New measurements of molecular iodine in the Arctic show that even a tiny amount of the element can deplete ozone in the lower atmosphere.
This is surprising because iodine is so scarce in the Arctic snowpack compared to its close relatives and known ozone-killers, chlorine and bromine. Less than one part per trillion of iodine is enough to have a significant effect on ozone concentration in the lower atmosphere, according to a study published Sept. 5 in Proceedings of the National Academy of Sciences.
“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,” said Paul Shepson, a Purdue University professor of analytical and atmospheric chemistry who worked on the study. “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.
Shepson’s group 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 found that the air above sea ice is unique.
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Image via Kerri Pratt, Purdue University