Oxidation of Volatile Organic Compounds as the Major Source of Formic Acid in a Mixed Forest Canopy

Hariprasad Alwe, Dylan B Millet, Xin Chen, Jonathan D. Raff, Zachary C. Payne, Kathryn Fledderman

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

Formic acid (HCOOH) is among the most abundant carboxylic acids in the atmosphere, but its budget is poorly understood. We present eddy flux, vertical gradient, and soil chamber measurements from a mixed forest and apply the data to better constrain HCOOH source/sink pathways. While the cumulative above-canopy flux was downward, HCOOH exchange was bidirectional, with extended periods of net upward and downward flux. Net above-canopy fluxes were mostly upward during warmer/drier periods. The implied gross canopy HCOOH source corresponds to 3% and 38% of observed isoprene and monoterpene carbon emissions and is 15× underestimated in a state-of-science atmospheric model (GEOS-Chem). Gradient and soil chamber measurements identify the canopy layer as the controlling source of HCOOH or its precursors to the forest environment; below-canopy sources were minor. A correlation analysis using an ensemble of marker volatile organic compounds suggests that secondary formation, not direct emission, is the major source driving ambient HCOOH.

Original languageEnglish (US)
Pages (from-to)2940-2948
Number of pages9
JournalGeophysical Research Letters
Volume46
Issue number5
DOIs
StatePublished - Mar 16 2019

Bibliographical note

Funding Information:
This research was supported by NSF (grants AGS‐1428257, AGS‐1148951 and AGS‐1352375). GEOS‐Chem model development and simulations were supported by NASA (grant NNX14AP89G). Computing resources were provided by MSI (www.msi.umn. edu). Soil flux measurements were supported by DOE (grant DE‐ SC0014443). We thank Steve Bertman, Phil Stevens, all other PROPHET‐ AMOS collaborators, UMBS, the US‐ UMB Ameriflux team, and the University of Houston/Rice group for providing meteorological measurements. We acknowledge Timothy Griffis and Julian Deventer for helpful discussions, plus John Poehlman, Jeremy Boshears, and colleagues for help designing and building the chamber system. High‐ frequency measurements used here (winds, HCOOH, and select other VOCs) are available online (https://doi. org/10.13020/D6JQ3R). Processed fluxes and other VOC data are available from the authors upon request. GEOS‐ Chem model code is available online (www.geos‐chem.org).

Funding Information:
This research was supported by NSF (grants AGS-1428257, AGS-1148951 and AGS-1352375). GEOS-Chem model development and simulations were supported by NASA (grant NNX14AP89G). Computing resources were provided by MSI (www.msi.umn.edu). Soil flux measurements were supported by DOE (grant DE-SC0014443). We thank Steve Bertman, Phil Stevens, all other PROPHET-AMOS collaborators, UMBS, the US-UMB Ameriflux team, and the University of Houston/Rice group for providing meteorological measurements. We acknowledge Timothy Griffis and Julian Deventer for helpful discussions, plus John Poehlman, Jeremy Boshears, and colleagues for help designing and building the chamber system. High-frequency measurements used here (winds, HCOOH, and select other VOCs) are available online (https://doi.org/10.13020/D6JQ3R). Processed fluxes and other VOC data are available from the authors upon request. GEOS-Chem model code is available online (www.geos-chem.org).

Publisher Copyright:
©2019. The Authors.

Keywords

  • Eddy co-variance fluxes
  • Formic acid

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