Air Pollution
By
Dr. Ashraf Hussain
Msc., PhD. Community Medicine
Air pollution:
Definition:
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The presence in the atmosphere of one or more air contaminants in such
quantities that are harmful to human, plant, or animal life, or that interfere
with the comfortable enjoyment of life or the conduct of business or other
human activities
Constituents of air
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Air is a mechanical mixture of gases, The normal composition of external air
by volume is approximately as follows:
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Nitrogen 78%,
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Oxygen 21%,
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CO
2
0.03%,
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Argon, Neon, Helium, Krypton &Xenon <1%
In addition to these gases, air also contains water vapour, traces of ammonia and
suspended matter such as dust, bacteria, spores and vegetable debris.
According to a WHO assessment,
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The requirement for air is rela vely constant (about 10-20m3 per day)
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more than 3 million premature deaths each year can be a ributed to the
effects of ambient (outdoor) air pollution.
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4.3 million deaths every year as a result of household exposure to smoke
from dirty cookstoves and fuels
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92%of the world’s popula on lives in places where air quality exceeds WHO
guideline limits
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More than half of this disease burden is borne by the populations of
developing countries.
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Factors contributing to air pollution;
Air is rendered impure by
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Respiration of men and animals
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Combustion of coal, gas, oil, etc.
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Decomposition of organic matter and
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Trade, traffic and manufacturing processes which give off dust, fumes,
vapours and gases.
Under ordinary conditions, the composition of outdoor air is remarkably constant.
Air cleansing mechanism
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Wind: Wind dilutes and sweeps away the impurities by its movement.
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Sunlight : The atmospheric temperature and sunlight play their own part by
oxidizing impurities, and killing bacteria.
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Rain : It cleanses the atmosphere by removing the suspended and gaseous
impurities.
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Plant life : The green plants utilize the carbon dioxide and generate oxygen;
this process is reversed during the night time.
When the rate of pollution becomes too high or when the cleansing process
becomes ineffective, it constitutes a health hazard.
Air pollutants
More than 100 substances which pollute air have been iden fied.
The important ones are
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carbon monoxide, carbon dioxide, hydrogen sulphide, sulphur dioxide, and
nitrous oxide.
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Organic compounds (e.g., hydrocarbons, aldehydes, ketones, organic acids),
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Metallic contaminants (e.g., arsenic, zinc, iron resulting from smelting
operation),
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radio-active compounds as radon
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photochemical oxidants (e.g., ozone).
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Air pollutants may be either emitted into the atmosphere or formed within the
atmosphere itself.
SO, they are either:
Primary air pollutants :
Primary air pollutants are those that are emitted into the atmosphere from a source
such as a factory chimmey or exhaust pipe, or through suspension of contaminated
dusts by the wind.
In principle it is possible to measure the amounts emitted at the source itself.
Secondary air pollutants are those formed within the atmosphere itself.
They arise from chemical reactions of primary pollutants, possibly involving the
natural components of the atmosphere, especially oxygen and water. The most
familiar example is ozone,
Because of this mode of formation, secondary pollutants cannot readily be included
in emissions inventories.
Another important distinction must be is the physical state of a pollutant.
Gaseous air pollutants are those present as gases or vapours.
As individual small molecules capable of passing through filters, provided they do
not adsorb to or chemically react with the filter medium.
Gaseous air pollutants are readily taken into the human respiratory system, although
if water-soluble, they may very quickly be deposited in the upper respiratory tract
and not penetrate to the deep lung.
Particulate air pollutants comprise material in solid or liquid phase suspended in the
atmosphere.
Such particles can be either primary or secondary and cover a wide range of sizes.
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It consists of a complex mixture of solid and liquid particles of organic and
inorganic substances.
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The major components of PM are sulfate, nitrates, ammonia, sodium
chloride, black carbon, mineral dust and water.
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Par culate ma er of diameter smaller than 2.5 μm are more dangerous
since, when inhaled, there is high probability of deposition in the smaller
conducting airways and alveoli, so interfere with gas exchange inside the
lungs.
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Chronic exposure to particles contributes to the risk of developing
cardiovascular and respiratory diseases, as well as of lung cancer.
