Gas/particle partitioning of atmospheric PCDD/Fs in a satellite town in Eastern China

Abstract

Gas/particle partitioning of polychlorinated dibenzo- p-dioxins and dibenzofurans (PCDD/Fs) in ambient air was investigated in a satellite town in Eastern China from April 2007 to January 2008 comprehending large temperature variations (from 3 to 34 °C, daily average). Molecular weight, molecular structure and ambient temperatures are the three major factors that govern the gas/particle partitioning of atmospheric PCDD/Fs throughout the year. Generally, good agreements were obtained (except for winter) between measured particulate fractions and theoretical estimates of both the Junge–Pankow adsorption model and Harner Bidleman absorption model using different sets of subcooled liquid vapor pressure ( P L o ) and octanol–air partition coefficient ( K oa ) , respectively. Models utilizing P L o estimates, derived from gas chromatographic retention indices (GC-RIs), are more accurate than that of entropy-based. Moreover, during winter, the K oa -based model using the GC-RIs approach performs better on lower chlorinated PCDD/Fs than that of P L o -based. Furthermore, possible sources of mismatch between measured and predicted values in winter (3–7 °C) were discussed. Gas adsorption artifact was demonstrated to be of minor importance for the phenomena observed. On the other hand, large deviations of slopes ( m r ) and intercepts ( b r ) in log K p vs. log P L o ( Pa ) / log K oa plots from theoretical values are observed in the literature data and these are found to be linearly correlated with ambient temperatures ( P < 0.001 ) in this study. This indicates that the non-equilibrium partitioning of PCDD/Fs in winter may be significantly influenced by the colder temperatures that may have slowed down the exchange between gaseous and particulate fractions.