Air Pollution 1

Air pollution
Air pollutant Air pollution is the introduction of chemicals, particulate matter, or
biological materials that cause harm or discomfort to humans or other living organisms, or
cause damage to the natural environment or built environment, into the atmosphere. The
atmosphere is a complex dynamic natural gaseous system that is essential to support life on
planet Earth. Stratospheric ozone depletion due to air pollution has long been recognized as a
threat to human health as well as to the Earth's ecosystems. Indoor air pollution and urban air
quality are listed as two of the world's worst pollution problems
A substance in the air that can cause harm to humans and the environment is known as an air
pollutant. Pollutants can be in the form of solid particles, liquid droplets, or gases. In addition,
they may be natural or man-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. Rather, they form in the air when primary pollutants react or interact.

Major primary pollutants produced by human activity include:

 Sulphur oxides (SOx) - especially sulfur dioxide, a chemical compound with the formula SO 2.
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 NO 2, forms H2SO4, and thus acid rain. This
is one of the causes for concern over the environmental impact of the use of these fuels as
power sources.
 Nitrogen oxides (NOx) - especially nitrogen dioxide are 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 NO 2. It is one of the several nitrogen oxides. This
reddish-brown toxic gas has a characteristic sharp, biting odor. NO 2 is one of the most
prominent air pollutants.
 Carbon monoxide (CO)- is a colourless, odorless, 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 major source of carbon monoxide.
 Carbon dioxide (CO2) - a colourless, odorless, 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. In this field they
are often divided into the separate categories of methane (CH 4) and non-methane (NMVOCs).
Methane is an extremely efficient greenhouse gas which contributes to enhanced global
warming. Within the NMVOCs, the aromatic compounds benzene, toluene and xylene are
suspected carcinogens and may lead to leukemia through prolonged exposure. 1,3-butadiene is
another dangerous compound which is often associated with industrial uses.

T Paul Lazarus, Asst. Professor (SS), Dept. of Agril. Economics, College of Agriculture, KAU, Vellayani – 695 522,
Thiruvananthapuram
 Air Pollution 2

 Particulate matter - Particulates, alternatively 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 the gas together. Sources of particulate matter can be man 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 the burning of fossil fuels in
vehicles, power plants and various industrial processes also generate significant amounts of
aerosols.

 Persistent free radicals connected to airborne fine particles could cause cardiopulmonary
disease.
 Toxic metals, such as lead, cadmium and copper.
 Chlorofluorocarbons (CFCs) - harmful to the ozone layer emitted from products currently
banned from use.
 Ammonia (NH3) - emitted from agricultural processes. Ammonia is a compound with the
formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia
contributes significantly to the nutritional needs of terrestrial organisms 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.
 Odors — such as from garbage, sewage, and industrial processes
 Radioactive pollutants - produced by nuclear explosions, nuclear events, war explosives, and
natural processes such as the radioactive decay of radon.

Secondary pollutants include:

 Particulate matter formed from gaseous primary pollutants and compounds in photochemical
smog. Smog is a kind of air pollution; the word "smog" is a portmanteau of smoke and fog.
Classic smog results from large amounts of coal burning in an area caused by a mixture of
smoke and sulfur dioxide. Modern smog does not usually come from coal but from vehicular
and industrial emissions that are acted on in the atmosphere by ultraviolet light from the sun to
form secondary pollutants that also combine with the primary emissions to form photochemical
smog.
 Ground level ozone (O3) formed from NOx and VOCs. Ozone (O3) is a key constituent of the
troposphere. It is also an important constituent of certain regions of the stratosphere commonly
known as the Ozone layer. Photochemical and chemical reactions involving it drive many of
the chemical processes that occur in the atmosphere by day and by night. At abnormally high
concentrations brought about by human activities (largely the combustion of fossil fuel), it is a
pollutant, and a constituent of smog.
 Peroxyacetyl nitrate (PAN) - similarly formed from NOx and VOCs.

