Acidic Deposition on the Coast of the Okhotsk Sea in Japan

Masashi MITANI, Hiroshi YOKOHIRA and Izumi NOGUCHI†

Department of Liberal arts, Dohto University; Ochiishi-cho 7-1, Mombetsu-shi
094-8582 Japan
† Hokkaido Institute of Environmental Sciences; Kita-19 Nishi-12, Kita-ku,
Sapporo-shi 060-0819 Japan

Acidic deposition was observed semimonthly using bulk sampler on the coast of the Okhotsk Sea in Hokkaido from June 1994 to March 1997. The observation shows that the precipitation amount and the concentrations of major ions in precipitation are less than the means of these over most of observation sites in Japan. Especially, the depositions of the ions are 30 to 40 per cent of the mean values of these means.
The precipitation pH varies from 4.7 to 5.7 though the variation of reciprocal logarithm of input acidity, that is pAi, was relatively small, so that the molar fractional acidity defined as [H+]/(2~[nss-SO42-]+[NO3-]) varied from 0.05 in spring to 0.4 in summer. This may have resulted from the neutralization of the acidified precipitation with ammonia and calcium compound in atmosphere.
The monthly depositions of nss-SO42-, NO3- and NH4+ were found to depend upon the precipitation in manner which the depositions proportionally increase with monthly precipitation in the range of the precipitation less than 120 mm/month whereas the depositions of nss-Ca2+ and the ions originated in sea salt are independent of precipitation. Especially, it is found that the wind velocity may be important factor for the deposition of the ions originated in sea salt.


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