. New ground-based lidar enables volcanic CO2 flux measurements

There have been substantial advances in the ability to monitor the activity of hazardous volcanoesin recent decades. However, obtaining early warning of eruptions remains challenging, because thepatterns and consequences of volcanic unrests are both complex and nonlinear. Measuring volcanicgases has long been a key aspect of volcano monitoring since these mobile fluids should reach thesurface long before the magma. There has been considerable progress in methods for remote andin-situ gas sensing, but measuring the flux of volcanic CO2—the most reliable gas precursor to aneruption—has remained a challenge. Here we report on the first direct quantitative measurementsof the volcanic CO2 flux using a newly designed differential absorption lidar (DIAL), which wereperformed at the restless Campi Flegrei volcano. We show that DIAL makes it possible to remotelyobtain volcanic CO2 flux time series with a high temporal resolution (tens of minutes) and accuracy(<30%). The ability of this lidar to remotely sense volcanic CO2 represents a major step forwardin volcano monitoring, and will contribute improved volcanic CO2 flux inventories. Our results alsodemonstrate the unusually strong degassing behavior of Campi Flegrei fumaroles in the currentongoing state of unrest.