Fumarolic CO2 emissions measured by drone at Campi Flegrei, Italy

Campi Flegrei, the largest restless caldera in Europe, has experienced increasing activity since 2004. This unrest is characterized by ground uplift, seismicity, intensified degassing, and opening of new fumaroles and mud pools. Quantifying carbon dioxide (CO2) emissions is particularly challenging at this volcano because sulfur dioxide (SO2) is efficiently scrubbed by the hydrothermal system, making conventional CO2 emission rate estimates that rely on remote sensing-based SO2 measurements not possible. As a result, CO2 emission rates from fumaroles at Campi Flegrei are measured by ground-based MultiGAS. However, the escalating level of activity could render such measurements impossible in the near future, highlighting the need for another approach to measure fumarolic CO2 emissions. Here, we present the first CO2 emission rate measurements at Campi Flegrei's main fumarolic site, Pisciarelli, using drone-based MultiGAS instrumentation, supported by simultaneous ground-based MultiGAS data. The drone-based average CO2 emission rate (218 ± 118 tons/day) closely matches the ground-based value (263 ± 90 tons/day), validating the drone approach. Our drone-based approach yields gas ratios of CO2/H2S = 295 ± 36 and CO2/H2O = 0.27 ± 0.06; combining these ratios with CO2 emission rates, we derive H2S and H2O emission rates of 0.57 ± 0.30 and 330 ± 193 tons/day, respectively. These results also closely agree with ground-based and direct sampling methods. Our 2024 measurements reveal a decline in CO2, H2S, and H2O emission rates compared to 2019, likely due to redistribution of the gas output pathways at Campi Flegrei through an expansion of the diffuse degassing zone. This study demonstrates that drone-based MultiGAS is a reliable, safe alternative for volcanic gas monitoring. We provide recommendations for further deployments at Campi Flegrei and other challenging volcanic environments