Volcanic eruptions emit significant quantities of carbon dioxide (CO₂) to the atmosphere. We present a new method for directly determining the CO₂ emission from a volcanic eruption on the island of La Palma, Spain, using an unpiloted aerial vehicle (UAV). We also collected samples of the emitted CO₂ and analyzed their isotopic composition. Together with the emission rate the isotopic data provide valuable information on the state of volcanic activity and the potential evolution of the eruption.