Mixing states of individual aerosol particles in spring Arctic troposphere during ASTAR 2000 campaign

[1] The present study mainly focuses on the mixing states of aerosol constituents and their vertical distribution in spring Arctic troposphere during the ASTAR 2000 campaign (T. Yamanouchi et al., Arctic Study of Tropospheric Aerosol and Radiation (ASTAR) campaign: An overview and first results, submitted to Bulletin of the American Meteorological Society, 2002) (hereinafter referred to as Yamanouchi et al., submitted manuscript, 2002). Sulfate and soot were identified as major aerosol under both Arctic haze and background conditions, and sea-salts are major only in lower troposphere (< 3 km above sea level). Mineral/dusts and unknown species were obtained as minor constituents during the ASTAR 2000 campaign. Airborne aerosol measurements were carried out under the Arctic haze (23 March), and aerosol-enriched (20 March and 12 April) conditions. The highest relative abundance of soot (similar to 94.7%) was observed in free troposphere on 23 March, when the heaviest Arctic haze condition during the ASTAR 2000 campaign (Yamanouchi et al., submitted manuscript, 2002) was transported directly from Russian industrial regions to the measuring area for several days. Moreover, whereas the external mixing of soot and sulfate dominated under the Arctic haze and aerosol enriched conditions, in the background conditions the internal mixing is dominant. On the other hand, most of aerosol particles containing sulfate had the external mixing states with soot and other aerosol constituents in the free troposphere under both the Arctic haze and background conditions. Sea-salts are dominant only in the lower troposphere (<3 km asl), although a few sea-salt particles were observed in the middle-upper troposphere (3-7 km). Some sea-salt particles were modified (Cl- depleted) in the lower troposphere (< 3 km) during the ASTAR 2000 campaign.