The 2005 AQG set for the first me a guideline value for par cular ma er (PM)
as:
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10 μg/m3 annual mean and 25 μg/m3 24-hour mean for PM2 .5
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and 20 μg/m3 annual mean and 50 μg/m3 24-hour mean for PM10
Carbon monoxide
most common and widely distributed air pollutants.
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It is a product of incomplete combustion of carbon containing materials, such
as in automobiles, industrial process, heating facilities and incinerators.
Concentrations in urban areas depend on weather and traffic density.
Variations in these levels are also influenced by topography.
Sulphur dioxide
Sulphur dioxide (S02) is a colourless gas with a sharp odour, results from the
combustion of sulphur containing fossil fuel, the smelting of sulphur-containing ores,
and other industrial processes.
Domestic fires, power generation and motor vehicles can also produce emissions
containing sulphur dioxide.
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S02 can affect the respiratory system and the func on of lungs, causes
irritation of eyes and exacerbation of asthma.
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This gas is a major contaminant in many urban and industrial areas.
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When S02 combines with water, it forms sulphuric acid; this is the main
component of acid rain which is a cause of deforestation.
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Its concentration is estimated in all air pollution surveys.
Lead
The combustion of alkyl lead additives in motor fuels accounts for the major part of
all lead emissions into the atmosphere.
An es mated 80-90 per cent of lead in
ambient air derives from the combustion of leaded petrol.
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The degree of pollution from this source differs from country to country, depending
on motor vehicle density and the efficiency of effort to reduce the lead content of
petrol.
Children up to 6 years of age are a popula on at increased risk for lead exposure, as
well as for adverse health effects due to:
A. a. children have behaviour characteristics (outdoor activity) which increase
the risk of lead exposure.
B. b. The blood-brain barrier is not yet fully developed in young children.
C. c. haematological and neurological effects of lead occur at lower threshold in
children than in adults.
Since the placenta is no effective biological barrier, pregnant women represent a
second group at the increased risk because of exposure of the foetus to lead.
Lead poisons many systems in the body and is particularly dangerous to children
developing brain and nervous system.
Elevated lead levels in children have been associated with impaired
neuropsychologic development as measured by loss of IQ, poor school performance
and behavioural difficulties
Carbon dioxide
This is not commonly regarded as an air pollutant, although man generates
enormous amount of it in combustion process using coal, oil and gas.
Carbon dioxide is a natural constituent of the air.
It does not take part in any significant chemical reactions with other substances in
the air.
However, its global concentration is rising above the natural level by an amount that
could increase global temperature enough to affect climate markedly
Hydrocarbons :
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Man-made sources of hydrocarbons include incineration, combustion of coal,
wood, processing and use of petroleum.
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Hydrocarbons exert their pollutant action by taking part in the chemical
reactions that cause photochemical smog.
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The main health effect is lung cancer.
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Ozone
Ozone at ground level not to be confused
with the ozone layer in the upper atmosphere is one of the
major constituents of photochemical smog.
It is formed by the photochemical reaction of sunlight with pollutants such as
nitrogen oxides from vehicle, industry emissions and volatile organic compounds
(VOCs) emitted by vehicles, solvents and industry.
Excessive ozone in the air can have a marked effect on human health. It can cause
breathing problems, trigger asthma, reduce lung function and cause lung diseases
Oxides of nitrogen :
The pollutant of far greater concern in relation to human health is nitrogen dioxide.
Coal is the most important fuel in this context, other sources are road traffic and
electricity generation.
Epidemiological studies have shown that symptoms of bronchitis in asthmatic
children increase in association with long-term exposure to nitrogen dioxide.
Reduced lung function growth is also linked to nitrogen dioxide at concentrations
currently measured (or observed) in the large cities.
Criteria Pollutants
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Criteria pollutants are the only air pollutants with national air quality
standards that define allowable concentrations of these substances in
ambient air.
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They are carbon monoxide, nitrogen dioxide, sulfur dioxide, ozone,
particulate matter, and lead.
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Exposure to these substances can cause health effects, environmental
effects, and property damage.
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Health effects include heart or lung disease, respiratory damage, or
premature death.
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Environmental effects include smog, acid rain, and ozone depletion.
