Surprisingly High Chlorine Levels In Arctic Air Are Both A Symptom And Cause Of Climate Change, According To New Study

By Ajit Jha on January 14, 2014 9:52 AM EST

Alaska Ice
As the ice caps in polar regions of Alaska keep melting, more and more molecular chlorine is released into the atmosphere. (Photo: Shutterstock)

Scientists have found unusually high levels of chlorine in the Arctic atmosphere off Barrow in Alaska, according to a new study published in Nature Geoscience.

Chlorine atoms are produced in this part of the world when molecular chlorine from sea salt released by melting sea ice comes in contact with sunlight. The chlorine atoms are strong oxidants and therefore are short lived in the atmosphere - they immediately react with other atmospheric chemicals (such as methane and elemental mercury) and turn into something else (like oxidized mercury). That's why scientists were surprised to find the concentration of molecular chlorine as high as 400 parts per trillion, which is significantly high in comparison to their normal levels.

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The researchers employed the method of chemical ionization mass spectrometry to measure molecular chlorine levels. The study was made over a six week period in the spring of 2009. Since the scientists doubted their initial findings, they spent years afterwards conducting similar experiments to ensure the validity of their findings. "No one expected there to be this level of chlorine in Barrow or in polar regions," said Dr. Greg Huey, a professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology in Atlanta, to Phys Org.

The dominance of chlorine molecules in Barrow, an area with low levels of oxidants is perplexing to the scientists. This area lacks water vapor and ozone, both of which were thought to be necessary precursors to making oxidants. The ultimate source of molecular chlorine in this area is the sodium chloride in sea salt perhaps from the snow-covered ice pack. However, the exact mechanism leading to the transformation of sea salt into molecular chlorine, according to Huey, is not known. However, Huey claims that 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."

In the meanwhile, scientists do know for sure that sea ice is changing rapidly. After every winter, there is a larger and larger area of the melted ice. So it could be possible that the seasonal variation in ice is responsible for release of more molecular chlorine into the atmosphere - which, in turn leads to further climate change. In the spring, the melting ice in this region releases chlorine and bromine into the air leading to the depletion of ozone and elemental mercury. Previous studies of polar regions, including Barrow, have shown that these areas tend to have high levels of oxidized mercury, a major source of which is coal burning plants around the world.

The scientists also found that the levels of atmospheric chlorine varied during different periods of day and night. Their concentrations peaked in day time (especially early morning and late afternoon) but fell to near zero levels in the night. The scientists could see a correlation between levels of molecular chlorine and ozone which led them to conclude that sunlight and ozone could be required for molecular chlorine formation.

The study, supported by the National Science Foundation (NSF) is a part of the international multidisciplinary OASIS program. 

Alaska image vis Shutterstock.

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