The detection of bromine atoms in the atmosphere has confirmed the reaction pathway through which mercury is removed from the atmosphere and enters the Arctic ecosystem during spring.
Mercury is a particularly toxic pollutant that is emitted largely through human activities such as power plants that burn coal. Because of its long life, it means that it does not react with many compounds in the atmosphere and accumulates in remote regions such as the Arctic, according to University of Michigan chemist Kerri Pratt.
Mercury can be a serious danger to public health. When it enters the ecosystem, it accumulates in the fish. The higher the fish is in the food chain, the more mercury accumulates.
Researchers have long suspected that bromine reacts with ozone, a greenhouse gas and mercury, but no one had measured the bromine atoms in the atmosphere. The main author Pratt and his team have published their results in the magazine «PNAS».
"Our findings have implications around the world," said Pratt. "Although this chemistry is more prevalent in the Arctic, reactions with mercury occur in the upper troposphere of the tropics, as well as in 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 that this is the chemistry that is happening. "
The unique chemistry occurs when sunlight hits the salt snow in the Arctic. The chemical reactions on the surface of the snow produce what is called molecular bromine: two atoms of bromine hooked. When sunlight hits this molecule, it breaks down to form bromine atoms.
Bromine is so reactive and at such low levels that it is very difficult to measure in the atmosphere, according to Wang, who led the work as a postdoctoral fellow in Pratt's lab. Together with the doctoral student from Pratt's laboratory, Stephen McNamara, they spent a lot of time in the laboratory synthesizing bromine atoms at extremely low levels to demonstrate their measurements in the Arctic.
The researchers installed sampling instruments in the Arctic tundra. The air is sucked through a carefully designed inlet into a device called a chemical ionization mass spectrometer. The spectrometer measures the masses of the products in the sample, which tells the researchers what was in the air.
Bromine atoms are also difficult to measure because there are few places on earth, according to Wang. These places include the Arctic and Antarctic snowbags and the tropics at the top of the troposphere, located about 8 kilometers from the Earth. Land.
"With this new ability to measure bromine atoms, we can improve our ability to predict the chemistry of mercury on a global scale," said Wang. "It was really exciting to be able to measure these atoms since it's a chemistry that had been hypothesized, but that could not be measured, for several decades, "said Pratt. .