[Ecology Unit Notes]
Ozone Depletion

Ozone is a natural occurring gas found in earth's atmosphere which consists of 3 oxygen atoms (O3) bonded together. It is formed naturally by lightning and is also formed as a byproduct of many internal combustion engines. Normally it is found at low altitudes in concentrations near 0.01 ppm (parts per million). Much higher levels at low altitudes results in air pollution, and is most visible in large cities about the world.

Concentrations in the stratosphere (12-30 miles) above the earth are more concentrated (about 1-10 ppm). This stratospheric layer of ozone is known as the ozone layer. The ozone layer helps protect the living organisms on earth.

Ozone absorbs high energy (short wave) radiation, and most importantly, ultraviolet radiation. The result is a reduction of harmful UV radiation reaching the Earth.

Ozone Depletion:

Levels of atmospheric ozone have decreased dramatically across the world since the mid 1900s. An ozone hole has developed over the Antarctic each summer for the last 2 decades. Ozone depletion could potentially allow enough UV radiation to reach Earth to damage all living things not submerged under several feet of water.

Ozone Hole Animation (US EPA)

Damaging Effects of UV Radiation:

a) Increases the mutation rates in DNA.

b) Causes severe sunburns and damage to eyes (cataracts).

c) Increases incidence of cancers (melanoma).

d) Reduces rate of photosynthesis in plants (lowers energy output of producers!).

Chlorine and Ozone Depletion:

A major cause of ozone depletion is the release of CFCs (chloro-fluro-carbons) into the atmosphere. CFCs have until recently been found as refrigerants in freezers, as a propellant in aerosol spray cans, and in certain plastic foams. When these plastics are burned or old refrigerators leak, the CFCs rise into the atmosphere. UV radiation causes the CFCs to break apart and release free chlorine atoms. Chlorine is very electronegative, and reacts readily with many compounds. When it strikes an ozone molecule, the ozone is converted to regular molecular oxygen (O2) which does not protect the Earth from UV light. One chlorine atom can continue to degrade literally thousands of ozone molecules.

Animation: How Ozone is Destroyed by CFCs


Combating Ozone Depletion:

Reducing or eliminating the use of CFCs worldwide has the best chance to reduce the rate of ozone depletion. Sadly, CFCs persist for many years in the atmosphere, so despite their elimination, their levels may continue to rise for another decade or so.

The Montreal Protocol was an international treaty signed in response to the danger of CFCs. It set target levels and dates to reduce the use of CFCs worldwide.

Other Measures for CFC Reduction include:

a) Take old refrigerators, freezers, and air conditioners to special companies which remove the CFCs before they are junked.

b) Eliminate the use of plastic foam packaging which has been gas-blown. (Example: MacDonalds converted from foam packaging to paper packaging.)

c) Use pump spray cans or those lacking CFCs as the propellant. (This has largely been done in North America already.)