During

springtime Springtime may refer to: * Spring (season), one of the four temperate seasons Film and television * ''Springtime'' (1920 film), an American silent comedy starring Oliver Hardy * ''Springtime'' (1929 film), a ''Silly Symphonies'' animated Disney ...

in the polar regions of Earth, unique photochemistry converts inert

halide In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fluor ...

salt ions (e.g. Br⁻) into reactive

halogen The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group is ...

species (e.g. Br atoms and BrO) that episodically deplete ozone in the

atmospheric boundary layer In meteorology, the planetary boundary layer (PBL), also known as the atmospheric boundary layer (ABL) or peplosphere, is the lowest part of the atmosphere and its behaviour is directly influenced by its contact with a planetary surface. On Ear ...

to near zero levels. Since their discovery in the late 1980s, research on these

ozone depletion Ozone depletion consists of two related events observed since the late 1970s: a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere, and a much larger springtime decrease in stratospheric ozone (the ozone l ...

events (ODEs) has shown the central role of bromine photochemistry. Due to the autocatalytic nature of the reaction mechanism, it has been called bromine explosion. It is still not fully understood how salts are transported from the ocean and oxidized to become reactive halogen species in the air. Other halogens ( chlorine and

iodine Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...

) are also activated through mechanisms coupled to bromine chemistry. The main consequence of halogen activation is chemical destruction of ozone, which removes the primary precursor of atmospheric oxidation, and generation of reactive halogen atoms/oxides that become the primary oxidizing species. The different reactivity of halogens as compared to OH and ozone has broad impacts on atmospheric chemistry, including near complete removal and deposition of

mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

, alteration of oxidation fates for organic gases, and export of bromine into the free troposphere. Recent changes in the climate of the Arctic and state of the Arctic sea ice cover are likely to have strong effects on halogen activation and ODEs.

External links

Halogens and their role in polar boundary-layer ozone depletion
Environmental chemistry Ozone depletion {{physical-chemistry-stub

See also

External links