The concentrations of polycyclic aromatic hydrocarbons (PAHs) in particulate matter (PM) with a diameter510 mm (PM 10 , 50% cut off) were investigated in the Kathmandu Valley, Nepal, during 2003. In order to understand the dynamics of atmospheric PAHs in winter, the PAH concentrations in total PM and in the gaseous phase were investigated in the valley in December 2005. Total of 45 PAH compounds ( P 45PAHs) were analysed by high-resolution gas chromatography/ high-resolution mass spectrometry (HRGC/HRMS). In 2003, the P 45PAH concentrations in PM 10 ranged between 4.3 and 89 ng m À3 (annual average; 27 AE 24 ng m À3 ). The average concentrations of P 45PAHs in December 2005 were 210 AE 33 ng m À3 in total PM and 430 AE 90 ng m À3 in the gaseous phase. The P 45PAH concentration in PM accounted for more than 30% of the sum of their particulate and gaseous forms. Phenanthrene (Ph) was the most predominant compound in the gaseous phase, whereas four-to seven-ring PAHs were predominant in total PM. The highest values of P 45PAHs occurred in the winter and spring. Estimates of emission sources based on diagnostic molecular ratios showed that atmospheric PAHs in the Kathmandu Valley mainly originated from the exhaust gas of diesel engine. In the winter and spring, PAH pollution would be accelerated by the operations of brick kilns and the frequent formation of an atmospherically stable layer in the valley.
We analyzed atmospheric particulate polycyclic aromatic hydrocarbons (PAHs) in Ho Chi Minh City, Vietnam, for 19 months. The average concentrations of total PAHs at dry and rainy seasons were 4.28 +/- 2.83 and 15.71 +/- 8.21 ng m(-3), respectively. The use of motorcycles without catalytic converters, estimated to be main emission sources of PAHs, would be higher during the dry season. PAH concentrations show a negative correlation with sunshine duration (r = -0.51). Furthermore, the ratio of average PAH concentration in the dry season to that in the rainy season shows a positive correlation with photolytic half-life (r = 0.94). Thus, seasonal changes in PAH concentrations are attributable to their photolytic degradation.
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