A CHEMICAL STUDY OF SNOW IN SAPPORO

Abstract

Samples of daily snowfall were collected in Sapporo during a period from December 1980 to March 1981. Samples were collected in plastic box having a cross-sectional area of 2, 800cm2. Collected snow was allowed to melt, and then was filtered through a 1.0 micron pore size membrane filter which had been washed beforehand with distilled water. Conductivity and pH were measured potentiometrically at 25°C. Sodium, potassium, mag-nesium and calcium were determined by atomic-absorption spectrophotometry, and chlo-ride and sulfate were determined by spectrophotometry. The rate of the dry deposition in the collected snow sample was estimated. The rates of the dry deposition of Na, Cl, Mg, K and SO4 were of low values, but that of Ca was relatively high. Because Ca was considered to be released into the atmosphere in a par-ticulate form. About two-thirds of the snow samples showed acidity (pH<5. 6) and volume-weighted average pH was 4.69. Since the early 1950's, acidity of precipitation has been reported in northwestern Europe and eastern North America. Similar phenomenon was also observed in Sapporo in winter. The ratio of Cl/Na concentration in the snow sample was nearly equal to that in the sea water. This result suggests that the origin of Na and Cl in the snow was sea water. The ratio of Mg/Na concentration in the snow sample was larger than that in the sea water, but the ratios of Mg/Na concentration of all samples had small variability. Average enrichment coefficient of Mg was 1.18. Several studies reported that chemical composition of maritime aerosol is different from that of sea water, and that Mg/Na of maritime aero-sol is larger than that of sea water. From these results, it was considered that Mg in the snow originated from the sea water. The location of cyclones affected Na concentration of the snow samples. When a cyclone was located south or west of Hokkaido, Na concentration of the snow was lower than 1 mg/1. When a cyclone was located east of Hokkaido, Na concentration of the snow was higher than 1 mg/1. These results suggested that Na concentration of the snow was related to cloud structure. A relation was observed between Na concentration of the snow and the heights of a convective mixing layer. It can be seen that Na concentration of the snow increased in proportion to the height of the convective mixing layer. The regression relationship between Na concentration of the snow and the heights of a convective mixing layer is C=0.29 e0.63H where C is Na concentration of the snow (mg/1) and H is the height of a convective mixing layer (km). The concentration of chemical constituents which originated from sea water increased in proportion to the activity of cloud convection.