Preprints
https://doi.org/10.5194/acp-2021-375
https://doi.org/10.5194/acp-2021-375

  17 May 2021

17 May 2021

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

Opinion: The Germicidal Effect of Ambient Air (Open Air Factor) Revisited

R. Anthony Cox1, Markus Ammann2, John N. Crowley3, Paul T. Griffiths4, Hartmut Herrmann5, Erik H. Hoffmann5, Michael E. Jenkin6, V. Faye McNeill7, Abdelwahid Mellouki8, Christopher J. Penkett9, Andreas Tilgner5, and Timothy J. Wallington10 R. Anthony Cox et al.
  • 1Centre for Atmospheric Science, Department of Chemistry, University of Cambridge, Cambridge CB2 1EP, UK
  • 2Laboratory of Environmental Chemistry, Paul Scherrer Institut, 5232 Villigen, Switzerland
  • 3Division of Atmospheric Chemistry, Max Planck Institute for Chemistry, 55128 Mainz, Germany
  • 4National Centre for Atmospheric Science, Department of Chemistry, Cambridge University, Cambridge, CB21EW, UK
  • 5Atmospheric Chemistry Department (ACD), Leibniz Institute for Tropospheric Research (TROPOS), 04318 Leipzig, Germany
  • 6Atmospheric Chemistry Services, Okehampton, Devon, EX20 4QB, UK
  • 7Department of Chemical Engineering, Columbia University, New York, NY 10027, USA
  • 8ICARE-CNRS, 45071 Orléans CEDEX 2, France
  • 9NIHR BioResource for Translational Research, University of Cambridge, Hills Road, Cambridge CB2 0QQ, UK
  • 10Ford Motor Company, Research and Advanced Engineering, Dearborn, MI 48121-2053, USA

Abstract. The term Open-Air Factor (OAF) was coined following microbiological research in the 1960s and 1970s which established that rural air had powerful germicidal properties and attributed this to Criegee intermediates formed in the reaction of ozone with alkenes. We have re-evaluated those early experiments applying the current state of knowledge of ozone-alkene reactions. Contrary to previous speculation, neither Criegee intermediates, nor the HO radicals formed in their decomposition, are directly responsible for the germicidal activity attributed to the OAF. We identify other potential candidates, which are formed in ozone-alkene reactions and have known (and likely) germicidal properties, but the compounds responsible for the OAF remain a mystery. There has been very little research into the OAF since the 1970s and this effect seems to have been largely forgotten. In this letter we remind the community of the germicidal open-air factor. Given the current global pandemic spread by an airborne pathogen, understanding the natural germicidal effects of ambient air, solving the mystery of the open-air factor, and determining how this effect can be used to improve human welfare should be a high priority for the atmospheric science community.

R. Anthony Cox et al.

Status: open (until 12 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-375', Anonymous Referee #1, 31 May 2021 reply
  • RC2: 'Comment on acp-2021-375', Anonymous Referee #2, 17 Jun 2021 reply

R. Anthony Cox et al.

R. Anthony Cox et al.

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Short summary
The term Open Air Factor was coined in the 1960s establishing that rural air had powerful germicidal properties possibly resulting from immediate products of the reaction of ozone with alkenes, unsaturated compounds ubiquitously present in natural and polluted environments. We have re-evaluated those early experiments applying the recently substantially improved of knowledge and put them into the context of the lifetime of aerosol borne pathogens that are so important in the Covid-19 pandemic.
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