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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 16 Jan 2019

Research article | 16 Jan 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Development of a protocol for the auto-generation of explicit aqueous-phase oxidation schemes of organic compounds

Peter Bräuer1,a, Camille Mouchel-Vallon2,b, Andreas Tilgner1, Anke Mutzel1, Olaf Böge1, Maria Rodigast1,c, Laurent Poulain1, Dominik van Pinxteren1, Ralf Wolke3, Bernard Aumont2, and Hartmut Herrmann1 Peter Bräuer et al.
  • 1Atmospheric Chemistry Department (ACD), Leibniz Institute for Tropospheric Research (TROPOS), Permoserstr. 15, 04318 Leipzig, Germany
  • 2Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR CNRS/INSU 7583, Université Paris Est Créteil et Université Paris Diderot, Institut Pierre Simon Laplace, 94010, Créteil, France
  • 3Modelling of Atmospheric Processes Department (MAPD), Leibniz Institute for Tropospheric Research (TROPOS), Permoserstr. 15, 04318 Leipzig, Germany
  • anow at: Wolfson Atmospheric Chemistry Laboratories and National Centre for Atmospheric Science, University of York, York, YO10 5DD, UK
  • bnow at: National Center for Atmospheric Research, Boulder, Colorado, USA
  • cnow at: Indulor Chemie GmbH & Co. KG Produktionsgesellschaft Bitterfeld, 0 6749 Bitterfeld-Wolfen, Germany

Abstract. This paper presents a new CAPRAM/GECKO-A protocol for mechanism auto-generation of aqueous-phase organic mechanisms. For the development, kinetic data in the literature was reviewed and a database with 464 aqueous-phase reactions of the hydroxyl radical with organic compounds and 130 nitrate radical reactions with organic compounds has been compiled and evaluated. Five different methods to predict aqueous-phase rate constants have been evaluated with the help of the kinetics database: gas-aqueous correlations, homologous series of various compound classes, radical reactivity comparisons, Evans-Polanyi-type correlations, and structure-activity relationships (SARs). The quality of these prediction methods was tested as well as their suitability for automated mechanism construction. Based on this evaluation, SARs form the basis of the new CAPRAM/GECKO-A protocol. Evans-Polanyi-type correlations have been advanced to consider all available H-atoms in a molecule besides the H-atoms with only the weakest bond dissociation enthalpy (BDE). The improved Evans-Polanyi-type correlations are used to predict rate constants for aqueous-phase NO3 + organic compounds reactions. Extensive tests have been performed on essential parameters and highly uncertain parameters with limited experimental data. These sensitivity studies led to further improvements in the new CAPRAM/GECKO-A protocol, but also showed current limitations. Biggest uncertainties were observed in uptake processes and the estimation of Henry's Law coefficients as well as radical chemistry, in particular the degradation of alkoxy radicals. Previous estimation methods showed several deficits, which impacted particle growth. For further evaluation, a mesitylene oxidation experiment has been performed at the aerosol chamber LEAK at high relative humidity conditions and compared to a multiphase mechanism using the MCMv3.2 in the gas phase and a methylglyoxal oxidation scheme of about 600 reactions generated with the new CAPRAM/GECKO-A protocol in the aqueous phase. While it was difficult to evaluate single particle constituents due to concentrations close to the detection limits of the instruments applied, the model studies showed the importance of aqueous-phase chemistry in respect to SOA formation and particle growth. The new protocol forms the basis for further CAPRAM mechanism development towards a new version 4.0. Moreover, it can be used as supplementary tool for aerosol chambers to design and analyse experiments of chemical complexity and help understanding them on a molecular level.

Peter Bräuer et al.
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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Peter Bräuer et al.
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Short summary
The article presents a new protocol for computer-assisted automated aqueous-phase chemistry mechanism generation, which has been validated against chamber experiments. Together with a large kinetics database and improved prediction methods for kinetic data, the novel protocol provides an unmatched tool, for detailed studies of tropospheric aqueous-phase chemistry in complex model studies and for the design and analysis of chamber experiments.
The article presents a new protocol for computer-assisted automated aqueous-phase chemistry...