Preprints
https://doi.org/10.5194/acp-2021-304
https://doi.org/10.5194/acp-2021-304

  29 Apr 2021

29 Apr 2021

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

Measurement report: Observation-based formaldehyde production rates and their relation to OH reactivity around the Arabian Peninsula

Dirk Dienhart1, John N. Crowley1, Efstratios Bourtsoukidis2, Achim Edtbauer1, Philipp G. Eger1, Lisa Ernle1, Hartwig Harder1, Bettina Hottmann1, Monica Martinez1, Uwe Parchatka1, Jean-Daniel Paris2,3, Eva Y. Pfannerstill1, Roland Rohloff1, Jan Schuladen1, Christof Stönner1, Ivan Tadic1, Sebastian Tauer1, Nijing Wang1, Jonathan Williams1,2, Jos Lelieveld1,2, and Horst Fischer1 Dirk Dienhart et al.
  • 1Atmospheric Chemistry Department, Max Planck Institute for Chemistry, Mainz, Germany
  • 2Climate and Atmosphere Research Centre, The Cyprus Institute, Nicosia, Cyprus
  • 3Laboratoire des Sciences du Climat et de l’Environnement, CEA-CNRS-UVSQ, UMR8212, IPSL, Gif-sur-Yvette, France

Abstract. Formaldehyde (HCHO) is the most abundant aldehyde in the troposphere. While its background-mixing ratio is mostly determined by the oxidation of methane, in many environments, especially in the boundary layer, HCHO can have a large variety of precursors, in particular biogenic and anthropogenic volatile organic compounds (VOCs) and their oxidation products. Here we present shipborne observations of HCHO, hydroxyl radical (OH) and OH reactivity (R(OH)), obtained during the Air Quality and Climate Change in the Arabian Basin (AQABA) campaign in summer 2017. The loss rate of HCHO was inferred from its reaction with OH, measured photolysis rates, and dry deposition. In photo-stationary state, the HCHO loss is balanced by production via OH initiated degradation of volatile organic compounds (VOCs), photolysis of oxygenated volatile organic compounds (OVOCs) and the ozonolysis of alkenes. The slope α from a scatter plot of the HCHO production rate versus the product of R(OH) and OH yields the fraction of R(OH) that contributes to HCHO production. Values of α varied between less than 2 % in rather clean air over the Arabian Sea and the southern Red Sea, and up to 32 % over the polluted Arabian Gulf (also known as the Persian Gulf), signifying that polluted areas harbour a larger variety of HCHO precursors. The HCHO yield from R(OH) depends on the absolute and relative contributions of alkanes, alkenes, oxygenated volatile organic compounds (OVOCs) and aromatics to R(OH), while no significant correlation to NOx mixing ratios was found, indicating that HCHO production was not NOx limited.

Dirk Dienhart et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-304', Anonymous Referee #1, 04 May 2021
  • RC2: 'Comment on acp-2021-304', Anonymous Referee #2, 19 May 2021

Dirk Dienhart et al.

Dirk Dienhart et al.

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Short summary
We present the first ship-based in situ measurements of formaldehyde (HCHO), hydroxyl radical (OH) and the OH reactivity around the Arabian Peninsula, which were used to perform a comparison between local HCHO production and the related OH chemistry. This regression analysis revealed the regional HCHO yield alpha, which was elevated in the Arabian Gulf (also known as the Persion Gulf) and highlights the area as a hotspot of photochemical air pollution.
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