Abstract
In order to unveil the chemical characteristics of rain water from 1 to 8 mm, rain water measurements were conducted in downtown Okayama for one year from March, 2004 to March 2005. Analytical parameters were pH, EC and the ion concentrations, F-, Cl-, NO2-, NO3-, SO42-, PO43-, Na+, NH4+, K+, Mg2+ and Ca2+.
The mean pH and EC values of the precipitations from 1 to 4 mm, which would be affected largely by the washout effect in the observational area, were 4.46 and 32.7μS/cm, respectively. And, the mean ion concentrations of NO3- and nss-SO42-, which were main acid rain constituents, were 1.1mg/l and 0.9 mg/l, respectively. The mean pH and EC values of the precipitations from 5 to 8 mm, which would be affected largely by the rainout effect, were 4.60 and 20.4μS/cm, respectively. The mean ion concentrations of NO3- and nss-SO42- were 1.6mg/l and 1.4mg/l, respectively.
The air mass back trajectory analysis was conducted for 5 days until the day of the rain event. The analyzed trajectories were classified into 4 typical routes advected from the Eurasian Continent, the central part of the North Pacific Ocean, Southeast Asia and the East Asian coast. And, the different chemical characteristics depending on the route were recognized. In the case of the Southeast Asia route, the ion concentrations of NO3- and nss-SO42- were highest, 2.4mg/l and 2.1mg/l, respectively. Then, in the case of the Eurasian Continent route, the concentrations were 1.5mg/l and 1.5mg/l. In the case of the East Asian coast route, the concentrations were 1.3mg/l and 1.1mg/l. In the case of the central part of the Pacific Ocean route, the concentrations were lowest, 0.7mg/l and 1.1mg/l, respectively.
