A multi-component gas analyzer system (Multi-GAS) is an instrument package used to take real-time high-resolution measurements of volcanic gas plumes. A Multi-GAS package includes an infrared spectrometer for CO2, two electrochemical sensors for SO2 and H2S, and pressure–temperature–humidity sensors, all in a weatherproof box weighing approximately 3 kg, as well as radio transmitters to transmit data to remote locations. The instrument package is portable, and its operation and data analysis are simple enough to be conducted by non-specialists.
Multi-GAS instruments have been used to measure volcanic gas plumes at Mount Etna, Stromboli, Vulcano Italy, Villarrica (volcano) Chile, Masaya Volcano Nicaragua, Mount Yasur and Ambrym Vanuatu, Miyake-jima and Mount Asama Japan, Soufrière Hills Montserrat, with permanent installations at Etna and Stromboli.
Multi-GAS measurements of CO2/SO2 ratios can allow detection of the pre-eruptive degassing of rising magmas, improving prediction of volcanic activity.