Chapter 20
Air Pollution Control
Limiting emissions into the air is both technically difficult and expensive. However,
since rain and deposition are the only air cleaning mechanisms available, and neither
is very efficient, good air quality depends on pollution prevention and on limiting
what goes into the air. The control of air emissions may be realized in a number of
ways. Figure 20-1 shows five separate possibilities for control. Dispersion is discussed
in Chap. 18, and the four remaining control points are discussed individually in this
chapter.
SOURCE CORRECTIONChanging or eliminating a process that produces a polluting air effluent is often easier
than trying to trap the effluent. A process or product may be needed or necessary, but
could be changed to control emissions. For example, automobile exhaust has caused
high lead levels in urban air. Elimination of lead from gasoline, which was needed for
proper catalytic converter operation, has also resulted in reducing lead in urban air.
Similarly, removal of sulfur from coal and oil before the fuel is burned reduces the
amount of SO2 emitted into the air. In these cases, the source of air pollution has been
corrected.
Processes may also be modified in order to reduce air pollution. Odors from
municipal incinerators may be controlled by operating the incinerator at a high enough
temperature to effect more complete oxidation of odor-producing organic compounds.
The 1990 Clean Air Act mandates the use of oxygenated fuels in urban areas in order
to limit CO emissions from automobiles.
Strictly speaking, such measures as process change, raw material substitution, and
equipment modification to meet emission standards are known as controls. In contrast,
abatement is the term used for all devices and methods for decreasing the quantity
of pollutant reaching the atmosphere, once it has been generated by the source. For
simplicity, however, we will refer to all of the procedures as controls.
COLLECTION OF POLLUTANTSCollection of pollutants for treatment is often the most serious problem in air pollu-
tion control. Automobile exhaust is a notorious polluter mainly because the effluent
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