Unprecedented High Levels of Molecular Chlorine Discovered in the Arctic Atmosphere

The Arctic is usually seen as one of the last "pristine" locations on Earth. Now, scientists have found that that's far from the case. They've discovered unprecedented levels of molecular chlorine in the air above the Arctic, revealing a bit more about the changing climate.

"No one expected there to be this level of chlorine in Barrow or in polar regions," said Greg Huey, one of the researchers, in a news release.

In order to measure the chlorine levels in the Arctic, the researchers used chemical ionization mass spectrometry over a six-week period in the spring of 2009. They then spent several years running other experiments to ensure their findings were accurate.

So what did they find? It turns out that the level of molecular chlorine above Barrow was as high as 400 parts per trillion. That's a high concentration considering that chlorine atoms are short-lived in the atmosphere because they are strong oxidants and are highly reactive with other atmospheric chemicals. The concentrations of this molecular chlorine peaked in the early morning and late afternoon, and fell to near-zero levels at night. Average daytime molecular chlorine levels were correlated with ozone concentrations, suggesting that sunlight and ozone may be required for molecular chlorine formation.

"Molecular chlorine is so reactive that it's going to have a very strong influence on atmospheric chemistry," said Huey in a news release.

The ultimate source of the molecular chlorine is the sodium chlorine in sea salt, most likely from the snow-covered ice pack. How the sea salt is transformed into molecular chlorine, though, is unknown.

"We don't really know the mechanism. It's a mystery to us right now. But the sea ice is changing dramatically, so we're in a time where we have absolutely no predictive power over what's going to happen to this chemistry," said Huey. "We're really in the dark about the chlorine."

The findings are published in the journal Nature Geoscience.