Laboratory and "eld investigation of the adsorption of gaseous organic compounds onto quartz "lters

A common method for measuring the mass of organic carbon in airborne particulate matter involves collection on a quartz "lter and subsequent thermal analysis. If unaccounted for, the adsorption of organic gases onto quartz "lters will lead to the overestimation of aerosol organic carbon concentrations (positive artifact). A recommended method of correction for the positive artifact involves sampling with a backup "lter. Placed behind either the primary quartz "lter, or behind a Te#on "lter and collected in parallel with the primary quartz "lter, the carbon content of the quartz backup "lter is a measure of the adsorbed organic material on the primary quartz "lter. In this paper, we illustrate the application of this technique to samples collected in Berkeley, California. While the tandem quartz "lter method can be successfully applied to correct for the positive artifact, we discuss two cases when this method will fail. We have found that the capacity for adsorption of organic gases is not uniform for all "lters. Instead, "lters manufactured by the same company, but having di!erent lot numbers, exhibit variable adsorption capacity. Thus, a "lter pair composed of "lters from di!erent lots may lead to signi"cant underor overestimation of particulate organic carbon concentration. Additionally, we have observed that the tandem "lter method under-corrects for the positive artifact if the sampling time is short (few hours). Laboratory experiments with vapors of single organic compounds corroborate results based on ambient samples. The evolution of adsorbed organic gases, particularly polar compounds, during thermal analysis indicates that a single compound may experience two distinct adsorbent}adsorbate binding energies. Adsorbed gases may co-evolve with particles at temperatures in excess of 2503C. Published by Elsevier Science Ltd.