Measurement and modeling the gas/particle partitioning of organochlorine pesticides (OCPs) in atmosphere at low temperatures

The gas/particle (G/P) partition of organochlorine pesticides (OCPs) has been widely investigated and well documented, but rare at low temperature. In this study, seventy-four pairs of air samples in two sampling sites in northeastern China at a wide ambient temperature range of ~63 °C (−40 to +23 °C) were simultaneously collected in both gaseous and particulate phases and eighteen OCPs in these samples were measured and analyzed, among which, partition quotient (KP) values for fifteen OCPs were determined. Seven models including those have never been used for OCPs were applied to predict the values of KP, and the results were compared with the monitoring data for the fifteen OCPs. It was found out that, L-M-Y model provided advantages over the other models, with the best agreement to the monitoring data for analyzed OCPs (90.1 ± 11.1% data points within ±1 log unit, RMSE: 0.53 ± 0.18). The predicted maximum partition (MP) domain for eleven OCPs was observed with high values of their logarithm of octanol-air partition coefficient (log KOA > 12.5), where the log KP values become a constant (−1.53), indicating that the G/P partition of OCPs is in steady state but not the equilibrium. The Li-Ma-Yang (L-M-Y model) model, considering the wet and dry depositions of particles, elucidates the necessity of non-equilibrium term for the OCPs at low temperature. These results indicate that the L-M-Y model is valid for OCPs, which renders it highly promising for describing the partition behaviors in atmosphere for SVOCs, particularly at low temperature. An equation to calculate the condensation temperature TC was also derived, which gave a new understanding on the situation of chemicals with equal distribution between gaseous and particulate phases of OCPs and other similar SVOCs, especially in Polar Regions.