TITLE: Non-LTE infrared emissions of CO2 in the atmosphere of Venus AUTHORS: Roldan, C., Lopez-Valverde, M. A., M. Lopez-Puertas and D. P. Edwards REFERENCE: Icarus, in press, 2000 ABSTRACT: A non-local thermodynamic equilibrium (non-LTE) radiative transfer model previously developed for the Martian atmosphere has been applied to the Venusian atmosphere to study the CO2 infrared emissions and its radiative equilibrium temperature profile. The model computes the populations of more than 60 vibrational levels of the four major isotopes of CO2, and the cooling and heating rates by more than 90 radiative transitions. The departure from LTE of all the CO2(0,nu2,0) levels is found to occur around 115 km (or 0.2 mu) during both night and daytime conditions, while it takes place around 105 and 90 km for the (0,0,1) level at night and day, respectively. The daytime populations of the (nu1,nu2,1) and high combination levels are very large. The cooling rate due to the 15-mu bands peaks around 125 km (10 nb) and amounts to 130 K/day for the reference nighttime model, being very dependent on the thermal structure. The 15-mu fundamental bands (FB) of the minor isotopes and the first hot bands of the major isotope produce much larger cooling than the FB of the main isotope between 110 and 125 km. The solar heating rate presents a double peak maximum between 120 and 135 km, with a very strong component from the 2.7-mu FB around 130 km. This component is much more important than its Martian counterpart, due to the larger relative abundance of atomic oxygen in the thermosphere of Venus. Radiative relaxation times have been computed with focus in the 80-130 km region. The relaxation at 15-mu varies from more than an Earth's week around 80 km to a minimum of 6 minutes around 130 km during daytime. It increases above this altitude, in clear contrast to LTE calculations. Sensitivity studies to evaluate the effects of the current uncertainties in the major rate coefficients, and comparisons with previous non-LTE models and data, as well as with similar situations in the atmosphere of Mars are also presented.