Scientists have discovered that the 2022 Hunga Tonga-Hunga Ha'apai volcanic eruption might have triggered a chemical process that helped break down some of the methane released into the atmosphere. This finding, based on satellite data, could change how scientists estimate methane pollution and may lead to new ways to slow near-term global warming. Methane is a potent greenhouse gas that contributes significantly to climate change, and understanding its fate in the atmosphere is crucial for accurate climate modeling. The eruption, one of the most powerful volcanic events in modern times, released about 300 gigagrams (Gg) of methane—equivalent to the annual emissions of over two million cows. Surprisingly, researchers found that the volcanic plume removed approximately 900 megagrams (Mg) of methane per day, an amount similar to the daily emissions of two million cows. This suggests that the eruption may have had a significant impact on atmospheric methane levels, even as it released a large amount of the gas. The process involved a unique combination of volcanic ash, seawater, and sunlight. Scientists first identified this chemical reaction in 2023, when they observed that Saharan dust mixed with sea salt could form iron salt aerosols. When sunlight hits these particles, chemical reactions release chlorine atoms, which then react with methane molecules and help break them apart. The Hunga Tonga eruption created ideal conditions for this process, as the volcano erupted underwater, sending large amounts of salty seawater and volcanic ash into the atmosphere. Some of this material reached the stratosphere, where sunlight triggered the formation of highly reactive chlorine atoms. These chlorine atoms then reacted with methane in the volcanic plume, breaking it down. Evidence for this process came from the detection of formaldehyde, a chemical produced when methane is destroyed. Formaldehyde only lasts a few hours in the atmosphere, so unusually high levels indicate active methane destruction. The presence of large amounts of formaldehyde in the volcanic plume confirmed that this chemical process was occurring. The discovery may lead scientists to revisit calculations of the global methane budget, as atmospheric dust has not been fully considered in previous estimates. If volcanic ash and other mineral dust can speed up methane destruction, scientists may need to adjust how they model the movement of methane through the atmosphere. This finding highlights the complex interactions between natural events and atmospheric chemistry, which are still not fully understood. Researchers used data from the TROPOMI instrument, which is aboard the European Space Agency's Sentinel-5P satellite, to detect formaldehyde in the volcanic plume in the stratosphere. However, the instrument was not originally designed to detect such conditions, so scientists had to make careful adjustments to confirm their findings. The study, published in Nature Communications, was conducted by researchers from the University of Copenhagen, Acacia Impact Innovation BV, the Royal Netherlands Meteorological Institute, and other institutions. It was supported by Spark Climate Solutions.