title: Contribution of carbonyl photochemistry to aging of atmospheric secondary organic aerosol.
abstract: The photodegradation of secondary organic aerosol (SOA) material by actinic UV radiation was investigated. SOA was generated via the dark reaction of ozone and d-limonene, collected onto quartz-fiber filters, and exposed to wavelength-tunable radiation. Photochemical production of CO was monitored in situ by infrared cavity ring-down spectroscopy. A number of additional gas-phase products of SOA photodegradation were observed by gas chromatography, including methane, ethene, acetaldehyde, acetone, methanol, and 1-butene. The absorption spectrum of SOA material collected onto CaF2 windows was measured and compared with the photolysis action spectrum for the release of CO, a marker for Norrish type-I photocleavage of carbonyls. Both spectra had a band at approximately 300 nm corresponding to the overlapping n --> pi* transitions in nonconjugated carbonyls. The effective extinction coefficient of freshly prepared SOA was estimated to be on the order of 15 L mol(-1) cm(-1) at 300 nm, implying one carbonyl group in every SOA constituent. The absorption by the SOA material slowly increased in the visible and near-UV during storage of SOA in open air in the dark, presumably as a result of condensation reactions that increased the degree of conjugation in the SOA constituents. These observations suggest that photolysis of carbonyl functional groups represents a significant sink for monoterpene SOA compounds in the troposphere, with an estimated lifetime of several hours over the continental United States.
authors.affiliation: Department of Chemistry, University of California, Irvine, California 92697, USA.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Mang
authors.forename: Dana K
authors.initials: DK
authors.lastname: Henricksen
authors.forename: Adam P
authors.initials: AP
authors.lastname: Bateman
authors.forename: Mads P Sulbaek
authors.initials: MP
authors.lastname: Andersen
authors.forename: Donald R
authors.initials: DR
authors.lastname: Blake
authors.forename: Sergey A
authors.initials: SA
authors.lastname: Nizkorodov
mesh_terms: D000079:Acetaldehyde / Q000737:chemistry; D000096:Acetone / Q000737:chemistry; D000336:Aerosols / Q000737:chemistry*; D000393:Air Pollutants / Q000737:chemistry*; D002849:Chromatography, Gas / Q000379:methods; D053138:Cyclohexenes / Q000737:chemistry; D005374:Filtration / Q000295:instrumentation / Q000379:methods; D000077222:Limonene; D009930:Organic Chemicals / Q000737:chemistry*; D010126:Ozone / Q000737:chemistry; D010316:Particle Size; D010777:Photochemistry; D011791:Quartz / Q000737:chemistry; D013729:Terpenes / Q000737:chemistry; D013997:Time Factors; D014466:Ultraviolet Rays; D014835:Volatilization
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D053138:Cyclohexenes; D009930:Organic Chemicals; D013729:Terpenes; D000096:Acetone; D011791:Quartz; D010126:Ozone; D000077222:Limonene; D000079:Acetaldehyde