Humans rely heavily on the absorption of ultraviolet B rays by the ozone layer because UV-B radiation causes skin cancer and can lead to genetic damage.
The ozone layer has historically protected the Earth from the harmful UV rays, although in recent decades this protection has diminished due to stratospheric ozone depletion. This "ozone hole" has extended to cover an area as large as The previous record of Figure courtesy of NASA. Ozone depletion is largely a result of man-made substances.
- Chlorine-catalyzed ozone depletion mechanism;
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Humans have introduced gases and chemicals into the atmosphere that have rapidly depleted the ozone layer in the last century. This depletion makes humans more vulnerable to the UV-B rays which are known to cause skin cancer as well as other genetic deformities.
Health and Environmental Effects of Ozone Layer Depletion
The possibility of ozone depletion was first introduced by scientists in the late 's as dreams of super sonic transport began to become a reality. The threat of ozone depletion from commercial super sonic transport was so great that it is often cited as the main reason why the US federal government pulled support for its development in Fear of ozone depletion was abated until when Sherwood Rowland and Mario Molina discovered that chlorofluorocarbons could be photolyzed by high energy photons in the stratosphere. The stratosphere is in a constant cycle with oxygen molecules and their interaction with ultraviolet rays.
This process is considered a cycle because of its constant conversion between different molecules of oxygen. The ozone layer is created when ultraviolet rays react with oxygen molecules O 2 to create ozone O 3 and atomic oxygen O. This process is called the Chapman cycle. It is important to keep in mind that ozone is constantly being created and destroyed by the Chapman cycle and that these reactions are natural processes, which have been taking place for millions of years. Because of this, the thickness the ozone layer at any particular time can vary greatly.
It is also important to know that O 2 is constantly being introduced into the atmosphere through photosynthesis, so the ozone layer has the capability of regenerating itself.
CFC molecules are made up of chlorine, fluorine and carbon atoms and are extremely stable. This extreme stability allows CFC's to slowly make their way into the stratosphere most molecules decompose before they can cross into the stratosphere from the troposphere. This prolonged life in the atmosphere allows them to reach great altitudes where photons are more energetic. Temperatures decrease with altitude in the troposphere.
As warm air rises, it cools, falling back to Earth. This process, known as convection, means there are huge air movements that mix the troposphere very efficiently. Virtually all human activities occur in the troposphere. Everest, the tallest mountain on the planet, is only about 5. The next layer, the stratosphere stratosphere The region of the atmosphere above the troposphere. The stratosphere extends from about 10km to about 50km in altitude.
Commercial airlines fly in the lower stratosphere. The stratosphere gets warmer at higher altitudes. In fact, this warming is caused by ozone absorbing ultraviolet radiation. Warm air remains in the upper stratosphere, and cool air remains lower, so there is much less vertical mixing in this region than in the troposphere. Most commercial airplanes fly in the lower part of the stratosphere. Health and Environmental Effects of Ozone Depletion. Ozone Layer Research and Technical Resources. Addressing Ozone Layer Depletion.
Adapting to a Changed Ozone Layer. Phasing Out Ozone-Depleting Substances. Managing Refrigerant Emissions. Most atmospheric ozone is concentrated in a layer in the stratosphere, about 9 to 18 miles 15 to 30 km above the Earth's surface see the figure below. Ozone is a molecule that contains three oxygen atoms. At any given time, ozone molecules are constantly formed and destroyed in the stratosphere. The total amount has remained relatively stable during the decades that it has been measured.
Source: Figure Q from Michaela I. Hegglin Lead Author , David W. Montzka, and Eric R. The ozone layer in the stratosphere absorbs a portion of the radiation from the sun, preventing it from reaching the planet's surface. UVB is a kind of ultraviolet light from the sun and sun lamps that has several harmful effects. It is a cause of melanoma and other types of skin cancer.
It has also been linked to damage to some materials, crops, and marine organisms. The ozone layer protects the Earth against most UVB coming from the sun.rappeporpalea.tk
Ozone Layer: Formation, Importance, Depletion Effects, Videos, Examples
It is always important to protect oneself against UVB, even in the absence of ozone depletion, by wearing hats, sunglasses, and sunscreen. However, these precautions will become more important as ozone depletion worsens. UVB has been linked to many harmful effects , including skin cancers, cataracts, and harm to some crops and marine life. Scientists have established records spanning several decades that detail normal ozone levels during natural cycles. Ozone concentrations in the atmosphere vary naturally with sunspots, seasons, and latitude. These processes are well understood and predictable.
Although CFCs are inert in the lower troposphere, Rowland realized that they can be broken down by UV radiation once they drift up into the stratosphere.
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Each chlorine atom would react immediately with an ozone molecule, setting off a chain reaction that would destroy thousands of ozone molecules. If CFC production continued, however, ozone loss would be even greater. In , the National Academies of Science issued a report affirming the destructive effects of CFCs on stratospheric ozone. Congressional hearings reached similar conclusions, and states and the federal government began exploring bans on the use of CFCs in aerosol cans.
When Rowland lectured on CFCs, industry groups often released statements disputing his claims. It seemed that, because of his focus on CFCs and ozone depletion, he started getting fewer invitations to speak. That bothered him. Rowland and Molina and the other scientists trying to understand stratospheric chemistry faced serious and fundamental challenges.
A significant number of chemical species were clearly involved in the interaction of CFCs and ozone in the stratosphere. Most are highly reactive and present in only trace amounts. Their chemistry was difficult to replicate in the laboratory. Additionally, stratospheric ozone concentrations fluctuate naturally by geography and by season.
The stratosphere is not an easy place to do research in. Measurements of ozone concentration were carried out by instruments carried into the stratosphere by balloons and aircraft. Ozone was also measured by instruments on satellites orbiting Earth, though satellite technology in the mids was still rather primitive. The crucial evidence supporting the CFC hypothesis came from British scientists working at the Halley Bay Station of the British Antarctic Survey, who had been taking ground-based measurements of total ozone for decades.
In , Joseph C. Farman and his colleagues at BAS studied the raw data and found that stratospheric ozone had decreased greatly since the s. The Antarctic ozone hole, as it came to be known, made depletion of the ozone layer a real and present danger to lawmakers and the public at large. Predictions of significant increases in the incidence of skin cancer resulting from continued use of CFCs spurred international action.
In , 56 countries agreed under what became known as the Montreal Protocol to cut CFC production and use in half.
Chlorofluorocarbons and Ozone Depletion
In subsequent years, the protocol was strengthened to require an eventual worldwide phaseout of the production of CFCs and other ozone depleting chemicals. It is a global problem. What is important is that it led to an international agreement that solved the problem. Their unprecedented advocacy ultimately led to the phasing out of CFCs worldwide through the passage of the Montreal Protocol in The research of Rowland and Molina brought worldwide attention to the impact of human-contributed pollution on a planetary scale.
Their work was among the first to directly effect a global shift in policy, preceding the current debate on climate change. ACS designated F.