LEARNING OBJECTIVES
The atmosphere has always been a sink—a place for deposition and storage—for
gaseous and particulate wastes. When the amount of waste entering the
atmosphere in an area exceeds the ability of the atmosphere to disperse or
breakdown the pollutants, problems result. After reading this chapter, you
should understand:
•
Why human activities that pollute the air, combined with meteorological
conditions, may exceed the natural abilities of the atmosphere to remove
wastes.
• What the major categories and sources of air pollutants are.
•
•
Why air pollution problems are different in different regions.
What acid rain is, how it is produced, what its environmental impacts are,
and how they might be minimized.
• What methods are useful in the collection, capture, and retention of
pollutants before they enter the atmosphere.
• What air quality standards are, and why they are important.
•
Why determining the economics of air pollution is controversial and
difficult.
Summary
• Every
year, approximately 150 million metric tons of primary
pollutants enter the atmosphere above the United States from
processes related to human activity. Considering the enormous volume
of the atmosphere, this is a relatively small amount of material. If
it were distributed uniformly, there would be little problem with air
pollution. Unfortunately, the pollutants generally are not evenly
distributed but are concentrated in urban areas or in other areas
where the air naturally lingers.
• The two major types of pollution sources are stationary and mobile.
Stationary sources have a relatively fixed position and include point
sources, area sources, and fugitive sources.
• There are two main groups of air pollutants: primary and secondary.
Primary pollutants are those emitted directly into the air:
particulates, sulfur dioxide, carbon monoxide, nitrogen oxides, and
hydrocarbons.
Secondary
pollutants
are
those
produced
through
reactions between primary pollutants and other atmospheric compounds.
A good example of a secondary pollutant is ozone, which forms over
urban
areas
through
photochemical
reactions
between
primary
pollutants and natural atmospheric gases.
• The effects of the major air pollutants are considerable. They
include effects on the visual quality of the environment, vegetation,
animals, soil, water quality, natural and artificial structures, and
human health.
• The combustion of large quantities of fossil fuels results in the
emission of sulfur and nitrogen oxides into the atmosphere, creating
acid rain. Environmental degradations associated with acid rain
include loss of fish and other life in lakes, damage to trees and
other plants, leaching of nutrients from soils, and damage to stone
statues and buildings in urban areas.
• There are two major types of smog: photochemical and sulfurous. Each
type of smog brings particular environmental problems that vary with
geographic region, time of year, and local urban conditions.
• Meteorological conditions greatly affect whether polluted air is a
problem in an urban area. In particular, restricted circulation in
the lower atmosphere associated with temperature inversion layers may
lead to pollution events.
• There are two major types of smog: photochemical and sulfurous. Each
type of smog brings particular environmental problems that vary with
geographic region, time of year, and local urban conditions.
• From an environmental viewpoint, the preferred method of reducing the
emission of air pollutants
practice energy efficiency
of fossil fuels are burned.
alternative energy sources,
emit air pollutants.
produced from burning fossil fuels is to
and conservation so that smaller amounts
Another option is to increase the use of
such as solar and wind power, that do not
• Methods to control air pollution are tailored to specific sources and
types of pollutants. These methods vary from settling chambers for
particulates to scrubbers that use lime to remove sulfur before it
enters the atmosphere.
• Efforts
to reduce air pollution in urban regions center on
automobiles, buses, and other vehicles, because they account for most
of the pollutants that enter the urban atmosphere.
• Emissions of air pollutants in the United States are decreasing. In
developing countries, air pollution in large urban centers is often a
serious problem.
• Air quality in U.S. urban areas is usually reported in terms of
whether the quality is good, moderate, unhealthy for sensitive
groups, unhealthy, very unhealthy, or hazardous. These levels are
defined in terms of the Air Quality Index (AQI).
• The relationships between emission control and environmental cost are
complex. The minimum total cost is a compromise between capital costs
to control pollutants and losses or damages resulting from pollution.
If additional controls are necessary to lower the pollution to a more
acceptable level, additional costs are incurred. Beyond a certain
level of pollution abatement, these costs can increase rapidly.