Laboratory-built passive samplers were used for monitoring of trace benzene, toluene and xylene (BTX) in Hat Yai from 28 July to 12 August, 2003. Sampler bottles contained activated Tenax TA 60/80 mesh and a lab-built thermal well were developed and evaluated for the sampling and analysis of BTX. The sampling was carried out for two weeks before the passive samplers were thermally desorbed, trapped in a sampling loop by a laboratory built purge and trap system and analysed by gas chromatography (GC) equipped with a flame ionization detector. After optimization and calibration, the developed method showed high selectivity, a good sensitivity with detection limits for BTX of 0.8, 1.1 and 13.0 µg/m3 respectively and an acceptable precision. Ambient BTX measurements were conducted at many monitoring site i.e. hot spots (high exposure), residential areas/work places (common exposure) and park (low exposure). The concentration at hot spots range from 3.2 to 5.4 µg/m3 for benzene, 38.0 to 80.3 µg/m3 for toluene and 29.7 to 66.7 µg/m3 for xylene. The low BTX were found at the city periphery (Tesco-Lotus billboard sampling stations, roof level) and in Hat Yai Municipal Park but no absolute background concentration could be defined. The monitoring results showed that at higher level from the street surface, the level of BTX tended to decrease and the BTX pollution built up along a street canyon (Sanehanuson Road) according to the wind direction. The highest BTX were found at the underground parking, 23.5 725.1 and 267.9 µg/m3 respectively where both WHO guideline for Benzene (16.3 µg/m3) and Toluene (260 µg/m3) were exceeded.
