REGIONALLY REPRESENTATIVE DAILY AIR CONCENTRATIONS OF ACID-RELATED SUBSTANCES IN CANADA - 1983-1987

Since 1979, the Atmospheric Environment Service (AES) of Canada has measured ambient air concentrations of particulate SO42-, NO3- and NH4+, and gaseous SO2 and HNO3 at several regionally representative sites across Canada. Between January 1983 and December 1987, nine sites were in operation. The present paper presents an analysis of the observed concentrations. The highest air concentrations of SO42-, NO3- and NH4+, SO2 and HNO3 were observed at Longwoods in southern Ontario, with medians of daily values equal to 6.7, 1.8, 1.6, 3.7 and 1.1-mu-g m-3, respectively. The lowest median daily concentrations were observed at Bay d'Espoir, Newfoundland, for SO2 and NH4+, and at Cree Lake, Saskatchewan, for SO42-, NO3- and NH4+. The concentrations were equal to 0.20, 0.09, 0.72, 0.03 and 0.06-mu-g m-3, respectively. A strong and statistically significant annual cycle existed for the SO2 daily concentrations at all sites. They were highest in winter and lowest in summer. A weaker and more complex annual cycle was also present in the SO42-, NO3-, NH4+ and HNO3 daily air concentrations. They were not statistically significant for some ion and site combinations. Gaseous SO2 generally exceeded particulate SO42- on a molar basis except during the summer months at all sites with the exception of Bay d'Espoir, where the latter dominated during all the year. On average, gaseous HNO3 dominated particulate NO3- except for the autumn to spring months at Longwoods, Kejimkujik and Bay d'Espoir. SO42-/NH4+ molar ratios varied between 0.3 and 3. The lowest values were observed at Longwoods and Sutton, and the highest at Cree Lake and Bay d'Espoir. In molar units, NH4+ concentrations were between 1 and 100 times larger than the NO3- concentrations. The NO3-/NH4+ molar ratios were highest at Longwoods and lowest at Cree Lake. Total SO42- (SO2 + SO42-) concentrations were, in molar units, between 2 and 20 times larger than the total NO3- (HNO3 + NO3-) concentrations.