Volcanic CO2 emissions play a key role in the geological carbon cycle, and monitoring of volcanic CO2 fluxes helps to forecast eruptions. The quantification of CO2 fluxes is challenging due to rapid dilution of magmatic CO2 in CO2-rich ambient air and the diffuse nature of many emissions, leading to large uncertainties in the global magmatic CO2 flux inventory. Here, we report measurements using a new DIAL laser remote sensing system for volcanic CO2 (CO2DIAL). Two sites in the volcanic zone of Campi Flegrei (Italy) were scanned, yielding CO2 path-amount profiles used to compute fluxes. Our results reveal a relatively high CO2 flux from Campi Flegrei, consistent with an increasing trend. Unlike previous methods, the CO2DIAL is able to measure integrated CO2 path-amounts at distances up to 2000 m using virtually any solid surface as a reflector, whilst also being highly portable. This opens a new frontier in quantification of geological and anthropogenic CO2 fluxes.

Abstract. Campi Flegrei caldera is located in the metropolitan nucleus of Naples (Italy), and has been undergoing different stages of unrest since 1950, evidenced by episodes of significant ground uplift followed by minor subsidence, increasing and fluctuating emission strengths of water vapor and CO2 from fumaroles, and periodic seismic crises. We deployed a scanning laser remote sensing spectrometer (LARSS) that measures path integrated CO2 concentrations at the Pisciarelli area in May 2017. The resulting mean CO2 flux is 578 ± 246 t d−1. Our data suggest a significant increase in CO2 flux at this site since 2015. Together with recent geophysical observations, this suggests a greater contribution of the magmatic source to the degassing and/or an increase of permeability at shallow levels. Thanks to the integrated path soundings, LARSS proves to give representative measurements from large regions containing different CO2 sources, including fumaroles, low-T vents, and degassing soils, helping to constrain the contribution of deep gases and their migration mechanisms towards the surface.

Abstract. Solfatara is part of the active volcanic zone of Campi Flegrei (Italy), a densely populated urban area where ground uplift and increasing ground temperature are observed, connected with rising rates of CO2 emission. A major pathway of CO2 release at Campi Flegrei is diffuse soil degassing, and therefore quantifying diffuse CO2 emission rates is of vital interest. Conventional in-situ probing of soil gas emissions with accumulation chambers is accurate over a small footprint but requires significant time and effort to cover large areas. An alternative approach is differential absorption LIDAR, which allows for a fast and spatially integrated measurement. Here, a portable hard-target differential absorption LIDAR has been used to acquire horizontal 1-D profiles of CO2 concentration at the Solfatara crater. To capture the non-isotropic nature of the diffuse degassing activity, a 2-D tomographic map of the CO2 distribution has been inverted from the 1-D profiles. The acquisition was performed from a single half space only, which increases the non-linearity of the inverse problem. Nonetheless, the result is in agreement with independent measurements and furthermore confirms an area of anomalous CO2 degassing along the eastern edge as well as the center of the Solfatara crater. The method has important implications for measurements of degassing features that can only be accessed from limited angles, such as airborne sensing of volcanic plumes. CO2 fluxes retrieved from the 2-D map are comparable, but modestly higher than emission rates from previous studies, perhaps reflecting a more integrated measurement.