Background pollution in the Arctic air mass and its relevance to North American acid rain studies

Abstract

The Arctic air mass is a unique meteorological feature of the northern hemispheric atmosphere. Possessing well-defined meteorological characteristics, it occupies not only the polar region but also a large fraction of the Canadian and Eurasian land masses during the period November to April. Poor pollutant removal by precipitation and dry deposition within the air mass and a strong transport pathway between Eurasian mid-latitudinal sources and the north, result in elevated levels of acidic anthropogenic aerosols and gases in the air mass during winter. In summer, weak north/south transport and strong pollutant removal between the Arctic and mid-latitudes and within the Arctic, results in lower airborne concentrations of acidic pollutants. Due to the presence of the relatively polluted Arctic air mass, ‘background’ air concentrations of SO₄ ⁼, SO₂ and total NO₃ ⁻ are elevated in western Canada during winter. Typical mean monthly concentrations from December to March are 0.8 to 2.1, 1.0 to 2.4 and 0.1 − 0.6 μg m⁻³, respectively. In the absence of the neutralizing influence of alkaline soil dust, the acidity of snow forming in western Canada during winter is expected to range from 5 to 20 μeq l ⁻¹.