24 Aug 2023
 | 24 Aug 2023
Status: this preprint is open for discussion.

Impacts of updated reaction kinetics on the global GEOS-Chem simulation of atmospheric chemistry

Kelvin Bates, Mathew Evans, Barron Henderson, and Daniel Jacob

Abstract. We updated the chemical mechanism of the GEOS-Chem global 3-D model of atmospheric chemistry to include new recommendations from the JPL chemical kinetics Data Evaluation 19-5 and from IUPAC, and to balance carbon and nitrogen. We examined the impact of these updates on the GEOS-Chem version 14.0.1 simulation. Notable changes include: eleven updates to reactions of reactive nitrogen species, resulting in a 7 % net increase in the stratospheric NOx (NO + NO2) burden; an updated CO + OH rate formula leading to a 2.7 % reduction in total tropospheric CO; adjustments to the rate coefficient and branching ratios of propane + OH, leading to reduced tropospheric propane (-17 %) and increased acetone (+3.5 %) burdens; a 41 % increase in the tropospheric burden of peroxyacetic acid due to a decrease in the rate coefficient for its reaction with OH, further contributing to reductions in peroxyacetyl nitrate (PAN; -3.8 %) and acetic acid (-3.4 %); and a number of minor adjustments to halogen radical cycling. Changes to the global tropospheric burdens of other species include -0.7 % for ozone, +0.3 % for OH (-0.4 % for methane lifetime against oxidation by tropospheric OH), +0.8 % for formaldehyde, and -1.7 % for NOx. The updated mechanism reflects the current state of the science including complex chemical dependencies of key atmospheric species on temperature, pressure, and concentrations of other compounds. The improved conservation of carbon and nitrogen will facilitate future studies of their overall atmospheric budgets.

Kelvin Bates et al.

Status: open (until 01 Nov 2023)

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Kelvin Bates et al.


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Short summary
Accurate representation of rates and products of chemical reactions in atmospheric models is crucial for simulating concentrations of pollutants and climate forcers. We update the widely used GEOS-Chem atmospheric chemistry model with reaction parameters from recent compilations of experimental data and demonstrate the implications for key atmospheric chemical species. The updates decrease tropospheric CO mixing ratios and increase stratospheric nitrogen oxide mixing ratios, among other changes.