Jeremy Smith - Secondary Organic Aerosol Production from Aqueous Reactions of Atmospheric Phenols with an Organic Triplet Excited State

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    Environ. Sci. Technol.201448 (2), pp 1049–1057, DOI: 10.1021/es4045715


        Condensed-phase chemistry plays a significant role in the   formation and evolution of atmospheric organic aerosols. Past   studies of the aqueous photoformation of secondary organic   aerosol (SOA) have largely focused on hydroxyl radical oxidation,   but here we show that triplet excited states of organic compounds   (3C*)   can also be important aqueous oxidants. We studied the aqueous   photoreactions of three phenols (phenol, guaiacol, and syringol)   with the aromatic carbonyl 3,4-dimethoxybenzaldehyde (DMB); all   of these species are emitted by biomass burning. Under simulated   sunlight, DMB forms a triplet excited state that rapidly oxidizes   phenols to form low-volatility SOA. Rate constants for these   reactions are fast and increase with decreasing pH and increasing   methoxy substitution of the phenols. Mass yields of aqueous SOA   are near 100% for all three phenols. For typical ambient   conditions in areas with biomass combustion, the aqueous   oxidation of phenols by 3C*   is faster than by hydroxyl radical, although rates depend   strongly on pH, oxidant concentrations, and the identity of the   phenol. Our results suggest that 3C*   can be the dominant aqueous oxidant of phenols in areas impacted   by biomass combustion and that this is a significant pathway for   forming SOA.

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