Jeremy Smith - Phenolic carbonyls undergo rapid aqueous photodegradation to form low-volatility, light-absorbing products

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      Publication Details (including relevant citation   information):

      Atmospheric Environment; 2015; In-press



      We investigated the aqueous photochemistry of six phenolic   carbonyls - vanillin, acetovanillone, guaiacyl acetone,   syringaldehyde, acetosyringone, and coniferyl aldehyde   that are emitted from wood   combustion. The phenolic carbonyls absorb significant amounts of   solar radiation and decay rapidly via direct photodegradation,   with lifetimes (τ) of   13140 min under   Davis, CA winter solstice sunlight at midday (solar zenith   angle = 62°). The one exception is guaiacyl acetone,   where the carbonyl group is not directly connected to the   aromatic ring: This species absorbs very little sunlight and   undergoes direct photodegradation very slowly (τ > 103 min). We   also found that the triplet excited states (3C*) of the phenolic carbonyls rapidly oxidize   syringol (a methoxyphenol without a carbonyl group), on   timescales of 15 h for solutions containing 5 μM   phenolic carbonyl. The direct photodegradation of the phenolic   carbonyls, and the oxidation of syringol by 3C*, both efficiently produce low volatility   products, with SOA mass yields ranging from 80 to 140%. Contrary   to most aliphatic carbonyls, under typical fog conditions we find   that the primary sink for the aromatic phenolic carbonyls is   direct photodegradation in the aqueous phase. In areas of   significant wood combustion, phenolic carbonyls appear to be   small but significant sources of aqueous SOA: over the course of   a few hours, nearly all of the phenolic carbonyls will be   converted to SOA via direct photodegradation, enhancing the POA   mass from wood combustion by approximately 35%

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