An atmospheric study using the SPICAV-UV instrument recently came to my attention where researchers (Montmessin, et al. 2011) used the data archive to identify (for the first time) a layer of ozone in the upper atmosphere of Venus (previously, ozone had only been identified in the atmospheres of Mars and Earth).
The team analyzed the complete SPICAV dataset, and determined that UV absorption by O3 was observed during a stellar occultation run on the night side of Venus during orbit #348. They confirmed ozone detection in 28 additional orbits, and isolated the ozone to a discrete layer no more than 10 km thick near a mean altitude of 100km.
The observed concentrations of 107 – 108 molecules per cubic centimeter are consistent with expected values if the upper atmosphere were dominated by the same chlorine-catalyzed destruction cycles present in Earth’s stratosphere.
Even if the same mechanisms are at work in he Venusian atmosphere, the authors state that the observed ozone layer seems too tenuous to filter out UV radiation and provide protection to organisms that could have existed on Venus.