Storms on Venus: Lightning-induced chemistry and predicted products

Observations by many spacecraft that have visited Venus over the last 40 years appear to confirm the presence of lightning storms in the Venus atmosphere. Recent observations by Venus Express indicate that lightning frequency and power is similar to that on Earth. While storms are occurring, energy deposition by lightning into Venus atmospheric constituents will immediately dissociate molecules into atoms, ions and plasma from the high temperatures in the lightning column (> 30,000 K) and the associated shock waves and heating, after which these atom and ion fragments of C,O,S,N,H-containing molecules will recombine during cooldown to form new sets of molecules. Spark and discharge experiments in the literature suggest that lightning effects on the main atmospheric molecules CO2, N-2, SO2, H2SO4 and H2O will yield carbon oxides and suboxides (COm, CnOm), sulfur oxides (SnO, SnOm), oxygen (O-2), elemental sulfur (S-n), nitrogen oxides (NO, N2O, NO2), sulfuric acid clusters (HnSmOx-. aH(n)S(m)O(x) e.g. HSO4-.mH(2)SO(4)), polysulfur oxides, carbon soot and other exotic species. While the amounts generated in lightning storms would be much less than that derived from photochemistry, during storms these species can build up in a small area and so their local concentrations may increase significantly. For a storm of 100 x 100 km, the increase could be similar to 5 orders of magnitude if they remain in the storm region for a period before becoming well-mixed. Some of these molecular species may be detectable by instruments onboard Venus Express while they are concentrated in the storm regions. We explore the diversity of new products likely created in lightning storms on Venus. (C) 2014 Elsevier Ltd. All rights reserved.