur emissions may cause littlechange in the sulfate-induced health impact over downwind continents.However, SO emission reductions may significantly reduce the sulfateconcentrations and the resulting negative radiative forcing over the NorthPacific and the United States, thus providing a warming tendency.
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