Measurement of dry deposition and air-water exchange of polycyclic aromatic hydrocarbons with the water surface sampler

Abstract

Recent work has shown that dry deposition and gas exchange of semivolatile organic compounds in the Great Lakes is important. However, there is no generally accepted method for collecting particulate dry deposition or gas exchange. in this work the Water Surface Sampler (WSS) was modified and used in combination with dry deposition plates to measure the particulate dry deposition and gas exchange of PAHs. Simultaneous dry deposition and ambient air samples were collected between June and October 1995 in Chicago, II. Total (particulate + gas) fluxes were measured with the WSS, while particulate fluxes were measured with dry deposition plates. Average Sigma(14)-PAH and particulate Sigma(14)-PAH fluxes were 360 +/- 146 mu g/m(2) d and 144 +/- 60 mu g/m(2) d, respectively. Gas-phase fluxes, determined by subtracting the dry deposition plate fluxes (particulate) from WSS fluxes (particulate + gas), averaged 170 +/- 72 mu g/m(2) d. The measured particulate dry deposition and gas exchange fluxes were substantially higher than those previously reported for the Great Lakes and nonurban areas, probably due to the significantly higher ambient PAH concentrations found in Chicago. Particulate phase overall dry deposition velocities calculated using the dry de position fluxes and ambient concentrations averaged 6.7 +/- 2.8 cm/s. This value is higher than values estimated using dry deposition models; however, it is in good agreement with values determined using similar techniques.