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Published July 24, 2007 | Published
Journal Article Open

Secondary organic aerosol formation from m-xylene, toluene, and benzene


Secondary organic aerosol (SOA) formation from the photooxidation of m-xylene, toluene, and benzene is investigated in the Caltech environmental chambers. Experiments are performed under two limiting NOₓ conditions; under high-NOₓ conditions the peroxy radicals (RO₂) react only with NO, while under low-NOₓ conditions they react only with HO₂. For all three aromatics studied (m-xylene, toluene, and benzene), the SOA yields (defined as the ratio of the mass of organic aerosol formed to the mass of parent hydrocarbon reacted) under low-NOx conditions substantially exceed those under high-NOx conditions, suggesting the importance of peroxy radical chemistry in SOA formation. Under low-NOₓ conditions, the SOA yields for m-xylene, toluene, and benzene are constant (36%, 30%, and 37%, respectively), indicating that the SOA formed is effectively nonvolatile under the range of Mₒ (>10 μg m⁻³) studied. Under high-NOₓ conditions, aerosol growth occurs essentially immediately, even when NO concentration is high. The SOA yield curves exhibit behavior similar to that observed by Odum et al. (1996, 1997a, b), although the values are somewhat higher than in the earlier study. The yields measured under high-NOx conditions are higher than previous measurements, suggesting a "rate effect" in SOA formation, in which SOA yields are higher when the oxidation rate is faster. Experiments carried out in the presence of acidic seed aerosol reveal no change of SOA yields from the aromatics as compared with those using neutral seed aerosol.

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© Author(s) 2007. This work is licensed under a Creative Commons License. Received: 1 March 2007 – Published in Atmos. Chem. Phys. Discuss.: 28 March 2007. Revised: 28 June 2007 – Accepted: 13 July 2007 – Published: 24 July 2007. This research was funded by the U.S. Environmental Protection Agency Science to Achieve Results (STAR) Program grant number RD-83107501-0, managed by EPA's Office of Research and Development (ORD), National Center for Environmental Research (NCER), and by U.S. Department of Energy Biological and Environmental Research Program DE-FG02-05ER63983.

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