The newly launched imaging spectrometer TROPOMI onboard the Sentinel-5 Precursor satellite provides atmospheric column measurements of sulfur dioxide (SO₂) and other gases with a pixel resolution of 3.5 × 7 km². This permits mapping emission plumes from a vast number of natural and anthropogenic emitters with unprecedented sensitivity, revealing sources which were previously undetectable from space. Novel analysis using back-trajectory modelling of satellite-based SO₂ columns allows calculation of SO₂ flux time series, which would be of great utility and scientific interest if applied globally. Volcanic SO₂ emission time series reflect magma dynamics and are used for risk assessment and calculation of the global volcanic CO₂ gas flux. TROPOMI data make this flux time series reconstruction approach possible with unprecedented spatiotemporal resolution, but these new data must be tested and validated against ground-based observations. Mt. Etna (Italy) emits SO₂ with fluxes ranging typically between 500 and 5000 t/day, measured automatically by the largest network of scanning UV spectrometers in the world, providing the ideal test-bed for this validation. A comparison of three SO₂ flux datasets, TROPOMI (one month), ground-network (one month), and ground-traverse (two days) shows acceptable to excellent agreement for most days. The result demonstrates that reliable, nearly real-time, high temporal resolution SO₂ flux time series from TROPOMI measurements are possible for Etna and, by extension, other volcanic and anthropogenic sources globally. This suggests that global automated real-time measurements of large numbers of degassing volcanoes world-wide are now possible, revolutionizing the quantity and quality of magmatic degassing data available and insights into volcanic processes to the volcanological community.

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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.

Studying the quantity and origin of CO₂ emitted by back‐arc mud volcanoes is critical to correctly model fluid‐dynamical, thermodynamical, and geochemical processes that drive their activity and to constrain their role in the global geochemical carbon cycle. We measured CO₂ fluxes of the Bledug Kuwu mud volcano on the Kendeng Fold and thrust belt in the back arc of Central Java, Indonesia, using scanning remote sensing absorption spectroscopy. The data show that the expelled gas is rich in CO₂ with a volume fraction of at least 16 vol %. A lower limit CO₂ flux of 1.4 kg s⁻¹ (117 t d⁻¹) was determined, in line with the CO₂ flux from the Javanese mud volcano LUSI. Extrapolating these results to mud volcanism from the whole of Java suggests an order of magnitude total CO₂ flux of 3 kt d⁻¹, comparable with the expected back‐arc efflux of magmatic CO₂. After discussing geochemical, geological, and geophysical evidence we conclude that the source of CO₂ observed at Bledug Kuwu is likely a mixture of thermogenic, biogenic, and magmatic CO₂, with faulting controlling potential pathways for magmatic fluids. This study further demonstrates the merit of man‐portable active remote sensing instruments for probing natural gas releases, enabling bottom‐up quantification of CO₂ fluxes.

The Campi Flegrei caldera is located in the metropolitan area 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 measured path-integrated CO₂ concentrations in 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 in permeability at shallow levels. Thanks to the integrated path soundings, LARSS may help to give representative measurements from large regions containing different CO₂ sources, including fumaroles, low-temperature vents, and degassing soils, helping to constrain the contribution of deep gases and their migration mechanisms towards the surface.

Atmospheric visibility, or meteorological optical range (MOR), is governed by light extinction by aerosols. State-of-the-art visibility sensors, such as employed in meteorological observatories and airports, infer MOR by measuring either transmittance or scattering. While these sensors yield robust measurements with reasonable accuracy (10 % to 20 %), they measure in situ. MOR from these sensors may thus not be representative of MOR further away, for example, under conditions with stratified aerosol types. This includes off-shore sites near the sea surface during conditions with advection fog, sea spray or mist. Elastic backscatter lidar can be used to measure light extinction and has previously demonstrated to be a powerful method to infer visibility. Lidar can measure visibility not just near the instrument but also further away (remotely) and single-ended whilst also being capable of measuring profiles of MOR along atmospheric slant paths. Continuous-wave (CW) Doppler wind lidar systems make up one of the most widespread type of elastic backscatter lidar and are typically used in wind resource assessment. Using these existing platforms for remote and single-ended measurement of MOR profiles could allow for new and valuable applications. However, the low-light extinction associated with this type of lidar excludes the use of the extinction coefficient for MOR retrieval but leaves the backscatter coefficient as a possible proxy for MOR, though with an accuracy expected to be inferior to the former method. We analysed backscatter data from CW wind lidar and co-measured MOR from visibility sensors from two campaigns (Cabauw, Netherlands, and Pershore, United Kingdom) and found backscatter from CW wind lidar to be a viable proxy of MOR if calibrated against a visibility sensor. The expected accuracy of the method is low and of the order of few kilometres. This means MOR from CW wind lidar could be used in safety-uncritical problems, such as assessment of visibility of manmade objects, including wind turbines.