The ozone layer 臭氧層 can be depleted by free radical catalysts, including nitric oxide(NO), nitrous oxide (N2O), hydroxyl (OH), atomic chlorine (Cl), and atomic bromine(Br). While there are natural sources for all of these species, the concentrations of chlorine and bromine increased markedly in recent decades because of the release of large quantities of man-made organohalogen compounds, especially chlorofluorocarbons (CFCs) 冷氣機 噴霧劑and bromofluorocarbons.[10] These highly stable compounds are capable of surviving the rise to the stratosphere, where Cl and Br radicals are liberated by the action of ultraviolet light. Each radical is then free to initiate and catalyze a chain reaction capable of breaking down over 100,000 ozone molecules. By 2009, nitrous oxide was the largest ozone-depleting substance (ODS) emitted through human activities
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