what are the chlorine and bromine reactions that destroy stratospheric ozone
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Answer:
Reactive gases containing chlorine and bromine destroy stratospheric ozone in “catalytic” cycles made up of two or more separate reactions. As a result, a single chlorine or bromine atom can destroy many hundreds of ozone molecules before it reacts with another gas, breaking the cycle.
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Answer:
Numerous laboratory investigations and analyses of worldwide measurements made in the stratosphere have demonstrated that chlorine- and bromine-containing chemicals destroy ozone molecules.
Research studies in the laboratory show that chlorine (Cl) reacts very rapidly with ozone. They also show that the reactive chemical chlorine monoxide (ClO) formed in that reaction can undergo further processes that regenerate the original chlorine, allowing the sequence to be repeated very many times (a chain reaction). Similar reactions also take place between bromine and ozone.
But do these ozone-destroying reactions occur in the "real world"? All the accumulated scientific experience demonstrates that the same chemical reactions do take place in nature. Many other reactions (including those of other chemical species) are often also taking place simultaneously in the stratosphere. This makes the connections among the changes difficult to untangle. Nevertheless, whenever chlorine (or bromine) and ozone are found together in the stratosphere, the ozone-destroying reactions are taking place.
Sometimes a small number of chemical reactions are so dominant in the natural circumstance that the connections are almost as clear as in laboratory experiments. Such a situation occurs in the Antarctic stratosphere during the springtime formation of the ozone hole. Independent measurements made by instruments from the ground and from balloons, aircraft, and satellites have provided a detailed understanding of the chemical reactions in the Antarctic stratosphere. Large areas reach temperatures so low (less than 80oC, or 112oF) that stratospheric clouds form, which is a rare occurrence, except during the polar winters. These polar stratospheric clouds allow chemical reactions that transform chlorine species from forms that do not cause ozone depletion into forms that do cause ozone depletion. Among the latter is chlorine monoxide, which initiates ozone destruction in the presence of sunlight. The amount of reactive chlorine in such regions is therefore much higher than that observed in the middle latitudes, which leads to much faster chemical ozone destruction. The chemical reactions occurring in the presence of these clouds are now well understood from studies under laboratory conditions that mimic those found naturally in the atmosphere.