Gas-particle partitioning of atmospheric PCDD/Fs: Measurements and observations on modeling

The gas-particle partitioning of 2-8PCDD/Fs in ambient air was investigated at a semirural U.K, site, sampled with glass microfiber filters (GFFs) and polyurethane foam (PUF) plugs, and quantified by HRGC-HRMS. Nine samples, each similar to 1000 m(3) of air, were collected over different periods of 7 days between May and Aug, when the average ambient temperatures varied between 12 and 17 degrees C for the different sampling periods. The proportion of the different homologues associated with the PUF plugs (i.e., operationally defined as the gas phase) varied greatly. 2CDFs were almost exclusively (>99.5%) in the gas phase, along with 82-96% of the 4CDD/Fs, 15-65% of the 6CDD/Fs, and 2-20% of the 8CDD/Fs. PCDFs tended to be slightly more associated with the gas phase than the equivalent homologue group of the PCDDs. Plots of the log partitioning coefficient (K-p) versus the log subcooled liquid vapor pressure (p(L)(0)) gave slopes in the range -0.64 to -0.79 ((x) over bar -0.68) and intercepts of -6.49 to -7.32 ((x) over bar, -6.73) for the homologue groups. The data set was used to compare the Junge-Pankow adsorptive gas-particle distribution model and a parametrization of Pankow's absorption model by Harner and Bidleman. Although uncertainties remain over the physicochemical property data reported for PCDD/ Fs, the former overpredicted the proportion of PCDD/Fs found associated with the particulate phase by between a factor of 1.1 and 5. The latter gave better agreement, to within a factor of 1.2-1.5, despite the requirement to use calculated rather than measured values for the octanol: air partition coefficient (K-oa).