Deposition of anthropogenic sulfate and Pb-210 in the western North Pacific area.

Abstract

The monthly deposition rates of sodium, calcium, chloride, sulfate and Pb-210 from the atmosphere were measured at 12 stations in various parts of the Japanese Islands for two years. The deposition rates of sea salt particles were higher in the coastal region near the Sea of Japan in winter, demonstrating the fact that the strong winter monsoon produces many sea salt particles. Amounts of chloride, sulfate and calcium in excess of the sea salt component were always observed. The rather uniform annual deposition rates of excess sulfate (3-10g/m2/y) suggest that a large part of this excess sulfate originates in global air pollution. Pb-210, much of which is of upper atmospheric origin, is also deposited in significant amounts in winter . This seasonal change may be due to the replacement of lower air masses over the continental margin area , which yields a two-layer model for the atmospheric transport of chemical constituents. The geographical variation of Pb-210 deposition can be explained using the two-layer model and by assuming a 12 day residence time for the tropospheric aerosols. The deposition rates for sulfate over the ocean area decrease more rapidly with distance from the continental coast than those for Pb-210. This result may show that the atmospheric residence time of sulfate is shorter than that of Pb-210.

An attempt to evaluate dry deposition velocity of airborne210Pb in a forest ecosystem

“…These values lie in the range of 166-383 Bq/m 2 (1-2.3 dpm/cm2), in which higher values are found in the areas facing the Sea of Japan. Although the total deposition (833-1054Bq/m 2) of 21~ found here was 2-3 times higher than the highest value (383 Bq/m 2) found by TSUNOGAI et al 16 and YOKOTA, 17 we believe that the resuspension of soil particles during the deposition sampling will not contribute more than 15-20%.…”

“…Thus, about half of the total deposition of 21~ and 7Be per year occurs during winter. This cyclic trend of seasonal variations has been observed especially in heavy snowfall areas facing the Sea of Japan 14 and is due to the addition of 21~ transported from the continent and the effective scavenging of aerosols in air by snowfall during winter l5 21 TSUNOGAI et al 16 and YOKOTA 17 have reported on the annual deposition rates of 21~ at various locations in Japan. These values lie in the range of 166-383 Bq/m 2 (1-2.3 dpm/cm2), in which higher values are found in the areas facing the Sea of Japan.…”

Deposition of non-sea salt sulfate observed at Toyama facing the Sea of Japan for the period of 1981-1991.

“…In the regions along the Sea of Japan, strong northwest wind prevails in winter. Thus, the large deposition rate of sodium in winter is due to the transport of sea salt particles from the Sea of Japan (Tsunogai et al, 1985). As shown in Fig.…”

“…These facts strongly suggest that the large increases in sulfate deposition rates in winter at Toyama and Wajima were not caused by the local discharge, but by transport of the anthropogenic sulfur dioxide from the Asian continent with a strong northwest winter monsoon. The increases in sulfur deposition rate in winter have been ob served in various regions along the Sea of Japan (e.g., Tsunogai et al, 1985;Kitamura et al, 1991;Toriyama et al, 1991a;Yamaguchi et al, 1991). They could also be attributed to the long distance transport of sulfur dioxide from the Asian continent.…”

Variations of210Pb concentrations in surface air at Thessaloniki, Greece (40°N)

“…[6] estimated the (AMAD) of 210 Pb of 0.53 μm and [7] 0.56 μm. 210 Pb has been extensively used to determine the mean residence time of atmospheric aerosols [8], to trace chemical compound that may have broadly similar source distributions, for example sulphur [9], and to study the transport of continental aerosols across the sea or into Polar Regions [10,11].…”