Airborne fine particles of PM2.5-10 and PM2.5 in Bangkok,
Nonthaburi, and Ayutthaya were measured from December
22, 1998, to March 26, 1999, and from November 30,
1999, to December 2, 1999. Almost all the PM10 values in
the high-polluted (H) area exceeded the Thailand National
Ambient Air Quality Standards (NAAQS) of 120 µg/m3
.
The low-polluted (L) area showed low PM10 (34–74 µg/m3
in the daytime and 54–89 µg/m3 at night). PM2.5 in the H
area varied between 82 and 143 µg/m3 in the daytime
and between 45 and 146 µg/m3 at night. In the L area,
PM2.5 was quite low both day and night and varied between
24 and 54 µg/m3
, lower than the U.S. Environmental
Protection Agency (EPA) standard (65 µg/m3). The
personal exposure results showed a significantly higher
proportion of PM2.5 to PM10 in the H area than in the L
area (H = 0.80 ± 0.08 and L = 0.65 ± 0.04).