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Ambient Volatile Organic Compounds (VOCs) were examined in a heavy traffic urban area in Bangkok, Thailand, on focusing monoaromatic compounds of benzene, toluene, ethylbenzene, m-, p- and o-xylene (BTEX). Passive samplers were used to measure ambient BTEX concentrations in the environment close to very congested roads. Prior to the measurement, the validity of passive sampler performance was investigated to be acceptable for actual use. The monitoring was made five times on weekly basis in April-June in 2003. It was observed that averages of BTEX concentrations were as follows: 12.7 μg m-3 for benzene, 72.8 μg m-3 for toluene, 6.0 μg m-3 for ethylbenzene, 25.7 μg m-3 for m-, p-xylene and 13.6 μg m-3 for o-xylene. They are considered to be at very high concentration levels compared to other countries. Their distributions seemed to be in the form of logarithmic normal distribution. On the other hand, cluster analysis suggested that ambient BTEX in this study were derived from automobile exhaust gases. [ABSTRACT FROM AUTHOR]

Air samples of particulate matter (PM) with an aerodynamic diameter less than 10 µm (PM10) were collected from six sites in Bangkok, Thailand, using high-volume air samplers. Daily samples were taken at intervals of 12 days from November 1999 to November 2000. Size-selected sampling using a multislit Andersen size-fractionated cascade impactor was undertaken at one site in central Bangkok to identify particulate size distribution. The annual average PM10 concentration at all six sites exceeded the Thailand National Ambient Air Quality Standard (NAAQS) of 50 µg/m3. The daily PM10 concentrations at heavy traffic roadside areas ranged between 30 and 160 µg/m3. The highest PM10 level occurred during the winter period (November–February), which is the dry season. From our results, which are based on a 1-yr survey, it can be observed that the particulate concentrations are associated with traffic volumes and seasonal factors (temperature and rainfall). The relative importance of size fractions in contributing to PM load is presented and discussed. Twenty polycyclic aromatic hydro-carbons (PAHs) associated with PM have been identified and quantified. The summed PAHs based on the 20 species had an average concentration of 60 ng/m3. Benzo(e)pyrene, indeno(123cd)pyrene, and benzo(ghi)perylene were the major compounds with average concentrations of 8, 10, and 13 ng/m3, respectively. Results indicate that more than 97% of PAHs were found in the small particulate size range of <0.95 µm. [ABSTRACT FROM AUTHOR]