Photo-tautomerization of acetaldehyde as a photochemical source of formic acid in the troposphere

Miranda F. Shaw, Bálint Sztáray, Lisa K. Whalley, Dwayne E. Heard, Dylan B. Millet, Meredith J.T. Jordan, David L. Osborn, Scott H. Kable

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36 Scopus citations


Organic acids play a key role in the troposphere, contributing to atmospheric aqueous-phase chemistry, aerosol formation, and precipitation acidity. Atmospheric models currently account for less than half the observed, globally averaged formic acid loading. Here we report that acetaldehyde photo-tautomerizes to vinyl alcohol under atmospherically relevant pressures of nitrogen, in the actinic wavelength range, λ = 300-330 nm, with measured quantum yields of 2-25%. Recent theoretical kinetics studies show hydroxyl-initiated oxidation of vinyl alcohol produces formic acid. Adding these pathways to an atmospheric chemistry box model (Master Chemical Mechanism) demonstrates increased formic acid concentrations by a factor of ∼1.7 in the polluted troposphere and a factor of ∼3 under pristine conditions. Incorporating this mechanism into the GEOS-Chem 3D global chemical transport model reveals an estimated 7% contribution to worldwide formic acid production, with up to 60% of the total modeled formic acid production over oceans arising from photo-tautomerization.

Original languageEnglish (US)
Article number2584
JournalNature communications
Issue number1
StatePublished - Dec 1 2018

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