Preprints
https://doi.org/10.5194/acp-2021-820
https://doi.org/10.5194/acp-2021-820

  11 Oct 2021

11 Oct 2021

Review status: this preprint is currently under review for the journal ACP.

Source and variability of formaldehyde (HCHO) at northern high latitude: an integrated satellite, ground/aircraft, and model study

Tianlang Zhao1, Jingqiu Mao1, William R. Simpson1, Isabelle De Smedt2, Lei Zhu3, Thomas F. Hanisco4, Glenn M. Wolfe4, Jason M. St. Clair4,5, Gonzalo González Abad6, Caroline R. Nowlan6, Barbara Barletta7, Simone Meinardi7, and Donald R. Blake7 Tianlang Zhao et al.
  • 1University of Alaska Fairbanks, Department of Chemistry and Biochemistry & Geophysical Institute, Fairbanks, AK, United States
  • 2Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
  • 3Southern University of Science and Technology, School of Environmental Science and Engineering, Shenzhen, China
  • 4NASA Goddard Space Flight Center, Atmospheric Chemistry and Dynamics Lab, Greenbelt, MD, United States
  • 5University of Maryland Baltimore County, Baltimore, MD, United States
  • 6Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, United States
  • 7University of California Irvine, Irvine, CA, United States

Abstract. Here we use satellite observations of HCHO vertical column densities (VCD) from the TROPOspheric Monitoring Instrument (TROPOMI), ground-based and aircraft measurements, combined with a nested regional chemical transport model (GEOS-Chem at 0.5° × 0.625° resolution), to understand the variability and sources of summertime HCHO better in Alaska. We first evaluate GEOS-Chem with in-situ airborne measurements during Atmospheric Tomography Mission 1 (ATom-1) aircraft campaign and ground-based measurements from Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS). We show reasonable agreement between observed and modeled HCHO, isoprene and monoterpenes. In particular, HCHO profiles show spatial homogeneity in Alaska, suggesting a minor contribution of biogenic emissions to HCHO VCD. We further examine the TROPOMI HCHO product in Alaska during boreal summer, which is in good agreement with GEOS-Chem model results. We find that HCHO VCDs are dominated by free-tropospheric background in wildfire-free regions. During the summer of 2018, the model suggests that the background HCHO column, resulting from methane oxidation, contributes to 66–80 % of the HCHO VCD, while wildfires contribute to 14 % and biogenic VOC contributes to 5–9 % respectively. For the summer of 2019, which had intense wildfires, the model suggests that wildfires contribute to 40 to 65 %, and the background column accounts for 30 to 50 % of HCHO VCD in June and July. In particular, the model indicates a major contribution of wildfires from direct emissions of HCHO, instead of secondary production of HCHO from oxidation of larger VOCs. We find that the column contributed by biogenic VOC is often small and below the TROPOMI detection limit. The source and variability of HCHO VCD above Alaska during summer is mainly driven by background methane oxidation and wildfires. This work discusses challenges for quantifying HCHO and its precursors in remote pristine regions.

Tianlang Zhao et al.

Status: open (until 22 Nov 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Tianlang Zhao et al.

Tianlang Zhao et al.

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Short summary
Monitoring formaldehyde (HCHO) can help understanding Arctic vegetation change. Here we compared satellite data and model and show that Alaska summertime HCHO is largely dominated by background from methane oxidation during mild wildfire year and is dominated by wildfire (largely from direct emission of fire) during strong fire year. Consequently, it is challenging to use satellite HCHO to study vegetation change in the Arctic region.
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