Abstract
Rain samples were collected using sequential sampler during winter 1981-1982 and summer 1982 in Higashiroshima City. for investigating rain water pollution. Analyses included major pollution indexes (pH, turbidity, COD, electric conductivity), Cl^- and NO^-_3. In most cases, the analyses suggested the values of COD and turbidity in first flush are higher than those specified by Japan's water quality standards for water supply. Considering the values of the items, the authors proposed a formula to express the relation of the contaminant amount w(mg) in the collected water to the rainfall amount R(mm) as follows : w=C_rR+ W_x(1-e`<-kxR>)+ W_y where, C_r is the contaminant amount per unit rainfall amount from the frontal cloud, W_x is the contaminant total amount removed slowly from the air column included the collecting surface, k_x is the removal constant of W_x, and W_y is the contaminant amount removed rapidly from the collecting surface. Using the formula and the values in 21 cases by 3 approaches, the authors considered removal amounts of first flush in order that collected rain water qualities might be lower than those specified by the standards. The results indicate that the amounts are under 3 mm in any amount of rainfall.
