Closing the Reactive Carbon Flux Budget: Observations From Dual Mass Spectrometers Over a Coniferous Forest

Michael P. Vermeuel, Dylan B. Millet, Delphine K. Farmer, Matson A. Pothier, Michael F. Link, Mj Riches, Sara Williams, Lauren A. Garofalo

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

We use observations from dual high-resolution mass spectrometers to characterize ecosystem-atmosphere fluxes of reactive carbon across an extensive range of volatile organic compounds (VOCs) and test how well that exchange is represented in current chemical transport models. Measurements combined proton-transfer reaction mass spectrometry (PTRMS) and iodide chemical ionization mass spectrometry (ICIMS) over a Colorado pine forest; together, these techniques have been shown to capture the majority of ambient VOC abundance and reactivity. Total VOC mass and associated OH reactivity fluxes were dominated by emissions of 2-methyl-3-buten-2-ol, monoterpenes, and small oxygenated VOCs, with a small number of compounds detected by PTRMS driving the majority of both net and upward exchanges. Most of these dominant species are explicitly included in chemical models, and we find here that GEOS-Chem accurately simulates the net and upward VOC mass and OH reactivity fluxes under clear sky conditions. However, large upward terpene fluxes occurred during sustained rainfall, and these are not captured by the model. Far more species contributed to the downward fluxes than are explicitly modeled, leading to a major underestimation of this key sink of atmospheric reactive carbon. This model bias mainly reflects missing and underestimated concentrations of depositing species, though inaccurate deposition velocities also contribute. The deposition underestimate is particularly large for assumed isoprene oxidation products, organic acids, and nitrates—species that are primarily detected by ICIMS. Net ecosystem-atmosphere fluxes of ozone reactivity were dominated by sesquiterpenes and monoterpenes, highlighting the importance of these species for predicting near-surface ozone, oxidants, and aerosols.

Original languageEnglish (US)
Article numbere2023JD038753
JournalJournal of Geophysical Research Atmospheres
Volume128
Issue number14
DOIs
StatePublished - Jul 27 2023

Bibliographical note

Funding Information:
This work was supported by NSF (AGS, 1932771 and 1932849). Measurement capabilities at UMN were also enhanced by support from the Alfred P. Sloan Foundation. The tower used in this project is maintained by NCAR and supported by the USFS. We thank Steven Alton and Paula Fornwalt of USFS for their support with site and logistics. We also thank Glenn M. Wolfe for publicly providing the MATLAB‐based FluxToolbox of analysis scripts, portions of which were altered for use in this analysis. Computing resources were provided by the Minnesota Supercomputing Institute ( http://www.msi.umn.edu ) at the University of Minnesota. We acknowledge that this project occurred on the traditional territory of the Ute and Cheyenne peoples.

Funding Information:
This work was supported by NSF (AGS, 1932771 and 1932849). Measurement capabilities at UMN were also enhanced by support from the Alfred P. Sloan Foundation. The tower used in this project is maintained by NCAR and supported by the USFS. We thank Steven Alton and Paula Fornwalt of USFS for their support with site and logistics. We also thank Glenn M. Wolfe for publicly providing the MATLAB-based FluxToolbox of analysis scripts, portions of which were altered for use in this analysis. Computing resources were provided by the Minnesota Supercomputing Institute (http://www.msi.umn.edu) at the University of Minnesota. We acknowledge that this project occurred on the traditional territory of the Ute and Cheyenne peoples.

Publisher Copyright:
© 2023 The Authors.

Keywords

  • biosphere-atmosphere exchange
  • eddy covariance
  • mass spectrometry
  • volatile organic compounds

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