Why care about ozone
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Why care about ozone?. The topic of ozone makes headlines on a regular basis, but why does a single molecule merit such media coverage?

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Why care about ozone l.jpg
Why care about ozone?

  • The topic of ozone makes headlines on a regular basis, but why does a single molecule merit such media coverage?

  • How important is the ozone in our atmosphere and why are scientists so concerned about its increase near the surface of the earth and its disappearance higher up in the atmosphere?

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What is ozone?

  • Ozone is made of three oxygen atoms

  • The oxygen we find in our atmosphere is made up of two oxygen atoms

  • Because of its chemical formulation, a single atom of oxygen (O) is unstable.

    • It wants to combine with something else. That is why oxygen is almost always found in pairs, in its (diatomic) form, where it is more stable.

    • O3 is less stable than O2 , because it wants to return to the diatomic state by giving up an oxygen atom.

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How is ozone formed?

  • Ozone is formed naturally in the upper stratosphere by short wavelength ultraviolet radiation.

  • Wavelengths less than ~240 nanometers are absorbed by oxygen molecules (O2), which dissociate to give O atoms.

  • The O atoms combine with other oxygen molecules to make ozone:

  • O2 + hv (light) -> O + O (wavelength < 240 nm)

  • O + O2 -> O3

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What is the ozone layer?

  • The ozone layer is a concentration of ozone molecules in the stratosphere. About 90% of the planet's ozone is in the ozone layer.

  • The layer of the Earth's atmosphere that surrounds us is called the troposphere. The stratosphere, the next higher layer, extends about 10-50 kilometers above the Earth's surface.

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What are the names of the levels of the atmosphere?What does the temperature of the atmosphere look like as we go up in altitude?



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Ozone filters UV

  • Stratospheric ozone is a naturally-occurring gas that filters the sun's ultraviolet (UV) radiation.

  • http://svs.gsfc.nasa.gov/vis/a000000/a000800/a000834/a000834.mpg

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How CFC’s interact with Ozone


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Click on this link and watch the animations

  • http://www.ucar.edu/learn/1_6_1.htm

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How is the ozone layer being depleted?

  • Ozone is produced naturally in the stratosphere. But this "good" ozone is gradually being destroyed by man-made chemicals referred to as ozone-depleting substances (ODS), including chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl bromide, carbon tetrachloride, and methyl chloroform. These substances were formerly used and sometimes still are used in coolants, foaming agents, fire extinguishers, solvents, pesticides, and aerosol propellants.


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How is the ozone layer being depleted?

  • Once released into the air these ozone-depleting substances degrade very slowly. In fact, they can remain intact for years as they move through the troposphere until they reach the stratosphere. There they are broken down by the intensity of the sun's UV rays and release chlorine and bromine molecules, which destroy the "good" ozone. Scientists estimate that one chlorine atom can destroy 100,000 "good" ozone molecules.


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How is the ozone layer being depleted?

  • Even though we have reduced or eliminated the use of many ODSs, their use in the past can still affect the protective ozone layer. Research indicates that depletion of the "good" ozone layer is being reduced worldwide. Thinning of the protective ozone layer can be observed using satellite measurements, particularly over the Polar Regions.


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Why care about diminished ozone?

  • A diminished ozone layer allows more radiation to reach the Earth's surface.

  • For people, overexposure to UV rays can lead to skin cancer, cataracts, and weakened immune systems.

  • Increased UV can also lead to reduced crop yield and disruptions in the marine food chain. UV also has other harmful effects.


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What is being done about the depletion of the ozone layer?

  • The United States, along with over 180 other countries, recognized the threats posed by ozone depletion and in 1987 adopted a treaty called the Montreal Protocol to phase out the production and use of ozone-depleting substances.


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What is being done about the depletion of the ozone layer?

  • EPA has established regulations to phase out ozone-depleting chemicals in the United States. Warning labels must be placed on all products containing CFCs or similar substances and nonessential uses of ozone-depleting products are prohibited. Releases into the air of refrigerants used in car and home air conditioning units and appliances are also prohibited. Some substitutes to ozone-depleting products have been produced and others are being developed. If the United States and other countries stop producing ozone-depleting substances, natural ozone production should return the ozone layer to normal levels by about 2050.


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Ozone layer animations 1979 and 1992

  • Figure 7e-2: Quicktime Animation of Antarctic Ozone Levels 1978-1992.

  • The following two animations describe 1979 and 1992 ozone levels at the South Pole for the period September 15 to November 15. View these images for comparison:

  • Figure 7e-3: Quicktime Animation of Antarctic Ozone Levels 1979; and

  • Figure 7e-4: Quicktime Animation of Antarctic Ozone Levels 1992.

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Figure 7e-5: Average areal coverage of the ozone hole from 1979 to 2004. In this analysis, the ozone hole is defined as the area for which ozone is less than 220 Dobson Units. The ozone hole has grown from a few million square kilometers in 1981 to an area larger than North America (about 24 million square kilometers) in the year 2000. (Source: NASA, TOMS Multimedia).

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Current Ozone Watch

  • http://ozonewatch.gsfc.nasa.gov/ozone_maps/movies/OZONE_D1979-10%25P1Y_G%5e360X240.LSH.mp4

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Tropospheric Ozone and Human Health Basics

  • Ozone is also found in the troposphere, where it can damage living tissue and human-produced objects. It is generated both from certain types of pollution and natural sources.

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Ozone on the ground

  • In the troposphere, the ground-level or "bad" ozone is an air pollutant that damages human health, vegetation, and many common materials.

  • It is a key ingredient of urban smog. In the stratosphere, we find the "good" ozone that protects life on earth from the harmful effects of the sun's ultraviolet rays.

  • For more info: http://www.epa.gov/oar/oaqps/gooduphigh/

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  • 1. How is ozone formed?

  • From Ozone: Good Up High, Bad Nearby answer the following questions. 2. Does ozone occur naturally in the stratosphere? 3. How does stratospheric ozone become depleted? 4. How does the depletion of stratospheric ozone affect humans and the environment? 5. What are the major sources of ozone precursors in the troposphere? (include percentages) 6. How does tropospheric ozone affect humans and the environment?