Dewwater was collected from January 1993 to December 2000 in Yokohama, Japan, and analyzed for weak acid anions with other major chemical components. The volume-weighted average and medium pH of the dewwater were 4.88 and 6.08, respectively, at our sampling site. Weak acids (carbonate, nitrite, sulfite, formate, and acetate ions) were the major species in the dewwater and were several times higher than those in the rain- and fogwater. The concentrations of these species and ammonium ion can be estimated by the resistance model. The estimated values of N(III) correlate relatively well with the measured values, which shows the origin of N(III) in dewwater is nitrous acid in the ambient air. On the other hand, ammonium ion in the dewwater originated from not only gaseous ammonia but also aerosol ammonium ions. Hydrogensulfite ions in the dewwater which originated from sulfur dioxide are an important species as the precursor of the sulfate and they were stabilized by forming hydroxyalkanesulfonate (HASA). Formic acid and acetic acid in the dewwater originated mainly from gas, while the oxalic acid is from aerosol.
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