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+.