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Iodine is scarce in the Arctic snowpack compared to its close relatives and known ozone-killers, chlorine and bromine. But a new study shows that even less than one part per trillion of iodine is enough to have a significant effect on ozone concentration in the lower atmosphere.

“Where we live, the air is relatively clean because of ozone. It’s like a Pac-Man of the atmosphere—it helps to gobble up pollution.”

“Where we live, the air is relatively clean because of ozone. It’s like a Pac-Man of the atmosphere—it helps to gobble up pollution,” says Paul Shepson, professor of analytical and atmospheric chemistry at Purdue University. “But it’s also toxic at high concentrations and regulated by the Clean Air Act. We need a Goldilocks amount of ozone in the atmosphere—not too much, not too little.”

When sun shines on snow that is on or near sea ice, a chemical reaction takes place, releasing iodine, chlorine, and bromine into the atmosphere. These compounds are two halogen atoms bonded together, and when they react with sunlight, they break apart to release those two highly reactive atoms. Often, those atoms collide with ozone near the ground and destroy it. They also react with other pollutants, like mercury, to help remove them.

For the study in the Proceedings of the National Academy of Sciences, researchers went to snow-covered Barrow, Alaska, the northernmost city in the United States, to try to learn more about the natural amount of ozone in the atmosphere. They thought it would look like it does here, just without human impact. But, they discovered that the air above sea ice is unique.

“There’s a part of the planet that we don’t understand very well, and it’s the part covered with sea ice. But sea ice is melting,” Shepson says. “A natural process controls how much ozone is in the atmosphere, and that process is likely to change dramatically in the polar regions due to climate change.”

There are two kinds of ozone on earth: high up (stratospheric) and near the ground (tropospheric). Stratospheric ozone protects life on Earth from harmful radiation, while tropospheric ozone supports a natural cleaning mechanism.

“This kind of science is about having a crystal ball…”

The atmosphere uses ozone, water vapor, and sunlight to clean itself. However, there’s less water vapor in higher latitudes because it’s cold, which slows down the natural cleaning mechanism. In regions covered with sea ice, the strange chemistry involving halogens released by salty ice creates a different cleaning mechanism; if sea ice is removed by climate change, this mechanism could disappear.

As people continue to explore and develop the Arctic region in search of oil and gas, the atmosphere’s ability to rid itself of pollutants is going to become increasingly important.

Although too little ozone can be bad, too much can be even worse. Long-term exposure to the pollutant, which is also a greenhouse gas, can lead to asthma and permanent lung damage.

The global distribution of ozone is another looming question for scientists. It lives in the atmosphere for several weeks, which means it could be transported long distances. Thus, more ozone in the Arctic could mean more ozone in lower latitudes. Without sea ice, background ozone levels in the Arctic are likely to increase, making it more difficult to control ozone in polluted environments.

Understanding the processes that regulate ozone in the atmosphere will help scientists create better climate models and, in turn, better air quality models, Shepson says.

“This kind of science is about having a crystal ball. We want to predict the future state of the planet, and the atmosphere is an important part of that.”

Source: Purdue University