Atmospheric Chemistry and Physics (Jan 2012)

Acid-yield measurements of the gas-phase ozonolysis of ethene as a function of humidity using Chemical Ionisation Mass Spectrometry (CIMS)

  • K. E. Leather,
  • M. R. McGillen,
  • M. C. Cooke,
  • S. R. Utembe,
  • A. T. Archibald,
  • M. E. Jenkin,
  • R. G. Derwent,
  • D. E. Shallcross,
  • C. J. Percival

DOI
https://doi.org/10.5194/acp-12-469-2012
Journal volume & issue
Vol. 12, no. 1
pp. 469 – 479

Abstract

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Gas-phase ethene ozonolysis experiments were conducted at room temperature to determine formic acid yields as a function of relative humidity (RH) using the integrated EXTreme RAnge chamber-Chemical Ionisation Mass Spectrometry technique, employing a CH<sub>3</sub>I ionisation scheme. RHs studied were <1, 11, 21, 27, 30 % and formic acid yields of (0.07±0.01) and (0.41±0.07) were determined at <1 % RH and 30 % RH respectively, showing a strong water dependence. It has been possible to estimate the ratio of the rate coefficient for the reaction of the Criegee biradical, CH<sub>2</sub>OO with water compared with decomposition. This analysis suggests that the rate of reaction with water ranges between 1×10<sup>−12</sup>–1×10<sup>−15</sup> cm<sup>3</sup> molecule<sup>−1</sup> s<sup>−1</sup> and will therefore dominate its loss with respect to bimolecular processes in the atmosphere. Global model integrations suggest that this reaction between CH<sub>2</sub>OO and water may dominate the production of HC(O)OH in the atmosphere.