Smog

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Smog
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Smog is a result of physical and chemical activities between various pollutants released from smoke stacks in the presence of fog (thus the word smog). Classical smog refers mainly to plume of sulfur oxides and particulate matter generated from the combustion of coals and
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Figure 8-6
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Oiled crow in the aftermath of the Exxon Valdez oil spill
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20 “Valdez Spill Toll is Now Called Far Worst,” New York Times, April 18, 1992.
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188
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petroleum products. It is formed primarily in the early morning, during
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winter months, and in places of high humidity where condensation of
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water vapor over smoke particles is easier. The notorious London “fog”
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discussed above is a good example of this type of smog.
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Photochemical smog is very different from classical smog because
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it is formed under specific meteorological conditions and only when
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a large amount of sunlight is available. It forms when nitric oxides and
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hydrocarbons react in the presence of sunlight to produce ozone;
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this ozone can be further oxidized to produce nitric dioxide and other
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photochemical oxidants.
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NO + 1/2 O2 NO2
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NO2 + HC NO + O
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O + O2 O3
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h ν
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The Los Angeles Basin is a prime location for photochemical activities
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because of the large number of cars and power stations, the availability of
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sunlight, and its proximity to water. Furthermore, the basin is surrounded
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on three sides by the San Fernando mountain range, which prevents the
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dispersion of the pollutants. To make the matter worse, Los Angeles has
 +
many days in which a thermal (or temperature) inversion layer blankets
 +
the basin and prevents the upward mixing of pollutants with atmospheric
 +
air. Thermal inversion refers to the condition where, as a result of a large
 +
amount of emissions from cars and smoke stacks, temperature increases
 +
rather than decreases with height (Figure 8-7). Under these conditions,
 +
a warm layer is sandwiched between a layer of cold air near the surface
 +
and another cold layer in the upper atmosphere. Thermal inversion is
 +
more severe when wind is calm and pollutants can stay in place for many
 +
hours or even days. The smaller the inversion’s height, the less volume is
 +
available where pollutants can mix and the greater their concentration.
 +
The situation can be visualized as having a pot (mountains) filled with
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Normal Pa�ern
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POLLUTION
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Cooler air
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Warm air
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Cool air
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POLLUTION
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Cooler air
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Warm air
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Cool air
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�ermal Inversion
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Figure 8-7
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Thermal inversion
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Figure 8-8
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The Los Angeles Basin
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189
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Chapter 8 - Air Pollution
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water (oceans) and other ingredients (pollutants) with the lid closed (the inversion layer) to prepare a stew (photochemical smog). All that is missing is the heat, which is provided by the abundant Southern California sun (Figure 8-8).
==References==
==References==

Revision as of 00:14, 29 June 2010

Smog Smog is a result of physical and chemical activities between various pollutants released from smoke stacks in the presence of fog (thus the word smog). Classical smog refers mainly to plume of sulfur oxides and particulate matter generated from the combustion of coals and Figure 8-6 Oiled crow in the aftermath of the Exxon Valdez oil spill 20 “Valdez Spill Toll is Now Called Far Worst,” New York Times, April 18, 1992. 188 petroleum products. It is formed primarily in the early morning, during winter months, and in places of high humidity where condensation of water vapor over smoke particles is easier. The notorious London “fog” discussed above is a good example of this type of smog. Photochemical smog is very different from classical smog because it is formed under specific meteorological conditions and only when a large amount of sunlight is available. It forms when nitric oxides and hydrocarbons react in the presence of sunlight to produce ozone; this ozone can be further oxidized to produce nitric dioxide and other photochemical oxidants. NO + 1/2 O2 NO2 NO2 + HC NO + O O + O2 O3 h ν The Los Angeles Basin is a prime location for photochemical activities because of the large number of cars and power stations, the availability of sunlight, and its proximity to water. Furthermore, the basin is surrounded on three sides by the San Fernando mountain range, which prevents the dispersion of the pollutants. To make the matter worse, Los Angeles has many days in which a thermal (or temperature) inversion layer blankets the basin and prevents the upward mixing of pollutants with atmospheric air. Thermal inversion refers to the condition where, as a result of a large amount of emissions from cars and smoke stacks, temperature increases rather than decreases with height (Figure 8-7). Under these conditions, a warm layer is sandwiched between a layer of cold air near the surface and another cold layer in the upper atmosphere. Thermal inversion is more severe when wind is calm and pollutants can stay in place for many hours or even days. The smaller the inversion’s height, the less volume is available where pollutants can mix and the greater their concentration. The situation can be visualized as having a pot (mountains) filled with Normal Pa�ern POLLUTION Cooler air Warm air Cool air POLLUTION Cooler air Warm air Cool air �ermal Inversion Figure 8-7 Thermal inversion Figure 8-8 The Los Angeles Basin 189 Chapter 8 - Air Pollution water (oceans) and other ingredients (pollutants) with the lid closed (the inversion layer) to prepare a stew (photochemical smog). All that is missing is the heat, which is provided by the abundant Southern California sun (Figure 8-8).

References

Further Reading

External Links