Dry deposition fluxes and deposition velocities of PAHs at an urban site in Turkey

Abstract

Even though dry deposition and air-water exchange of semivolatile organic compounds (SOCs) are important for surfaces in and around the urban areas, there is still no generally accepted direct measurement technique for dry deposition. In this study, a modified water surface sampler (WSS) configuration, including a filter holder and an XAD-2 resin column, was employed to investigate the polycyclic aromatic hydrocarbon (PAH) dry deposition in an urban area. The measured total (particle+dissolved) PAH fluxes to the WSS averaged to be 34 960±16 540 ng m-2 d-1. Average particulate PAH flux, determined by analyzing the filter in the WSS, was about 8% of the total PAH flux. Temporal flux variations indicated that colder months (October-April) had the highest PAH fluxes. This increase could be attributed to the residential heating as well as meteorological effects including lower mixing height. A high volume air sampler was concurrently employed to collect ambient air concentrations. The average total (gas+particle) atmospheric PAH concentration (456±524 ng m-3) was within the range of previously measured values at different urban locations. PAH concentrations in urban areas are more than two orders of magnitude higher than those measured in pristine areas and this result may indicate that urban areas have major source sectors and greater deposition rates are expected near to these areas. The average contribution of particle phase was about 10% in total concentration. Simultaneous particulate phase dry deposition and ambient air samples were collected in this study. Then, particulate phase apparent dry deposition velocities were calculated using the fluxes and concentrations for each PAH compound and they ranged from 0.1 to 1.2 cm s-1. These values are in good agreement with previously reported values.