A study of the oxygen isotopic composition of precipitation sulphate in eastern Newfoundland

The properties of stable oxygen isotopes make them useful for studying proc esses involved in the atmospheric oxidation of sulphur compounds. Experimen tal work in the 1980s reported that the formation of primary combustion sul phate; by high temperature oxidation of SO2(g) to SO4 leads to delta(18)O(S O4) values between +40 and +45 parts per thousand. This study reports sulph ate oxygen isotopic compositions from precipitation events collected at two sites in eastern Newfoundland. Values as high as +41.7 parts per thousand were measured in natural precipitation samples collected near a small oil-f ired power plant located on the campus of Memorial University of Newfoundla nd in St. John's. These values are higher by 16 parts per thousand 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 report ed ranges for precipitation, despite its proximity to a much larger oil-fir ed, thermal generating station, suggesting that different oxidation mechani sms were dominant there. Oxygen isotopic compositions of precipitation sulp hates can be an important complementary tool to other isotopic, trace metal and meteorological analysis in the tracing of sources of atmospheric sulph ur compounds.