The real-time ambient mass sampler (RAMS) is a continuous monitor based on particle concentrator, denuder, drier, and tapered element oscillating microbalance TEOM) monitor technology. It is designed to measure PM2.5 mass, including the semi-volatile species NH4NO3 and semi-volatile organic material, but not to measure PM2.5 water content. The performance of the RAMS in an urban environment with high humidity was evaluated during the July 1999 NARSTO-Northeast Oxidant and Particles Study (NEOPS) intensive study at the Baxter water treatment plant in Philadelphia, PA. The results obtained with the RAMS were compared to mass measurements made with a TEOM monitor and to constructed mass obtained with a Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS) sampler designed to determine the chemical composition of fine particles, including the semi-volatile species. An average of 28 of the fine particulate material present during the study was semi-volatile organic material lost from a filter during particle collection, and 1 was NH4NO3 that was also lost from the particles during sampling. The remaining mass was dominantly nonvolatile (NH4)(2)SO4 (31) and organic material (37), with minor amounts of soot, crustal material, and nonvolatile NH4NO3, Comparison of the RAMS and PC-BOSS results indicated that the RAMS correctly monitored for fine particulate mass, including the semi-volatile material. In contrast, the heated filter of the TEOM monitor did not measure the semi-volatile material. The comparison of the RAMS and PC-BOSS data had a precision of +/-4.1 mug/m(3) (+/-9.6). The precision of the RAMS data was limited by the uncertainty in the blank correction for the reversible adsorption of water by the charcoal-impregnated cellulose sorbent filter of the RAMS monitor. The precision of the measurement of fine particulate components by the PC-BOSS was 6-8. References: 30
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