First direct measurements of atomic bromine in the atmosphere reported

The first direct measurements of atomic bromine in the atmosphere confirm that the trace chemical plays an important role in reactions that result in depletion of low-lying ozone and deposition of toxic mercury on land (Proc. Natl. Acad. Sci. U.S.A. 2019, DOI: 10.1073/pnas.1900613116).

Previous research showed that atomic bromine enters the atmosphere in the Arctic thanks to photochemistry involving the interplay of sunshine, salty sea spray, and reflective snow. But scientists had never directly observed bromine’s subsequent chemistry, University of Michigan atmospheric chemist Kerri Pratt says.

Pratt’s lab had to adapt existing detection technology to trace very small concentrations of the short-lived atom, then get the equipment to a remote area outside Utqiaġvik, Alaska. “Think about putting a chemical ionization mass spec on an airplane, then transporting it over the tundra on the back of a sled in the snow, then getting it to work the best it can at its detection limit,” Pratt says.

During spring of 2012, Pratt’s group found atomic bromine levels as high as 14 parts per trillion in the Arctic atmosphere. Previously, researchers used proxies such as satellite observations of BrO to estimate atomic Br levels. The actual Br levels were 3 to 10 times as great as these estimates. There’s no substitute for the direct measurement, Pratt says. These measurements, she says, also confirm that atmospheric Br plays an important role in depleting ozone and oxidizing mercury. Whether and how climate change will shift this chemistry is an open question, she says.