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Air samples of particulate matter (PM) with an aerodynamic diameter less than 10 microm (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 microg/m3. The daily PM10 concentrations at heavy traffic roadside areas ranged between 30 and 160 microg/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 hydrocarbons (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 microm.

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In recent years, mercury (Hg) pollution generated by municipal waste incinerators (MWIs) has become the subject of serious public concern. On Samui Island, Thailand, a large-scale municipal waste incinerator has been in operation for over 7 years with a capacity of 140 tons/day for meeting the growing demand for municipal waste disposal. This research assessed Hg contamination in environmental matrices adjacent to the waste incinerating plant. Total Hg concentrations were determined in municipal solid waste, soil and sediment within a distance of 100 m to 5 km from the incinerator operation in both wet and dry seasons. Hg analyses conducted in municipal solid waste showed low levels of Hg ranging between 0.15-0.56 mg/kg. The low level was due to the type of waste incinerator. Waste such as electrical appliances, motors and spare parts, rubber tires and hospital wastes are not allowed to feed into the plant. As a result, low Hg levels were also found in fly and bottom ashes (0.1-0.4 mg/kg and