アイスランドにおける大気降下物質の量的年変化

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This paper describes the chemical characteristics of monthly precipitation in Iceland. Monthly precipitation had been collected at Rjupnahaed from January 1958 till December 1979, and had been collected at Vegatunga from September 1960 till April 1973. Since 1980, monthly precipitation has been collected at Irafoss. In this paper, we discuss the chemistry of monthly precipitation at Rjupnahaed and Vegatunga. Monthly precipitation was collected by using an open sampler. The open sampler collects bulk precipitation contaning the wet and dry deposition of chemical constituents. Bulk precipitation displays the combined effects of all water soluble airborne components of precipitation. The data of chemical composition of monthly precipitation has several errors. These are mainly due to the procedures of collection and analysis of precipitation. The errors of using data are eliminated by the three steps. The time series of the amount of monthly precipitation, pH and monthly chemical depositions at Rjupnahaed are shown in Fig. 4. Before the middle 1960s, pH of the monthly precipitation had decreased gradually. The coal for house heating has not been consumed since the middle 1960s in Iceland, and the consumption of clean energy (geothermal and electrical) has been increasing. The change of the energy form is considered to be the reason for the variation of pH of the monthly precipitation, . As may be seen from Fig. 4, the monthly depositions have the seasonal variation. The amount of chemical deposition in winter is more than that in summer. The evident tendency of the long-range fluctuation of the amount of monthly chemical deposition has not been observed. The monthly depositions of sodium, potassium and magnesium show the same variation as that of chlorine. We will discuss the chemical characteristics of monthly precipitation by using the mean data for each month, since the monthly chemical depositions clearly have the annual variation, as described before. The sources of the chemical constituents are discussed by using the data of mean monthly depositions (Fig. 5). The predominant source of chlorine, sodium, potassium and magnesium is considered to be sea water. On the other hand, a part of sulfur in the precipitation comes from sea water, and anthropogenic emission in North America is considered to play an important role. Calcium depositions vary with location to a great degree. This result suggests that the source of the excess calcium exists in Iceland. The mean monthly deposition of sea salt in Iceland is larger in winter than in sum-mer. However, the mean monthly depositions of excess sulfur and excess calcium do not indicate the annual variation. In winter, the mean wind speed at 850mb is higher and the pressure at the surface is lower. This evidence suggests that the activity of air convection is stronger in winter. The activity of air convection is considered to govern the annual variation of the deposition of sea salt.

アイスランドにおける大気降下物質の量的年変化

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