A study of atmospheric n-alkanes and PAHs and their distributions between the gaseous and particulate phases

The extent to which a compound is removed from the atmosphere and transported to other compartments will depend in part on how that compound is distributed between the gaseous and particulate phases. Recent theoretical advances indicate that a compound's vapor pressure and the ambient temperature will play large roles in determining the extent to which the compound partitions to atmospheric particulate matter. However, the testing of such theory requires artifact free values of the gas and particulate phase concentrations. A field study designed to minimize sampling artifacts was conducted in Portland, OR during 1988. During this study, the concentrations of n-alkanes (C16 through C31) and eleven polynuclear aromatic hydrocarbons (PAHs) were measured in the gas and particulate phases over a range of ambient temperatures (7-31{dollar}spcirc{dollar}C).; Two air samplers were built to collect gas and particulate phase samples. One of the samplers utilized two quartz fiber filters (QFFs) in series and followed by two polyurethane foam sheets (PUFSs). The second sampler utilized a Teflon membrane filter (TMF) followed by a QFF and two PUFSs. Gas phase adsorption to the QFFs, as measured on the backup QFFs, was found to be a significant artifact for all of the more volatile n-alkanes as well as some of the PAHs studied. It was also determined that the QFF behind the TMF provided the best estimate of the extent of gas phase adsorption to the QFFs.; Atmospheric partitioning was examined in the context of an equilibrium distribution constant K and a compound's temperature corrected subcooled liquid vapor pressure (p{dollar}spcircsb{lcub}rm L{rcub}{dollar}). The parameter K is defined as A(TSP)/F where A and F are the gas and particulate phase concentrations (ng/m{dollar}sp3{dollar}), respectively, and TSP is the total suspended particulate matter concentration ({dollar}mu{dollar}g/m{dollar}sp3{dollar}). As predicted by equilibrium adsorption theory, the correlation between log K vs. log p{dollar}spcircsb{lcub}rm L{rcub}{dollar} was generally quite high. When the gas and particulate phase concentrations were corrected for gas phase adsorption to the QFFs, the correlation (r{dollar}sp2{dollar}) between log K and log p{dollar}spcircsb{lcub}rm L{rcub}{dollar} increased from {dollar}sim{dollar}0.74 to {dollar}sim{dollar}0.90.