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Analyses of aerosol and precipitation samples collected during a transatlantic research cruise
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1984
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[PDF-127.90 MB]
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Description:A study of temporal and spatial variation of marine aerosols' physicochemical properties has demonstrated clear and significant dependencies of aerosol characteristics on air trajectories at different levels. Aerosols are not only a physical mixture of air masses of diverse origin, but also products of chemical reactions that occur in the marine atmosphere. When maritime aerosol mixed with North American continental aerosol and anthropogenic pollution, the Aitken particle concentration increased. Small particles were predominantly sulfate; larger particles were also coated with sulfate and nitrate. Long-range transport of Sahara dust to the western Atlantic Ocean was identified by an aerosol's size distribution and chemical composition. The pulses of dust arrivals correlated very well with eastern winds at low (1000 mb) and middle (850 mb) levels. Maritime aerosols, which are less subject to continental influence, are mainly sea salts. However, individual particles do not have the same chemical composition as ocean water. They vary from pure crystals of NaCl, KC1, CaSO^, etc., to vastly diversified combinations of all ocean-water components. The mechanism of their formation may be recrystallization in sea-spray drops followed by drying and fractionation. Compared with ocean water, maritime aerosol is enriched with sulfate, especially in small particles. The ocean appears to be a strong source of natural sulfate particles, which are probably formed by S02-gas-to-S04 -particle conversion in the atmosphere. The precursors of S02 could be (CH^S, CH^SH, H2S, CS2, COS, etc., from the ocean. Rain samples collected over the ocean were acidic; pH values varied from 4.0 to 4.7. Compared with seawater, rainwater enrichment was 1000 to 10,000 times greater for H30+; 3 to 7 times greater for S04=; 10 to 50 times greater for N03". Comparisons of aerosol size distributions before and after rain show that below-cloud washout is an effective removal mechanism for aerosol particles of all sizes.
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Rights Information:CC0 Public Domain
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