Sulfur monoxide dimer chemistry as a possible source of polysulfur in the upper atmosphere of Venus

Joseph P Pinto,Franklin P Mills,Daria Evdokimova,Jiazheng Li,Yuk L Yung,Emmanuel Marcq,Denis Belyaev

doi:10.1038/s41467-020-20451-2

Abstract

The abundance of SO dimers (SO)2 in the upper atmosphere of Venus and their implications for the enigmatic ultraviolet absorption has been investigated in several studies over the past few years. However, the photochemistry of sulfur species in the upper atmosphere of Venus is still not well understood and the identity of the missing ultraviolet absorber(s) remains unknown. Here we update an existing photochemical model of Venus’ upper atmosphere by including the photochemistry of SO dimers. Although the spectral absorption profile of SO dimers fits the unknown absorber, their abundance is found to be too low for them to contribute significantly to the absorption. It is more likely that their photolysis and/or reaction products could contribute more substantively. Reactions of SO dimers are found to be important sources of S2O, and possibly higher order SnO species and polysulfur, Sn. All of these species absorb in the critical ultraviolet region and are expected to be found in both the aerosol and gas phase. indicating that in-situ high resolution aerosol mass spectrometry might be a useful technique for identifying the ultraviolet absorber on Venus.

Highlights

The abundance of sulfur monoxide (SO) dimers (SO)[2] in the upper atmosphere of Venus and their implications for the enigmatic ultraviolet absorption has been investigated in several studies over the past few years
We find that the SO dimers are more likely to be important intermediaries in the formation of more complex S species that could be responsible for the UV absorption
Calculated values are slightly higher than the interquartile range and the mean of Venus Express (VEx) measurements within ±20° latitude; but the data include a large number of spikes, as indicated by the difference between the median and mean observations

Summary

Introduction

The abundance of SO dimers (SO)[2] in the upper atmosphere of Venus and their implications for the enigmatic ultraviolet absorption has been investigated in several studies over the past few years. The photochemistry of sulfur species in the upper atmosphere of Venus is still not well understood and the identity of the missing ultraviolet absorber(s) remains unknown. Ref. 4 suggested that the dimers of sulfur monoxide (SO), (SO)[2], formed from the self-recombination of SO, could contribute substantially to the ultraviolet (UV) absorption found on Venus. Reference 7 found evidence for the formation of the cis-OSSO, trans-OSSO, and C1-S2O2 (cyclic OS (=O)S) dimers, along with several other isomeric forms in much lower abundance, following condensation into a solid matrix with N2 and subsequent irradiation. S2 was formed initially from dissociation of the ethylene episulfoxide used as source of SO; further irradiation at 365 nm depleted the 370 nm band, which they ascribed to destruction of syn-OSSO (cis-OSSO) This depletion occurred simultaneously with an increase in absorption in the 287 nm band of S2. Our model chemistry is applied to interpret data from the European Space Agency’s Venus Express (VEx) mission that was recently processed and analyzed and to provide input to plans for future missions

Methods

Results

Conclusion