PM 2.5 Semivolatile Organic Material at Riverside, California: Implications for the PM 2.5 Federal Reference Method Sampler

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Abstract
Particulate semivolatile organic compounds can be lost from particles on a filter during sample collection and storage, resulting in a negative artifact. Gas-phase organic compounds can adsorb on a quartz filter to cause a positive artifact. A sampler (Particle Concentrator-Brigham Young University Organic Sampling System: PC-BOSS) has been developed that uses a cyclone and virtual impactor (particle concentrator) inlet to provide a concentrated stream of 0.1-2.5 w m particles. The concentrator is followed by a BOSS diffusion denuder to remove interfering gas-phase compounds and filter packs to collect particles, including any semivolatile species lost from the particles during sampling. The sampler can be used for the determination of both fine particulate nitrate and semivolatile organic material without significant "positive" or "negative" sampling artifacts. The sampler has been evaluated at Riverside, CA. The collection efficiency of the particle concentrator was stable, being 65% - 2% and 61% - 1% for particulate sulfate and soot, respectively. Results obtained with the PC-BOSS for the determination of PM 2.5 organic material including semivolatile components agreed with results from a BOSS, but not with filter pack results. The precision of the PC-BOSS results for particulate organic material was - 8%. An average of 50% of the particulate organic material was lost from the particles during sampling for all samplers used. As a result of the loss of semivolatile organic material and nitrate, the PM 2.5 Federal Reference Method sampler underdetermined PM 2.5 by an average of 34% with the under measurement varying from negligible to 27 w g/m 3 , averaging 8.9 w g/m 3 .