Deposition of polycyclic aromatic hydrocarbons (PAHs) and their mass transfer coefficients determined at a trafficked site

Abstract

It is difficult to determine the deposition levels of gaseous polycyclic aromatic hydrocarbons (PAHs), as even atmospheric PAHs mainly exist in the gas phase. Gaseous PAH fluxes across the air-water interface were measured in Merinos, Bursa, Turkey. Direct gaseous fluxes of PAHs were measured intermittently for the period August 2004 through May 2005 when there was no precipitation. A modified water surface sampler (WSS), including a filter holder and an XAD-2 resin column, was employed to collect the flux samples. Average gaseous PAH flux into the WSS, determined by analyzing the XAD-2 resin column, was 31,068 +/- 16,035 ng m(-2) d(-1). This flux value was about 90% of the total (gaseous + particulate) PAH flux, which may indicate that gas exchange is a major removal mechanism for atmospheric PAHs in our sampling site. Variations in gas exchange fluxes likely resulted from changes in both meteorological conditions and concentrations whose level depends on many parameters including fuel characteristics and strength, combustion types, and their efficiencies. Vapor phase PAH fluxes were divided by ambient air concentrations measured with a high volume sampler to calculate overall gas phase PAH mass transfer coefficients (MTCs) (K(G)). The calculated average PAH MTC was 0.38 +/- 0.17 cm s(-1). The average MTC is comparable with ones calculated using a similar configuration of a WSS.