Minor air pollutants include:

 A large number of minor hazardous air pollutants. Some of these are regulated in USA under
the Clean Air Act and in Europe under the Air Framework Directive.
 A variety of persistent organic pollutants, which can attach to particulate matter.

T Paul Lazarus, Asst. Professor (SS), Dept. of Agril. Economics, College of Agriculture, KAU, Vellayani – 695 522,
Thiruvananthapuram
 Air Pollution 3

Persistent organic pollutants (POPs) are organic compounds that are resistant to environmental
degradation through chemical, biological, and photolytic processes. Because of this, they have
been observed to persist in the environment, to be capable of long-range transport,
bioaccumulate in human and animal tissue, biomagnify in food chains, and to have potential
significant impacts on human health and the environment.

Sources of air pollution

Sources of air pollution refer to the various locations, activities or factors which are responsible
for the releasing of pollutants into the atmosphere. These sources can be classified into two
major categories which are:

Anthropogenic sources (human activity) mostly related to burning different kinds of fuel

 "Stationary Sources" include smoke stacks of power plants, manufacturing facilities

(factories) and waste incinerators, as well as furnaces and other types of fuel-burning heating
devices. In developing and poor countries, traditional biomass burning is the major source of
air pollutants; traditional biomass includes wood, crop waste and dung.[6][7]

 "Mobile Sources" include motor vehicles, marine vessels, aircraft and the effect of sound etc.

 Chemicals, dust and controlled burn practices in agriculture and forestry management.
Controlled or prescribed burning is a technique sometimes used in forest management,
farming, prairie restoration or greenhouse gas abatement. Fire is a natural part of both forest
and grassland ecology and controlled fire can be a tool for foresters. Controlled burning
stimulates the germination of some desirable forest trees, thus renewing the forest.

 Fumes from paint, hair spray, varnish, aerosol sprays and other solvents

 Waste deposition in landfills, which generate methane. Methane is not toxic; however, it is
highly flammable and may form explosive mixtures with air. Methane is also an asphyxiant
and may displace oxygen in an enclosed space. Asphyxia or suffocation may result if the
oxygen concentration is reduced to below 19.5% by displacement

 Military, such as nuclear weapons, toxic gases, germ warfare and rocketry

Natural sources

 Dust from natural sources, usually large areas of land with little or no vegetation
 Methane, emitted by the digestion of food by animals, for example cattle

 Radon gas from radioactive decay within the Earth's crust. Smoke and carbon monoxide
from wildfires
 Vegetation, in some regions, emits environmentally significant amounts of VOCs on warmer
days. These VOCs react with primary anthropogenic pollutants—specifically, NO x, SO2, and

T Paul Lazarus, Asst. Professor (SS), Dept. of Agril. Economics, College of Agriculture, KAU, Vellayani – 695 522,
Thiruvananthapuram
 Air Pollution 4

anthropogenic organic carbon compounds—to produce a seasonal haze of secondary

pollutants.[8]
 Volcanic activity, which produce sulfur, chlorine, and ash particulates

Reduction efforts

There are various air pollution control technologies and land use planning strategies available to
reduce air pollution. At its most basic level land use planning is likely to involve zoning and
transport infrastructure planning. In most developed countries, land use planning is an important
part of social policy, ensuring that land is used efficiently for the benefit of the wider economy
and population as well as to protect the environment.

Efforts to reduce pollution from mobile sources includes primary regulation (many developing
countries have permissive regulations] expanding regulation to new sources (such as cruise and
transport ships, farm equipment, and small gas-powered equipment such as lawn trimmers,
chainsaws, and snowmobiles), increased fuel efficiency (such as through the use of hybrid
vehicles), conversion to cleaner fuels (such as bioethanol, biodiesel, or conversion to electric
vehicles).A number of control devices are available for pollution control which are used by
industries.

T Paul Lazarus, Asst. Professor (SS), Dept. of Agril. Economics, College of Agriculture, KAU, Vellayani – 695 522,
Thiruvananthapuram