Seasonal change of gas/particle partitioning of atmospheric dioxins

Abstract

Air samples were collected at suburban Kanazawa and concentrations of dioxins in both gaseous and particulate phases were determined separately. The concentrations of the gaseous phase of dioxins increased with increasing temperature. Co-planar polychlorinated biphenyls (co-PCBs), whose vapor pressures are higher than those of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), were mainly in the gaseous phase samples in all the seasons. The gaseous phase ratios [gaseous phase/(gaseous phase + particulate phase)] of tetrachloro dibenzop-dioxins and dibenzofurans (TeCDD/DFs) were high regardless of the temperature. However, the gaseous phase ratios of penta-hepta CDD/DFs varied widely depending on the temperature. Gas/particle partitioning of atmospheric dioxins depended on not only the number of chlorine-substitutions but also the positions of the chlorine-substitutions. The position of chlorine-substitution in an isomer affects the isomer's molecular polarity. Dioxin isomers with higher molecular polarity, which have shorter retention times on the selected ion monitoring (SIM) chromatograms of their homologues, tended to be distributed unevenly in the gaseous phase. In addition, the differences in the gaseous phase ratios between the isomers with higher molecular polarity and those with lower molecular polarity increased with decreasing temperature.