Air Pollution in the Stratosphere

VIII-2.1 The Earth s Atmosphere, 330 VIII-2.2 Atmospheric Air Pollution, 332 VIII-2.3 Photochemical Air Pollution in the Troposphere, 332 VIFI-2.4 Air Pollution in the Stratosphere, 340 VI11-3 Photochemistry of the Atmospheres of Other Planets, 352 VH1—3.1 Photochemistry of the Mars Atmosphere, 352 VII 1—3,2 Photochemistry of the Venus Atmosphere. 356 VIIl-3.3 Photochemistry of the Jovian Atmosphere, 357... 

Photochemical air pollution in the troposphere results from a complex interplay between sunlight and primary air pollutants emitted in ambient air that leads to the formation of ozone and other oxidizing and cye-irritaling agents. On the other hand, pollutants injected into the stratosphere by such human activities as supersonic transports (SST s) and release ofchlorofiuoro-methancs in air by their use as aerosol propellants and refrigerants may eventually reduce the protective layer of ozone from harsh solar ultraviolet radiation. Although the full impact of injected air pollutants in the stratosphere is not apparent at present, various model calculations show conclusively that the continuous future release of chlorofluoromethanes and NO (NO and N02) would result in substantial reduction of ozone in the stratosphere. 

Studies of the photochemical processes of small molecules are not only of intrinsic interest but also are important in understanding the photochemistry of isotope enrichment, of air pollution in the troposphere and stratosphere, and of the atmospheres of other planets. 

An important effect of air pollution on the atmosphere is change in spectral transmission. The spectral regions of greatest concern are the ultraviolet and the visible. Changes in ultraviolet radiation have demonstrable adverse effects e.g., a decrease in the stratospheric ozone layer permits harmful UV radiation to penetrate to the surface of the earth. Excessive exposure to UV radiation results in increases in skin cancer and cataracts. The worldwide effort to reduce the release of stratospheric ozone-depleting chemicals such as chlorofluorocarbons is directed toward reducing this increased risk of skin cancer and cataracts for future generations. 

The temperature inversion at the tropopause prevents mixing between the stratosphere and troposphere, with hotter air (less dense) sitting on top of cooler air (more dense). Pollutants (such as chlorofluorocarbons) present in the stratosphere have very long lifetimes (of order 30 years) and become persistent problems, especially... 

Sticksel discussed vertical profile measurements of ozone in the stratosphere and the troposphere over the last several years. Transient ozone maximums in the troposphere are illustrated and explained by three possible mechanisms a channel-like r on conducted ozone from the stratosphere into the troposphere ozone-laden air descended from the stratosphere and was compressed as it subsided and ozone-rich layers leaked through the break between the polar and middle tropopauses by differential advection. Surface variations of ozone soundings were mostly attributed to anthropogenic pollution however, relatively thick high-... 

As a result, while such methods have been very useful in the past and continue to be applied for initial surveys of air quality in areas in which measurements have not been made in the past, they have generally been abandoned in favor of instrumental methods of analysis. As a result, this chapter focuses on the most commonly used instrumental, often spectroscopic, methods for measuring air pollutants, trace gases, and particles in air (e.g., see Roscoe and Clemitshaw, 1997). The focus is on tropospheric measurements, although, in most cases, the same techniques are used in the stratosphere. 

Ozone is formed from automobile emissions and is an urban air pollutant, but it is also formed naturally in the stratosphere. At altitudes of 20 to 30 kilometers, high-energy ultraviolet (UV) radiation breaks diatomic oxygen down to atomic oxygen, which then reacts with additional Oz to form ozone ... 

Radicals such as OH and CIO are now believed to play key roles in air pollution of the troposphere and stratosphere, which is discussed in Section VIII 2. 

As the residence time of aerosols in the stratosphere is 2 yr and in the troposphere 1 week, the Be/ Be ratio of the two air masses is distinctive. Tropospheric air shows the ratio of Be relative to Be of 1.8, whereas stratospheric air has a ratio of 0.13. It is therefore possible to distinguish stratospheric air injected into the troposphere by considering the ratio of Be/ Be. Of course, the stratospheric air will also be higher in Be than the tropospheric air. As stratospheric air will also contain ozone, the interest in this source has been strong to distinguish from pollution-based tropospheric ozone. 

It is important to know whether molecules being released in the lower atmosphere can reach the stratosphere and affect the amount of ozone in it. Certain types of air pollution give rise to radicals that catalyze ozone depletion. A radical is a chemical species that contains an odd (unpaired) electron, and it is usually formed by the rupture of a covalent bond to form a pair of neutral species. One pressing concern involves chlorofluorocarbons (CFCs)—compounds of chlorine, fluorine, and carbon used as refrigerants and as propellants in some aerosol sprays. CFCs are nonreactive at sea level but can photodissociate in the stratosphere ... 

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