A global three-dimensional model is used to examine the export of anthropogenic sulfur from northern midlatitude continents and to assess the relative importance of anthropogenic and natural sources to sulfate levels in different regions of the troposphere.
Export is relatively more efficient in summer than in winter.
There is little nonlinearity between the magnitude of sulfur emissions in the northern midlatitude continents and the export of this sulfur to the global atmosphere. Anthropogenic influence decreases rapidly with altitude because of efficient scavenging of SO 2 and sulfate in deep convective updrafts. The disproportionality between source and column contributions reflects the rapid deposition of anthropogenic SO 2 and sulfate at low altitudes. It thus appears that the anthropogenic contribution to the sulfate aerosol optical depth is much less than would be expected simply on the basis of emissions.