Scientists have long known lightning creates ozone molecules, but just last year, scientists were astonished to learn that thunderstorms can destroy ozone just as easily as they can create it.
A group of NASA-funded scientists from Harvard University learned that when powerful thunderstorms burst into the stratosphere, they provide the last few ingredients that CFCs need to destroy ozone: warm, moist air. Ozone can't be harmed by CFCs until sunlight breaks these molecules apart. This chemical reaction can't proceed if the temperature isn't right, and that "activation" temperature is also sensitive to humidity. If the air is wetter, the temperature must be higher for the reaction to occur. Summertime conditions in the lower stratosphere are usually warm and dry enough to suppress this reaction, but when thunderstorms add moisture to the stratosphere, ozone can be destroyed rapidly at the stratosphere's ambient temperature.
Photo courtesy of NASA.
When scientists were collecting data, they found that thunderstorms were injecting water vapor into the atmosphere much more frequently than they had expected: about 50 percent of the time, and sometimes the moist-air remnants spread out over 100 kilometers (about 62 miles) and lingered for days. Both of these observations suggest that a single thunderstorm could destroy ozone molecules across an area much larger than itself for days. Needless to say, if these thunderstorms become more frequent in the future, ozone depletion could accelerate as well.
(Sources: Anderson, James G., David M. Wilmouth, Jessica B. Smith, and David S. Sayres, 2012, "UV Dosage Levels in Summer: Increased Risk of Ozone Loss from Convectively Injected Water Vapor," Science, 337:6096; Henry Fountain, "Storms Threaten Ozone Layer Over U.S., Study Says," The New York Times, July 26, 2012.)
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