R.S. Martin

High‐resolution size distributions and emission fluxes of trace elements from Masaya volcano, Nicaragua

Active volcanoes are significant natural sources of trace elements to the atmosphere yet the processes of emission and the impacts of deposition into terrestrial and aquatic environments remain poorly understood. The varying contributions of volatile degassing and magma ejection (i.e., spattering, spraying, extrusion and fragmentation) to the emission of trace elements from Masaya volcano (Nicaragua) are investigated through measurement of high-resolution trace element size distributions using cascade impactors in 2009 and 2010. The volatile elements (e.g., As, Cd, Tl, Cu, Pb, Zn) are strongly correlated across the size distribution and exist in the plume primarily as fine sulfate (0.6 μm diameter) with lesser amounts transported as coarse sulfates (3.5 μm diameter) and coarse chlorides (11 μm diameter). These results suggest that trace elements released from the magma as chlorides react rapidly with H2SO4 in the plume to form sulfates. In contrast, the non-volatile elements (e.g., alkali earth and rare earth) exist primarily as particles in the 1–10 μm range and show no correlation with sulfate, chloride or the volatile elements, suggesting that they are emitted primarily by magma ejection. Trace element emission fluxes from Masaya in 2010 were estimated using filter pack measurements, with emissions of Cu, Zn, As, Tl, Rb and Cd each in excess of 10 kg d−1. These emission fluxes are similar to those measured in 2000–2001 suggesting notable decadal stability in the emission of trace elements from Masaya.

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

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.