On the residence time of the Antarctic ice sheet sulfate aerosol

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Abstract
Optical extinction caused primarily by light scattering from suspended sulfate particles above Antarctica provides a relative measure of the amount of overlying sulfate mass. It has been found that the optical extinction, and hence the column‐integrated amount of sulfate, varies systematically with altitude, decreasing with increasing heights on the ice sheet, approximately as exp (−h/H) with 3.2 < H < 6.8, with a most probable estimate of 4.05 km. No particular tendency is found for the aerosol to disappear as one moves inland (to South Pole station); this is interpreted with an eddy diffusion model to mean that the SO4= aerosol over the ice sheet has a residence time, TR > 1 month. Other data, notably the shape of the aerosol size spectrum and the observed rate of surface deposition of SO4=, also suggest a long residence time for the SO4= aerosol. It is shown that nucleation of SO2 over the continent is unlikely to contribute substantially to the sulfate aerosol mass. Though it can be concluded that the SO4= aerosol is directly imported to the continent in the form of particles, whether the transport is tropospheric or stratospheric cannot be deduced. It is suggested that 0.1 μm radius particles from growing industrialization are the ones most likely to show an increase in concentration in the future. Though not optically important, such particles may have relevancy in cloud microphysical process on large scales of distances.