FY 1989

Sulfur isotope ratios: tracers of non-sea salt sulfate in the remote atmosphere

Calhoun, J.A., and T.S. Bates

In Biogenic Sulfur in the Environment, E.S. Saltzman and W.J. Cooper (eds.), American Chemical Society Symposium Series No. 393, 367–379 (1989)

The atmospheric biogeochemical sulfur cycle is being significantly impacted by increasing anthropogenic sulfur emissions. The effect of these emissions on the concentration of sulfate aerosol particles in the remote marine atmosphere is difficult to assess due to uncertainties surrounding the relative contributions of natural and anthropogenic sources. Sulfur isotope ratios can be used to determine the relative magnitude of these sources in the remote atmosphere provided 1) the isotopic ratios of the potential sulfur sources are known, 2) the isotopic compositions of the various sources are different from one another, and 3) the isotopic changes that occur during transformations are thoroughly documented. In the text which follows, these aspects of sulfur isotope chemistry are addressed. Isotopic interpretation of sulfur sources to the remote atmosphere is severely limited by the absence of critical isotopic measurements, yet it appears that continental sulfur sources are isotopically distinguishable from seasalt or marine biogenic sulfur sources. Improved analytical techniques will soon provide the means to obtain the necessary data.