A review of selected issues concerning the chemistry in Venus' middle atmosphere

Even after decades of study using advanced observing instruments and sophisticated numerical models, a number of significant questions remain unanswered concerning the composition and chemistry of Venus' atmosphere. The primary chemical cycles and the interactions among sulfur and chlorine radicals in Venus' middle atmosphere are reviewed to assess the current status of our knowledge, identify unresolved questions, and assess how the Venus Express mission may contribute to their resolution.