Surface Wetness as an Unexpected Control on Forest Exchange of Volatile Organic Acids

S. R. Fulgham, D. B. Millet, H. D. Alwe, A. H. Goldstein, S. Schobesberger, D. K. Farmer

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


We report bidirectional exchange of volatile acids, including isocyanic and alkanoic acids, over a pine forest across multiple seasons. The exchange velocity of these acids is well correlated with dew point depression, suggesting an equilibrium-driven continuum of flux. Wetness on forest surfaces impacts the vertical exchange of gases, and we suggest that water films and droplets drive equilibrium partitioning, with acids being solvated in surface wetness and released through evaporation. Despite their volatility, these acids partition into neutral-to-alkaline aqueous films, consistent with reported dew pH. This relationship between exchange velocity and dew point depression holds for a wetter mixed forest, but not a very dry orchard. Dew point depression is an excellent indicator of acid fluxes so long as the canopy is occasionally wetted.

Original languageEnglish (US)
Article numbere2020GL088745
JournalGeophysical Research Letters
Issue number15
StatePublished - Aug 16 2020

Bibliographical note

Funding Information:
We thank William Massman (U.S. Forest Service) and Frank Wania (University of Toronto) for assistance, and NOAA (NA14OAR4310141), the Academy of Finland (310682), and NSF (AGS‐1932771, AGS‐1428257) for funding.

Publisher Copyright:
©2020. The Authors.


  • biosphere-atmosphere exchange
  • isocyanic acid
  • organic acids
  • surface wetness


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