Comparison of integrated samplers for mass and composition during the 1999 Atlanta Supersites project

[1] The first of the U. S. Environmental Protection Agency's (EPA) Particulate Matter (PM) Supersites projects was established in Atlanta, GA, during the summer of 1999 in conjunction with the Southern Oxidants Study. The short-term primary focus was a one month intensive field campaign to evaluate advanced PM measurement methods for measuring PM mass and the chemical and physical properties of PM. Long-term objectives are being met through coordination and cooperation with existing programs in Atlanta and the southeastern United States. Three categories of PM instruments were deployed during August 1999: time-integrated or discrete filter-based methods like those used in EPA's PM2.5 Chemical Speciation Network; continuous or semicontinuous species specific methods, most of which are still in development; and single particle mass spectrometers, the most advanced methods looking at the chemical composition of single particles. The focus of this paper is on comparison of the discrete filter-based methods. Samples were collected by 12 discrete filter-based samplers on an every other day basis during the study period at the Jefferson Street Southeastern Aerosol Research and Characterization (SEARCH) study site. Samples were analyzed for PM2.5 mass, sulfate, nitrate, ammonium, organic carbon, elemental carbon, and trace elements, the latter by XRF. Samplers used a variety of filters; denuder-filter combinations in the case of nitrate and organic carbon, particle size fractionating devices, and flow rates. Ambient concentrations for most species were sufficiently above detection limits for testing comparability among samplers, with nitrate being the most notable exception for the major components having an average reported value of 0.5 mug/m(3). Several trace species, e. g., As and Pb, also were often below limits of detection of the analysis method. Results indicate that real differences exist among the samplers tested for most species, with sulfate and ammonium being the exceptions, under the conditions tested. Differences are due to sampler design, and in the case of elemental carbon, also due to the use of different chemical analysis methods. Comparability among most of the samplers for a given species was: mass (+/-20%); sulfate (+/-10%); nitrate (+/-30-35%); ammonium (+/-10-15%); organic carbon either with or without denuders (+/-20%) or including samplers both with and without denuders (+/-35-45%); elemental carbon (+/-20 to +/-200%, the latter if different analysis methods are used); and minor and trace elements (+/-20-30%). A net organic carbon-sampling artifact on quartz-fiber filters was estimated from the comparison of denuded versus undenuded samples and is in the range of 1-4 mug/m(3).