Risk evaluation of particle-bound polycyclic aromatic hydrocarbons (pPAHs) at roadside air environment in Bangkok by time-series analysis and its application to urban traffic management

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Continuous monitoring of pPAHs (particle-bound polycyche aromatic hydrocarbons) by using PAS (photoelectron aerosol sensor) at three roadside monitoring stations and two general stations with a permission by Pollution Control Department (PCD), Thailand for one month in April (dry seasons) this year. Comparing the results obtained in last September (rainy season), the concentration level was unexpectedly low. This was not due to the traffic amount change but mainly due to the difference in seasonal pattern of wind direction. Furthermore, particles were separately collected by a size-wise particle collector and twelve PAHs to which the unit cancer risk is respectively given, such as benzo(a)pyrene, were analyzed by a GC/MS. The particle-wise PAH composition was clearly changed at the particle size of 1μm, judging from the result of cluster analysis. The composition of PAHs of particles at above 1μm was different between the dry season and the rainy season. This is probably due to an increase in lower molecule-size PAHs by a decrease in particle residence time in air environment by a periodical shower in the rainy season. In addition, the unit emission of PAHs from different type of vehicles (16 heavy duty vehicles and 12 light duty vehicles) at a standard driving mode in Thailand, was measured at a PCD laboratory. This was done in collaboration with Dr.Tassanee, Chulalonkorn University. By using our field survey results and presently available data, different scenarios of modal shift, regulation of vehicle type, and so on, was evaluated in the light of risk reduction of PAHs exposure, giving an idea of the way for traffic management. These results was summarized in the final report.