A long-term study of atmospheric ammonia and particulate ammonium concentrations in Yokohama, Japan

A long-term study of concentrations of NH₃ and particulate NH₄⁺ has been performed at Hiyoshi, in Yokohama. From January 1987 to December 1991, daily measurements of NH₃ and particulate NH₄⁺ were made simultaneously five times a month. The results were discussed from the standpoint of seasonal variations and annual trends, meteorological effects, and special characteristics. The monthly mean NH₃ concentrations were in the range of 2.4-11.9 ppb and showed regular seasonal variations with the highest concentrations during summer and the lowest during winter. The seasonal trends seemed to be largely affected by air temperature. The NH₃ concentrations increased exponentially with increasing air temperature, and a high correlation was obtained (r = 0.74). The NH₃ concentrations were not affected by wind direction and velocity. The monthly mean concentrations of particulate NH₄⁺ were within the range of 1.5-3.1 μg m^-3 and the variation in the range was relatively small. The NH₄⁺ concentrations decreased steeply with increasing wind velocity. For the five-year period, there were no long-term trends in the concentrations of NH₃ and particulate NH₄⁺.