Apportionment of Pollutant S in an Urban Airshed: Calgary, Canada, A Case Study
Sources of pollutant sulphur in the city of Calgary, in western Canada were identified using natural stable sulphur and oxygen isotope abundance ratios, and a simple apportionment model was applied to quantify pollutant emissions. Three sources of isotopically distinct sulphur found in Calgary air were vehicle exhaust at +9 ‰, oil recycling plant emissions near −8 ‰, and sour gas flaring and processing emissions advected to the city near +20 ‰. Based on the lack of δ34S values lower than +9 ‰ for SO2 and aerosol sulphate, emissions from the oil recycling plant were deemed an insignificant contributor to the pollutant sulphur load in Calgary. A simple apportionment model showed that, on average 77% of the SO2, 64% of aerosol sulphate, and 55 % of precipitation sulphate in Calgary was derived from emissions from the oil and gas industry. A model of 20% primary sulphate mixed with secondary sulphate from heterogeneous SO2 oxidation in the presence of dilute Fe3+ was consistent with measured oxygen isotope compositions for precipitation sulphate. An association of higher δ34S and δ18O values in both precipitation and aerosol sulphate suggest primary sulphate was largely from sour gas flaring activities. In contrast, secondary sulphate was derived from both vehicle exhaust a sour gas processing. Upwind at a relatively pristine mountain site, sulphate in snow had δ34S values near +5 ‰ but at concentrations lower than that for Calgary precipitation, confirming the input of atmospheric sulphur from oil and gas and vehicle exhaust to the city.
KeywordsIsotope Composition Oxygen Isotope Isotope Fractionation Sewage Treatment Plant Precipitation Sulphate
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