APES Chapter Summary – Air Pollution (chpt 18 in MILLER LITE 17th Ed.)
1. The layers of the atmosphere are the troposphere, stratosphere, mesosphere, and thermosphere.
2. Major classes of air pollutants include carbon, sulfur, and nitrogen oxides, volatile organic compounds, suspended
particulate matter, photochemical oxidants, radioactive substances, and hazardous chemicals that can cause health
problems. Primary sources of these pollutants include cars, industry, and natural phenomena such as volcanic
eruptions.
3. The two types of smog are the photochemical and the industrial, or gray-air, smog.
4. Acid deposition includes wet deposition of acidic rain, snow, fog, and cloud vapor with pH less than 5.6, and dry
deposition of acidic particles. Major sources of acid deposition are nitrogen oxides produced during fossil fuel
combustion and sulfur oxides produced primarily from coal-fired power plants.
5. Harmful effects of air pollution include various respiratory diseases, premature deaths, damage to plants, and
materials such as buildings, cars, statues, etc.
6. We can reduce air pollution by reducing emission through the use of low-sulfur coal, shifting to less polluting fuels
(e.g., coal to natural gas), removal of pollutants after combustion or lower emissions through the use of mass transit
or alternative transportation, improving fuel efficiency, and tax incentives.
Glossary
Chapter 18
acid
deposition
The falling of acids and acid–forming compounds from the atmosphere to the earth’s surface. Acid
deposition is commonly known as acid rain, a term that refers to the wet deposition of droplets of
acids and acid–forming compounds.
acid rain
See acid deposition.
air pollution
One or more chemicals in high enough concentrations in the air to harm humans, other animals,
vegetation, or materials. Excess heat is also considered a form of air pollution. Such chemicals or
physical conditions are called air pollutants. See primary pollutant, secondary pollutant.
atmospheric
pressure
Force or mass per unit area of air, caused by the bombardment of a surface by the molecules in air.
EPA
U.S. Environmental Protection Agency; responsible for managing federal efforts to control air and
water pollution, radiation and pesticide hazards, environmental research, hazardous waste, and
solid waste disposal.
industrial
smog
Type of air pollution consisting mostly of a mixture of sulfur dioxide, suspended droplets of sulfuric
acid formed from some of the sulfur dioxide, and suspended solid particles. Compare
photochemical smog.
inversion
See temperature inversion.
metropolitan
area
See urban area.
nitrogen
oxides (NOx)
See nitric oxide and nitrogen dioxide.
ozone (O3)
ozone
depletion
Colorless and highly reactive gas and a major component of photochemical smog. Also found in the
ozone layer in the stratosphere. See photochemical smog.
Decrease in concentration of ozone (O3) in the stratosphere. See ozone layer.
ozone layer
Layer of gaseous ozone (O3) in the stratosphere that protects life on earth by filtering out most
harmful ultraviolet radiation from the sun.
PANs
Peroxyacyl nitrates; group of chemicals found in photochemical smog.
particulates
Also known as suspended particulate matter (SPM); variety of solid particles and liquid droplets
small and light enough to remain suspended in the air for long periods. About 62% of the SPM in
outdoor air comes from natural sources such as dust, wild fires, and sea salt. The remaining 38%
comes from human sources such as coal–burning electric power and industrial plants, motor
vehicles, plowed fields, road construction, unpaved roads, and tobacco smoke.
photochemical Complex mixture of air pollutants produced in the lower atmosphere by the reaction of
smog
hydrocarbons and nitrogen oxides under the influence of sunlight. Especially harmful components
include ozone, peroxyacyl nitrates (PANs), and various aldehydes. Compare industrial smog.
primary
pollutant
Chemical that has been added directly to the air by natural events or human activities and occurs in
a harmful concentration. Compare secondary pollutant.
secondary
pollutant
Harmful chemical formed in the atmosphere when a primary air pollutant reacts with normal air
components or other air pollutants. Compare primary pollutant.
smog
Originally a combination of smoke and fog but now used to describe other mixtures of pollutants in
the atmosphere. See industrial smog, photochemical smog.
stratosphere
Second layer of the atmosphere, extending about 17–48 kilometers (11–30 miles) above the earth’s
surface. It contains small amounts of gaseous ozone (O3), which filters out about 95% of the
incoming harmful ultraviolet radiation emitted by the sun. Compare troposphere.
sulfur dioxide
(SO2)
Colorless gas with an irritating odor. About one–third of the SO2 in the atmosphere comes from
natural sources as part of the sulfur cycle. The other two–thirds come from human sources, mostly
combustion of sulfur–containing coal in electric power and industrial plants and from oil refining and
smelting of sulfide ores.
suspended
particulate
matter
temperature
inversion
thermal
inversion
See particulates.
Layer of dense, cool air trapped under a layer of less dense, warm air. It prevents upward–flowing
air currents from developing. In a prolonged inversion, air pollution in the trapped layer may build up
to harmful levels.
See temperature inversion.
troposphere
Innermost layer of the atmosphere. It contains about 75% of the mass of earth’s air and extends
about 17 kilometers (11 miles) above sea level. Compare stratosphere.
urban area
Geographic area containing a community with a population of 2,500 or more. The number of people
used in this definition may vary, with some countries setting the minimum number of people at
10,000–50,000.
volatile
organic
compounds
(VOCs)
Organic compounds that exist as gases in the atmosphere and act as pollutants, some of which are
hazardous.
Case studies, concepts, and other terms to know:
Clean Air Act
South Asian Brown Clouds
Lichens as biological indicators