Aerosol chemical components in Alaska air masses: 1. Aged pollution

Abstract

A 4‐year Alaska chemical data set of aerosols or “dust” in the air clearly reveals a mixture of distinct aerosol components with different and interesting chemical composition, one or two being ascribed to pollution imported to Alaska by winds all the way from other continents. Of particular note is a strong chemical contrast between what we imagine to be highly scavenged, orographically lifted, northern Pacific air (Pacific marine air mass) and stagnant Arctic air (polar air mass), the latter containing seasonal average concentrations of between 2–4 times the concentration of the former, at least for pollution markers noncrustal vanadium, noncrustal manganese, arsenic, selenium, bromine, and antimony. The findings concur our old discovery that Arctic air is persistently polluted (Arctic haze), but Pacific air is relatively clean, in spite of the fact that Alaska is downwind of major pollution sources in the Orient. This is remarkable. In this the first of a two‐part paper, we concentrate on the pollution component found primarily during incursion of Arctic polar air. Two major occurrences of visual haze with optical depths of approximately 0.2 and elevated aerosol concentration lasting about a month (spring 1985 and 1986) were affiliated with strong incoming transport of polar air, temperatures ranging from 10° to 20°C below normal (polar air) and air trajectory hindcasts leading back to industrial pollution sources in Eurasia. These long‐range transport pollution events brought metal‐rich aerosol of removal‐resistant submicron particles. The size, chemistry, and meteorology all strongly suggest the presence of a well‐aged (10–100 day) polluted air mass. An important implication is that in spring a large fraction of the Arctic polar air mass becomes charged with by‐products of industrial pollution. In this multiyear chemical data set one finds a notable summer‐winter contrast, changing by factors of 2 to 4 for pollution markers As, Se, Sb, and noncrustal manganese (NcMn) with the minima occurring in the summer months and the maxima in March and April. There is also a twofold‐threefold decrease in pollution markers between the interior or geographic center of Alaska and Barrow in Arctic Alaska, a gradient, completely in accord with the picture of a generally polluted Arctic air mass system about the size of Africa in area.