Abstract A climatological box model is applied to wet deposition of sulfur in eastern North America using the extreme assumption that all wet-deposited sulfates originate in sulfate aerosol. The measured sulfate in precipitation during 1977–1979 constrains the probability that an SO 2 molecule emitted in the eastern United States is oxidized before deposition or outflow from the region to values greater than 0.5 and more likely near 1.0. This result implies that uniform SO 2 emission reductions will produce nearly proportional reductions in wet sulfates originating in those emissions and deposited on land. A similar result was obtained previously using the more likely assumption that oxidation and removal of SO 2 in precipitating clouds is the major source of wet deposition of sulfur. Therefore, it is argued that uniform regional reductions in annual average SO 2 emissions will produce nearly proportional reductions in wet sulfur deposited on land and originating in those emissions. The amount of wet sulfate deposition is demonstrated to constrain the mean scale of transport along air parcel trajectories for the precursor of wet sulfur, whether SO 2 or sulfate aerosol, to values greater than 900 km. An examination of previous microscopic photochemical models indicates that the sulfate aerosol formation rate is roughly proportional to local SO 2 concentrations, an inference which is consistent with the result of the climatological model.