Introduction to OzoneHow important is the ozone in our atmosphere and why are scientists soconcerned about its increase near the surface of the earth and its disappearancehigher up in the atmosphere?First: what is ozone?Ozone is made of three oxygen atoms (O3). Theoxygen we find in our atmosphere is made up of twooxygen atoms (O2). Because of its chemicalformulation, a single atom of oxygen (O) is unstable.That is, it wants to combine with something else. Thatis why oxygen is almost always found in pairs, in its(O2) (diatomic) form, where it is more stable. (O3) isless stable than (O2), because it wants to return to the diatomic stateby giving up an oxygen atom.When enough ozone molecules are present, they form a pale bluegas. It is an unstable molecule that readily combines with other atoms.Ozone has the same chemical structure whether it is found in thestratosphere or the troposphere.In the troposphere, the ground-level or "bad" ozone is an air pollutantthat damages human health, vegetation, and many commonmaterials. It is a key ingredient of urban smog. In the stratosphere, wefind the "good" ozone that protects life on earth from the harmfuleffects of the ultraviolet rays that reach from the sun.
Second: Electromagnetic SpectrumTo understand how ozone is generated and the functions it serves inthe earths atmosphere, it is important to know something about theelectromagnetic spectrum — the energy emitted from the sun.Electromagnetic energy is sometimes described as traveling in wavesand sometimes as traveling in packets of energy referred to asphotons.Progressing from short wavelengths to long wavelengths, scientistshave identified gamma rays, x-rays, ultraviolet radiation, visible light(between 400 and 700 nanometers), infrared radiation (heat),microwaves, and radio waves. Short wavelengths have more energyper photon than long wavelengths.Ozone is constantly being formed in the earths atmosphere by theaction of the suns ultraviolet radiation on oxygen molecules.Ultraviolet light splits the molecules apart by breaking the bondsbetween the atoms. A highly reactive free oxygen atom then collideswith another oxygen molecule to form an ozone molecule. Becauseozone is unstable, ultraviolet light quickly breaks it up, and theprocess begins again.
Third: Ozone in the StratosphereOzone and oxygen molecules in the stratosphere absorb ultravioletlight from the sun, providing a shield that prevents this radiation frompassing to the earths surface. While both oxygen and ozone togetherabsorb 95 to 99.9% of the suns ultraviolet radiation, only ozoneeffectively absorbs the most energetic ultraviolet light, known as UV-Cand UV-B, which causes biological damage. The protective role of theozone layer in the upper atmosphere is so vital that scientists believelife on land probably could not exist today - without it.The term "shield" as a description of ozone in the stratosphere is a bitmisleading because the molecules do not form an impermeablesphere around the earth. Ozone continuously breaks apart into itsoxygen atoms and reforms as ozone molecules, so a particular ozonemolecule doesnt last very long. The "shield" changes constantly, butthe atmospheric chemical processes maintain a dynamic equilibriumthat keeps the overall amount of ozone constant - that is; if humansdid not contribute to the chemical processes.About 90% of the ozone in the earths atmosphere lies in the regioncalled the stratosphere between 16 and 48 kilometers (10 and 30miles) above the earths surface. Ozone forms a kind of layer in thestratosphere, where it is more concentrated than anywhere else, buteven there it is relatively scarce. Its concentrations inthe ozone layer is typically only 1 to 10 parts of ozoneper 1 million parts of air, compared with about 210,000parts of oxygen per 1 million parts of air.
Fourth: Ozone in the TroposphereThe other 10% of the ozone in the earths atmosphere is found in thetroposphere, which is the portion of the atmosphere from the earthssurface to about 12 km or 7 miles up. In the troposphere, ozone is notwanted. Ozone is even more scarce in the troposphere than thestratosphere with concentrations of about 0.02 to 0.3 parts per million.But even in such small doses, this molecule can do a lot of damage.And just to confuse things even further, ozone in the troposphere isone of the greenhouse gases. As discussed in the Greenhouse Effectsection, the naturally occurring greenhouse gases (including ozone)are what make earth habitable for life as we know it. But scientists arevery concerned about the warming effects of increased greenhousegases caused by human activities. So, in the troposphere, acceleratedozone levels deal us a double whammy - as a key ingredient in smogand as a powerful greenhouse gas.
Finally: Concluding ThoughtsOzone is found in two different layers of the atmosphere - thetroposphere and the stratosphere. The stratospheric ozone, or "goodozone," protects life on earth from harmful effects of the suns UVrays. We have good reason to be concerned about the thinning of theozone layer in the stratosphere. Tropospheric ozone, or "bad ozone,"is an air pollutant that damages human health, vegetation, and manycommon materials. We have good reason to be concerned about thebuildup of ozone in the troposphere.This scientific essay talks about ozone and why it is considered to bebad when found in the troposphere, and good when found in thestratosphere. Ozone has the same chemical structure whether it isfound in the stratosphere or troposphere.The general concepts found in this section include the following: Ozone is a form of oxygen. The molecule contains three oxygen atoms (O3) Ozone is unstable and will combine with other atoms. Ozone is found in the stratosphere, where it blocks the suns ultraviolet (UV) waves and prevents them from reaching the earths surface. 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.