Environmental Engineering Reference
In-Depth Information
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 distri-
bution 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 (O
3
) to create
chlorine monoxide
(ClO) and molecular oxygen (O
2
). Then
the chlorine monoxide further reacts with another ozone molecule to produce two molecular oxygen molec-
ules, 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 com-
pound. CFCs were first manufactured in 1931 as safer substitutes for ammonia and sulfur dioxide, the toxic re-
frigerants 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 strato-
sphere, 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 (com-
monly known as methyl bromide [CH
3
Br]) 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. Methyl bromide is also produced by phytoplankton in the world's oceans and is found in
the smoke plumes of burning biomass.
