The Atmospheric Infrared Sounder (AIRS) instrument aboard NASA's Aqua satellite detected volcanic sulfur dioxide (SO₂) plumes from the Hayli Gubbi volcano in Ethiopia, which erupted on November 23^rd, 2025, for the first time in nearly 12,000 years. The AIRS images shown here were taken from satellite overpasses during the subsequent days, capturing the eastward propagation of SO₂ volcanic plumes from Ethiopia to Japan, crossing Asia within three days.

Hayli Gubbi started erupting around 11:30 AM local time on November 23^rd. The top frame in the figure shows a red patch that represents an SO₂ plume detected by the AIRS instrument close to the volcano within a few hours (around 2 pm local time) as the Aqua satellite passed over. The middle frame is taken from satellite overpasses in the early hours of November 24^th (around 2 am locally where the satellite passes over), showing the red and orange SO₂ plume stretched like a filament to the Northeast, having reached North India within a day, where it caused significant delays and cancellations of air traffic. The bottom frame shows the subsequent nighttime overpasses (around 2 am locally on November 25^th) where the plume has travelled across Asia, reaching Japan within three days from the start of the eruption.

SO₂ can be harmful to the human respiratory system when inhaled. In the atmosphere, it can also lead to the formation of other gaseous sulfur oxides (SOₓ). These substances can react with other chemicals to form particulate-matter pollution, which can cause breathing problems, contribute to acid rain, and reduce sky visibility.

AIRS measures the amount of radiation reaching the instrument from the top of the atmosphere at more than 2,000 different wavelengths. Brightness temperature (BT) is a measure of the amount of radiation, and the images and animation show the difference between BT observed at two different wavelengths. One of the wavelengths (wavenumber 1361.44 cm^-1 or 7.3 µm) is sensitive to atmospheric SO₂, and the other (wavenumber 1433.06 cm^-1 or 7.0 µm) is not, so the difference between the two measurements can give a reliable signal of volcanic SO₂ plumes.

A fully automated volcanic plume detection rapid response system that uses AIRS data has been developed at the Jet Propulsion Laboratory in Southern California. This tool is available at the AIRS Rapid Response website, where detections of the most recent volcanic SO₂, dust, and clouds, in visible and infrared images, are updated in near real-time when a volcanic event anywhere on Earth triggers the system. AIRS historical detections of volcanic SO₂ and dust are archived on the site at https://airs.jpl.nasa.gov/volcanic_plumes/.

AIRS, in conjunction with the Advanced Microwave Sounding Unit (AMSU), senses emitted infrared and microwave radiation from Earth to provide a three-dimensional look at the planet's weather and climate. Working in tandem, the two instruments make simultaneous observations down to Earth's surface. With more than 2,000 channels sensing different regions of the atmosphere, the system creates a global map of atmospheric temperature and humidity, cloud amounts and heights, greenhouse gas concentrations, and many other atmospheric phenomena. Launched into Earth orbit in 2002 aboard NASA's Aqua spacecraft, the AIRS and AMSU instruments are managed by JPL, under contract to NASA. JPL is a division of Caltech.