Ca/Na ratios in precipitation collected at many localities have been reported to be consistently higher than the Ca/Na ratio of sea water. The sources of excess Ca have been pointed out to be crustal material, such as soil, and industrial wastes. Precipitations collected at Kichijoji, Tokyo, are high in pH and Ca concentration when an air mass responsible for precipitation flows in from the north. In the north of Kichijoji there are many limestone quarries, cement-producing and related factories. The emitted Ca-bearing fine particles should be the source of excess Ca and cause high pH in precipitations of Kichijoji.