AIR POLLUTION
Chapter 18
Pollution means foul or unclean.
Chemical and physical changes brought about by either natural processes or human activities, resulting in
air quality degradation is called air pollution.
Natural causes of pollutants are volcanoes, bacterial metabolism in decaying organic matter in swamps,
intestine of ruminants and termites, pollen, spores, viruses, dust, etc.
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.
POLLUTANTS
U.S. has declared seven major pollutants: sulfur dioxide, carbon monoxide, particulates, hydrocarbons,
nitrogen oxides photochemical oxidants, and lead.
They are the major contributors to ambient air degradation.
There are natural sources for some of these pollutants.
Sulfur dioxide and other sulfur compounds
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Are produced by burning fuel, burning biomass, volcanoes and oceans.
Cause acid rain when dissolves and reacts with water.
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.
Cause acid rain and health hazards.
Carbon monoxide
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Is produced by the incomplete combustion of fossil fuels and anaerobic decomposition of
organic material.
Inhibits cellular respiration by combining with hemoglobin.
Lead is a metabolic poison and a neurotoxin that binds to enzymes and inactivates them.
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Gasoline and ore smelting are major sources of lead in the ambient air.
Mercury is a neurotoxin that accumulates in biological systems.
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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.
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Sources are spray propellants, refrigeration compressors and foam blowing.
Volatile organic compounds (VOCs)
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Are released into the atmosphere by plants and animals and by human activities: burning fuel,
industry, chemical plants, 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).
Nitrogen dioxide + UV  nitric oxide + single atom of oxygen
Oxygen atom + oxygen gas (O2)  ozone (O3)
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Zone is strong oxidant and damages vegetation, paints, plastics, rubber, and sensitive tissues
in eyes and lungs.
Unconventional pollutants.
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All are anthropogenic, toxic or hazardous.
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Emissions standards have been set by the Environmental Protection Agency (EPA).
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Asbestos, mercury, benzene, polychlorinated biphenyls (PCB), beryllium and vinyl chloride.
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Aesthetic degradation includes undesirable changes in the atmosphere like odors, loud noise
and bright lights
Indoor air pollution.
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Concentrations of air pollutants are often higher than outdoors. Sometimes up to 20 times
higher.
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Formaldehyde is used in more than 3,000 products, including building material like insulating
foam, particle boards, waferboard, etc.
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Tobacco smoking is one of 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.
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".
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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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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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 pH changes.
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 forest 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
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.
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.
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 protect human health.
 Secondary standards 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.
4) In 1997 another set of changes to the U.S Clean Air act was approved.
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Lowering the standards for ambient ozone, soot and dust emissions, hydrocarbons and
organic compounds.
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
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.
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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.
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Mexico City and Santiago de Chile are notorious for their fowl air.
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China has done nothing significant to improve the polluted air in its cities.
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The high incidence of lung cancer in Shanghai is thought to be linked to air pollution.