1fs. Depletion of the Ozone LayerIn 1972 Sherwood Rowland and Mario
Molina, atmospheric chemists then working at the University of
California at Irvine, proposed that certain human-produced chemicals
called chlorofluorocarbons (CFCs) could be carried naturally into the
stratosphere and damage the ozone layer. At that time CFCs were widely
used in refrigeration and air conditioning, in the manufacture of
plastic foams, and as solvents in the electronics industry.Solving the
Ozone PuzzleKnowing that CFCs do not easily react with other molecules
in the lower atmosphere, Rowland and Molina needed to explain how CFCs
could affect ozone. They proposed that these molecules could reach the
stratosphere intact, where they would break down and release free atoms
of chlorine (Cl). Under certain circumstances, chlorine atoms can
effectively destroy ozone molecules. In the first step of this process, a
chlorine atom reacts with an ozone molecule to produce O2 and chlorine
monoxide (ClO). Next, an oxygen atom (O) reacts with ClO, creating
another O2 molecule while freeing the chlorine atom (Cl). Note that the
chlorine atom that first reacted with the ozone molecule is still
present and capable of reacting again with another ozone molecule. This
fact makes chlorine atoms able to repeatedly break down ozone molecules.
In fact, as many as 100,000 ozone molecules can be removed from the
atmosphere for every chlorine molecule present. Rowland and Molina’s
theory is now accepted, and the two scientists were rewarded for their
work with a Nobel Prize in 1995.Seasonality and Geographic
DistributionThe most severe ozone depletion occurs every October (spring
in the Southern Hemisphere) and persists for several months. Why is the
ozone hole found over the Antarctic during the spring? The answer is
fairly complex, but a variety of factors can be cited here. First, air
currents surrounding Antarctica isolate the region from the rest of the
hemisphere, so there is less mixing with ozone-rich air from the north.
Another factor is the unusual chemistry of clouds found in the Antarctic
stratosphere. At the very low temperatures found there, clouds are
largely made up of nitric acid and water, rather than ordinary water
ice. Processes involving these clouds allow certain chlorine compounds
to accumulate. When the dark Antarctic winter ends, the burst of
ultraviolet radiation breaks apart these compounds to create free
chlorine atoms (Cl). These Cl free radicals readily destroy ozone, as
described previously. A very recent discovery shows that depletion
begins at the rim of Antarctica, where sunlight arrives first, and works
its way poleward. Thus, depletion begins in June at 65° S but not until
late August at 75° S. We should emphasize that chlorine is not usually
abundant in the Antarctic stratosphere. Rather, what chlorine exists is
in a form able to destroy ozone, thanks to the unique conditions that
take place in the spring (see Figure 1-3-1).Significant stratospheric
ozone depletion has also been detected over much of Europe and North
America, including a less pronounced hole over the Arctic. Nobody knows
how long the ozone will continue to decrease, or how depleted it may
become, but in November 1999 satellite and land-based data revealed
abnormally low ozone levels over northwestern Europe. Stratospheric
ozone values were 30 percent below normal for that time of year,
resulting in levels nearly as low as those normally observed over the
Antarctic.Society’s Response to Ozone DepletionGovernment and private
industry have taken action to help reduce the amount of CFCs entering
the atmosphere. In accordance with the Montreal Protocol of 1987 and
subsequent conferences, the world’s developed countries have ceased
production of CFCs. Continued production in developing countries was
permitted by the protocol and many have done so (by 2007 China was the
world’s largest producer). CFCs have lifetimes in the atmosphere of
about 100 years, so an immediate reduction in the ozone hole will not
occur. But progress has been made; since 1997 there has been a decline
in the amount of chlorine in the stratosphere, and the size of the ozone
hole appears to have stabilized, although significant year-to-year
variations still occur due to weather conditions. A 2006 United Nations
study predicted that Antarctic ozone levels may return to pre-1980
levels sometime between 2060 and 2075—a slow but significant
improvement. Thus, curbing CFC emissions illustrates how solid science,
combined with international cooperation, can have a major impact on the
protection of the environment.Where and when does the ozone hole occur? Get solution
