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Good and bad ozone: new study sheds light on the Ocean’s role in removing and protecting us from harmful ozone
08 September 2025
While ozone shields us in the upper atmosphere, nearer the surface it harms health and ecosystems. New research reveals clues as to how the Ocean helps clear it away.
What is the ozone layer?
The ozone layer is the common name for the high concentration of ozone (O3) – also called trioxygen – that is found in the stratosphere (around 15–35km above the earth’s surface). It covers the entire planet and is vitally important to life on Earth by absorbing harmful ultraviolet (UV) radiation from the sun. Without it, far more UV-B and UV-C rays would reach the Earth’s surface, harming all life – people, animals, and ecosystems in the land and in the Ocean.
However, whilst the upper ozone layer in the stratosphere shields life on Earth, ozone in the troposphere – near the surface where we live and breathe – is a harmful air pollutant and a powerful greenhouse gas, damaging human health, crops and ecosystems, and contributing to climate change.
One of the biggest natural sinks for ozone in the troposphere – where we live – is the Ocean, due to substances in the water that react with ozone at the sea surface, driving chemical reactions that remove it from the atmosphere. However, until now, the chemical reactants driving such removal have been poorly understood.
A landmark new study led by Dr Ming-Xi Yang, Chemical Oceanographer at Plymouth Marine Laboratory (PML), has shed light on this mystery by using a new technique to map out the compounds in the surface ocean that react with ozone on a trans-Atlantic research cruise.
In 2019, through the Atlantic Meridional Transect cruise (AMT29), researchers collected data from the UK to Chile on a six-week research expedition. The researchers found that iodide* and organic compounds* in surface seawater are playing key roles in reacting with ozone, with their relative importance varying across different latitudes.
Image: The AMT29 research cruise track
Lead author Dr Ming-Xi Yang said:
“We developed a novel method to continuously measure the chemical uptake of ozone by near surface waters on the ship – a huge advancement over previous discrete methods that only worked when stationary. Coupled with laboratory calibration after the cruise, this method enabled us to map out the distributions of ozone-reacting substances over nearly 100 degree latitude range in the Atlantic, which is unprecedented in scale.”
“We find that the rate of ozone uptake varies a lot spatially, in contrast to many global models that assume a constant uptake everywhere. Implementing this new finding should improve the model representation of ozone cycling in the lower troposphere, which is important for air quality, human health, climate change, and agriculture.”
*Iodide: In the ocean, iodide is a form of dissolved iodine, existing alongside iodate and dissolved organic iodine. Iodide is crucial for the ocean-atmosphere iodine cycle, reacting with ozone to form gaseous iodine, which then affects atmospheric chemistry, climate, and air quality. This interaction also acts as a major sink for ozone.
Dr Yang adds, “Iodide is an essential nutrient for humans too, and people living near the coast get iodide easily from sea spray and seafood. Iodide deficiency used to be a problem for people living further inland, which is why iodide started to be added to table salt.”
*Organic Compounds (OCs): OCs in the ocean, derived primarily from marine organisms, include a wide range of substances such as lipids (fatty acids, esters, alcohols), hydrocarbons, carbohydrates, proteins, and halogenated organic compounds.
In tropical waters, iodide dominated the chemical uptake of ozone, while in temperate waters, organic compounds played a stronger role.
Surprisingly, the study also revealed that deep waters – which are usually considered biologically inactive – showed significant reactivity toward ozone. This suggests that when deep waters mix to the surface, even biologically inactive organic matter can help scrub ozone from the atmosphere.
Dr Yang added:
“Our study highlights how the ocean and the atmosphere interact in unexpected ways to keep our environment on Earth livable. Understanding these processes, and how they vary across regions, will improve climate and air quality models, while also deepening our appreciation of the Ocean’s hidden role in regulating the atmosphere.”
