Composition of the atmosphere of Venus below the clouds

Abstract

[1] The composition of Venus' lower atmosphere, beneath the clouds, has been investigated through both in situ measurements and remote-sensing observations. In 1978 the mass spectrometers and gas chromatographs aboard the Venera 11-12 landers and Pioneer Venus Large probe returned unique information on the abundances of carbon dioxide, nitrogen, noble gases, and other minor species. Radio occultations from the Pioneer and Magellan spacecraft provided measurements of the vertical profile of sulfuric acid vapor. In the 1980s and 1990s the discovery of near-infrared emission from the night side of Venus, through narrow spectral windows in the 0.9-2.5 micron region, opened a new opportunity of probing the lower atmosphere and surface. The abundances of water vapor, halides, carbon monoxide, sulfur dioxide, and carbonyl sulfide were determined, as well as the deuterium-to-hydrogen ratio. The vertical profile of water vapor in the 0-to 45-km-altitude range and the CO and OCS mean vertical gradients in the 30-to 40-km region have been determined from various analyses. In addition, evidence for latitudinal variations of these two species was found from Galileo and recent ground-based nightside observations. Conflicting results have been reported on the SO 2 abundance below 35 km and on the H 2 O profile below 20 km. The whole set of available measurements provides important constraints on the chemistry and dynamics of Venus' lower atmosphere. However, key information is still missing, including the abundances of CO and sulfur compounds near the surface, composition maps at high latitudes, and possible small-scale and temporal variability of trace compounds.

Atmospheric composition, chemistry, and clouds

“…Subsequent observations [Marcq et al, 2005; found a global average cO mixing ratio of 24 ± 2 ppm at 36 km with a vertical gradient of 0.6 ± 0.3 ppm/km and a larger abundance of cO at 20-40° S latitude than at 0-20° S. Marcq et al [2005; also found a global average OcS mixing ratio of 0.55 ± 0.15 ppm at 36 km with a vertical gradient of -0.28 ± 0.1 ppm/km and a smaller abundance of OcS at 20-40° S latitude than at 0-20° S. The newer observations of cO are quantitatively consistent with the earlier results where the observational altitudes agree, although the best fit vertical gradient for cO is a factor of two smaller in the newer results. The smaller gradient in cO mixing ratio from Marcq et al [2005; is more consistent with measurements by instruments on Pioneer Venus and Venera 12 [Bezard and de Bergh, 2007] as shown in Plate 3. The best fit mixing ratio and the vertical gradient for OcS from the newer observations are a factor of eight and five, respectively, smaller than the earlier results.…”

“…recently published measurements of their abundances are summarized in Table 1, Table 3, de Bergh et al [2006], and Bezard and de Bergh [2007]. h 2 S was reported by Pioneer Venus below 20 km [Hoffman et al, 1980], but it was never confirmed by an independent measurement and the reported value is at least an order of magnitude larger than would be expected from thermochemical equilibrium calculations [Fegley et al, 1997b].…”

“…retrieved OcS abundances are the blue asterisks [Marcq et al, 2006] and the red asterisk . The range of h 2 SO 4 vapor abundances retrieved from observations is indicated by the magenta hatched region [Bezard and de Bergh, 2007]. recommended values [Taylor et al, 1997] for cO are the cyan triangles and for OcS are the cyan asterisks.…”

“…recommended values [Taylor et al, 1997] for cO are the cyan triangles and for OcS are the cyan asterisks. composition of Venus' lower atmosphere [Bezard and de Bergh, 2007] and Venus' atmosphere below 100 km altitude [de Bergh et al, 2006].…”

Initial products of Akatsuki 1-μm camera

“…The 1.7-and 2.3-μm windows have mainly been used for quantification of gas abundances such as CO, H 2 O and HCl (e.g., Bezard and de Bergh 2007;Tsang et al 2008;Iwagami et al 2008Iwagami et al , 2010Marcq et al 2008;Barstow et al 2012;Arney et al 2014) below the cloud (not exactly at the surface). They found an average H 2 O abundance of 25-35 ppmv with nearly uniform hemispherical distribution.…”