2fs. Depletion of the Ozone LayerIn 1972 Sherwood Rowland and Mario Molina, atmospheric chemists then working at the University of California at Irvine, proposed that certain human-produced chemicals called chlorofluorocarbons (CFCs) could be carried naturally into the stratosphere and damage the ozone layer. At that time CFCs were widely used in refrigeration and air conditioning, in the manufacture of plastic foams, and as solvents in the electronics industry.Solving the Ozone PuzzleKnowing that CFCs do not easily react with other molecules in the lower atmosphere, Rowland and Molina needed to explain how CFCs could affect ozone. They proposed that these molecules could reach the stratosphere intact, where they would break down and release free atoms of chlorine (Cl). Under certain circumstances, chlorine atoms can effectively destroy ozone molecules. In the first step of this process, a chlorine atom reacts with an ozone molecule to produce O2 and chlorine monoxide (ClO). Next, an oxygen atom (O) reacts with ClO, creating another O2 molecule while freeing the chlorine atom (Cl). Note that the chlorine atom that first reacted with the ozone molecule is still present and capable of reacting again with another ozone molecule. This fact makes chlorine atoms able to repeatedly break down ozone molecules. In fact, as many as 100,000 ozone molecules can be removed from the atmosphere for every chlorine molecule present. Rowland and Molina’s theory is now accepted, and the two scientists were rewarded for their work with a Nobel Prize in 1995.Seasonality and Geographic DistributionThe most severe ozone depletion occurs every October (spring in the Southern Hemisphere) and persists for several months. Why is the ozone hole found over the Antarctic during the spring? The answer is fairly complex, but a variety of factors can be cited here. First, air currents surrounding Antarctica isolate the region from the rest of the hemisphere, so there is less mixing with ozone-rich air from the north. Another factor is the unusual chemistry of clouds found in the Antarctic stratosphere. At the very low temperatures found there, clouds are largely made up of nitric acid and water, rather than ordinary water ice. Processes involving these clouds allow certain chlorine compounds to accumulate. When the dark Antarctic winter ends, the burst of ultraviolet radiation breaks apart these compounds to create free chlorine atoms (Cl). These Cl free radicals readily destroy ozone, as described previously. A very recent discovery shows that depletion begins at the rim of Antarctica, where sunlight arrives first, and works its way poleward. Thus, depletion begins in June at 65° S but not until late August at 75° S. We should emphasize that chlorine is not usually abundant in the Antarctic stratosphere. Rather, what chlorine exists is in a form able to destroy ozone, thanks to the unique conditions that take place in the spring (see Figure 1-3-1).Significant stratospheric ozone depletion has also been detected over much of Europe and North America, including a less pronounced hole over the Arctic. Nobody knows how long the ozone will continue to decrease, or how depleted it may become, but in November 1999 satellite and land-based data revealed abnormally low ozone levels over northwestern Europe. Stratospheric ozone values were 30 percent below normal for that time of year, resulting in levels nearly as low as those normally observed over the Antarctic.Society’s Response to Ozone DepletionGovernment and private industry have taken action to help reduce the amount of CFCs entering the atmosphere. In accordance with the Montreal Protocol of 1987 and subsequent conferences, the world’s developed countries have ceased production of CFCs. Continued production in developing countries was permitted by the protocol and many have done so (by 2007 China was the world’s largest producer). CFCs have lifetimes in the atmosphere of about 100 years, so an immediate reduction in the ozone hole will not occur. But progress has been made; since 1997 there has been a decline in the amount of chlorine in the stratosphere, and the size of the ozone hole appears to have stabilized, although significant year-to-year variations still occur due to weather conditions. A 2006 United Nations study predicted that Antarctic ozone levels may return to pre-1980 levels sometime between 2060 and 2075—a slow but significant improvement. Thus, curbing CFC emissions illustrates how solid science, combined with international cooperation, can have a major impact on the protection of the environment.Think about the production of CFCs and the release of carbon dioxide from fossil fuel burning. If society wanted to limit future carbon dioxide levels, would it be easy to achieve success like that seen with CFCs? Get solution
