Deposition of coarse soil particles and ambient gaseous components dominating dew water chemistry

Dew water characteristics are not as acidic as those of rainwater and fog water, and they are abundant in weak acid components. The dew water components are dominated by the coarse-mode aerosol rather than the fine-mode aerosol, and calcium carbonate, the component of soil, is the important chemical species raising the pH of the dew water. Carbon dioxide is deposited as calcium carbonate into dew water and is the only major component released from dew water. The total concentration of carbon dioxide increased with an increase in the dew water pH, while the degassing rate increased with the decrease in dew water pH. In the low-pH region, the pε values in dew water are lower than those in rainwater, and the dew water is in a reductive state. The concentration of the representative oxidant, hydrogen peroxide, was much lower in the dew water than in the rainwater in Yokohama (dew water, 0.4 μM; rainwater, 13.1 μM in 1998). The representative conjugate base ions of a weak acid, sulfite and hydrogen sulfite ions, are easily oxidized by hydrogen peroxide, and the lower concentration of hydrogen peroxide in dew water may cause the higher concentration of sulfite ion in dew water than in rainwater. The dew water pH is higher than the rainwater and fog water pH, and a weak acid is easily dissolved into the dew water. Therefore these weak acid ions are more abundant in dew water than in rainwater and fog water.