Long-term air concentrations, wet deposition, and scavenging ratios of inorganic ions, HNO3, and SO2 and assessment of aerosol and precipitation acidity at Canadian rural locations

摘要

This study analyzed long-term air concentrations and annual wetdeposition of inorganic ions and aerosol and precipitation acidity at 31 Canadian sites from 1983 to 2011. Scavenging ratios of inorganic ions andrelative contributions of particulate- and gas-phase species toNH, NO, and SO wet deposition weredetermined. Geographical patterns of atmospheric Ca, Na,Cl, NH, NO, and SO were similarto wet deposition and attributed to anthropogenic sources, sea-saltemissions, and agricultural emissions. Decreasing trends in atmosphericNH (1994–2010) and SO (1983–2010) were prevalent.Atmospheric NO increased prior to 2001 and then declinedafterwards. These results are consistent with SO, NO andNH emission trends in Canada and the USA. Widespread declines inannual NO and SO wet deposition ranged from0.07 to 1.0 kg ha a (1984–2011). Acidic aerosols andprecipitation impacted southern and eastern Canada more than western Canada;however, both trends have been decreasing since 1994. Scavenging ratios ofparticulate NH, SO and NO differedfrom literature values by 22 %, 44 %, and a factor of 6, respectively,because of the exclusion of gas scavenging in previous studies. Average gasand particle scavenging contributions to total wet deposition were estimatedto be 72 % for HNO and 28 % for particulate NO,37 % for SO and 63 % for particulate SO, and 30 %for NH and 70 % for particulate NH.