LEVELS OF VOLATILE HALOGENATED HYDROCARBONS IN TOKYO RAIN AND THEIR SEASONAL, TIME-SERIES CHANGES

Rain samples were collected at Tokyo, Japan, during 11 periods of precipitation from October, 1989 to September, 1990. Five volatile halogenated hydrocarbons in the rain samples were determined by an automated purge trap/on-column cryofocusing method using capillary gas chromatography with Ni-63-ECD. The levels of volatile halogenated hydrocarbons during the above period were averaged as 261 ng/l for chloroform, 369 ng/l for 1,1,1-trichloroethane, 46 ng/l for carbon tetrachloride, 136 ng/l for 1,1,2-trichloroethylene and 99 ng/l for 1,1,2,2-tetrachloroethylene. The levels determined in this study were compared with those of other reports. The levels of volatile halogenated hydrocarbons in Tokyo rain showed seasonal fluctuations, presumably because of climatic factors such as atmospheric temperature and other factors such as reaction with OH radical. In some cases, the level of all determined compounds decreased with time-series during an event, which might be due to a wash-out effect. Some compounds with high solubility in water showed rapid decrease, which leads to a certain selectivity of this effect. The scavenging effect of volatile halogenated hydrocarbons by a rain event could be traced by the simultaneous analysis of ambient air and rainwater.