Pollution is the effect of undesirable changes in
our surroundings that have harmful effects on
plants, animals and human beings. This occurs when only short-term economic gains are made
at the cost of the long-term ecological benefits
for humanity. No natural phenomenon has led
to greater ecological changes than have been
made by mankind. During the last few decades, we have contaminated our air, water and land
on which life itself depends on a variety of
Air pollution occurs due to the presence of undesirable solid or gaseous particles in the air in quantities that are harmful to human health and the environment. Air may get polluted by natural causes such as volcanoes, which release ash, dust, sulphur and other gases, or by forest fires that are occasionally naturally caused by lightning. However, unlike pollutants from human activity, naturally occurring pollutants tend to remain in the atmosphere for a short time and do not lead to permanent atmospheric change.
Pollutants of air pollution
Pollutants that are emitted directly from identifiable sources are produced both by natural events (for example, dust storms and volcanic eruptions) and human activities (emission from vehicles, industries, etc.). These are called primary pollutants. There are five primary pollutants that together contribute about 90 percent of the global air pollution. These are carbon oxides (CO and CO2), nitrogen oxides, sulfur oxides, volatile organic compounds (mostly hydrocarbons) and suspended particulate matter.
Pollutants that are produced in the atmosphere when certain chemical reactions take place among the primary pollutants are called secondary pollutants. Eg: sulfuric acid, nitric acid, carbonic acid, etc.
Carbon monoxide is a colourless, odourless and toxic gas produced when organic materials such as natural gas, coal or wood are incompletely burnt. Vehicular exhausts are the single largest source of carbon monoxide. The number of vehicles has been increasing over the years all over the world. Vehicles are also poorly maintained and several have inadequate pollution control equipment resulting in the release of greater amounts of carbon monoxide. Carbon monoxide is however not a persistent pollutant. Natural processes can convert carbon monoxide to other compounds that are not harmful. Therefore the air can be cleared of its carbon monoxide if no new carbon monoxide is introduced into the atmosphere.
Sulfur oxides are produced when sulfur-containing fossil fuels are burnt. Nitrogen oxides are found in vehicular exhausts. Nitrogen oxides are significant, as they are involved in the production of secondary air pollutants such as ozone. Hydrocarbons are a group of compounds consisting of carbon and hydrogen atoms. They either evaporate from fuel supplies or are remnants of fuel that did not burn completely.
Hydrocarbons are washed out of the air when it rains and run into surface water. They cause an oily film on the surface and do not as such cause a serious issue until they react to form secondary pollutants. Using higher oxygen concentrations in the fuel-air mixture and using valves to prevent the escape of gases, fitting of catalytic converters in automobiles, are some of the modifications that can reduce the release of hydrocarbons into the atmosphere.
Particulates are small pieces of solid material (for
example, smoke particles from fires, bits of asbestos, dust particles and ash from industries)
dispersed into the atmosphere. The effects of
particulates range from soot to the carcinogenic
(cancer-causing) effects of asbestos, dust particles and ash from industrial plants that are dispersed into the atmosphere. Repeated exposure
to particulates can cause them to accumulate
in the lungs and interfere with the ability of the
lungs to exchange gases.
Lead is a major air pollutant that remains largely unmonitored and is emitted by vehicles. High lead levels have been reported in the ambient air in metropolitan cities. Leaded petrol is the primary source of airborne lead emissions in Indian cities.
Various causes of air pollution
Aerosols and CFCs
According to the ozone layer depletion research, CFCs are leading pollutants. These CFCs (Chloro-Fluro-Carbons) are extremely stable, non-flammable, non-toxic and harmless to handle. This makes them ideal for many industrial applications like aerosols, air conditioners, refrigerators and fire extinguishers. Many cans, which give out foams and sprays, use CFCs (eg: perfumes, room fresheners, etc.) CFCs are also used in making foams for mattresses and cushions, disposable Styrofoam cups, glasses, packaging material for insulation, cold storage etc
Combustion from Industry
Industrial processes produce all of the common air pollutants. Combustion of fossil fuels that drive the industrial process results in particulates, ozone and nitrogen oxides.
Combustion of gasoline and diesel produce carbon monoxide, nitrogen oxides, particulate matter, and unburned hydrocarbons that contribute to air pollution.
Methane is a gas that contributes to the greenhouse effect that allows global warming. It arises from intestinal gas released by livestock. Ammonia enters the air as a gas from heavily fertilized fields and livestock waste that combines with pollutants from combustion to create tiny solid particles, or aerosols.
Everyday activities such as heating, cleaning, painting and decorating contribute to indoor air pollution. Smoking tobacco through the use of cigarettes and cigars also releases toxic pollutants into the air.
Forests, that convert oxygen from carbon dioxide, are the lifeline of aerobic organisms. Burning of forests not only interrupts CO2 to oxygen conversion but also release CO2 due to combustion. It also produces fine smoke particles which are small enough to be able to get into the lungs and damage the lungs and the heart.