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Concept Review
The Air Around Us
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Air pollution is the most widespread form of global pollution.
Air quality has improved over the last 20 years due to technological
developments to burn cleaner fuels more efficiently.
Natural Sources of Air Pollution
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Air pollution occurs naturally as plants decompose, volcanoes erupt, forest
fires burn, and storms blow across loose soils.
Human-Caused Air Pollution
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Primary pollutants are harmful molecules sent into the atmosphere.
o Fugitive emissions enter the air from soil erosion, strip mining, and
construction.
o Sulfur compounds enter as sea spray and volcanic emissions.
Secondary pollutants become hazardous as they react with other
chemicals in the air.
o Sulfur dioxide (SO2) from industry and combustion oxidize into SO3
to form acid precipitation (H2SO4).
o Nitrogen oxides combine with H2O to form nitric acid (HNO3).
o CO2 from fossil fuel combustion is a leading cause of global
warming.
o Carbon monoxide (CO), also produced by fuel combustion, forms
ozone (O3) in chemical reactions.
Particulates affect human health, as well as reducing visibility and sunlight
penetration.
Heavy metals are metabolic poisons that affect water quality and living
things.
Volatile Organic Compounds (VOCs) form photochemical smog and
combine with the atmospheric oxygen to form ozone, which is a strong
oxidizer, damaging materials and plants.
Other Hazardous Air Pollutants (HAPs) are chemicals that pose a risk by
bioaccumulation and/or persistence.
Aesthetic degradation includes those things, such as noise and odors, that
reduce the quality of life but are not necessarily life threatening.
As building construction becomes more efficient in preventing heat loss to
the outdoors, indoor air pollution has become more concentrated and
dangerous. Smoking is the most important air pollutant in its effects on
human health.
Climate, Topography, and Atmospheric Processes
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Temperature inversions trap pollutants near the earth’s surface as warmer
air overlays cooler air.
Air pollutants are heated by sunlight and other pollutants are added,
concentrating and increasing contaminant levels.
Concentrations of buildings and roads in urban areas create heat islands
by blocking winds, preventing runoff, and decreasing vegetation.
Changing wind patterns move pollutants globally from warm areas to
cooler ones, where they precipitate out as temperature changes.
Stratospheric ozone levels are depleted as CFCs and other industrial
gases are dispersed.
The Montreal Protocol of 1987 was instrumental in phasing out CFC
production by the year 2000.
Effects of Air Pollution
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An estimated 5–6 million people die each year due to air pollution.
Bronchitis, asthma, and chronic respiratory diseases are caused by
pollutants obstructing or breaking down lung tissues.
Plants are also affected as cells are damaged with exposure or as
environmental factors combine (synergistic effect), causing damage.
Acid precipitation affects aquatic ecosystems, forests, and buildings.
Air Pollution Control
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While minimizing the production of air pollutants would be the best
approach to reducing pollution levels, technology can be used to
o remove particulates by filtering
o switch to cleaner-burning fuels
Clean Air Legislation
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The Clean Air Act was updated in 1990 to change the regulation of
pollution controls in industries and power plants, limiting levels of sulfur
dioxides, nitrogen oxides, and particulates.
Current Conditions and Future Prospects
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Air quality has improved since the 1970s.
Automobile traffic still contributes significantly to air pollution levels.
Further changes in lifestyle and technology will improve air quality in the
future.