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Chemistry of Venus’ Atmosphere Vladimir A. Krasnopolsky

Chemistry of Venus’ Atmosphere Vladimir A. Krasnopolsky. Photochemical model for 47-112 km Chemical kinetic model for the lower atmosphere (0-47 km) Nighttime atmosphere and night airglow. Modeling of H 2 SO 4 vapor and its photolysis rate: Initial data ( Icarus 215, 197, 2011).

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Chemistry of Venus’ Atmosphere Vladimir A. Krasnopolsky

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  1. Chemistry of Venus’ AtmosphereVladimir A. Krasnopolsky • Photochemical model for 47-112 km • Chemical kinetic model for the lower atmosphere (0-47 km) • Nighttime atmosphere and night airglow

  2. Modeling of H2SO4 vapor and its photolysis rate: Initial data (Icarus 215, 197, 2011)

  3. Calculated H2SO4 is 10-13 at 96 km, smaller than adopted by Zhang et al. (2012) by a factor of 2x106. This source of SOX may be neglected.

  4. Photochemical model at 47-112 km: Main features (Icarus 218, 230, 2012) • Improved numerical accuracy: step = 0.5 km instead of 2 km that is comparable with H ≈ 5 km • NUV absorption is based on the Venera 14 data • H2O is calculated and not adopted in the model • Standard ClCO cycle, not scaled by a factor of ≈40 • NO and OCS chemistries • Column rates are given for all reactions

  5. CO: Model and observations

  6. Main feature of Venus’ photochemistry is formation of sulfuric acid in a narrow layer at 66 km that greatly reduces SO2 and H2O above the layer. Minor variations of eddy diffusion and/or SO2/H2O can greatly change the delivery of SO2 and H2O through this bottleneck and chemistry above the clouds

  7. SO2, OCS, SO, and Sa

  8. H2O: variations of SO2 = ±5% at 47 km

  9. Oxygen species • O2 column is similar to that in MA07 and both exceed the observed upper limit by a factor of 10 • Ozone is similar to that observed by SPICAV at night (Montmessin et al. 2011)

  10. Conclusions to Photochemistry at 47-112 km • Formation of sulfuric acid in a narrow layer near 66 km is a key feature that greatly reduces SO2 and H2O above the clouds • Delivery of SO2 and H2O through this bottleneck is controlled by eddy diffusion and SO2/H2O ratio. Minor variations of atmospheric dynamics in the cloud layer induce strong variations in chemistry above the clouds • H2SO4, CO, and SO2Cl2 are photochemical products delivered into the lower atmosphere and processed by thermochemistry there. • While the overall agreement with the observational data is very good, some aspects deserve discussion: • O2 column significantly exceeds the observed upper limit, and I do not have ideas how to solve the problem; • The model does not provide a source of SOX above 90 km. The interpretation of the SOX observations may be not unique; • SO2 = 9.7 ppm at 47 km disagrees with SO2 = 130 ppm at 35 km.

  11. S3 and S4 Abundances and Improved Chemical Kinetic Model for the Lower Atmosphere of Venus (Icarus, submitted) • Improved retrieval of S3 and S4 from analysis of Venera 11 by Maiorov et al. (2005) • S4 cycle by Yung et al. (2009) • Reduction of the H2SO4 and CO fluxes from the middle atmosphere by a factor of 4 relative to Kr07 • OCS is completely calculated by the model (its abundance at the surface was a free parameter in Kr07) • Some minor improvements

  12. Absorption spectra of S3 and S4

  13. Χ2-fitting of the true absorption spectra (Maiorov et al. 2005) by sums of S3 and S4: S3 = 11±3 ppt at 3-10 km and 18±3 ppt at 10-19 kmS4 = 4±4 ppt at 3-10 km and 6±2 ppt at 10-19 km

  14. Main reactions in KP94 and Kr07: SO3 + OCS → CO2 + (SO)2 (SO)2 + OCS → CO + SO2 + S2 Net SO3 + 2 OCS → CO2 + CO + SO2 + S2 • S4 cycle (Yung et al. 2009): S2 + S2 + M → S4 + M S4 + hv → S3 + S S3 + hv → S2 + S 2(S + OCS → CO + S2) Net 2 OCS → 2 CO + S2

  15. Model: 89 reactions of 28 species, some improvements to Kr07 • S3 + hν → S2 + S I=0.017*10-3 *(4.4+1.36h+0.063h2) • S4 + hν → S2 + S2 I = 0.01*(1.4+0.535h–0.0013h2) • S4 + hv → S + S3 I=1*10-5*(8.5+2.4h+0.15h2)

  16. Models with (solid) and without (thin) S4 cycle

  17. Basic species in the model

  18. Model for nighttime atmosphere and nightglow at 80-130 km (Icarus 207, 17, 2010) • Involves 61 reactions of 24 species • Odd hydrogen and chlorine chemistries • Fluxes of O, N, and H at 130 km as input parameters • Requires 45% of the dayside oxygen production above 80 km to fit the observed mean O2 1.27 μm emission of 0.5 MR • Comparison with GCMs by Bougher et al. (1990) and Brecht et al. (2011)

  19. Calculated vertical profiles

  20. Nightglow profiles4πIO2 = 0.158(ΦO/1012)1.14 MR4πINO = 224(ΦN/109)(ΦO/1012)0.38 R4πIOH (1-0) = 1.2(ΦO/1012)1.46 X0.46-0.048 ln XkR, X=ΦH/108

  21. Problems • SPICAV stellar occultations result O3 ≈ 5x107 cm-3 at 90-100 km that agrees with the global-mean model but much smaller than that in the nighttime model • Is the SPICAV low ozone compatible with the observed OH nightglow that is excited mostly by H + O3 → OH* + O2 ?

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