Wet deposition and scavenging efficiency of gaseous and particulate phase polycyclic aromatic compounds at a central European suburban site

The concentration of 15 3-6-ring polycyclic aromatic hydrocarbons (PAHs) in atmospheric precipitation was monitored over 18 months in the years 2006-2008, using an automatic wet-only sampler at a suburban site in Brno, Czech Republic. The PAH concentration in rainwater varied between 2.8 and 571 ng L(-1) and the volume weighted mean was 93 ng L(-1) with fluoranthene, pyrene, phenanthrene and benzo(b)fluoranthene contributing most. The contribution of particle-associated PAH (sum of 15) to the wet deposition flux was by average 51%, 82% in summer and 47% in winter. The median total (gas and particulate) scavenging ratios, W(t) (m(3) L(-1)), varied between 450 for acenaphthene and 3.1 x 10(4) for fluoranthene. Estimates of the scavenged fraction in the column of air subject to precipitation suggest that typically only a few percent or less of the airborne PAHs are washed out during a precipitation event. The contribution of particle scavenging to total PAH scavenging varied between 7 and 98% among events. Its median was 41%. Scavenging efficiency seems to be influenced by mass size distribution. It is concluded that wet deposition of PAHs is less efficient than dry deposition. (C) 2011 Elsevier Ltd. All rights reserved.