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Air pollution

Adarsh KanojiyaLast Seen: Mar 14, 2024 @ 3:28pm 15MarUTC
Adarsh Kanojiya

27th February 2024 | 2 Views
Milyin » 569116 » Air pollution

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Definition of Air Pollution
Air pollution is the presence of foreign substances in the air. There are some specific
definitions available for air pollution:
“Air pollution is defined as the presence of contaminants or pollutant
substances in the air that interfere with human health or welfare, or produce
harmful environmental effects” (the United States Environmental Protection
Agency, 2007).
“Air pollution is the presence of substances in air in sufficient
concentration and for sufficient time, so as to be, or threaten to be injurious to
human, plant or animal life, or to property, or which reasonably interferes with
the comfortable enjoyment of life and property” (WHO,1972)

Classification of Air Pollutants
A substance in the air that can cause harm humans and the environment is known as
an air pollutant. Pollutants can be in the form of solid particles, liquid droplets, or gases.
Besides, they may be natural or human-made.
Pollutants can be classified as primary or secondary. Usually, primary pollutants are
directly emitted from a process, such as ash from a volcanic eruption, the carbon
monoxide gas from a motor vehicle exhaust or sulfur dioxide released from factories.
Secondary pollutants are not emitted directly. Instead, they form in the air when
primary pollutants react or interact. An important example of a secondary contaminant
is ground-level ozone — one of the many secondary pollutants that make up
photochemical smog. Some pollutants may be both primary and secondary: they are
both emitted directly and formed from other primary pollutants.

Major primary pollutants produced by human activity include
• Sulphur oxides (SOx): SO2 is produced by volcanoes and in various industrial
processes. Since coal and petroleum often contain sulfur compounds, their
combustion generates sulfur dioxide. Further oxidation of SO2, usually in the
presence of a catalyst such as NO2, forms H2SO4 and acid rain. This is one of the
causes for concern over the environmental impact of using these fuels as power

• Nitrogen oxides (NOx): especially nitrogen dioxide is emitted from high-
temperature combustion, and are also produced naturally during thunderstorms by

electrical discharge. Can be seen as the brown haze dome above or plume
downwind of cities. Nitrogen dioxide is the chemical compound with the formula
NO2. It is one of the several nitrogen oxides. This reddish-brown toxic gas has a
characteristic sharp, biting odour. NO2 is one of the most prominent air pollutants.
• Carbon monoxide (CO): is a colourless, odourless, non-irritating but very
poisonous gas. It is a product by incomplete combustion of fuel such as natural gas,
coal or wood. Vehicular exhaust is a significant source of carbon monoxide.
• Carbon dioxide (CO2): is a colourless, odourless, non-toxic greenhouse gas also
associated with ocean acidification, emitted from sources such as combustion,
cement production, and respiration. It is otherwise recycled in the atmosphere in
the carbon cycle.
• Volatile organic compounds: VOCs are an important outdoor air pollutant. They
are often divided into separate categories of methane (CH4) and non-methane
(NMVOCs) in this field. Methane is an extremely efficient greenhouse gas that
contributes to enhanced global warming. Other hydrocarbon VOCs is also
significant greenhouse gases via their role in creating ozone and prolonging
methane’s life in the atmosphere. However, the effect varies depending on local air
quality. Within the NMVOCs, the aromatic compounds benzene, toluene, and
xylene are suspected carcinogens and may lead to leukaemia through prolonged
exposure. 1,3-butadiene is another dangerous compound that is often associated
with industrial uses.
• Atmospheric particulate matter: Particulates, referred to as particulate matter
(PM) or fine particles, are tiny particles of solid or liquid suspended in a gas. In

contrast, aerosol refers to particles and gas together. Sources of particulate matter
can be human-made or natural. Some particulates occur naturally, originating from
volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray.
Human activities, such as burning fossil fuels in vehicles, power plants and various
industrial processes, also generate significant amounts of aerosols. Averaged over
the globe, anthropogenic aerosols—those made by human activities—currently
account for about 10 per cent of the total amount of aerosols in our atmosphere.
Increased fine particles levels are linked to health hazards such as heart disease,
altered lung function, and lung cancer.
• Chlorofluorocarbons (CFCs): harmful to the ozone layer emitted from
refrigerators, air conditioners used as a coolant and in plastic foam such as a
• Ammonia (NH3): emitted from agricultural processes. Ammonia is a compound with
the formula NH3. It is usually encountered as a gas with a characteristic pungent
odour. Ammonia contributes significantly to terrestrial organisms’ nutritional needs
by serving as a precursor to foodstuffs and fertilizers. Ammonia, either directly or
indirectly, is also a building block for the synthesis of many pharmaceuticals.
Although in wide use, ammonia is both caustic and hazardous.
• Radioactive pollutants: produced by nuclear explosions, nuclear events, war
explosives, and natural processes such as the radioactive decay of radon.

Adarsh KanojiyaLast Seen: Mar 14, 2024 @ 3:28pm 15MarUTC

Adarsh Kanojiya



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