The January 2022 Hunga Tonga–Hunga Ha’apai underwater volcano eruption in Tonga was one of the most powerful in modern times.

It injected huge amounts of water vapor, ash, sulfur dioxide, and other materials high into the stratosphere.

While it had some warming effects from the water vapor (a greenhouse gas), a new study highlights an unexpected “self-cleaning” side effect involving methane.

The eruption released significant methane (CH₄), a potent greenhouse gas, along with volcanic ash and seawater (rich in salts like chloride) and the plume mixed these materials high in the atmosphere.

Sunlight then drove chemical reactions: the salty aerosols and ash helped produce highly reactive chlorine species. These chlorine atoms reacted with methane, breaking it down into other compounds (with formaldehyde detected as a key byproduct/sign of this process).

In short, the volcano partially “cleaned up” some of its own methane emissions through this rare stratospheric chemistry. Researchers estimate it removed an amount of methane equivalent to the daily emissions of roughly two million cows.

Methane is mostly broken down in the troposphere by hydroxyl radicals (OH). This volcanic process created an additional, efficient destruction pathway in the stratosphere involving chlorine—something not previously observed or expected at this scale from a volcanic event.

Volcanoes were known to emit methane, but the idea that their ash and plume chemistry could actively remove some of it (acting like a natural scrubber) is new. The findings come from satellite observations tracking formaldehyde spikes and modeling the plume’s composition.

Context

Not a climate fix: This was a one-off event tied to the unique underwater nature of the eruption (seawater + ash + high injection). It doesn’t offset the eruption’s other climate impacts or broader human methane emissions.

Scientific interest: It demonstrates a natural methane sink mechanism that could inspire research into engineered ways to accelerate methane breakdown (e.g., for mitigating agricultural or fossil fuel emissions).

The study was recently published/ highlighted in outlets like Nature Communications or related reports, explaining the wave of headlines in May 2026.

This is a fascinating example of complex atmospheric chemistry—volcanoes can have both warming and cooling effects, plus these unexpected feedbacks. The Hunga Tonga event continues to yield new insights years later due to its scale and the quality of modern satellite monitoring.

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Satellite quantification of enhanced methane oxidation applied to the stratospheric plume following Hunga Tonga-Hunga Ha’apai eruption

This is a detailed, open-access study demonstrating a novel satellite-based method to quantify enhanced methane (CH₄) oxidation using formaldehyde (HCHO) as a proxy, applied as a proof-of-concept to the 2022 Hunga Tonga–Hunga Ha’apai (HTHH) stratospheric plume.

Core Methodology and Innovations

HCHO as tracer: Methane oxidation (primarily by OH, secondarily by Cl) produces ~1 HCHO molecule per CH₄ oxidized. HCHO is short-lived (hours in the stratosphere due to photolysis + reactions with radicals), making sustained enhancements strong evidence of ongoing production rather than direct volcanic injection.

TROPOMI strengths/limitations addressed: UV-based observations work over oceans (unlike IR CH₄ retrievals). Authors applied critical corrections for:

• Stratospheric altitude (higher sensitivity → AMF correction factor ~4.85).
• SO₂ spectral interference (up to +40% in one cloud initially, reduced later).
• Aerosol/cloud effects (±20% uncertainty estimated).

Quantification combined direct integration (background subtraction) with correlations to co-emitted tracers (SO₂, sulfate aerosol from volcanic ash RGB, AOD). These agreed well, building confidence.

Key Quantitative Results

Peak HCHO: Up to ~12 ppb (±10%) at ~30 km in the plume (vs. typical stratospheric background <<0.1 ppb). Column enhancements up to 1.6 × 10¹⁵ molecules/cm².

Methane oxidation: 900 ± 220 Mg (metric tons) per day on Jan 16, with midday peaks ~75 ± 18 Mg/hour (60 ppb/day locally). Lower but detectable rates persisted (e.g., ~8 ppb/day on later days). Total suggests at least 330 Gg volcanic CH₄ injected into the stratosphere.

Chlorine requirement: To drive this, ongoing primary Cl production of 2–5 Gg Cl per day was needed — higher than prior model estimates for injected active Cl (~1.3 Gg total).

Persistence: Signal tracked for ≥10 days (up to Jan 25 in parts), consistent with Cl-driven chemistry tied to aerosols (not just initial injection). Correlated with ClO enhancements, O₃ depletion, and CO increases.

Proposed Mechanism

Photochemical Cl production from iron-chloride in sulfate-coated volcanic ash (enabled by submarine eruption: magma-seawater interaction provided salts + ash). Sunlight activates this even in the stratosphere, outside typical marine boundary layer contexts. This explains sustained HCHO without rapid decline. It also ties into low BrO observations.

Lead author note:

Maarten van Herpen (Acacia Impact Innovation BV) has a related patent on satellite quantification for engineered methane removal (distinct from this natural case). This is transparently declared.

This is rigorous atmospheric chemistry detective work leveraging an exceptional event. The full paper is freely available and includes extensive supplementary data/figures.

Natural methane (CH₄) sink processes remove most emitted methane from the atmosphere, maintaining a rough balance in pre-industrial times. Methane’s atmospheric lifetime is about 9–12 years, primarily due to these sinks.

Published: Nature Communications 

DOI: 10.1038/s41467-026-72191-4

Authors: Maarten M.J.W. van Herpen, 
Isabelle De Smedt, 
Daphne Meidan, 
Alfonso Saiz-Lopez, 
Matthew S. Johnson, 
Thomas Röckmann & 
Jos de Laat 

Abstract

Methane is a powerful greenhouse gas whose atmospheric sink remains uncertain, and emerging strategies to enhance its removal will require quantification and monitoring to verify any hypothetical future methane removal. Here we present satellite quantification of enhanced atmospheric methane oxidation, based on TROPOMI observations of a short-lived intermediate in methane oxidation, HCHO. We find a large HCHO enhancement of up to 12 ppb±10% at 30 km altitude, in the plume from the Hunga Tonga-Hunga Ha’apai eruption, persisting for ten days or more, and also explaining its low BrO levels. Total methane oxidation is 900 ± 220 Mg/day, suggesting at least 330 Gg of volcanic methane was injected into the stratosphere. The observed methane oxidation requires an estimated ongoing primary production of 2-5 Gg Cl per day that appears unexplained by known mechanisms. We show that chlorine production by iron-chloride photochemistry in sulfate-coated volcanic ash is a plausible mechanism, even outside the marine boundary layer. This method of measuring methane loss using formaldehyde can be sufficiently sensitive to quantify the impact of hypothetical future enhanced atmospheric methane oxidation approaches.