Chapter 16
AIR POLLUTION
Pollution means foul or unclean.
Chemical and physical changes brought about by either natural processes or human activities,
resulting in air quality degradation are called air pollution.
Air pollution is generally the most widespread and obvious kind of environmental damage.
NATURAL CAUSES
Natural causes of pollutants are volcanoes, bacterial metabolism in decaying organic matter in
swamps, intestine of ruminants and termites, pollen, spores, viruses, dust, etc.
In many cases the chemical composition of natural and human pollutants are the identical and
their effects are inseparable, e. g. CO2, hydrogen sulfide (H2S).
Many natural pollutants are harmless at natural occurring levels, but when humans add to these
natural levels disruption of natural cycles may occur.
ANTHROPOGENIC CAUSES
Primary pollutants are released directly from the source into the air in a harmful form.
Secondary pollution occurs when chemicals are modified into a harmful form once they are in
the atmosphere or are produced by a chemical reaction in the air.
Fugitive emissions are those that do not go through a smokestack, e. g. dust, burning of fossil,
leaks.
CONVENTIONAL POLLUTANTS
U.S. Clean Air Act of 1970 designated seven major pollutants: sulfur dioxide, carbon
monoxide, particulates, hydrocarbons, nitrogen oxides photochemical oxidants, and
lead.
They are the major contributors to ambient air degradation.
These pollutants are also called “criteria” pollutants
There are natural sources for some of these pollutants.
Sulfur dioxide and other sulfur compounds
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Are produced by erosion of sulfate-containing soil, burning fuel, burning biomass,
volcanoes and oceans.
In urban areas anthropogenic sources make 90% of the sulfur in the air.
Cause acid rain when dissolves and reacts with water.
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U.S. and China are major produces of sulfur in the air mostly through the burning of
coal.
Sulfur dioxide reacts with water in the air and makes sulfuric acid which is a major
component of acid rain.
Nitrogen oxides
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Are produced when nitrogen in fuel or air is heated to temperatures above 650oC
(1200oF) in the presence of oxygen, or when soil bacteria oxidize nitrogen containing
compounds.
Nitrogen monoxide reacts in the atmosphere to produce nitrogen dioxide, which in
turn reacts with water to produce nitric acid.
Nitric acid causes acid rain and health hazards.
Carbon oxides
CO2
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Carbon dioxide is the most common form of carbon in the air.
90% of the CO2 produced each year is from respiration.
Some of the CO2 is reabsorbed by photosynthesis, and the rest accumulates in the
atmosphere.
Carbon dioxide is a greenhouse gas.
CO
 Is produced by the incomplete combustion of fossil fuels and anaerobic
decomposition of organic material.
 Inhibits cellular respiration by combining with hemoglobin.
 About 90% of the CO in the air is consumed in photochemical reactions that
produce ozone.
Particulate matter
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An aerosol is any solid particles or liquid droplets suspended in a gaseous medium, e.g.
air.
Atmospheric aerosols include dust, ash, soot, lint, smoke, pollen, spores, algal and fungi
cells, and many other materials.
Many of these aerosols reduce visibility and leave deposits on windows and other
surfaces.
Particles smaller than 2.5 micrometers can be drawn into the lungs during breathing and
cause asthma and the destruction of respiratory tissues.
Metals and halogens
Many metals are released in the atmosphere in the form of metal fumes or suspended
particulates by fuel combustion, ore smelting, and disposal of wastes.
Lead is a metabolic poison and a neurotoxin that binds to enzymes and inactivates
them.
 Gasoline and ore smelting are major sources of lead in the ambient air.
Mercury is a neurotoxin that accumulates in biological systems.
 Major source of mercury in the air are coal-burning power plants and waste
incinerators.
Other toxic metals are beryllium, cadmium, thallium, uranium, cesium and plutonium.
Halogens (chlorine, fluorine, bromine, iodine) are highly reactive and destroy animal and
plant tissues.
 Chlorofluorocarbons (CFC) destroy the ozone layer by releasing fluorine and
chlorine.
 The ozone layer protects the earth from ultraviolet radiation.
 Sources are spray propellants, refrigeration compressors and foam blowing.
