Stable sulfur isotope analysis of SO2 pollution impact on vegetation.

The δ34S value of SO2 emitted by natural gas refineries is about +25, which is higher than that for non-industrial sulfur sources in our study areas. Terrestrial mosses absorb SO2 from the atmosphere and have a δ34S value which is directly related to the degree of SO2 stress to which they are subjected. The δ34S values for conifer needles are lower than for mosses at the same collection site, which indicates that trees obtain sulfur from both atmospheric and soil sources.Potted conifers were transferred to sites differing in their degree of SO2 stress. This difference is reflected by the change of δ34S values of their needles. SO2 absorbant pot covers, such as charcoal and moss, reduce the amount of airborne sulfur which is available to tress. Moss also may reduce SO2 absorbed by soils in forest stands. We have used analysis of δ34S values to (1) help define SO2 dispersion patterns; (2) reveal the rates at which plants accumulate this pollutant; and (3) associate suspected SO2 injury more closely to an emission source.