Comparison of N-Alkane and PAH concentrations collected on quartz fiber and teflon membrane filters in an urban environment

Abstract

Artifact-free gas and particulate phase concentration measurements are crucial primary inputs into compartmental models used to predict the transport and fate of a compound in the environment. A modified high volume air sampler was designed to minimize volatilization from a particulate laden filter; volatilization is one of the major sampling artifacts associated with the collection of ambient aerosols. This study also considers two other major sampling artifacts, gas adsorption to the filter, and chemical reactions on the filter. Concentrations of 16 n-alkanes (hexadecane - hentriacontane) and 8 PAHs (phenanthrene - benzo(a)pyrene) were measured from aerosols collected on quartz fiber filters (QFFs) and Teflon membrane filters (TMFs) for 12 sampling events in Portland, Oregon in 1988 over a range of ambient temperatures (7–31°C). The extent to which gas adsorption is important can be examined from the ratios of the concentrations of the target compounds collected on the QFFs to TMFs. It was determined that even though the coefficients of variation in the QFF / TMF ratios were as high as 60%, greater than 50% of the target compounds were collected in significantly higher concentrations on the QFFs. The most likely cause of elevated ratios is gas adsorption to the QFFs, creating artificially high QFF / TMF ratios. Gas adsorption to QFFs can lead to a significant over-estimation of a compound's particulate phase concentration.