2fs. Depletion of the Ozone LayerIn 1972 Sherwood Rowland and Mario Molina, atmospheric chemists then working at the University of California at Irvine, proposed that certain human-produced chemicals called chlorofluorocarbons (CFCs) could be carried naturally into the stratosphere and damage the ozone layer. At that time CFCs were widely used in refrigeration and air conditioning, in the manufacture of plastic foams, and as solvents in the electronics industry.Solving the Ozone PuzzleKnowing that CFCs do not easily react with other molecules in the lower atmosphere, Rowland and Molina needed to explain how CFCs could affect ozone. They proposed that these molecules could reach the stratosphere intact, where they would break down and release free atoms of chlorine (Cl). Under certain circumstances, chlorine atoms can effectively destroy ozone molecules. In the first step of this process, a chlorine atom reacts with an ozone molecule to produce O2 and chlorine monoxide (ClO). Next, an oxygen atom (O) reacts with ClO, creating another O2 molecule while freeing the chlorine atom (Cl). Note that the chlorine atom that first reacted with the ozone molecule is still present and capable of reacting again with another ozone molecule. This fact makes chlorine atoms able to repeatedly break down ozone molecules. In fact, as many as 100,000 ozone molecules can be removed from the atmosphere for every chlorine molecule present. Rowland and Molina’s theory is now accepted, and the two scientists were rewarded for their work with a Nobel Prize in 1995.Seasonality and Geographic DistributionThe most severe ozone depletion occurs every October (spring in the Southern Hemisphere) and persists for several months. Why is the ozone hole found over the Antarctic during the spring? The answer is fairly complex, but a variety of factors can be cited here. First, air currents surrounding Antarctica isolate the region from the rest of the hemisphere, so there is less mixing with ozone-rich air from the north. Another factor is the unusual chemistry of clouds found in the Antarctic stratosphere. At the very low temperatures found there, clouds are largely made up of nitric acid and water, rather than ordinary water ice. Processes involving these clouds allow certain chlorine compounds to accumulate. When the dark Antarctic winter ends, the burst of ultraviolet radiation breaks apart these compounds to create free chlorine atoms (Cl). These Cl free radicals readily destroy ozone, as described previously. A very recent discovery shows that depletion begins at the rim of Antarctica, where sunlight arrives first, and works its way poleward. Thus, depletion begins in June at 65° S but not until late August at 75° S. We should emphasize that chlorine is not usually abundant in the Antarctic stratosphere. Rather, what chlorine exists is in a form able to destroy ozone, thanks to the unique conditions that take place in the spring (see Figure 1-3-1).Significant stratospheric ozone depletion has also been detected over much of Europe and North America, including a less pronounced hole over the Arctic. Nobody knows how long the ozone will continue to decrease, or how depleted it may become, but in November 1999 satellite and land-based data revealed abnormally low ozone levels over northwestern Europe. Stratospheric ozone values were 30 percent below normal for that time of year, resulting in levels nearly as low as those normally observed over the Antarctic.Society’s Response to Ozone DepletionGovernment and private industry have taken action to help reduce the amount of CFCs entering the atmosphere. In accordance with the Montreal Protocol of 1987 and subsequent conferences, the world’s developed countries have ceased production of CFCs. Continued production in developing countries was permitted by the protocol and many have done so (by 2007 China was the world’s largest producer). CFCs have lifetimes in the atmosphere of about 100 years, so an immediate reduction in the ozone hole will not occur. But progress has been made; since 1997 there has been a decline in the amount of chlorine in the stratosphere, and the size of the ozone hole appears to have stabilized, although significant year-to-year variations still occur due to weather conditions. A 2006 United Nations study predicted that Antarctic ozone levels may return to pre-1980 levels sometime between 2060 and 2075—a slow but significant improvement. Thus, curbing CFC emissions illustrates how solid science, combined with international cooperation, can have a major impact on the protection of the environment.Think about the production of CFCs and the release of carbon dioxide from fossil fuel burning. If society wanted to limit future carbon dioxide levels, would it be easy to achieve success like that seen with CFCs? Get solution
