Ozone Depletion

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Ozone (O3) is found in two different parts of our atmosphere. Ground level ozone, a human health irritant and component of smog, is found in the lower atmosphere (troposphere) and has nothing to do with the "ozone hole." However, ozone in the stratosphere—the layer of atmosphere above the troposphere _ accounts for the vast majority of atmospheric ozone. Stratospheric ozone is protective for human health as it absorbs ultraviolet radiation from the sun, preventing the radiation from hitting Earth's surface and harming living organisms from this biologically dangerous radiation.




The stratospheric ozone layer shields life on Earth from the Sun’s harmful ultraviolet radiation. Chemicals that destroy ozone are formed by industrial and natural processes. With the exception of volcanic injection and aircraft exhaust, these chemicals are carried up into the stratosphere by strong upward-moving air currents in the tropics. Methane (CH₄), chlorofluorocarbons (CFCs), nitrous oxide (N₂O) and water are injected into the stratosphere through towering tropical cumulus clouds. These compounds are broken down by the ultraviolet radiation in the stratosphere. Byproducts of the breakdown of these chemicals form “radicals”—such as nitrogen dioxide (NO₂) and chlorine monoxide (ClO)—that play an active role in ozone destruction. Aerosols and clouds can accelerate ozone loss through reactions on cloud surfaces. Thus, volcanic clouds and polar stratospheric clouds can indirectly contribute to ozone loss.


 

(CFCs, freons, halons.) CFCs and other contributory substances are referred to as ozone-depleting substances (ODS).

Since the ozone layer prevents most harmful UVB wavelengths (280–315 nm) of ultraviolet light (UV light) from passing through the Earth's atmosphere, observed and projected decreases in ozone have generated worldwide concern leading to adoption of the Montreal Protocol that bans the production of CFCs, halogens  and other ozone-depleting chemicals such as carbon tetrachloride and trichloroethane. It is suspected that a variety of biological consequences such as increases in skin cancer, cataracts, damage to plants, and reduction of plankton populations in the ocean's photic zone may result from the increased UV exposure due to ozone depletion.




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