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Published June 21, 2012 | Supplemental Material
Journal Article Open

Secondary Organic Aerosol Formation from Low-NO_x Photooxidation of Dodecane: Evolution of Multigeneration Gas-Phase Chemistry and Aerosol Composition


The extended photooxidation of and secondary organic aerosol (SOA) formation from dodecane (C_(12)H_(26)) under low-NO_x conditions, such that RO_2 + HO_2 chemistry dominates the fate of the peroxy radicals, is studied in the Caltech Environmental Chamber based on simultaneous gas and particle-phase measurements. A mechanism simulation indicates that greater than 67% of the initial carbon ends up as fourth and higher generation products after 10 h of reaction, and simulated trends for seven species are supported by gas-phase measurements. A characteristic set of hydroperoxide gas-phase products are formed under these low-NO_x conditions. Production of semivolatile hydroperoxide species within three generations of chemistry is consistent with observed initial aerosol growth. Continued gas-phase oxidation of these semivolatile species produces multifunctional low volatility compounds. This study elucidates the complex evolution of the gas-phase photooxidation chemistry and subsequent SOA formation through a novel approach comparing molecular level information from a chemical ionization mass spectrometer (CIMS) and high m/z ion fragments from an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Combination of these techniques reveals that particle-phase chemistry leading to peroxyhemiacetal formation is the likely mechanism by which these species are incorporated in the particle phase. The current findings are relevant toward understanding atmospheric SOA formation and aging from the "unresolved complex mixture," comprising, in part, long-chain alkanes.

Additional Information

© 2012 American Chemical Society. Received: November 30, 2011. Publication Date (Web): March 16, 2012. Special Issue: A. R. Ravishankara Festschrift. This work was supported by the Office of Science (Biological and Environmental Research), U.S. Department of Energy Grant (DE-SC 0006626), and National Science Foundation Grants AGS-1057183 and ATM-0650061. We acknowledge John D. Crounse and Jason M. St. Clair for helpful discussions on CIMS data analysis, Reddy L. N. Yatavelli and ManNin Chan for useful discussions, and Andreas Zuend, Xuan Zhang, and Steve Compernolle for assistance with the vapor-pressure estimations. L.D.Y., J.S.C., and C.L.L. were supported by National Science Foundation Graduate Research Fellowships

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