Dept. of Environmental Science and Engineering
Oregon Graduate Institute of Science & Technology
Partitioning between the gas phase and suspended particle phase plays an important role in determining the fate and transport of airborne semi-volatile organic compounds (SOCs). Current theoretical work suggests that varying environmental conditions, sampling procedures, and particulate characteristics can complicate the measurement of the corresponding gas particle partitioning coefficients. These factors can also make it difficult to assess the relative importance of surface adsorption and phase absorption in determining the values of the partitioning coefficients. A series of experiments were designed to measure the gas solid partitioning of SOCs to a model atmospheric particulate material (APM). An apparatus designed to control temperature, relative humidity, SOC concentration and particulate characteristics was constructed. The SOCs studied included six Î·-alkanes, namely heptadecane, nonadecane, eicosane, heneicosane, docosane and tricosane, along with five polycyclic aromatic hydrocarbons (PAHs), namely 2-methyl phenanthrene, fluoranthene, pyrene, benzo[Î²]fluorene, and benz[Î±]anthracene. The model APM was a pre-baked quartz fiber filter (QFF). The QFF was exposed to the gas phase SOCs until equilibrium was achieved as suggested by equivalent gas phase concentrations upstream and downstream of the filter. Gas phase concentrations were determined by adsorption/thermal desorption (ATD) using Tenax as a sorbent, and sorbed concentrations were determined by extraction of the QFF in methylene chloride. If the quartz is assumed to be non-porous, the sorption that was measured represents simple physical adsorption. The measured partitioning coefficients have been expressed in both a K[subscript p](m[superscript 3] Âµg[superscript-1]) and K[subscript p], (m[superscript 3] m[superscript -2]) format, and are compared to corresponding values for urban particulate material (UPM) at ambient relative humidity (RH). K[subscript p] is the ratio of the sorbed concentration (ng Âµg[superscript -1]) to the gaseous concentration (ng m[superscript -3]). K[subscript p], is the ratio of the surface-area normalized concentration (ng m[superscript -2]) to the gaseous concentration(ng m[superscript -3]). The measured relationship between log K[subscript ps] and log p[superscript 0][subscript L], the sub-cooled liquid vapor pressure, is highly-correlated and agrees well with the same relationship for the PAHs on UPM. The close agreement between the quartz surface and the UPM suggests that partitioning to APM can be modeled by non-specific, physical adsorption.
Storey, John Morse Elliot, "Gas/particle partitioning of semi-volatile organic compounds to model atmospheric particulate material" (1993). Scholar Archive. 327.