On the impact of using new CO2-collisional parameters for H2O retrievals in CO2-rich atmospheres

For Venus, whose atmosphere is dominated by CO 2 , the choice of appropriate collisional parameters is critical for accurate water vapor retrievals. In this study, we investigate the impact of using non-representative collisional parameters by comparing simulations based on newly derived H 2 O CO 2 collisional parameters with retrievals performed using air-collisional parameters. Systematic differences are observed. In the deep atmosphere, where high pressures and temperatures enhance collisional effects, retrievals may fail to find a significant value when inappropriate collisional parameters are used. Above the cloud tops, where collisional effects are weaker, retrievals can reproduce the spectra more closely but still lead to a significant overestimation of H 2 O. Applying an empirical scaling factor to air-collisional parameters reduces part of this discrepancy at low pressure but remains insufficient under denser atmospheric conditions. These results highlight the importance of including collisional parameters adapted to CO 2 -rich environments in spectroscopic databases. This would provide easier access to appropriate data and facilitate intercomparisons between studies using consistent spectroscopic inputs.