Volatile organic compounds (VOCs)
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VOCs are organic chemicals that exist as gases in the air.
Are released into the atmosphere by plants and animals and by human activities:
burning fuel, industry, chemical plants, and refineries.
Plants release isoprenes and terpenes.
Wetlands, rice paddies, bacteria and animals release large amounts of methane.
Industry releases benzene, chloroform, formaldehyde, phenols, etc.
They are converted to CO, CO2 and photochemical oxidants.
Photochemical oxidants
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Are secondary pollutants, produced by atmospheric gases when they react in
sunlight.
One of the most important of these reactions forms a single oxygen atom.
It eventually produces ozone that damages plant and animal tissues, and building
material (paint, plastic, rubber).
Step 1: Nitrogen dioxide (NO2) + UV  nitric oxide (NO) + single atom of oxygen (O)
Step 2: Oxygen atom (O) + oxygen gas (O2)  ozone (O3)
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Ozone is strong oxidant and damages vegetation, paints, plastics, rubber, and
sensitive tissues in eyes and lungs.
Air toxins
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Hazardous air pollutants (HAPs) are monitored by EPA.
These chemicals include carcinogens, neurotoxins, mutagens, teratogens, endocrine
system disrupters and other highly toxic compounds.
Twenty of the most persistent bioaccumulative compounds require special reporting and
management; they remain in the ecosystem for a long time.
Most of these chemicals are metal compounds, chlorinated hydrocarbons or volatile
organic compounds.
The best source of information is the Toxics Release Inventory, TRI, collected by the
EPA.
“What is TRI?
The Toxics Release Inventory (TRI) is a publicly available EPA database that contains information on toxic chemical
releases and other waste management activities reported annually by certain covered industry groups as well as
federal facilities. This inventory was established under the Emergency Planning and Community Right-to-Know Act of
1986 (EPCRA) and expanded by the Pollution Prevention Act of 1990.” http://www.epa.gov/tri/
Unconventional pollutants.
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All are anthropogenic.
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Aesthetic degradation includes undesirable changes in the atmosphere like odors,
loud noise and bright lights
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Many are not life threatening but reduce the quality of life, e. g. noise and bad odors.
Indoor air pollution.
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Concentrations of air pollutants are often higher than outdoors. Sometimes up to
70 times higher, e. g. chloroform, benzene, carbon tetrachloride, formaldehyde and
styrene.
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Formaldehyde is used in more than 3,000 products, including building material like
insulating foam, particle boards, wafer board, etc.
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Tobacco smoking is the most serious indoor pollutant in the U. S. A.
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Combustion smoke produced by burning wood, charcoal and dried dung is the most
serious pollutant in many poor areas of the world.
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Other household pollutants are radon, vinyl chloride and asbestos.
CLIMATE, TOPOGRAPHY AND ATMOSPHERIC PROCESSES
They play a role in the transport, concentration, dispersal and removal of pollutants.
Inversions
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Temperature inversions occur when a layer of warmer air overlays a layer of cooler air. It
is a reversal of normal temperature patterns in the lower atmosphere.
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Normally the atmosphere is heated from below by heat by solar radiation absorbed by
the earth surface and the released to the air in contact with it.
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Warm air rises.
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“A warm air mass moving over a colder one can "shut off" the convection effects,
keeping the cooler air mass trapped below. (see capping inversion). It commonly occurs
at night: when solar heating ceases, the surface cools by radiation, and cools the
immediately overlying atmosphere.”
http://www.answers.com/topic/temperature-inversion
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“Temperature inversion may occur during the passage of a cold front or result from the
invasion of sea air by a cooler onshore breeze. Overnight radiative cooling of surface air
often results in a nocturnal temperature inversion that is dissipated after sunrise by the
warming of air near the ground.” http://www.answers.com/topic/temperature-inversion
Dust domes and heat islands
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High level of concrete and glass allows rainfall to run off quick and increase heat absorption
during the day and radiation at night
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Tall buildings create convective updrafts that sweep pollutants into the air.
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Heat air masses over the cities concentrate pollutants in a "dust dome".
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Dust and aerosols seem to trigger lightning strikes.
