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, Wt (m3 L−1), varied between 450 for acenaphthene and 3.1 × 104 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.