Wet deposition of ammonium and atmospheric distribution of ammonia and particulate ammonium in Japan

Compilation of data on ammonia emission flux, ammonia and particulate ammonium distribution, and ammonium wet deposition is urgently needed by modellers, if our understanding of chemical mechanisms in the atmosphere and transboundary air pollution is to be improved. We conducted several kinds of field surveys to obtain information on the distribution and deposition of reduced nitrogen compounds. Total ammonium (gas + particulate) concentrations remained nearly constant at around 350 neq m−3 in a suburban area, Fukuoka (F). The non-sea-salt sulfate concentrations at F and Goto (G), a remote Japanese island, were well correlated with each other (correlation coefficient 0.63), although the concentrations at G were lower than those at F. The variations in non-sea-salt sulfate and particulate ammonium concentrations, wind fields in the East Asian region and backward trajectory analysis indicated long-range transport of air pollutants from the Asian continent to Goto. The level of wet deposition ammonium in Japan is similar to that in most of central and eastern Europe. The largest deposition flux of ammonium was found in the Tokyo metropolitan area and indicates ammonia emission from urban human activities.