Long-range transport
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Air pollution from heavily industrialized regions of America and Europe is transported by
circumpolar winds to the Arctic.
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Volatile compounds evaporate from warm areas, travel through the atmosphere, then
condense and precipitate in cooler regions.
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Over several years, contaminants accumulate in the coldest places, generally at high
latitudes where they bioaccumulate in food chains.
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It contains aerosols of sulfates, vanadium, manganese, lead, soot, dust, etc.
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Tracing the source is difficult.
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It is often an international sensitive problem.
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Some places traditionally considered clean like Greenland, Antarctica and Samoa have
heavy metals, pesticides and radioactive chemicals in their air.
Stratospheric ozone
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In the upper atmosphere, ozone screens UV radiation.
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Without this screen, organisms will be subjected to harmful radiation that could kill or cause
genetic damage.
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Ozone depletion has been occurring at least since the 1960s.
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In the spring of 1997, 10% of the ozone worldwide was destroyed. All the ozone between 14
and 20 km altitude was destroyed in an area of 22 million km2.
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For every 1% loss of ozone there is a 2% increase of UV reaching the earth surface.
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Chlorofluorocarbons (CFC) destroy the ozone layer.
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Freon is a chlorofluorocarbon; it is cheaply produced, nontoxic, nonflammable, chemically
inert and with many applications.
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In 1989, eighty nations agreed to phase out the production of CFC by the end of the century.
EFFECTS OF AIR POLLUTION
Human health
Sulfur oxides, nitrogen oxides and ozone are irritants and damage the delicate tissues in the
eyes and respiratory passages.
Carbon monoxide binds to hemoglobin and prevents oxygen transport.
Bronchitis is a persistent inflammation of the air passages that become constricted creating
cough and muscle spasms.
Emphysema is an irreversible lung disease in which the respiratory passages become
permanently constricted and the alveoli damaged.
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Breathing becomes difficult and not enough oxygen is absorbed into the blood.
Plant pathology
There are two ways in which air pollution can damage plants:
1. Pollutants can be directly toxic, damaging tissues.
2. Some pollutants act as metabolic regulators when absorbed by plant cells and disrupt the
normal metabolism of the cells, e.g. ethylene.
Certain combinations have synergistic effects like ozone and sulfur dioxide.
Important consequences for agriculture and forestry.
Acid deposition
Acid deposition causes changes in soil and water pH, forest damage, destruction of buildings
and monuments and visibility reduction.
Sulfuric acid and nitric acid are produced in the atmosphere.
Fog, snow, mist and rain deposit atmospheric pollutants changing the pH the soil and bodies of
water.
Many aquatic organisms are sensitive to pH changes and disappear.
Egg and fish fry of many species of fish are especially sensitive to a pH of 5 or below.
Their death causes a disruption of the food chain. Sweden has about 18,000 lakes so acidic that
they cannot support life.
Air pollution and deposition of atmospheric acids thought to be the leading causes of forest
destruction in many areas.
European forests are dying at an alarming rate.
High altitude forests on the Appalachian mountains have been affected or killed by air pollution,
e. g. spruce forests in Vermont and North Carolina.
Buildings and monuments made of limestone and marble are damage very fast by acid rain.
Paintings, statues, stained glass windows are affected by acid.
Oxidation and acid damage paint, rubber and steel.
Foul air obscures the sky above industrialized cities.
Haze can reduce visibility up to 80%.
AIR POLLUTION CONTROL
“Mix and dilute! Dilution is the solution to pollution!”
The best method to reduce pollution is to minimize pollution.
We have made considerable progress in designing pollution-control equipment to reduce the
major conventional pollutants.
There are many types of filters, catalysts, scrubbers, fuel modification processes and new
burning techniques for controlling air pollution.
Electrostatic precipitators give an electrical charge to particles as they travel in the effluent
stream and this causes the particle to migrate and get deposited on the plate with the opposite
charge.
Catalytic converters oxidize sulfur oxides to produce sulfuric acid, elemental sulfur and
ammonium sulfate. These products have a commercial value.
Several methods use limestone to remove sulfur for burning coal.
Sulfur oxides react with calcium in the limestone to produce calcium sulfate and other
compounds of calcium and sulfur.
