Journal of Atmospheric Chemistry 6 (1988) 363-374. 363 © 1988 by Ktuwer Academic Publishers. Origin of Calcium in Aerosols over the Western North Pacific T. SUZUKI and S. TSUNOGAI Department of Chemistry. Faculty of Fisheries, Hokkaido University, Hakodate 041, Japan (Received: 5 May 1987; in revised form: 21 October 1987) Abstract. Weekly aerosol samples were collected from March 1981 to June 1983 at the six stations in the western North Pacific region and analyzed for Ca and Na. By coupling data with those previously reported for Al (Tsunogai et al., 1985), the following results and conclusion have been obtained. There was a positive correlation between the atmospheric concentration of Al and the concentration of nonsea salt Ca (nssCa). The nssCa/Al ratios from the six stations, however, con- siderably varied (from 0.84 +_0.36 to 3.00 _+ 1.91), and the ratios were usually larger than those of the crustal average or of usual soil in Japan. The Ca/AI ratios of Asian desert soil and loess vary from 0.52 to 1.29, which are similar to the nssCa/A1 ratios of aerosols in the surface air over the western North Pacific region except at Onna, Okinawa. The exception may be due to a local effect of coral. These results suggest that a large part of nonsea salt Ca in the surface air over the western North Pacific is derived from arid regions in Asia and that the nssCa/Al ratio in aerosol varies with that of the source material. Key words. Calcium in aerosols, western North Pacific, long-range transport, Asian dust, desert soil, loess. I. Introduction Sugawara et al. (1949) found that the Ca/Na ratio of rain water in Japan was higher than that of sea water, and suggested that this was due to the chemical fractionation of sea salt components. This hypothesis, however, has not been supported by more recent studies (Hoffman and Duce, 1977; Hoffman et al., 1977). Another hypothesis has been proposed, stating that the atmospheric Ca/Na ratio may be increased by airborne terrigenous materials. There are some patterns of long range aeolian transport of terrigenous materials evident in the sediments (Rex and Goldberg, 1958; Griffin et al., 1968), and in the surface water of the Pacific Ocean (Tsunogai and Nozaki, 1971; Nozaki et al., 1976; Uematsu et al., 1985a), and there are some observations on mineral dust, Kosa, in maritime air (Ysunogai et al., 1972; Duce et al., 1980; Ishizaka et al., 1981; Darzi and Winchester, 1982; Tsunogai and Kondo, 1982; Iwasaka et al., 1983; Parrington et al., 1983) and in atmospheric deposition (Miyake et al., 1956; Tsunogai and Shinagawa, 1977; Ishizaka, 1972, 1973; Uematsu et al., 1985b). Ichikuni (1978) observed the Sr/Ca ratio of rain in Sendai, Japan and have concluded the excess Ca relative to sea water composition may be derived from calcite contained in soil dust transported from North China. It is well known