Gas/particle partitioning and particle size distribution of PCDD/Fs and PCBs in urban ambient air.

Urban ambient air samples, including gas-phase (PUF), total suspended particulates (TSP), PM, PM and PM airborne particle fractions were collected to evaluate gas-particle partitioning and size particle distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs). Clausius-Clapeyron equation, regressions of logKp vs logP and logK and human respiratory risk assessment were used to evaluate local or long-distance transport sources, gas-particle partitioning sorption mechanisms, and implications for health. Total ambient air levels (gas phase+particulate phase) of TPCBs and TPCDD/Fs, were 437 and 0.07pgm (median), respectively. Levels of PCDD/F in the gas phase (0.004-0.14pgm, range) were significantly (p<0.05) lower than those found in the particulate phase (0.02-0.34pgm). The concentrations of PCDD/Fs were higher in winter. In contrast, PCBs were mainly associated to the gas phase, and displayed maximum levels in warm seasons, probably due to an increase in evaporation rates, supported by significant and strong positive dependence on temperature observed for several congeners. No significant differences in PCDD/Fs and PCBs concentrations were detected between the different particle size fractions considered (TSP, PM, PM and PM), reflecting that these chemicals are mainly bounded to PM. The toxic content of samples was also evaluated. Total toxicity (PUF+TSP) attributable to dl-PCBs (13.4fg-TEQ m, median) was higher than those reported for PCDD/Fs (6.26fg-TEQ m). The inhalation risk assessment concluded that the inhalation of PCDD/Fs and dl-PCBs pose a low cancer risk in the studied area.