An international Canadian-led research project on ozone and mercury in the Arctic has detected surprisingly high levels of chlorine gas over the ice sheet north of Barrow, Alaska.
Greg Huey, a Georgia Institute of Technology scientist whose team made the unexpected finding, said the next step is to find out if chlorine gas is found widely across the Arctic. He suspects it is and that it could be an important piece in a puzzle concerning ozone and mercury in the northern atmosphere.
Scientists have known for years that when the Arctic sun comes up each spring, chemical reactions take place over the sea ice that remove all of the ground-level ozone and most of the mercury from the air. It is thought the mercury moves from the air to the snowpack and then to the ocean, from which it could move into the human population.
Working with researchers from the United States and Europe, an Environment Canada research project known as OASIS (for ocean, atmosphere, sea ice and snowpack) has been trying to figure out what is happening and whether climate change, which is melting sea ice, will lead to an increase or decrease of mercury in the Arctic ecosystem.
Dr. Huey, whose work is part of that international effort, said the chlorine gas he found was created by the same interaction of sunlight, low temperatures, ice and sea salt that leads to the formation of mercury and ozone.
"We went to Barrow to study bromine [or seawater salt] chemistry that leads to ozone depletion and mercury oxidization – and we were very surprised to find there was a lot of chlorine chemistry too," he said in an interview.
What role the chlorine gas plays in the process is not yet known, but Dr. Huey said he suspects it activates and intensifies mercury oxidation and ozone depletion.
He detected the chlorine gas using a mass spectrometer, an instrument that measures the mass and concentrations of atoms and molecules.
"The next question is how widespread is the chlorine … in the Arctic?" he said. "These are the first measurements … so we can't be sure it happens across the Arctic. However, we have no reason to believe that it doesn't, and we obviously want to go back and look in other places."
Dr. Huey said a funding proposal has been made to NASA to repeat the study in other locations across the Arctic in 2015.
He said the atmospheric chemistry he is studying is not causing the Arctic ozone hole that has long been a subject of scientific interest and public concern.
"The ozone hole is at high altitude. We're measuring at low altitude," he said. "The chemistries are somewhat similar, but the halogens [or chemical elements] in the stratosphere that cause the ozone hole are from CFCs and other [human-made] sources. The halogens that occur near the surface of the sea ice are natural and the ultimate source of those is sea salt."
Dr. Huey said his findings show how much scientists have yet to learn about the chemistry of the Arctic atmosphere, "especially in relationship to a changing sea-ice environment."
Environment Canada officials could not be reached for immediate comment, but the agency's website describes the OASIS project as part of an effort to understand the presence of ozone and mercury in the Arctic environment.
"Every year when the sun comes up in the Arctic spring, the potent greenhouse gas ozone and the toxic chemical mercury disappear from the air near the ground along the coast of the frozen ocean," states Environment Canada. "With this project we hope to learn what truly causes the 'disappearing act' of these two polluting chemicals, and whether the disappearing mercury ends up in the animals living in the marine world."