Volcanic lightning as a source of reactive radical species in eruption plumes

Abstract

Volcanic lightning has accompanied most recent major explosive eruptions and provides a source of intense thermal energy to drive the formation of reactive radical species. These radicals may have an impact upon the chemical evolution of the eruption plume and its interaction with the atmosphere. Equilibrium modeling shows that within each lightning channel >1% of total N, O, and F and ∼100% of H, Cl, Br, and I may remain as radicals after quenching. The production of radicals generally increases with the quenching temperature of the gas mixture and the dilution of the eruption plume and decreases with increasing atmospheric pressure. Despite the small volume fraction of the plume directly exposed to volcanic lightning (i.e., <10−4), the production of O, H, F, and NO is predicted to be quantitatively significant over the entire plume. Furthermore, these radicals may indirectly lead to the production of Br, Cl, HO2, and O3 through reactions occurring at low temperature. We suggest that volcanic lightning may promote the oxidation of magmatic gases (e.g., HBr and SO2) and result in a wide range of atmospheric impacts, including tropospheric ozone depletion, the production of fixed nitrogen species, and the formation of cloud condensation nuclei.