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 can be destroyed more quickly than it is naturally created. Some compounds release chlorine or bromine when they are exposed to intense UV light in the stratosphere. These compounds contribute to ozone depletion, and are called ozone-depleting substances ODS ODS A compound that contributes to stratospheric ozone depletion.
ODS include chlorofluorocarbons CFCs , hydrochlorofluorocarbons HCFCs , halons, methyl bromide, carbon tetrachloride, hydrobromofluorocarbons, chlorobromomethane, and methyl chloroform.
ODS are generally very stable in the troposphere and only degrade under intense ultraviolet light in the stratosphere. When they break down, they release chlorine or bromine atoms, which then deplete ozone. ODS that release chlorine include chlorofluorocarbons chlorofluorocarbons Gases covered under the Montreal Protocol and used for refrigeration, air conditioning, packaging, insulation, solvents, or aerosol propellants.
Since they are not destroyed in the lower atmosphere, CFCs drift into the upper atmosphere where, given suitable conditions, they break down ozone. These gases are being replaced by other compounds: hydrochlorofluorocarbons, an interim replacement for CFCs that are also covered under the Montreal Protocol, and hydrofluorocarbons, which are covered under the Kyoto Protocol. All these substances are also greenhouse gases.
See hydrochlorofluorocarbons, hydrofluorocarbons, perfluorocarbons, ozone depleting substance. CFCs , hydrochlorofluorocarbons hydrochlorofluorocarbons Compounds containing hydrogen, fluorine, chlorine, and carbon atoms. Although ozone depleting substances, they are less potent at destroying stratospheric ozone than chlorofluorocarbons CFCs. The scientific community has observed the chemical reactions that attack ozone over the polar regions in winter, but the important combination of observations that define the cause and the rate of stratospheric ozone loss have never been made over the central US in summer.
The researchers are calling for extensive characterization of the stratosphere over the central United States in order to forecast short-term and long-term ozone loss related to increasing frequency and intensity of storm systems, higher levels of atmospheric carbon dioxide and methane, and other factors.
Topics: Climate. Leah Burrows lburrows seas. Climate , Environment. First study to quantify the degree to which increases in PM2. Evidence shows increased risk of ozone loss over the United States in summer Researchers link the need forforecasts of ozone lossover theGreat Plainsto climate change.
Press contact. June 5, Facebook Twitter Email LinkedIn. Cutting-edge science delivered direct to your inbox. Scientist Profiles. Steven C. James G. Because all sunlight contains some UVB, even with normal stratospheric ozone levels, it is always important to protect your skin and eyes from the sun. See a more detailed explanation of health effects linked to UVB exposure. EPA uses the Atmospheric and Health Effects Framework model to estimate the health benefits of stronger ozone layer protection under the Montreal Protocol.
UVB radiation affects the physiological and developmental processes of plants. Despite mechanisms to reduce or repair these effects and an ability to adapt to increased levels of UVB, plant growth can be directly affected by UVB radiation. Indirect changes caused by UVB such as changes in plant form, how nutrients are distributed within the plant, timing of developmental phases and secondary metabolism may be equally or sometimes more important than damaging effects of UVB.
These changes can have important implications for plant competitive balance, herbivory, plant diseases, and biogeochemical cycles.
Phytoplankton form the foundation of aquatic food webs. Phytoplankton productivity is limited to the euphotic zone, the upper layer of the water column in which there is sufficient sunlight to support net productivity. Exposure to solar UVB radiation has been shown to affect both orientation and motility in phytoplankton, resulting in reduced survival rates for these organisms. Scientists have demonstrated a direct reduction in phytoplankton production due to ozone depletion-related increases in UVB.
UVB radiation has been found to cause damage to early developmental stages of fish, shrimp, crab, amphibians, and other marine animals. The most severe effects are decreased reproductive capacity and impaired larval development. Small increases in UVB exposure could result in population reductions for small marine organisms with implications for the whole marine food chain.
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