Chapter 12: Air
pollution
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A brief history of air pollution
Types and sources of air pollutants
Factors that affect air pollution
Air pollution and the urban environment
Acid deposition
A brief history of air
pollution
A brief history of air pollution
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London’s historical problems
disastrous London smog event of 1952
Donora, Pennsylvania pollution episode,
1948
U.S. Clean Air Act, 1970, 1990
Types and sources of
air pollutants
Principal air pollutants
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primary and secondary pollutants
particulate matter
PM10, PM2.5
Carbon monoxide
Sulfur dioxide
• Globally, a large percentage of air pollution sources
are natural. Within localized areas, however,
human-caused sources are often the largest contributors
Principal air pollutants
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Volatile organic compounds
nitrogen oxides
• Along with ozone, VOCs and NOx are major components
of photochemical smog
Ozone in the troposphere
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photochemical smog
ozone
• Photochemical smog is a problem on most major cities
of the world
Ozone in the stratosphere
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relationship to ultraviolet radiation
chlorine compounds
Montreal Protocol
• When scientists first measured extremely low ozone
values in the Antarctic stratosphere, they thought the
instruments were malfunctioning.
Air pollution: trends and
patterns
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Primary air quality standards
secondary air quality standards
Air Quality Index (AQI)
• Secondary air pollutants are particularly difficult to control,
because they are not emitted directly into the atmosphere
Factors that affect air
pollution
The role of the wind
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dilution
turbulence
mixing
• “Dilution is the solution to pollution” in the 1950s this motto led to the construction of
tall smokestacks for large factories. Pollution was
released higher in the atmosphere where winds were
stronger. Air quality improved locally but suffered
downwind.
The role of stability and
inversions
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temperature lapse rates
inversions
mixing depth
• The mixing layer can often be easily seen from an airplane.
The role of topography
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cold air drainage
air blockage by mountain ranges
Severe air pollution potential
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sources
high pressure
inversions
stagnation
• Some locations, like Los Angeles and Mexico City, have
an unfortunate combination of surrounding topography,
frequent inversions, abundant emissions and plentiful sunlight perfect conditions for photochemical smog.
Air pollution and the
urban environment
Air pollution and the urban
environment
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urban heat island
country breeze
Acid deposition
Acid deposition
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pH
wet deposition
dry deposition
acid fog
acid rain effects
• Strangely enough, an acidified lake looks crystal clear
and beautiful. But the beauty is false; it’s only clear
because nothing is alive in it.