Airborne polycyclic aromatic hydrocarbons (PAH) in Bangkok urban air: PartII. Level and distribution

The gas-particle partitioning and particle size distributions of airborne P AH in Bangkok urban air were investigated using an 8 stage size fractionati ng cascade impactor (Andersen "low volume" sampler) and a downstream XAD-2 adsorbent tube for sample collection. Nine PAH classified as carcinogenic a nd co-carcinogenic compounds-Pyrene (PYR), Benz(a)Anthracene (BaA), Benzo(e )Pyrene (BeP), Dibenz(a,c)Anthracene (DBacA), Benzo(k)Fluoranthene (BkF), B enzo(a)Pyrene (BaP), Dibenz(a,h)Anthracene (DBahA), Benzo(ghi)Perylene (Bgh iP) and Trimethylcholanthrene (3MC)-were quantified. The lower molecular we ight (MW) PAH such as PYR, BeP and BaA were present mainly in the gaseous p hase (80%, 40% and 24%, respectively) while higher MW compounds were presen t almost totally in the particulate fraction. The results show that 30%-60% of each PAH by mass were found on particles smaller than 0.43 mum and more than 70% on particles with diameter less than 2.1 mum. In addition, the re lationship between the particle/gas partition coefficient (K-p) and the sub -cooled liquid vapor pressure (p degrees (L)) was also determined to descri be the gas-particle partitioning of those PAH compounds in a tropical atmos phere.