cities. Measurements indicate that about 50% of PM10 in
Bangkok consists of fine particles (PM2.5—particles less
than 2.5 m in diameter) generated in large part from diesel-
and gasoline-powered automobiles, and from two-stroke
motorcycle engines.1 In the most congested areas
of Bangkok, some daily PM2.5 concentrations of 100 mg/
m3 or more have been recorded.