Reduction of the Positive Organic Artifact on Quartz Filters

Abstract

Quartz fiber filters are routinely used to collect particulate matter for organic analysis. Such collections may be subject to filtration artifacts: enhancement due to the adsorption of gas-phase organic species or diminishment caused by the volatilization of organic particulate matter. The magnitudes of these competing processes are usually difficult to evaluate separately, although significant amounts of organic carbon on second quartz fiber filters (back filters) downstream of the primary sampling filter indicate that these sampling artifacts are present. In an experiment to reduce the enhancement when sampling organic particulate matter, a diffusive denuder consisting of separated layers of quartz fiber filter was used under the hypothesis that it would selectively remove only those gaseous organic species that normally are retained by the filter medium. This denuder reduced the organic carbon on the back filter by more than a factor of four, to levels comparable to those of the filter blank; the organic carbon on the front filter was reduced by the same absolute amount. The conclusion is that a quartz fiber filter denuder nearly eliminates the enhancement artifact.