Seasonal variation of the size distribution of urban particulate matter and associated organic pollutants in the ambient air

Size-segregated samples of urban particulate matter (<0.95, 0.95-1.5, 1.5-3.0, 3.0-7.5, >7.5 mu m) were collected in Thessaloniki, northern Greece, during winter and summer of 2007-2008, in order to study the size distribution of organic compounds such as polycyclic aromatic hydrocarbons (PAHs), aliphatic hydrocarbons (AHs) including n-alkanes and the isoprenoids pristane and phytane, organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). All organic compounds were accumulated in the particle size fraction <0.95 mu m particularly in the cold season. Particulate matter displayed a bimodal normalized distribution in both seasons with a stable coarse mode located at 3.0-7.5 pm and a fine mode shifting from 0.95-1.5 mu m in winter to <0.95 mu m in summer. Unimodal normalized distributions, predominant at 0.95-1.5 mu m size range, were found for most organic compounds in both seasons, suggesting gas-to-particle transformation after emission. A second minor mode at larger particles (3.0-7.5 mu m) was observed for C-19 and certain OCPs suggesting redistribution due to volatilization and condensation. (C) 2009 Elsevier Ltd. All rights reserved.