H2CO, O3, NH3, HCN, N2O, NO2, NO, and HO2 upper limits of detection in the Venus lower-mesosphere using SOIR on board Venus Express

Abstract

We report on mean upper limit number densities and volume concentrations of H2CO, O3, NH3, HCN, N2O, NO2, NO, and HO2 at the Venus terminator above the cloud layer, computed from the SOIR/Venus Express transmittances measured during hundreds of solar occultations. An unsuccessful attempt to detect these species using the statistical algorithm described in Mahieux et al. (2023a) is reported, and upper limits of detection using the method presented by Trompet et al. (2021) are provided.The mean upper limit volume mixing ratios at an altitude of ∼80 km at the Venus terminator are equal to 43 ± 6 ppb ppt for H2CO, 3.76 ± 5.7 ppm for O3, 0.69 ± 0.28 ppm for NH3, 38.3 ± 7.9 ppm for HCN, 0.14 ± 0.02 ppm for N2O, 0.47 ± 0.32 ppm for NO2, 6.15 ± 1.84 ppm for NO, and 99.5 ± 62.2 ppb for HO2.