Latitudinal variations of CO and OCS in the lower atmosphere of Venus from near-infrared nightside spectro-imaging

Atmospheric composition, chemistry, and clouds

“…The gradients for cO and OcS in the newer results, however, are still approximately equal in magnitude and opposite in sign. Further, the spatial anticorrelation between cO and OcS mixing ratios observed by Marcq et al [2005;6] is qualitatively consistent with the anticorrelation in the vertical gradients of cO and OcS seen by Pollack et al [1993] and Marcq et al [2005;6] and suggests conversion between cO and OcS, possibly due to surface buffering [Fegley and Treiman, 1992], thermochemical equilibrium chemistry [Krasnopolsky and Parshev, 1979], or kinetic conversion of OcS to cO 2 and cO [Krasnopolsky and Pollack, 1994].…”

“…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.…”

“…The relationships among the reactions at any specific altitude are more complicated, as shown in Plate 3 along with the observational data from Pollack et al [1993], Marcq et al [2005;, and other sources. This scheme, which has been updated and extended in a recently accepted manuscript [Krasnopolsky, 2007], is the only kinetic model proposed for the lower atmosphere of Venus that is consistent with SO 2 as the dominant sulfur species.…”

Hemispherical distribution of CO above the Venus’ clouds by ground-based 2.3μm spectroscopy

“…In contrast to that above the clouds, the latitudinal distributions of CO found below the clouds represent larger mixing ratios (around 30 ppm) at high latitudes than at low latitudes (around 25 ppm) (Collard et al, 1993;Marcq et al, 2005Marcq et al, , 2008Tsang et al, 2008Tsang et al, , 2009. It is usually explained by downward transport of CO-rich air in the polar region from the producing region above 70 km (Collard et al, 1993;Taylor, 1995).…”

“…There have been reported several measurements of CO abundance below the clouds (Collard et al, 1993;Marcq et al, 2005Marcq et al, , 2008Tsang et al, 2008Tsang et al, , 2009) based on the 2.3 lm nightside spectroscopy, and a pole-ward increase in the CO abundance has been found. To explain such a distribution, downward transport of COrich air in the polar region from the producing region located above the clouds (Collard et al, 1993;Taylor, 1995) and chemical destruction of CO during equator-ward meridional circulation such as discussed by Imamura and Hashimoto (1998) have been proposed.…”