Study of effect of drying of droplets in the environment on material cycle-Dependence of size of droplets on the reaction pathway-

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Dew contains high concentrations of nitrite and ammonium ions. Nitrous acid and ammonia gases are dissolved in dew at night, and the concentrations in the atmosphere decrease. Nitrous acid plays a very important role in the atmospheric photochemistry since it is a main OH radical source in the early morning. The decrease in the concentration of nitrous acid in the atmosphere depresses the photo-activity of the atmosphere, and ozone concentration is expected to decrease. In the present research, we found that nitrous acid concentration in the atmosphere decreases when dew forms, the concentration of nitrite in the dew is very high, and nitrite is decomposes to react with ammonium in the dew to produce N_2. Furthermore, we found that ozone concentration in the morning is lower when the dew forms than that when the dew does not form from the monitoring data. The decrease in ozone concentration was also confirmed by the CBM-IV box model calculations.We found that the fate of nitrite in the dew after drying changes with the difference in droplet size. Nitrite remain as dried salts or evaporate into the atmosphere as HONO, convert to NO and NO_2, or produce N_2 by reacting with ammonium ion. When the drying speed is fast, N_2 production was dominant. The size of real dew is very small, and the dew dries very quickly after sunrise, and therefore, most nitrite in the dew decomposes to N_2. When the dew forms, nitrous acid in the atmosphere is dissolved in dew, but nitrite is decomposed to N2 when the dew dries, as a result, the concentration of HONO in the atmosphere in the morning decreased and the ozone concentration decreases. Dew forms in fine day and no wind and no cloud day, and the ozone concentration is expected to increased under this meteorological condition. From the present study, it is speculated that the dew formation depress the ozone concentration in the atmosphere in the real environment.