Sunlit Snow Triggers Atmospheric Cleaning, Ozone Depletion in the Arctic
by Staff Writers
Washington DC (SPX) Apr 26, 2013
Kerri Pratt, an NSF Postdoctoral Fellow in Polar Regions Research, conducts a snow-chamber experiment in -44F windchill near Barrow, Alaska. Credit: Photo credit Paul Shepson, Purdue University.
National Science Foundation-funded researchers at Purdue University have discovered that sunlit snow is the major source of atmospheric bromine in the Arctic, the key to unique chemical reactions that purge pollutants and destroy ozone.
The new research also indicates that the surface snowpack above Arctic sea ice plays a previously unappreciated role in the bromine cycle and that loss of sea ice, which been occurring at an increasingly rapid pace in recent years, could have extremely disruptive effects in the balance of atmospheric chemistry in high latitudes.
The team’s findings suggest the rapidly changing Arctic climate–where surface temperatures are rising three times faster than the global average–could dramatically change its atmospheric chemistry, said Paul Shepson, an NSF-funded researcher who led the research team. The experiments were conducted by Kerri Pratt, a postdoctoral researcher funded by the Division of Polar Programs in NSF’s Geosciences Directorate.
“We are racing to understand exactly what happens in the Arctic and how it affects the planet because it is a delicate balance when it comes to an atmosphere that is hospitable to human life,” said Shepson, who also is a founding member of the Purdue Climate Change Research Center. “The composition of the atmosphere determines air temperatures, weather patterns and is responsible for chemical reactions that clean the air of pollutants.”
A paper detailing the results of the research, some of which was funded by NSF and some by the National Aeronautics and Space Administration, was recently published online at Nature Geoscience.
Ozone in the lower atmosphere behaves differently from the stratospheric ozone involved in the planet’s protective ozone layer. This lower atmosphere ozone is a greenhouse gas that is toxic to humans and plants, but it also is an essential cleaning agent of the atmosphere.
Interactions between sunlight, ozone and water vapor create an “oxidizing agent” that scrubs the atmosphere of most of the pollutants human activity releases into it, Shepson said.
Temperatures at the poles are too cold for the existence of much water vapor and in the Arctic this cleaning process appears instead to rely on reactions on frozen surfaces involving molecular bromine, a halogen gas derived from sea salt.
This gaseous bromine reacts with and destroys atmospheric ozone. This aspect of the bromine chemistry works so efficiently in the Arctic that ozone is often entirely depleted from the atmosphere above sea ice in the spring, Shepson noted.
“This is just a part of atmospheric ozone chemistry that we don’t understand very well, and this unique Arctic chemistry teaches us about the potential role of bromine in other parts of the planet,” he said. “Bromine chemistry mediates the amount of ozone, but it is dependent on snow and sea ice, which means climate change may have important feedbacks with ozone chemistry.”
While it was known that there is more atmospheric bromine in polar regions, the specific source of the natural gaseous bromine has remained in question for several decades, said Pratt, a Polar Programs-funded postdoctoral fellow and lead author of the paper.
“We thought that the fastest and best way to understand what is happening in the Arctic was to go there and do the experiments right where the chemistry is happening,” Pratt said.
She and Purdue graduate student Kyle Custard performed the experiments in -45 to -34 Celsius (-50 to -30 Fahrenheit) wind chills near Barrow, Alaska. The team examined first-year sea ice, salty icicles and snow and found that the source of the bromine gas was the top surface snow above both sea ice and tundra.
- Sunlit snow triggers atmospheric cleaning and ozone depletion in the Arctic (earthsky.org)
- Sunlit snow triggers atmospheric cleaning, ozone depletion in the Arctic (eurekalert.org)
- Sunlit snow triggers atmospheric cleaning, ozone depletion in the Arctic (rdmag.com)
- Sunlight on snow reacts to clean Arctic air (futurity.org)
- Sunlit Snow Triggers Atmospheric Cleaning, Ozone Depletion in the Arctic (terradaily.com)
- Origin Of Arctic Bromine Identified (cen.acs.org)
- Another atmospheric surprise (jllowe.wordpress.com)
- Causes of 2011 Arctic ozone hole determined (sciencedaily.com)
- NASA Pinpoints Causes of 2011 Arctic Ozone Hole (terradaily.com)
- Ozone overdose confuses pollinators (science.nbcnews.com)