Ambient air samples were collected in Southeast Asian cities (Beijing,
Bangkok, Kuala Lumper and Jakarta etc.) by passive samplers. Sulfur d
ioxide (SO2) was analyzed as sulfate ion in solution by FIA with a BaS
O4-immobilized on-line reaction column. The method was based on the re
action of sulfate ion with barium-dimethylsulfonazo-III complex. The r
esults agreed with those obtained by ion chromatography. The results s
howed that the SO2 concentrations in theses cities were in the range o
f 24-140 ppb.