EGUsphere EGUsphere EGUsphere EGUsphere Copernicus Publications Göttingen, Germany 10.5194/egusphere-2025-4703 Trace Organic Gas Analyzer Time-of-Flight mass spectrometer (TOGA-TOF) system for airborne observations of formaldehyde Jeong Daun 1 13 14 Hornbrook Rebecca S. https://orcid.org/0000-0002-6304-6554 2 Hills Alan J. 2 Diskin Glenn https://orcid.org/0000-0002-3617-0269 3 Halliday Hannah S. https://orcid.org/0000-0001-9499-9836 3 DiGangi Joshua P. https://orcid.org/0000-0002-6764-8624 3 Fried Alan 4 Richter Dirk 4 Walega James 4 Weibring Petter https://orcid.org/0000-0001-9567-3803 4 Hanisco Thomas F. https://orcid.org/0000-0001-9434-8507 5 Wolfe Glenn M. https://orcid.org/0000-0001-6586-4043 5 St. Clair Jason https://orcid.org/0000-0002-9367-5749 5 Peischl Jeff https://orcid.org/0000-0002-9320-7101 6 15 Wisthaler Armin 7 8 Mikoviny Tomas 7 Nowak John B. https://orcid.org/0000-0002-5697-9807 3 Piel Felix https://orcid.org/0000-0002-8191-8029 7 Tomsche Laura 3 Holmes Christopher D. https://orcid.org/0000-0002-2727-0954 9 Soja Amber 3 Gargulinski Emily 10 Crawford James H. 3 Dibb Jack 11 Warneke Carsten 12 Schwarz Joshua https://orcid.org/0000-0002-9123-2223 12 Apel Eric C. https://orcid.org/0000-0001-9421-818X 2 Advanced Study Program, NSF National Center for Atmospheric Research, Boulder, CO, USA Atmospheric Chemistry Observations & Modeling Laboratory, NSF National Center for Atmospheric Research, Boulder, CO, USA NASA Langley Research Center, Hampton, VA, USA Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO, USA NASA Goddard Space Flight Center, Greenbelt, MD, USA Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA Department of Chemistry, University of Oslo, Oslo, Norway Institute for Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria Department of Earth, Ocean, and Atmospheric Science, Florida State University, Tallahassee, FL, USA National Institute of Aerospace, Hampton, VA, USA Earth Systems Research Center, University of New Hampshire, Durham, NH, USA Chemical Science Laboratory, National Oceanic and Atmospheric Administration (NOAA), Boulder, CO, USA now at: Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA now at: Chemical Science Laboratory, National Oceanic and Atmospheric Administration (NOAA), Boulder, CO, USA now at: Global Monitoring Laboratory, National Oceanic and Atmospheric Administration (NOAA), Boulder, CO, USA 14 10 2025 2025 1 34 Copyright: © 2025 Daun Jeong et al. 2025 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2025/egusphere-2025-4703/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2025/egusphere-2025-4703/egusphere-2025-4703.pdf

Formaldehyde (HCHO) is a ubiquitous atmospheric constituent, originating from primary emissions (natural and anthropogenic) and secondary production via the oxidation of volatile organic compounds (VOCs). In addition to being a regulated pollutant, HCHO is a key species used as a tracer of recent photochemical activity due to its short atmospheric lifetime and its role as a source of HO<sub>x</sub> radicals. Given its diverse sources and high spatial variability, HCHO is challenging to represent accurately in chemical transport models, often resulting in significant discrepancies with observations. Airborne in-situ measurements of HCHO, especially when combined with VOC precursor data, offer valuable insights into its atmospheric distributions for evaluating models. Here, we present HCHO observations from the NSF NCAR Trace Organic Gas Analyzer with Time-of-Flight mass spectrometer (TOGA-TOF), deployed during the 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign. While most HCHO instruments target at most a few selected species for measurement, the TOGA-TOF employs a rapid gas chromatography-mass spectrometry (GC/MS) technique and provides discrete VOC measurements&mdash;including &gt;100 C<sub>1</sub>&ndash;C<sub>10</sub> species&mdash;at a time resolution of less than 2 minutes. We compare TOGA-TOF HCHO data to measurements from three 1-Hz instruments aboard the NASA DC-8: the Compact Atmospheric Multi-species Spectrometer (CAMS), the In Situ Airborne Formaldehyde (ISAF) instrument, and a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS). The wide dynamic range of observed HCHO concentrations (from &lt; 100 ppt to ~100 ppb) during FIREX-AQ enabled a robust intercomparison. TOGA-TOF HCHO agreed well with CAMS (slope = 1.1), with similar agreement with the PTR-ToF-MS, while larger discrepancies were observed with ISAF (slope = 1.5), likely due to differences in calibrations. Normalized excess mixing ratios (NEMRs) of HCHO relative to CO in wildfire plumes exhibited consistent trends with plume age across instruments. These findings highlight the TOGA-TOF&rsquo;s capability for highly sensitive and accurate airborne HCHO measurements.