A Study of the Oxygen Isotopic Composition of Precipitation Sulphate in Eastern Newfoundland

The properties of stable oxygen isotopes make them useful for studying processes involved in the atmospheric oxidation of sulphur compounds. Experimental work in the 1980s reported that the formation of primary combustion sulphates by high temperature oxidation of SO2(g) to SO4 leads to δ18OSO4 values between +40 and +45‰. This study reports sulphate oxygen isotopic compositions from precipitation events collected at two sites in eastern Newfoundland. Values as high as +41.7‰ were measured in natural precipitation samples collected near a small oil-fired power plant located on the campus of Memorial University of Newfoundland in St. John's. These values are higher by 16‰ than any previously reported for precipitation in the literature and in conjunction with other chemical data implicate the power plant as the pollution source. Values from the second site (Seal Cove) were similar to previously reported ranges for precipitation, despite its proximity to a much larger oil-fired, thermal generating station, suggesting that different oxidation mechanisms were dominant there. Oxygen isotopic compositions of precipitation sulphates can be an important complementary tool to other isotopic, trace metal and meteorological analysis in the tracing of sources of atmospheric sulphur compounds.