Gas/solid partitioning of semivolatile organic compounds (SOCs) to air filters. 1. Partitioning of polychlorinated dibenzodioxins, polychlorinated dibenzofurans and polycyclic aromatic hydrocarbons to teflon membrane filters

Gas/particle distributions of semi-volatile organic compounds (SOCs) in the atmosphere are often measured using filter/sorbent samplers. Unfortunately, the adsorption of gaseous SOCs onto a filter can cause positive biases in the measured particle-phase concentrations, and negative biases in the measured gas-phase concentrations. In order to permit estimation of the magnitudes of these errors when Teflon membrane filters (TMFs) are used, surface-area-normalized gas/Teflon partition coefficient ( K p,s) values were measured for a range of polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polycyclic aromatic hydrocarbons (PAHs). Sorption isotherms were linear over three orders of magnitude. A 10° change in temperature ( T) caused the K p,s values to decrease by factors of 2.4–3.4. Changes in relative humidity (RH) between 21 and 52% did not affect the measured K p,s values. The dependence of the partitioning on the sub-cooled liquid vapor pressures of the subject compounds was investigated. Within each of the three individual compound classes, plots of log K p,s vs. log p L o were linear with slopes of approximately −1. The pooled data for the three compound classes yielded a single log K p,s vs. log p L o plot for 25°C that was correlated nearly as well ( r 2=0.96) as the plots for the individual compound classes ( r 2≈0.95). Since backup TMFs used in filter/sorbent sampling in urban areas yielded the same K p,s values as did clean TMFs, assessment of the magnitude of the gas adsorption artifact for TMFs can be carried out using K p,s values obtained with clean and/or ambient backup TMFs.