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Hazardous Air Pollutants
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Hazardous air pollutants, also known as toxic air pollutants or air toxics, are
those pollutants that are known or suspected to cause cancer or other
serious health effects, such as reproductive effects or birth defects, or
adverse environmental effects.
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Examples of air toxics include dioxin, asbestos, toluene, and metals such as
cadmium, mercury, chromium, and lead compounds.
Smog
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Smog (a combination of the words "smoke" and "fog") forms when sunlight
acts on a cocktail of pollutant gases such as nitrogen and sulfur oxides,
unburned hydrocarbons, and carbon monoxide; that's why it's sometimes
called photochemical smog
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One of the most harmful constituents of smog is the ozone, which can cause
serious breathing difficulties and even, sometimes, death.
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When smog is rich in ozone, it tends to be a blueish color, otherwise it's more
likely to be brown.
Monitoring of air pollution
The best indicators of air pollution are sulphur dioxide, smoke and suspended
particles. These are monitored on a daily basis over several sites. The results are
then collected by a central agency.
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Smoke or soiling index: A known volume of air is filtered through a white
filter paper under specified conditions and the stain is measured by
photoelectric meter. Smoke concentration is estimated and expressed as
micrograms/ cubic metre of air as an average level over a period of time.
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Grit and dust measurement : Deposit gauges collect grit, dust and other
solids. These are analyzed monthly.
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Sulphur dioxide: This gas is a major contaminant in many urban and
industrial areas and Its concentration is estimated in all air pollution
surveys.
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Coefficient of haze : A factor used, particularly in the USA in assessing the
amount of smoke or other aerosol in air.
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Effects of air pollution
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Health aspects :
The health effects of air pollution are both immediate and delayed.
The immediate effects are borne by the respiratory system, the resulting state is
acute bronchitis.
If the air pollution is intense, it may result even in immediate death by suffocation.
This has taken place in the air pollu on epidemic which occurred in London in 1952.
The delayed effects most commonly linked with air pollution are chronic bronchitis,
lung cancer, bronchial asthma, emphysema, and respiratory allergies
Elderly, children, smokers and those with chronic respiratory difficulties are most
vulnerable.
(b) Social and economic aspects :
These comprise destruction of plant and animal life; corrosion of metals; damage to
buildings; cost of cleaning and maintenance and repairs and aesthetic nuisance.
Air pollution also reduces visibility in towns.
It can soil and damage clothings.
Prevention and control of air pollution
The WHO has recommended the following procedures for the prevention and
control of air pollution
Containment : That is, prevention of escape of toxic substances into the ambient air.
Containment can be achieved by a variety of engineering methods such as enclosure,
ventilation and air cleaning. A major contribution in this field is the development of
"arresters" for the removal of contaminants.
Replacement : That is, replacing a technological process causing air pollution, by a
new process that does not. Increased use of electricity, solar power generation,
natural gas, and central heating in place
of coal have greatly helped in smoke reduction.
There is a move now to reduce lead in petrol which is a cumulative poison.
Dilution : Dilution is valid so long as it is within the selfcleaning capacity of the
environment. For example, some air pollutants are readily removed by vegetation.
The establishment of "green belts" between industrial and residential areas is an
attempt at dilution. The capacity for dilution is, however, limited and trouble occurs
when the atmosphere is overburdened with pollutants.
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Legislation: Air pollution is controlled in many countries by suitable legislation, e.g.,
Clean Air Acts. Legislation covers such matters as height of chimneys, powers to local
authorities to carry out investigations, research and education concerning air
pollution, creation of smokeless zones and enforcement of standard for ambient air
quality.
International action : To deal with air pollution on a world-wide scale, the WHO has
established an international network of laboratories for the monitoring and study of
air pollution.
These centres will issue warnings of air pollution where and when necessary.
Indoor Air Pollution and Health
originating from both outdoor and indoor sources, people spend a large part of
their time each day indoors.
Indoor Air Pollutants Sources
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Outdoor air pollutants
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Fuel-burning combustion appliances
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Tobacco products
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Products for household cleaning and maintenance, personal care, or hobbies
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Central heating and cooling systems and humidification devices
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Excess moisture
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Emissions from construction materials and furnishings
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Deteriorated asbestos-containing insulation
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Newly installed flooring, upholstery or carpet
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Cabinetry or furniture made of certain pressed wood products
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