Researchers at the University of Michigan have detected bromine atoms in the atmosphere for the first time. With this new information, Siyuan Wang, Stephen M. McNamara, Christopher W. Moore, Daniel Obrist, Alexandra Steffen, Paul B. Shepson, Ralf M. Staebler, Angela R. W. Raso and Kerri A. Pratt identified the reaction pathway where mercury is removed from the atmosphere and transferred into the springtime Arctic ecosystem.
Mercury, an especially toxic pollutant to the Earth's atmosphere, is often emitted through human activities such as the burning of fossil fuels and dumping of mass municipal or medical waste. Because it's long-lived — as it does not react with many compounds in the atmosphere — it collects in various remote regions like the Arctic, explained University of Michigan professor of chemistry, Kerri Pratt to the Michigan News.
Mercury poisoning is slowly becoming a global, public health crisis. When mercury initially enters the ecosystem, the toxin becomes ingested in fish and then slowly reaches up the food chain to humans. At this time, 39 states — including Michigan — have released fish consumption advisories over the past few years.
Although researchers have suspected bromine reacts with ozone and mercury, no one has measured bromine atoms found in the atmosphere — until now. Pratt, along with lead author Siyuan Wang, now an Advanced Study Program postdoctoral fellow at the National Center for Atmospheric Research, recently published their findings in the Proceedings of the National Academy of Science.
"Our findings have implications across the world," Pratt said. "Even though this chemistry is most prevalent in the Arctic, the reactions with mercury occur in the upper troposphere of the tropics as well as other marine locations. The reaction of bromine atoms with ozone and mercury had been hypothesized for decades, but no one had been able to actually measure this chemical species to confirm this is the chemistry that is happening."
According to Wang, bromine atoms are extremely difficult to measure simply because there are very few places they exist on Earth and because bromine is only reactive at lower levels. A few places bromine can be identified include above the Arctic and Antarctic snow packs and above the tropics in the upper troposphere, about 8 miles above the Earth.
The researchers made their way to the Arctic tundra, hauling a device called the chemical ionization mass spectrometer. This machine allows air to be sucked through a slim inlet and into the device to measure the masses of the products in the sample. Then by observing the masses of the products, the researchers identified what was in the air: bromine.
Bromine is synthesized when sunlight meets the Arctic snow, causing a chemical reaction in the snow's surface to produce molecular bromine — two bromine atoms hooked together. With another touch of sunlight, the molecule seperates to form singular bromine atoms and thus spreads into the atmosphere.
Wang is optimistic these new discoveries could help aid in preventing ozone depletion caused by mercury around the world.
“With this new capability of measuring bromine atoms, we can improve our ability to predict mercury chemistry on a global scale,” Wang said.