Impact of uncertainties in CO2, HCl, and H2O cross sections on simulations of Venus mesospheric chemistry

The atmospheres of Venus and Mars are primarily CO₂ which photolyses at wavelengths ∼<200 nm to CO and O. Direct recombination via CO+O+M → CO₂+M is very slow so the rate of production of CO₂ to balance its loss via photolysis is controlled by the abundances of trace radicals that catalyse production of CO₂ (e.g., Yung and DeMore, Icarus 51, 199, 1982). These trace radicals, such as OH and ClCO, are derived directly or indirectly from photolysis of H₂O and HCl. Previous large uncertainties in the rates of some of the key reactions that comprise these catalytic processes have been significantly reduced (eg., Mills and Allen, PSS 55, 2007; Marcq et al., Space Sci Rev 214, 10, 2018; Chao et al., AGU Fall Mtg Abst P11B-2985, 2024). In addition, several studies in the past 15 years have refined our understanding of the UV cross sections of CO₂ and H₂O (e.g., Archer et al., JQSRT 117, 88, 2013; Schmidt et al., PNAS 110, 17691, 2013; Ranjan et al., Astrobio 17, 687, 2017; Venot et al., A & A 609, A34, 2018; Ranjan et al., Ap J 896, 148, 2020). Consequently, it is appropriate to examine again the impact on mesospheric simulations of the remaining uncertainties in the photolysis and extinction cross sections for CO₂, HCl, and H₂O.