Diurnal Variation, Vertical Distribution and SourceApportionment of Carcinogenic Polycyclic AromaticHydrocarbons (PAHs) in Chiang-Mai, Thailand

Diurnal variation of particulate polycyclic aromatic hydrocarbons (PAHs) was investigated by collecting PM10at three different sampling altitudes using high buildings in the city center of Chiang-Mai, Thailand, during therelatively cold period in late February 2008. At site-1 (12 m above ground level), B[a]P concentrations rangedfrom 30.3 -1,673 pg m-3 with an average of 506±477 pg m-3, contributing on average, 8.09±8.69% to ΣPAHs. Indand B[b]F concentrations varied from 54.6 to 4,579 pg m-3 and from 80.7 to 2,292 pg m-3 with the highest averageof 1,187±1,058 pg m-3 and 963±656 pg m-3, contributing on average, 19.0±19.3% and 15.4±12.0% to ΣPAHs,respectively. Morning maxima were predominantly detected in all observatory sites, which can be described bytypical diurnal variations of traffic flow in Chiang-Mai City, showing a morning peak between 6 AM. and 9 AM.Despite the fact that most monitoring sites might be subjected to specific-site impacts, it could be seen that PAHprofiles in Site-1 and Site-2 were astonishingly homogeneous. The lack of differences suggests that the sourcesignatures of several PAHs become less distinct possibly due to the impacts of traffic and cooking emissions fromground level.