Chemical studies of the winter precipitation were conducted in Tohkamachi city. The relationships between the chemical property of winter precipitation and the weather condition were studied.
Samples of daily precipitation were collected in Tohkamachi during winter periods from December 24, 1990 to April 9, 1991, from December 17, 1991 to April 10, 1992 and from December 15, 1992 to April 10, 1993.
The samples were filtered, and conductivity and pH were measured with a conductivity meter and pH meter, respectively. Anions and cations were determined by an ion chromatography (Dionex 2020 i/SP).
The ratios of Cl^-/Na⁺ and Mg²⁺/Na⁺ in all samples of winter precipitation are nearly equal to those in the sea water. This result suggests that the origin of Na⁺, Mg²⁺ and Cl^- in the winter precipitation is sea water. The origin of NO₃^- and NH₄⁺ in the winter precipitation is considered to be non sea salt. The origins of SO₄^2- and Ca²⁺ are both sea water and non sea salt. NO₃^- and nssSO₄^2- are the acidic materials and decline pH value of the winter precipitation. NH₄⁺ and nssCa²⁺ are the neutralization materials of acid precipitation.
Weighted average pH of precipitation is 4.46 for 1991 winter, 4.16 for 1992 winter and 4.22 for 1993 winter. pH values of all samples are less than 5.2. winter precipitation in Tohkamachi shows acidity, and pH of winter rain shows more acidic than that of solid precipitation.
The synoptic weather conditions affect chemical properties of winter precipitation. Sea salt materials are dominated in the precipitation formed under the winter monsoon pressure pattern. On the other hand, non sea salt materials are dominated in precipitation formed by a low pressure systems on the Sea of Japan or on the Pacific Ocean. The larger ratio of acidic materials in precipitation indicates the stronger acidity of precipitation formed by a low pressure systems on the Pacific Ocean.

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