Depletion of Ozone in the Stratosphere

Comment In principle, any photon with a wavelength of 240 nm or shorter can 

Practice Exercise Calcnlate the wavelength (in nm) of a photon needed to dissociate t iARiS an O3 molecule  

Support for this explanation came inadvertently in 1991, when astronauts aboard Discovery released various gases, including carbon dioxide, neon, xenon, and nitric oxide, from the cargo bay in the course of an unrelated experiment. Expelled one at a time, these gases scattered onto the surface of the shuttle s tail. The nitric oxide caused the normal shuttle glow to intensify markedly, but the other gases had no effect on it. 

What is the source of the nitric oxide on the outside of the spacecraft Scientists believe that some of it may come from the exhaust gases emitted by the shuttle s rockets and that some of it is present in the surrounding atmosphere. The shuttle glow does not harm the vehicle, but it does interfere with spectroscopic measurements on distant objects made from the spacecraft. 

As the NO2 leaves the shell of the spacecraft, it emits photons at a wavelength of 

As mentioned earlier, ozone in the stratosphere prevents UV radiation emitted by the sun from reaching Earth s surface. The formation of ozone in this region begins with the photodissociation of oxygen molecules by solar radiation at wavelengths below 240 mn  

The highly reactive O atoms combine with oxygen molecules to form ozone as follows  

The process continues when O and O2 recombine to form O3 as shown in Equation 21.2, further warming the stratosphere. 

If all the stratospheric ozone were compressed into a single layer at STP on Earth, that layer would be only about 3 nun thick Although the concentration of ozone in the stratosphere is veiy low, it is sufficient to filter out (i.e., absorb) solar radiation in the 200- to 300-nm range (see Equation 21.3). In the stratosphere, it acts as our protective shield against UV radiation, which can induce skin cancer, cause genetic mutations, and destroy crops and other forms of vegetation. 

Because of their relative inertness, the CFCs slowly diffuse unchanged up to the stratosphere, where UV radiation of wavelengths between 175 and 220 nm causes them to decompose  

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Nitrous oxide contributes severely to global warming and the depletion of ozone in the stratosphere (Crutzen 1981, Bouwman 1996). Almost 90% of the global atmospheric N2O is formed during the microbial transformation of nitrate (NO ) and ammonia (NH ) in soils and water. In OECD countries the agricultural contribution to N2O emissions is estimated at 58% (IPCC 2001). Soils fertilised with inorganic fertilisers and manure stores are seen as the largest sources (Chadwick et al. 1999, Brown ef al. 2002). 

The depletion of ozone in the stratosphere can be summarized by the net equation 2 03(g) - 3 02(g). (a) From values in Appendix 2A, calculate the standard reaction free energy and the standard reaction entropy for the reaction, (b) What is the equilibrium constant of the reaction at 25°C What is the significance of your answers with regard to ozone depletion ... 

Draw Lewis structures for the following chlorofluo-rocarbons (CFCs), which are partly responsible for the depletion of ozone in the stratosphere (a) CFCI3, (b) CF2CI2, (c) CHF2CI, (d) CF3CHF2. 

One of the steps involved in the depletion of ozone in the stratosphere by nitric oxide may be represented as... 

The ozone layer protects Earth s surface from damaging ultraviolet (UV) radiation. Therefore, if the concentration of ozone in the stratosphere decreases substantially, more UV radiation wiU reach Earth s surface, causing unwanted photochemical reactions, including reactions correlated with skin cancer. Satellite monitoring of ozone, which began in 1978, has revealed a depletion of ozone in the stratosphere that is particularly severe over Antarctica, a phenomenon known as the ozone hole ( FIGURE 18.6). The first scientific paper on this phenomenon appeared in 1985, and the National Aeronautics and Space Administration (NASA) maintains an Ozone Hole Watch website with daily updates and data from 1999 to the present. 

A reaction that contributes to the depletion of ozone in the stratosphere is the direct reaction of oxygen atoms with ozone ... 

Air pollution is caused by the domestic and industrial burning of carbonaceous fuels, by industrial processes, and by gases in car exhausts. Among recent problems are industrial emissions of sulfur(IV) oxide, a cause of acid rain, and emissions of chlorofluorocarbons (CFCs), previously widely used in refrigeration, aerosols, etc., and linked to the depletion of ozone in the stratosphere. Carbon dioxide, produced by burning fossil fuels, is slowly building up in the atmosphere, which could result in an... 

The depletion of ozone in the stratosphere by Cl atoms provides an example of the lowering of activation energy by a catalyst. Ozone is normally present in the stratosphere and provides protection against biologically destructive, short-wavelength ultraviolet radiation from the sun. Some recent ozone depletion in the stratosphere is believed to result from the Cl-catalyzed decomposition of O3. Cl atoms in the stratosphere originate from the decomposition of chlorofiuorocarbons (CFCs), which are compounds manufactured as refrigerants, aerosol propellants, and so forth. These Cl atoms react with ozone to form CIO and O2, and the CIO reacts with O atoms (normally in the stratosphere) to produce Cl and O2. 

In 1991 it was discovered that nitrous oxide (N2O) is produced in the synthesis of nylon. This compound, which is released into the atmosphere, contributes both to the depletion of ozone in the stratosphere and to the greenhouse effect, (a) Write equations representing the reactions between N2O and oxygen atoms in the stratosphere to produce nitric oxide (NO), which is then oxidized by ozone to form nitrogen dioxide, (b) Ls NiO a more effective greenhouse gas than carbon dioxide Explain. 

Carbon dioxide is not the only greenhouse enhancing gas almost any organic compounds as well as water vapor can act as a greenhouse gas. The third kind causes depletion of ozone in the stratosphere. 

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