Seasonal Changes in the Concentrations of Major Cations and Anions in Precipitations in Urban Nagoya, Japan

摘要

A continuous sampling at every 0.5mm of precipitation during rain (average sampling time of 19 minutes) and analyses of ions involved in the rainwater were carried out from April 1, 1993 to March 31, 1994 in Nagakute, 16km east of Nagoya, Japan, to understand temporal changes in ion concentrations in precipitation in detail. The average pH, nitrate (NO3-), and non-seasalt sulfate (nss-SO42-) in the collected rainwaters were 4.76, 14.5μeq l-1 and 18.0μeq l-1, respectively. The average concentrations of ions obtained in this study were about half of those obtained during 1984 and 1986 by the Japan Environmental Agency, which was thought to be caused by either the longer rainy season in 1993 or the reduction of sulfur dioxide emission in recent years.The seasonal changes in ion concentrations show that they were significantly influenced by Asian dust storms and typhoons. Asian dust storms and typhoons were found to play important role in characterizing the precipitation chemistry in Japan.A rapid change in ion concentrations during several minutes was frequently found in individual precipitation accompanied by weather change. Concentrations of NO3-, NH4+, and SO42- decreased with an increase in wind speed, while those of Na+ and Cl- increased, showing the differences in the production and the deposition processes of ions. Higher concentrations of NO3- and nss-SO42- in rain samples with southern wind direction were frequently observed, showing a clear relation to the industrial facilities of ion sources located in the southern direction. A greater amount of ammonium ion (NH4+) was observed to be transported from the suburbs of Nagoya rather than from the downtown area. This measurement (short period sampling and continuous observation) showed characteristics typical of a precipitation chemistry, especially for the seasonal concentration change in major cations and anions and ion transport processes, observed in suburbs in the eastern Asia region.