• Volcanic CO2 measurements via Tunable Diode Laser Spectrometer

The analysis of volcanic gas datasets offer key information to build/validate geological models relevant to a variety of volcanic processes and behaviours, including eruptions. In the last decades, near-infrared room-temperature diode lasers, though in an experimental phase, are finding applications in volcanic gas studies. Here, we report on the application of the GasFinder 2.0, a commercial tunable diode infrared laser-receiver unit, operating in the 1.3-1.7 μm wavelength range, to measuring CO2 concentrations in volcanic gas emissions. At first, our field tests were conducted in three different campaigns at Campi Flegrei volcano (near Pozzuoli, Southern Italy), and, subsequently, also in other degassing systems (Nea Kameni volcano, Greece; Hekla Volcano and Krýsuvík hydrothermal area, Iceland). GasFinder repeatedly measured the path-integrated mixing ratios of CO2 along cross-sections of the atmospheric plumes of the main fumarolic fields in the investigated areas. At each site, we used an ad-hoc designed measurement geometry, using the GasFinder unit and several retro-reflector mirrors, to scan the plumes from different angles and distances. From post-processing of the data, by using a tomographic Matlab routine, we resolved, for each of the manifestations, the contour maps of CO2 mixing ratios in their atmospheric plumes. From their integration (and after multiplication by the plumes’ transport speeds), we evaluated the CO2 fluxes. The so-calculated fluxes ranged from ∼5.7 (Krýsuvík) to ∼490 (Campi Flegrei) tons/day, supporting a significant contribution of fumaroles to the global CO2 budget.