###### Abstract  
Volcanologists have demonstrated that carbon dioxide (CO\({}_{2}\)) fluxes are precursors of volcanic eruptions. Controlling volcanic gases and, in particular, the CO\({}_{2}\) flux, is technically challenging, but we can retrieve useful information from magmatic/geological process studies for the mitigation of volcanic hazards including air traffic security. Existing techniques used to probe volcanic gas fluxes have severe limitations such as the requirement of near-vent in situ measurements, which is unsafe for operators and deleterious for equipment. In order to overcome these limitations, a novel range-resolved DIAL-Lidar (Differential Absorption Light Detection and Ranging) has been developed as part of the ERC (European Research Council) Project \"BRIDGE\", for sensitive, remote, and safe real-time CO\({}_{2}\) observations. Here, we report on data collection, processing techniques, and the most significant findings of the experimental campaigns carried out at the most hazardous volcanic areas in Italy: Pozzuoli Solfatara (Phegraen Fields), Stromboli, and Mt. Etna. The BrIdge voLcanic LIdar--BILLI has successfully obtained accurate measurements of in-plume CO\({}_{2}\) concentration and flux. In addition, wind velocity has also been retrieved. It has been shown that the measurements of CO\({}_{2}\) concentration performed by BILLI are comparable to those carried out by volcanologists with other standard techniques, heralding a new era in the observation of long-term volcanic gases. volcanic eruptions; volcanic plumes; CO\({}_{2}\) flux; DIAL-Lidar; data processing techniques 20  
serious losses to national/international economies. Cautious valuation of volcano comportment and activity state is required to mitigate these effects, which can be carried out by instruments dedicated to volcanic control [2]. Volcanologists can nowadays infer in real time, by modern technological and modeling developments, the signals coming from seismic and ground deformations that usually happen before eruptions. It is possible to know of an imminent eruption by detecting the stress changes and magma accumulation/flow, thanks to the improvements in broadband seismometers, models, and tools for processing seismic signals [3], and the constant implementation of satellite-based (GPS, Global Positioning System [4] and InSAR, Interferometric Synthetic Aperture Radar [5]) geodetic observations [6]. Volcanic plumes, fumaroles, and degassing grounds release incessantly magmatic volatiles (e.g., H\({}_{2}\)O, SO\({}_{2}\), and CO\({}_{2}\)) [7], representing the external appearance of deep magma degassing [8,9]. These volatiles are a source of priceless data for forecasting the likelihood of a volcanic eruption. Therefore, accurate knowledge of volcanic gas composition and flux can provide alerts on possible eruptions [10], and provide insights into the geophysical processes occurring in the inner parts of volcanoes. As far as abundancy is concerned, CO\({}_{2}\) is the second gas in volcanic fluids. Unfortunately, in contrast to SO\({}_{2}\), its measurements are much more complicated. In fact, efforts to achieve standoff detection of the volcanic CO\({}_{2}\) flux have been discouraged by technical challenges. This is mainly due to the large atmospheric background, about 400 parts per million (ppm), which makes it difficult to resolve the volcanic CO\({}_{2}\) signal. For these reasons, there are few volcanic CO\({}_{2}\) flux data in geophysical studies (see [11, 12, 13, 14] for fresh research). In fact, SO\({}_{2}\) can be found at the parts per billion concentration in the unperturbed atmosphere, therefore its volcanic flux can be detected via routinely collected data from the ground (e.g., DOAS, Differential Optical Absorption Spectroscopy [15]) and in space using UV (Ultraviolet) spectroscopy [16, 17, 18].