CaltechAUTHORS
Published June 17, 2021 | Version Accepted Version + Supplemental Material
Journal Article Open

HCOOH in the Remote Atmosphere: Constraints from Atmospheric Tomography (ATom) Airborne Observations

Creators

  • 1. ROR icon University of Minnesota
  • 2. ROR icon NOAA Chemical Sciences Laboratory
  • 3. ROR icon Cooperative Institute for Research in Environmental Sciences
  • 4. ROR icon Lamont-Doherty Earth Observatory
  • 5. ROR icon Harvard University
  • 6. ROR icon Earth System Research Laboratory
  • 7. ROR icon California Institute of Technology
  • 8. ROR icon National Center for Atmospheric Research
  • 9. ROR icon University of California, Irvine
  • 10. ROR icon University of Colorado Boulder
  • 11. ROR icon University of New Hampshire

Abstract

Formic acid (HCOOH) is an important component of atmospheric acidity but its budget is poorly understood, with prior observations implying substantial missing sources. Here, we combine pole-to-pole airborne observations from the Atmospheric Tomography Mission (ATom) with a chemical transport model (GEOS-Chem CTM) and back-trajectory analyses to provide the first global in situ characterization of HCOOH in the remote atmosphere. ATom reveals sub-100 ppt HCOOH concentrations over most of the remote oceans, punctuated by large enhancements associated with continental outflow. Enhancements correlate with known combustion tracers and trajectory-based fire influences. The GEOS-Chem model underpredicts these in-plume HCOOH enhancements, but elsewhere, we find no broad indication of a missing HCOOH source in the background free troposphere. We conclude that missing nonfire HCOOH precursors inferred previously are predominantly short-lived. We find indications of a wet scavenging underestimate in the model consistent with a positive HCOOH bias in the tropical upper troposphere. Observations reveal episodic evidence of ocean HCOOH uptake, which is well-captured by GEOS-Chem; however, despite its strong seawater undersaturation, HCOOH is not consistently depleted in the remote marine boundary layer. Over 50 fire and mixed plumes were intercepted during ATom with widely varying transit times and source regions. HCOOH:CO-normalized excess mixing ratios in these plumes range from 3.4 to >50 ppt/ppb CO and are often over an order of magnitude higher than expected primary emission ratios. HCOOH is thus a major reactive organic carbon reservoir in the aged plumes sampled during ATom, implying important missing pathways for in-plume HCOOH production.

Additional Information

© 2021 American Chemical Society. Received: February 17, 2021; Revised: April 29, 2021; Accepted: April 30, 2021; Published: May 13, 2021. This research was primarily supported by the National Aeronautics and Space Administration (Grant NNX14AP89G). We thank Armin Wisthaler and Hanwant Singh for their support of this project. Computing resources were provided by the Minnesota Supercomputing Institute (https://www.msi.umn.edu) at the University of Minnesota. We acknowledge the contributions of Steven Wofsy (Harvard QCLS and ATom CO.X), Daniel Murphy (NOAA CSL PALMS), Paul Wennberg (CIT-CIMS), Bernadett Weinzierl (University of Vienna CAPS), Glenn Wolfe and Thomas Hanisco (NASA GSFC ISAF), Thomas Ryerson (NOAA CSL NO_yO₃), and Robert Talbot (NASA GTE MC/IC). We thank Gordon Novak, Jeffery Pierce, and Anna Hodshire for helpful discussions. ATom was funded by the NASA Earth Venture program through Grant NNX15AJ23G. CIRES researchers (J.A.N., E.A.R., J.M.K., K.D.F., and G.P.S.) acknowledge support from NOAA Cooperative Agreement NA17OAR4320101. NCAR researchers (E.C.A. and R.S.H.) acknowledge support from the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under Cooperative Agreement 1852977. The CU Boulder HR-AMS team (B.A.N., P.C.-J., and J.L.J.) were supported by NASA Grants NNX15AH33A, 80NSSC19K0124, and 80NSSC18K0630. The authors declare no competing financial interest.

Attached Files

Accepted Version - nihms-1699235.pdf

Supplemental Material - sp1c00049_si_001.pdf

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Additional details

Identifiers

PMCID
PMC8216292
Eprint ID
109165
Resolver ID
CaltechAUTHORS:20210518-081920794

Funding

NASA
NNX14AP89G
NASA
NNX15AJ23G
National Oceanic and Atmospheric Administration (NOAA)
NA17OAR4320101
National Center for Atmospheric Research (NCAR)
NSF
AGS-1852977
NASA
NNX15AH33A
NASA
80NSSC19K0124
NASA
80NSSC18K0630

Dates

Created
2021-05-19
Created from EPrint's datestamp field
Updated
2022-07-12
Created from EPrint's last_modified field