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

The gas-particle partitioning and particle size distributions of airborne PAH in Bangkok urban air were investigated using an 8 stage size fractionating cascade impactor (Andersen "low volume" sampler) and a downstream XAD-2 adsorbent tube for sample collection. Nine PAH classified as carcinogenic and co-carcinogenic compounds-Pyrene (PYR), Benz(a)Anthracene (BaA), Benzo(e)Pyrene (BeP), Dibenz(a,c)Anthracene (DBacA), Benzo(k)Fluoranthene (BkF), Benzo(a)Pyrene (BaP), Dibenz(a,h)Anthracene (DBahA), Benzo(ghi)Perylene (BghiP) and Trimethylcholanthrene (3MC)-were quantified. The lower molecular weight (MW) PAH such as PYR, BeP and BaA were present mainly in the gaseous phase (80%, 40% and 24%, respectively) while higher MW compounds were present 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 relationship between the particle/gas partition coefficient (K-p) and the sub-cooled liquid vapor pressure (p degrees (L)) was also determined to describe the gas-particle partitioning of those PAH compounds in a tropical atmosphere.