Abstract
The benzene concentrations at background site and at roadside sites in Okinawa Prefecture were investigated by canister-GC/ MS analysis from April 2004 to March 2005. The results were as follows. 1) The benzene concentrations at the background site tended to be lower in summer than in any other season. By using backward trajectory analysis, it was found that inflows of air masses from the Pacific Ocean to Okinawa Island were seen in low benzene concentration cases, and inflows of polluted air masses from the continental side were seen in high benzene concentration cases. The annual average concentration of benzene at the background site in Okinawa Island was 0.44μg/m3. 2) The benzene concentration at roadside sites tended to be lower when the wind blew strong. The annual concentration of benzene obtained by continuous measurement was estimated by using the relationship formula between the observed benzene concentration and the wind velocity. Its annual average concentration was estimated to be approximately 20-30 percent lower than the annual average concentration calculated from 12 samples which were gathered over a 24 hour period once per month. 3) The annual cancer risk to the population associated with ambient benzene was estimated to be approximately O.24 annual cases per 1.35 million people living in Okinawa Prefecture.
