Volcanic ash in the air we breathe

Earth is no stranger to volcanism. Since proto-Earth and crustal formation, volcanoes have provided pathways for degassing and cooling of our planet’s interior. Volcanism played an important role in the formation of the early atmosphere, oceans and continents, and was likely a necessary component for the development of life. Throughout our species brief history, innumerable volcanoes have erupted, and many are the same volcanoes still active today. Volcanic eruptions have triggered the demise of ancient civilizations, and persist as an immense force that dwarfs modern technology. They are uncontrollable, unpredictable, and catastrophic to populations and modern cities built along their flanks. Eruptions cause adverse effects ranging from disruption of air travel, disturbance in local ecosystems, to profound changes in global climate. On average, 50 volcanoes erupt each year [1], thus reminding us that our planet is alive and constantly changing. Globally, nearly 1 in 10 persons live within 100 km of a historically active volcano [2]. Communities that live through a volcanic eruption can experience havoc, fear, loss of home and livelihood and suffer increased morbidity and mortality. Ash fall is a hazardous product of volcanic eruption that can affect large populations and create widespread economic chaos. Volcanic ash particles are fine-sized (<2 mm), pyroclastic fragments that form during eruption as gases exsolve from the magma, develop large bubbles that burst causing fragmentation, and are explosively propelled upward. Subsequent explosions violently shatter the surrounding vent rock and hurl it as fragments into the air. Once airborne, plumes of ash are subject to meteorological effects such as dispersion with wind and removal by rain. The severity of an eruption is a function of the volcanic explosivity index (VEI, range 0 to 8) [3]. Eruptions with low VEI’s 0–2 build volcanoes that passively degas and erupt lava effusively; whereas, high VEI’s are characteristic of explosive volcanism. The higher the VEI the greater the volume of ejecta, the greater degree of fragmentation creating more toxic fine ash, the higher the