CliffsNotes AP Environmental Science by Jennifer Sutton

Author:Jennifer Sutton
Language: eng
Format: epub
Publisher: Houghton Mifflin Harcourt
Published: 2012-01-25T16:00:00+00:00

Source: National Oceanic and Atmospheric Administration

In 1988, a similar but less severe hole was found in the ozone layer above the Arctic, occurring between February and June. The Arctic hole caused an 11 percent to 38 percent ozone loss (as compared to the 50 percent seasonal loss in Antarctica). As the ozone hole breaks up, it may move and linger over North America, Europe, and Asia. However, because the hole is not yet as thin as that in Antarctica, the increase in UVB radiation will not be nearly as extreme, so the effect on humans and local ecosystems will be less dramatic.

Chlorofluorocarbons (CFCs) are the primary man-made compounds involved in the depletion of ozone. They have commonly been used as refrigerants in air conditioners, refrigerators, and aerosol propellants. CFCs also are used as cleaning solvents for electrical parts and in the manufacturing of insulation. Prior to the 1980s, at least one million tons of CFCs were manufactured for consumer use every year, and the production and distribution of CFCs was a billion-dollar industry. The largest sources of environmental CFCs were leaks from car air conditioners and aerosols used in spray paints, deodorants, hairspray products, and other aerosol cans. Today, the use of CFCs as propellants is forbidden in the United States and most developed countries due to the strong link between CFCs and ozone depletion.

How Do CFCs Destroy Ozone?

When CFCs are released into the atmosphere, they rise through the troposphere and into the stratosphere. UV radiation breaks down the CFC molecule, releasing atomic chlorine (Cl). The released chlorine then detaches an oxygen molecule from ozone (O3) to create chlorine monoxide (ClO) and molecular oxygen (O2). Then the chlorine monoxide further reacts with another ozone molecule to produce two molecular oxygen molecules, freeing the chlorine to react with another ozone molecule and continue the cycle of ozone destruction. One freed atomic chlorine molecule from CFCs can destroy over 100,000 ozone molecules. The CFC may take many years to reach the stratosphere, where it can stay for 20 to 120 years, depending upon the exact compound. CFCs were first manufactured in 1931 as safer substitutes for ammonia and sulfur dioxide, the toxic refrigerants used at the time. The CFCs currently in the stratosphere may have been released any time since the development of CFCs.

Bromine levels in the stratosphere are about 150 times less than chlorine levels, but bromine is 10 to 100 times more influential in destroying ozone. This is because there is no stable, binding form of bromine in the stratosphere, and it is very easily photolyzed so that almost all the atmospheric bromine remains in a form that reacts with ozone. Approximately 20 percent of observed ozone depletion is caused by bromine. Bromine compounds are found in halons that are often used in dry-cleaning and fire-suppression equipment. Bromomethane (commonly known as methyl bromide [CH3Br]) is produced industrially and naturally. It was used extensively as a pesticide until it was phased out in most countries in the early 2000s due to its being recognized as an ozone-depleting chemical.

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