Vertical Distribution and Potential Risk of ParticulatePolycyclic Aromatic Hydrocarbons in High Buildings of Bangkok, Thailand

Vertical variations of polycyclic aromatic hydrocarbon (PAH) concentrations in PM10 were investigated inorder to assess the factors controlling their behavior in the urban atmosphere of Bangkok City, Thailand. Airsamples were collected every three hours for three days at three different levels at Bai-Yok Suit Hotel (site-1 andsite-2) and Bai-Yok Sky Hotel (site-3) in February 18th-21st, 2008. The B[a]P concentration showed a value 0.54fold, lower than the United Kingdom Expert Panel on Air Quality Standard (UK-EPAQS; i.e. 250 pg m-3) at thetop level. In contrast, the B[a]P concentrations exhibited, at the ground and middle level, values 1.50 and 1.43times higher than the UK-EPAQS standard respectively. PAHs displayed a diurnal variation with maximums atnight time because of the traffic rush hour coupled with lower nocturnal mixing layer, and the decreased windspeed, which consequently stabilized nocturnal boundary layer and thus enhanced the PAH contents aroundmidnight. By applying Nielsen’s technique, the estimated traffic contributions at Site-3 were higher than those ofSite-1: about 10% and 22% for Method 1 and Method 2 respectively. These results reflect the more complicatedemission sources of PAHs at ground level in comparison with those of higher altitudes. The average values ofincremental individual lifetime cancer risk (ILCR) for all sampling sites fell within the range of 10−7-10−6, beingclose to the acceptable risk level (10−6) but much lower than the priority risk level (10−4).