title: Photodegradation of Secondary Organic Aerosol Particles as a Source of Small, Oxygenated Volatile Organic Compounds.
abstract: We investigated the photodegradation of secondary organic aerosol (SOA) particles by near-UV radiation and photoproduction of oxygenated volatile organic compounds (OVOCs) from various types of SOA. We used a smog chamber to generate SOA from α-pinene, guaiacol, isoprene, tetradecane, and 1,3,5-trimethylbenzene under high-NOx, low-NOx, or ozone oxidation conditions. The SOA particles were collected on a substrate, and the resulting material was exposed to several mW of near-UV radiation (λ ∼ 300 nm) from a light-emitting diode. Various OVOCs, including acetic acid, formic acid, acetaldehyde, and acetone were observed during photodegradation, and their SOA-mass-normalized fluxes were estimated with a Proton Transfer Reaction Time-of-Flight Mass Spectrometer (PTR-ToF-MS). All the SOA, with the exception of guaiacol SOA, emitted OVOCs upon irradiation. Based on the measured OVOC emission rates, we estimate that SOA particles would lose at least ∼1% of their mass over a 24 h period during summertime conditions in Los Angeles, California. This condensed-phase photochemical process may produce a few Tg/year of gaseous formic acid, the amount comparable to its primary sources. The condensed-phase SOA photodegradation processes could therefore measurably affect the budgets of both particulate and gaseous atmospheric organic compounds on a global scale.
authors.affiliation: Department of Chemistry, University of California , Irvine, California 92697, United States.
authors.forename: Kurtis T
authors.initials: KT
authors.lastname: Malecha
authors.affiliation: Department of Chemistry, University of California , Irvine, California 92697, United States.
authors.forename: Sergey A
authors.initials: SA
authors.lastname: Nizkorodov
mesh_terms: D000336:Aerosols; D000393:Air Pollutants; D010782:Photolysis; D012905:Smog; D055549:Volatile Organic Compounds / Q000737:chemistry*
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D012905:Smog; D055549:Volatile Organic Compounds