bromscykel

The bromscykel, or bromine cycle, refers to the biogeochemical cycling of bromine through the Earth’s atmosphere, oceans, rocks, soils, and living organisms. Bromine is a trace element in the surface environment, and its largest reservoir is seawater, where bromine mainly exists as bromide (Br−). Other reservoirs include halite minerals and bromine contained in organic matter.

In the oceans, bromide can be converted into reactive bromine species such as Br2, BrO, and HOBr through photochemical reactions on sea-salt aerosols and in sea ice. These reactive bromine species participate in catalytic cycles that destroy ozone in the troposphere and, under certain conditions, in the stratosphere. The bromine cycle is closely linked to the chlorine and iodine cycles and is influenced by sunlight, temperature, sea-ice extent, and the presence of brominated organic compounds.

Natural sources include sea spray, volcanic emissions, and weathering of rocks. Human activities add bromine to the environment through products and processes such as brominated flame retardants, solvents, and fumigants like methyl bromide. These anthropogenic inputs can increase atmospheric reactive bromine and affect ozone chemistry and the atmospheric oxidative capacity.

Sinks remove bromine from active cycling through deposition to surfaces, incorporation into marine organic matter, and burial in sediments. Biological production of brominated organic compounds by marine organisms also integrates bromine into the biosphere.

The bromine cycle is environmentally relevant because of its impact on ozone chemistry, atmospheric composition, and interactions with other halogen cycles. Ongoing research explores sources, reservoirs, and how climate change and pollution influence the cycle.