Which contributes to the ozone hole

The ozone hole is the region over Antarctica with total ozone of Dobson Units or lower. This map shows the ozone hole on October 4, Many people have heard that the ozone hole is caused by chemicals called CFCs, short for chlorofluorocarbons. CFCs escape into the atmosphere from refrigeration and propellant devices and processes.

In the lower atmosphere, they are so stable that they persist for years, even decades. This long lifetime allows some of the CFCs to eventually reach the stratosphere.

In the stratosphere, ultraviolet light breaks the bond holding chlorine atoms Cl to the CFC molecule. A free chlorine atom goes on to participate in a series of chemical reactions that both destroy ozone and return the free chlorine atom to the atmosphere unchanged, where it can destroy more and more ozone molecules.

For those who know the story of CFCs and ozone, that is the part of the tale that is probably familiar. Most commercial airplanes fly in the lower part of the stratosphere.

Health and Environmental Effects of Ozone Depletion. Ozone Layer Research and Technical Resources. Information for students about the Ozone Layer. 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.

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. 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. Each natural reduction in ozone levels has been followed by a recovery. Beginning in the s, however, scientific evidence showed that the ozone shield was being depleted well beyond natural processes.

When chlorine and bromine atoms come into contact with ozone in the stratosphere, they destroy ozone molecules. One chlorine atom can destroy over , ozone molecules before it is removed from the stratosphere. Ozone-rich air from lower latitudes mixes back into the polar stratosphere, and the ozone hole disappears until the next spring. Thanks to the Montreal Protocol , the production and use of ozone-damaging chemicals has declined.

But CFCs are extremely long-lived under most atmospheric conditions, so it will be decades before the global concentration returns to pre levels.

Ozone-depleting gases reached their peak concentrations in the mid-latitudes purple in the mids and over Antarctica blue in the early s.

Because it takes decades for chlorofluorocarbons to degrade, it will be many decades before the ozone hole recovers. In the meantime, the size of the ozone hole in any given year is influenced by natural variability in global atmospheric circulation. These variations influence the spread of ozone-depleting chemicals into the polar stratosphere, and, most importantly, they determine the extent and severity of cold temperatures.

The final conversion of chlorine from degraded CFCs into its ozone-destroying, free radical form takes place only within polar stratospheric clouds. In general, the colder the winter, the more clouds. The more clouds, the larger the pool of highly reactive chlorine-containing gases, and the worse the ozone hole in spring. Because the ozone layer normally blocks ultraviolet UV light, an ozone hole allows more UV light than usual to reach the surface.

How small? Well, the vast majority of sunlight is the light we can see—visible light with wavelengths of nanometers. UV light is only about 8 percent of all sunlight to begin with, and the ozone layer and oxygen both of which absorb UV only permit a fraction of that to reach the surface. Reasons for the ozone hole The ozone hole has developed because people have polluted the atmosphere with chemicals containing chlorine and bromine.

A simplified description of the process involving CFCs is as follows: Once they reach the stratosphere, un-reactive CFCs can be broken down by UV radiation to release reactive chlorine. For this to occur, clouds need to be present in the stratosphere to provide ice crystal surfaces on which these chemical reactions can take place. ClO quickly breaks down to release the Cl atom which can repeat the process with another O3 molecule.

In this way, one chlorine can gobble its way through around molecules of ozone before it leaves the stratosphere. The problem and the solutions The ozone layer protects life from harmful UV-B radiation which can cause cancer and stunt the growth of plants.

Learn more about the Montreal Protocol: Australian Government. United States Environmental Protection Agency. United Nations Development Programme. Student activity 1 Write a summary Use the text above, and information from any of the links listed, to write your own summary of the ozone hole.

Address the following questions in your summary document: What is the ozone hole and why should we be concerned about it? Why does most ozone depletion happen in the spring in the polar regions? Why is the problem of ozone depletion more severe in the Southern Hemisphere? What steps have been taken by the international community to deal with the problem? Why will it take until roughly for the ozone layer to fully repair itself even though emissions of ozone depleting chemicals have been declining since the late s?

Student activity 2 Work with graphs Download the Excel spreadsheet which contains data for average October ozone measured above Halley Research Station and the global amount of CFC released annually to Make a graph plotting the average October ozone readings Dobson units against the years of record to Describe the trend in October ozone levels shown in the graph, work out the range between the highest and lowest readings in the data set, and give an approximate percentage for the total decline in ozone.

Make a graph plotting CFC release against years in this data set to Describe changes in CFC over this time period, and annotate the graph to show when the Montreal Protocol came into force. Make a third graph to examine the relationship between October ozone over Halley and annual CFC release between the years and Remember to plot the independent variable on the x-axis and the dependent variable on the y-axis. Add a trend line to the graph and create a caption that describes the nature of the relationship between the two variables and the strength of the relationship shown.

Download Ozone spreadsheet Excel. Student activity 3 Write an essay Using the information in both this section and Climate change: past and future , as well as any of the suggested links, write an essay answering this question: Why does tackling the problem of global warming present a bigger challenge to the international community than the problem of the ozone hole?