January 14, 2014
High Levels Of Atmospheric Chlorine Detected In Alaska
redOrbit Staff & Wire Reports - Your Universe Online
Researchers analyzing the atmosphere above the Alaskan city of Barrow have found unexpectedly high levels of molecular chlorine in the air, according to research appearing in Sunday’s edition of the journal Nature Geoscience.
The substance, which comes from sea salt that is released when ice in the region melts, interacts with sunlight to create highly reactive chlorine atoms, the researchers said. Those atoms can increase the degradation speed of methane and oxidize elemental mercury into more toxic forms.
The researchers used a technique known as chemical ionization mass spectrometry to measure molecular chlorine levels in the Arctic during a six-week period during spring 2009. According to Tamarra Kemsley of Nature World News, they detected levels of up to 400 parts per trillion during their analysis.
“No one expected there to be this level of chlorine in Barrow or in polar regions,” explained Greg Huey, one of the study authors and a professor at the Georgia Institute of Technology School of Earth and Atmospheric Sciences. “Molecular chlorine is so reactive that it’s going to have a very strong influence on atmospheric chemistry.”
According to Huey and his colleagues, 400 parts per trillion is an extremely high concentration of molecular chlorine, especially since the atoms tend to be short-lived in the atmosphere because they are strong oxidants that are very reactive with other atmospheric chemicals.
The chlorine concentrations are peaking during the early morning and late afternoon hours, the investigators added, and plummeting to near zero levels during the nighttime. The daytime levels were correlated with ozone concentration, suggesting that the molecular chlorine requires sunlight and ozone in order to form, they added.
“Previous Arctic studies have documented high levels of oxidized mercury in Barrow and other polar regions,” the school explained. “The major source of elemental mercury in the Arctic regions is coal-burning plants around the world. In the spring in Barrow, ozone and elemental mercury are often depleted from the atmosphere when halogens – chlorine and bromine – are released into the air from melting sea ice.”
The new research also concluded that chlorine atoms are the primary oxidant in Barrow, a region that otherwise has low levels of atmospheric oxidants. This is said to be due to the lack of ozone and water vapor, which are the primary predecessors to the creation of oxidants in several urban regions.
The primary source of the molecular chlorine in sodium chloride is sea salt, most likely originating from the snow-covered ice pack that covers much of the region. Exactly how that happens is not currently known.
“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.”
One thing that is certain though, he added, is that there is “definite climate change happening in the Arctic.” The amount of sea ice lasting from one season to another is on the decline, creating a larger area of melted ice that could be releasing more molecular chlorine into the atmosphere. In short, global warming is likely “changing the nature of the ice, changing the volume of the ice, changing the surface area and changing the chemistry of the ice.”