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Although sampling artifacts of acidity, ammonium, nitrate, and chloride in airborne particulate pollutants can be reduced by the use of denuders to absorb interfering gases, artifacts due to interparticle interactions still remain. In this study, the contribution of individual artifact reactions to particle evaporation and the effects of aerosol composition on the extents of sampling artifacts in PM[SUB2.5] were investigated. Samples were collected using a Harvard honeycomb denuder/filter-pack system at an urban site and a rural site in Hong Kong. The results show that the formation of artifacts can be categorized into two regimes: ammonium rich (AR) samples with a molar ratio [NH[SUB4][SUP+]]/[SO[SUB4][SUP2-]] greater than 1.5 and ammonium poor (AP) samples with a molar ratio [NH[SUB4][SUP+]]/[SO[SUB4][SUP2-] less than or equal to 1.5. The urban samples were all AR samples, and they were characterized by high nitrate and low in situ free acid concentrations. In contrast, the rural samples were all AP samples and they were characterized by low nitrate and high in situ free acid concentrations. We have developed a methodology to estimate the contribution of each artifact reaction to the sampling loss of nitrate, chloride, ammonium, and acidity. In the AR samples, the evaporation of HNO[SUB3] and HCl and concomitant evaporation of NH[SUB3] were the principal reactions in determining the extent of the sampling loss of nitrate and chloride. In the AP samples, the evaporation of HNO[SUB3] and HCl alone was the principal reaction instead, especially at high sampling loss. The in situ free acid concentration, a function of aerosol composition and ambient conditions, is a more useful parameter than strong acidity in understanding the sampling loss of acidity, nitrate, and chloride from the collected particles. [ABSTRACT FROM AUTHOR]

Performs an experimental study of the sampling artifact of chloride (Cl) depletion from collected sea salt aerosols. Possibility of Cl depletion as a result of particle-particle interactions in sampling; Size dependence of Cl depletion; Factors affecting depletion rate.

In this article the authors discuss aspects of the report "Atmospheric Particulate Matter Pollution During the 2008 Beijing Olympics" within the issue. They are critical of the quartz filter-based gravimetric method used by researchers to measure mass concentrations of particulate matter (PM) and suggest that its use was inappropriate. The authors reference a method for the determination of PM in the atmosphere which they feel should have been used by the researchers.