High levels of molecular chlorine found in Arctic atmosphere

The high levels of molecular chlorine could contribute to climate change, and researchers remain uncertain how it is being released into the atmosphere.
Posted By Ananth Baliga  |  Jan. 13, 2014 at 5:03 PM
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The atmosphere above the Arctic has unprecedented levels of molecular chlorine, coming from the sea salt present in the sea ice, though scientists aren't sure how.

Researchers are uncertain how this molecular chlorine is formed, but it now measures 400 parts per trillion over Barrow, Alaska. Scientists measured molecular chlorine levels using chemical ionization mass spectrometry in 2009 and were initially unsure about their findings, which were confirmed after further testing.

“No one expected there to be this level of chlorine in Barrow or in polar regions,” said Greg Huey, a professor at the Georgia Institute of Technology in Atlanta. The study is published in the journal Nature Geoscience.

Molecular chlorine originates from sea salt, which reacts with sunlight to produce chlorine atoms. These chlorine atoms are very reactive and are known to react with chemical elements and compounds found in the atmosphere, such as methane and elemental mercury.

The level of chlorine above Barrow was 400 parts per trillion, which is not a small number, because molecular chlorine oxidize quickly. They found the levels of chlorine peaked during the day and afternoon and fell to zero at night.

“Molecular chlorine is so reactive that it’s going to have a very strong influence on atmospheric chemistry,” Huey said.

Previous studies have shown high levels of oxidized mercury above Barrow, fed by elemental mercury from coal-buring plants across the world. While Huey is certain the source of the chlorine is sea salt he is unsure of the mechanism behind this transformation.

“We don’t really know the mechanism. It’s a mystery to us right now,” Huey said. “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. We’re really in the dark about the chlorine.”

[Georgia Institute of Technology] [Nature Geoscience]

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