Integrated and real-time diffusion denuder sampler for PM2.5

Particulate matter (PM) is a complex mixture of stable condensed phases, ad sorbed or dissolved gases, and semi-volatile materials, i.e. compounds that transfer between the gas and condensed phases. Fine particles in both rura l and urban environments contain substantial quantities of semi-volatile ma terial that can be lost from the particles during sample collection on a fi lter and during subsequent handling, storage and conditioning (or equilibra tion). These include ammonium nitrate, semi-volatile organic compounds and particle bound water. In addition, gas phase organic compounds can also be absorbed by a quartz filter. As a result, the concentrations of these speci es are often significantly in error for results obtained with a conventiona l single filter sampler. The accurate measurement of the mass and chemical components of fine particles will become more important as a result of the recent promulgation of fine particle standards by the US Environmental Prot ection Agency and the additional monitoring that will be required for imple mentation of those standards as well as for additional research on the sour ces and effects of PM. Past organic compound diffusion denuder samplers dev eloped by us (BOSS, BYU Organic Sampling System) are not amenable to routin e field use because of the need to independently determine the gas phase se mi-volatile organic material breakthrough of the denuder for each sample. T his problem has been eliminated in the Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS) using a combined virtual impac tor, particle-concentrator inlet to provide a concentrated stream of 0.1-2. 5 mu m particles. This is followed by a BOSS diffusion denuder and filter p acks containing particle collecting and sorbent fillers to collect particle s, including any semi-volatile organic material or ammonium nitrate lost fr om the particles during sampling. The PC-BOSS contains a sequential sampler to allow for the routine collection of several samples. A second sampler, the Real-rime Total Ambient Mass Sampler (RAMS), has been developed by comb ining the PC-BOSS with TEOM technology. In this sampler, a diffusion dryer to remove gas phase water follows the diffusion denuder, The dried aerosol stream is then sampled with a "sandwich" (TX40 and sorbent) filter on the T EOM tapered element to collect particles, including any semi-volatile speci es. Laboratory and field validation data indicate that the precision of det ermination of fine particulate material, including ammonium nitrate and sem i-volatile organic material is better than +/- 10%. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.