Submitted as: development and technical paper
26 May 2023
Submitted as: development and technical paper |  | 26 May 2023
Status: this preprint is currently under review for the journal GMD.

Development of a multiphase chemical mechanism to improve secondary organic aerosol formation in CAABA/MECCA (version 4.5.6-rc.1)

Felix Wieser, Rolf Sander, and Domenico Taraborrelli

Abstract. During the last decades, the impact of multiphase chemistry on secondary organic aerosol (SOA) has been demonstrated to be key in explaining lab experiments and field measurements. However, global atmospheric models still show large biases when simulating atmospheric observations of organic aerosols (OA). Major reasons for the model errors are the use of simplified chemistry schemes of gas-phase oxidation of vapors and parameterization of heterogeneous surface reactions. The photochemical oxidation of anthropogenic and biogenic volatile organic compounds (VOC) leads to products that either produce new SOA or are taken up by existing aqueous media like cloud droplets and deliquescent aerosols. After partitioning, aqueous-phase processing results in polyols, organosulfates, and other products with a high molar mass and oxygen content. In this work, we have introduced the formation of new low-volatility organic compounds (LVOC) into the multiphase chemistry box model CAABA/MECCA. Most notable is the addition of the SOA precursors limonene, long-chain alkanes (up to 8 C atoms), and a semi-explicit chemical mechanism for the formation of LVOC from isoprene oxidation in the gas- and aqueous-phase. Moreover, Henry’s law solubility constants and their temperature dependences have been estimated for the partitioning of organic molecules to the aqueous phase. Box model simulations indicate that the new chemical scheme predicts enhanced formation of LVOC, which are accounted for being precursor species to SOA. As expected, the model predicts that LVOC is positively correlated to temperature but negatively correlated to NOx levels. However, the aqueous-phase processing of isoprene-epoxydiols (IEPOX) displays a more complex dependence on these two key variables. Semi-quantitative comparison with observations from the SOAS campaign suggests that the model may overestimate methylbutane-1,2,3,4-tetrol (MeBuTETROL) from IEPOX. The extensions in CAABA/MECCA will be ported to the 3D-atmospheric model MESSy for a comprehensive evaluation of the impact of aqueous-phase chemistry on SOA at a global scale.

Felix Wieser et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CEC1: 'Comment on gmd-2023-102', Juan Antonio Añel, 19 Jun 2023
    • AC1: 'Reply on CEC1', Felix Wieser, 03 Jul 2023
      • CEC2: 'Reply on AC1', Juan Antonio Añel, 03 Jul 2023
        • AC2: 'Reply on CEC2', Felix Wieser, 04 Jul 2023
  • RC1: 'Comment on gmd-2023-102', Anonymous Referee #1, 27 Jul 2023
    • AC3: 'Reply on RC1', Felix Wieser, 29 Aug 2023
  • RC2: 'Comment on gmd-2023-102', Anonymous Referee #2, 16 Sep 2023

Felix Wieser et al.

Model code and software

CAABA/MECCA - SOA update - archive Felix Wieser

Felix Wieser et al.


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Short summary
The chemistry scheme of the atmospheric box model CAABA/MECCA was expanded to achieve an improved aerosol formation from emitted organic compounds. In addition to newly added reactions, temperature-dependent partitioning of all new species between the gas and aqueous phase was estimated and included in the preexisting scheme. Sensitivity runs show an overestimation of key compounds from isoprene, which can be explained by a lack of aqueous phase degradation reactions and box model limitations.