The emission strength of ammonia based on the volatilization generally increases as the temperature rises. Thus, the concentration of NH3 in the atmosphere is higher in summer, and the peak tends to appear in the daytime. However, in observations of atmospheric ammonia in summer 2002, although a high concentration of NH3 was observed in the daytime at Akagi, which is located in an agricultural area in the northern Kanto region, a high concentration was observed in the nighttime at Kagurazaka, which is located in the Tokyo urban area. This study evaluates the high concentration of NH3 in the nighttime at Kagurazaka by means of modeling analysis. The concentration of NH3 was simulated using Models-3/CMAQ with the meteorological fields of MM5. As a result, the calculated concentrations showed a good agreement with the observed concentrations for each site. The appearance of high concentration of NH3 in the nighttime at Kagurazaka was consistent with the results of a simulation.
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