Aerosols in Alaskan air masses

Results from measurements of the composition and size distribution of aerosol particles advected into central Alaska are reported. It is argued that the aerosol predominant in number, but not necessarily in mass, consists of submicron droplets of sulfuric acid. The major aerosol by mass in arctic air is a removal-resistant accumulation mode (radius 0.3 m) probably to large extent originating from pollution sources 10³ km upstream (mostly in central Eurasia) from the site in Alaska. The accumulation mode aerosol disappears when arctic air masses are replaced with relatively warmer air masses flowing in from the northern Pacific. The latter air mass systems have been strongly scavenged by clouds and precipitation associated with the Aleutian low pressure system and with forced orographic uplifting over the Alaska Mountain Range; nevertheless the Pacific air masses contain substantial (i.e., 500–1000 cm^-3) quantities of small (several hundredths of a micron in radius) particles. Arctic-derived air masses are enriched in large (i.e, 0.3 ) particles compared to Pacific Marine air masses, whereas the opposite trend is found for smaller, Aitken, particles. The smaller particles are found in greatest abundance in warmer air mass systems, presumably because of the relatively brief time since such air masses were last exposed to sunlight with attendant production of small particles from the gas phase.