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Trace Gas Abundances Below the Clouds of Venus

Presentation #502.09 in the session Venus I (Oral Presentation)

Published onOct 23, 2023
Trace Gas Abundances Below the Clouds of Venus

Scientific interest in trace gas species in Venus’s atmosphere has increased recently as it has become clear that photochemical models cannot explain their distributions. The trace species SO2, CO, and OCS are key constituents of Venus’s atmosphere, affecting the sulfur cycle and cloud production e.g. (Yung et al., 2009). SO2 has been shown to vary on timescales of hours to decades (Esposito, 1984; Marcq et al., 2021). In order to place significant constraints on the abundance and variability of trace gases in Venus’s atmosphere prior to the DaVinci probe’s descent, we obtained K, H, and J-band spectra of Venus’ night side using the ISHELL high resolution spectrometer on NASA’s IRTF telescope. Clear, dry weather on Maunakea enabled the acquisition of about 100 spectra of ~60% of Venus’s night side on 20 consecutive evenings, from June 11 to June 30, 2023. We used the SMART radiative transfer package (Meadows and Crisp, 1996) to calculate synthetic spectra for a variety of gas abundances and emission angles as part of a forward-modeling scheme to fit trace gases and cloud properties to observed spectra. With a spectral resolution of R=20,000, we were able to map the abundances of CO, H2O, OCS, and SO2 at mid-equatorial latitudes and show how the abundances of these gases changed from day to day and with latitude on Venus. The correlation of SO2 and H2O abundance with cloud opacity is of particular interest since H2SO4/H2O cloud aerosols are the product of sulfur cycle chemistry below the clouds. At the same time, CO is consumed below the clouds by thermochemical gas phase reactions. Our near-IR observations of Venus’ night side will shed light on the competing roles that atmospheric dynamics and chemical reactions have in the formation of Venus’ clouds and in explaining the cloud patterns that we see. Esposito, L. W., 1984. Sulfur dioxide: Episodic injection shows evidence for active Venus volcanism. Science. 223, 1072-1074. Marcq, E., Amine, I., Duquesnoy, M., Bézard, B., 2021. Evidence for SO2 latitudinal variations below the clouds of Venus. Astronomy & Astrophysics. 648, L8. Meadows, V. S., Crisp, D., 1996. Ground-based near-infrared observations of the Venus night side: The thermal structure and water abundance near the surface. Journal of Geophysical Research. 101, 4595-4622. Yung, Y. L., Liang, M. C., Jiang, X., Shia, R. L., Lee, C., Bézard, B., Marcq, E., 2009. Evidence for carbonyl sulfide (OCS) conversion to CO in the lower atmosphere of Venus. Journal of Geophysical Research (Planets). 114.

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