Air pollution may be defined as the presence
in the air (outdoor atmosphere) of one or
more contaminants or combinations
thereof in such quantities and of such
durations as may be or tend to be
injurious to human, animal or plant life,
or property, or which unreasonably
interferes with the comfortable
enjoyment of life or property or
conduct of business.
It is a substance or effect dwelling temporarily or
permanently in the air , which adversely alters the
environment by interfering with the health, the
comfort, or the food chain, or by interfering with the
property values of people.
A pollutant can be solid (large or sub-molecular), liquid
or gas .
It may originate from a natural or anthropogenic source
It is estimated that anthropogenic sources have changed
the composition of global air by less than 0.01%.
However, it is widely accepted that even a small change
can have a significant adverse effect on the climate,
ecosystem and species on the planet.
Examples of these are acid rain, ozone in the lower
atmosphere, and photochemical smog.
Health Effects of Nitrogen
• Short-term exposure at concentrations greater than
3 parts per million can measurably decrease lung
• Concentrations less than 3 ppm can irritate lungs.
• Concentrations as low as 0.1 ppm cause lung
irritation and measurable decreases in lung function
• Long-term lower level exposures can destroy lung
tissue, leading to emphysema.
• Children may also be especially sensitive to the
effects of nitrogen oxides.
• Seriously injure vegetation at certain
concentrations. Effects include:
– Bleaching or killing plant tissue.
– Causing leaves to fall.
– Reducing growth rate.
• Deteriorate fabrics and fade dyes.
• Corrode metals (due to nitrate salts
formed from nitrogen oxides).
• Reduce visibility.
Other Effects (Continued)
• Oxides of nitrogen, in the presence of
sunlight, can also react with
hydrocarbons, forming photochemical
oxidants or smog.
• Also, NOx is a precursor to acidic
precipitation, which may affect both
terrestrial and aquatic ecosystems.
Ninety-five percent of pollution related sulfur
oxide emissions are in the form of sulfur
dioxide (SO2), a heavy, colorless gas with an
odor like a struck match.
This gas combines easily with water vapor,
forming aerosols of sulfurous acid (H2SO3), a
colorless, mildly corrosive liquid.
This liquid may then combine with oxygen in
the air, forming the even more irritating and
corrosive sulfuric acid (H2SO4).
• Hydrogen sulfide (H2S) gas - rotten eggs.
• Mercaptans - skunk spray or decayed
garbage. (Added in trace amounts to natural
gas, providing a leak-detecting warning
Note: The amount of SO2 released from coal
fired power plants depends on the sulfur
content of coal, normally 0.7% to 2% by
weight. High sulfur coal sometimes contains
as much as 6% sulfur by weight. In India,
sulfur content is quite low.
Health Effects of Sulfur Oxides
• Sulfur dioxide not only has a bad odor, it can
irritate the respiratory system.
• Exposure to high concentrations for short
periods of time can constrict the bronchi and
increase mucous flow, making breathing
• Children, the elderly, those with chronic lung
disease, and asthmatics are especially
susceptible to these effects.
Sulfur dioxide can also:
• Immediately irritate the lung and throat at
concentrations greater than 6 parts per
million in many people.
• Impair the respiratory system's defenses
against foreign particles and bacteria, when
exposed to concentrations less than 6 ppm
for longer time periods.
• Apparently enhance the harmful effects of
ozone. (Combinations of the two gases at
concentrations occasionally found in the
ambient air appear to increase airway
resistance to breathing.)
Sulfur oxides Effects on Plants
• Sulfur dioxide easily injures many plant species and
varieties, both native and cultivated. Some of the
most sensitive plants include various commercially
valuable pines, legumes, red and black oaks, white
ash, alfalfa and blackberry. The effects include:
• Visible injury to the most sensitive plants at
exposures as low as 0.12 ppm for 8 hours.
• Visible injury to many other plant types of
intermediate sensitivity at exposures of 0.30 ppm for
• Positive benefits from low levels, in a very few
species growing on sulfur deficient soils.
• Increases in sulfur dioxide concentrations
accelerate the corrosion of metals, probably
through the formation of acids. (SO2 is a
major precursor to acidic deposition.) Sulfur
oxides may also damage stone and masonry,
paint, various fibers, paper, leather, and
• Increased SO2 also contributes to impaired
visibility. Particulate sulfate, much of which
is derived from sulfur dioxide emissions, is a
major component of the complex total
suspended particulate mixture.
Health Effects of Ozone
• Ozone acts as a powerful respiratory irritant
at the levels frequently found in most of the
nation's urban areas during summer months.
• Ozone exposure may lead to:
– Shortness of breath.
– Chest pain when inhaling deeply.
– Wheezing and coughing.
Long-term, repeated exposure to high levels
of ozone may lead to large reductions in
lung function, inflammation of the lung
lining, and increased respiratory