Determination of PM2.5 sulfate and nitrate with a PC-BOSS designed for routine sampling for semi-volatile particulate matter

Ambient particles contain substantial quantities of material that can be lo st from the particles during sample collection on a filter. These include a mmonium nitrate and semi-volatile organic compounds. As a result, the conce ntrations of these species are often significantly in error for results obt ained with a filter pack sampler. The accurate measurement of these semi-vo latile fine particulate species is essential for a complete understanding o f the possible causes of health effects associated with exposure to fine pa rticles. Past organic compound diffusion denuder samplers developed by the authors (e.g., the Brigham Young University Organic Sampling System [BOSS]) are not amenable to routine field use because of the need to independently determine the gas-phase semivolatile organic material efficiency of the de nuder for each sample. This problem has been eliminated using a combined vi rtual impactor, particle-concentrator inlet to provide a concentrated strea m of 0.1-2.5-mu m particles. This is followed by a BOSS diffusion denuder a nd filter packs to collect particles, including any semi-volatile species l ost from the particles during sampling. The sampler (Particle Concentrator- Brigham Young University Organic Sampling System [PC-BOSS]) contains a post -denuder multifilter pack unit to allow for the routine collection of sever al sequential samples. The PC-BOSS can be used for the determination of bot h fine particulate nitrate and semi-volatile organic material without signi ficant "positive" or "negative" sampling artifacts. Validation of the sampl er for the determination of PM2.5 sulfate and nitrate based on comparison o f results obtained at Riverside, CA with collocated PC-BOSS, annular denude r, and ChemSpec samplers indicates the PC-BOSS gives accurate results for t hese species with a precision of +/-5-8%. An average of 33% of the PM2.5 ni trate was lost from the particles during sampling for both denuder and sing le filter samplers.