Abstract
Abstract. This study analyzed long-term air concentrations and annual wet deposition of inorganic ions and aerosol and precipitation acidity at 31 Canadian sites from 1983 to 2011. Scavenging ratios of inorganic ions and relative contributions of particulate- and gas-phase species to NH4+, NO3−, and SO42− wet deposition were determined. Geographical patterns of atmospheric Ca2+, Na+, Cl−, NH4+, NO3−, and SO42− were similar to wet deposition and attributed to anthropogenic sources, sea-salt emissions, and agricultural emissions. Decreasing trends in atmospheric NH4+ (1994–2010) and SO42− (1983–2010) were prevalent. Atmospheric NO3− increased prior to 2001 and then declined afterwards. These results are consistent with SO2, NOx and NH3 emission trends in Canada and the USA. Widespread declines in annual NO3− and SO42− wet deposition ranged from 0.07 to 1.0 kg ha−1 a−1 (1984–2011). Acidic aerosols and precipitation impacted southern and eastern Canada more than western Canada; however, both trends have been decreasing since 1994. Scavenging ratios of particulate NH4+, SO42− and NO3− differed from literature values by 22 %, 44 %, and a factor of 6, respectively, because of the exclusion of gas scavenging in previous studies. Average gas and particle scavenging contributions to total wet deposition were estimated to be 72 % for HNO3 and 28 % for particulate NO3−, 37 % for SO2 and 63 % for particulate SO42−, and 30 % for NH3 and 70 % for particulate NH4+.
Highlights
The Canadian Air and Precipitation Monitoring Network (CAPMoN) measures trace gas concentrations and particulate inorganic ion concentrations in air and precipitation at rural locations across Canada
CAPMoN was developed to monitor trends in atmospheric pollutants contributing to smog and acid rain, and the data were later used to assess the impacts of environmental policies in the Canada–US Air Quality Agreement
The focus is on the particulate base cations (Ca2+, Mg2+, K+, Na+, NH+4 ), and acidic anions (Cl−, NO−3, and SO24−), nitric acid, and sulfur dioxide that have direct impacts on acid rain
Summary
The Canadian Air and Precipitation Monitoring Network (CAPMoN) measures trace gas concentrations and particulate inorganic ion concentrations in air and precipitation at rural locations across Canada. CAPMoN was developed to monitor trends in atmospheric pollutants contributing to smog and acid rain, and the data were later used to assess the impacts of environmental policies in the Canada–US Air Quality Agreement. This bilateral agreement signed in 1991 recognizes the impacts of transboundary pollution and sets objectives to reduce SO2 and NOx emissions. Nitrates and sulfates in acid rain reduce soil quality by causing the depletion of base cations, which are plant nutrients and are involved in neutralizing acids. Trees (e.g., red spruces and sugar maples) experienced damage to foliage, decreased adaptability to cold climates, slower growth, and mortality during 1960s–1980s from direct and indirect impacts of acid rain
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