The volcano that cleans its own pollution

University of Copenhagen researchers have discovered that the 2022 Hunga Tonga eruption used sea salt and sunlight to trigger a chemical reaction that stripped methane from the atmosphere

This “self-cleaning” phenomenon, which left a trail of formaldehyde across the Pacific, provides a new method for scientists to measure methane removal via satellite and could inspire new technologies to rapidly slow global warming.

The study from the University of Copenhagen, published in Nature Communications, reveals that the 2022 eruption of the Hunga Tonga–Hunga Ha’apai submarine volcano did something scientists thought impossible: it actively removed methane from the atmosphere.

By mimicking a chemical process usually seen in the Sahara Desert, the volcano effectively “cleaned up” after itself, offering a potential blueprint for human-led climate interventions.

Formaldehyde and volcanoes

Researchers using the European Space Agency’s Sentinel-5P satellite spotted record-high concentrations of formaldehyde in the volcanic plume. Because formaldehyde is a short-lived byproduct created when methane is destroyed, its presence for over 10 days—stretching all the way to South America—proved that a continuous methane-stripping reaction was occurring in the sky.

The chemistry of salt and sunlight

The discovery confirms that a rare chemical reaction, first identified in 2023 involving Saharan dust, can also happen in the stratosphere.

• The mixture:

  • The eruption blasted massive amounts of salty seawater and volcanic ash into the atmosphere.

• The reaction:

  • When sunlight hit this mixture of ash and sea salt, it created iron salt aerosols.

• The result:

  • These aerosols produced highly reactive chlorine atoms, which acted like a chemical detergent, aggressively breaking down methane molecules.

Impact by the numbers

The scale of this natural cleanup was immense, effectively neutralising a significant portion of the volcano’s own carbon footprint:

The volcano released approximately 300 gigagrams of methane (the annual equivalent of 2 million cows).

The natural reaction removed about 900 megagrams per day, matching the daily output of those same 2 million cows.

A roadmap for global warming

Methane is roughly 80 times more potent than CO₂ over a 20-year period, but it only lasts about a decade in the air. This makes methane reduction the “emergency brake” of climate change.

The study proves that we can use satellites to verify if methane-removal technology is actually working.

Engineers are now looking at whether they can safely replicate this “iron salt” process to artificially accelerate methane breakdown.

Climate scientists must now revise the “global methane budget,” as atmospheric dust—previously ignored—is clearly a major factor in how methane is removed from our air.