Nitrogen oxides can be reduced by 50% by carefully controlling the flow of air and fuel.
Hydrocarbons and volatile organic compounds are produced by incomplete combustion of
fuels or by solvent evaporation from chemical factories, paints, dry cleaning, plastic
manufacturing, printing and other industrial processes.
Close system that prevent the escape of fugitive gases can reduce many emissions, e.g. PCV in
automobiles.
Alternative sources of energy like wind and solar power are preferable to the burning of fossil
fuels and are becoming economically competitive.
CLEAN AIR LEGISLATION
1) The Clean Air Act of 1963 was the firs U.S. legislation aimed at air pollution control.
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It set up the National ambient Air Quality Standards or NAAQS.
2) Extensive amendments were made in 1970.
 Identified the criteria pollutants.
 Established national ambient quality standards.
 Primary standards aim to protect human health.
 Secondary standards aim to protect crops, climate, etc.
3) In 1990 the Clean Air Act was rewritten and updated. Important provision dealt with cutting
the emission standards for…
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Acid rain, urban smog, toxic air pollutants (189 instead of 7 as before) and marketing
pollution rights.
CFC and carbon tetrachloride will be phased out by the year 2000 in order to protect
the ozone layer.
Toxic organic compounds are regulated by standards that specify the manufacturing
facilities, storage, sampling methods, etc.
Nitrogen oxide emissions: improved standards for SUV and other vehicles.
4) Clear Skies plan.
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The plan eliminated the “new source review” which was implemented in 1977.
Congress agreed to exempt existing equipment from new pollution limits with the
stipulation that when they upgraded most stringent rules would apply.
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It resulted in keeping old facilities operating because they were exempted from
pollution control.
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According to the Bush administration, to determine which facility is old and which is
new is too cumbersome. This prompted the EPA to stop the new source review plan.
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Nine northeastern States that receive the pollutants from Midwest factories have
sued the EPA for abandoning the plan to combat dirty air.
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President Bush continues to resist calls for expensive greenhouse gas restrictions.
Diffuse sources like aerosol hair spray, deodorants, charcoal lighter fluids, gasoline-powered
lawnmowers, fireplaces, volatile paints and solvents, etc. contribute to air pollution.
CURRENT CONDITIONS AND FUTURE PROSPECTS
In the U.S. air quality has improved dramatically in the last 30 years.
Between 1970 and 1994 emissions of all criteria in the United States have decreased except for
nitrogen oxides.
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Lead has decreased by 98%.
SO2 is down by 32%.
Particulates have been reduced by 78%.
Baltimore, MD, and Birmingham, AL, have a very high level of particle emission.
Los Angeles, Anaheim and Riverside in southern California are within the extreme urban smog
category.
Cities like Baltimore, Chicago, New York, Houston, Philadelphia and San Diego have continuing
problems of air pollution and do not meet the standard set by the NAAQS.
About 80% of the US now meets the NAAQS goals.
Sweden and West Germany cut their sulfur emissions by 2/3 between 1970 and 1985.
Many large cities around the world have improved their air quality.
Some of the most serious problems exist are…
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Air pollution is particularly bad in the Czech Republic, Slovakia and southern Poland.
Life expectancy in some industrial towns of Romania and the Czech Republic is as much as
10 years lower than the national average. Foul air is blamed for this decrease in life
expectancy.
Mexico City and Santiago de Chile are notorious for their fowl air.
China has done nothing significant to improve the polluted air in its cities.
The high incidence of lung cancer in Shanghai is thought to be linked to air pollution.
Bad or clean air in U.S. cities and others:
http://www.environmentaldefense.org/cleanairforlife.cfm?subnav=aiyc_50cities
http://www.scorecard.org/
http://www.nationmaster.com/facts.php
http://www.climatehotmap.org/camerica.html
Top polluters:
http://www.scorecard.org/ranking/rankfacilities.tcl?how_many=100&drop_down_name=Air+releases&fips_state_code=Entire+
United+States&sic_2=All+reporting+sectors
Shelby county:
http://www.scorecard.org/community/index.tcl?zip_code=38104&set_community_zipcod
e_cookie_p=t&x=17&y=4