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.
Bibliographical noteFunding Information:
M.F.S., M.J.T.J., and S.H.K. acknowledge the Australian Research Council for support (DP130104326 and DP160101792). M.F.S. acknowledges the award of an Australian APA award in support of her PhD studies. L.K.W. and D.E.H. acknowledge the National Centre for Atmospheric Science, which is a distributed institute funded by the Natural Environment Research Council. B.S. acknowledges support of the National Science Foundation (NSF; CHE-1266407) and the U.S. Department of Energy (DOE) Visiting Faculty Program. D.B.M. acknowledges support from NSF (AGS-1148951), the National Aeronautics and Space Administration (NASA; NNX14AP89G), and the Minnesota Supercomputing Institute. D.L.O. acknowledges support from the U.S. DOE, Office of Science, Office of Basic Energy Sciences, which also funded all the experimental apparatus in this work. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. DOE’s National Nuclear Security Administration under contract DE-NA0003525.
© 2018 The Author(s).