AIR POLLUTION AND IT`S MAJOR POLLUTANTS

 DEFINITION

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 valcanoes,which release ash ,dust, Sulphur and other gases, or by forest fires that are occasionally naturally caused by lightning,However,unlike pollutants from human activities ,naturally occuring pollutants tend to remain in the atmosphere for a short time and do not lead to permanent atmospheric change.

                                                      

TYPES OF POLLUTANTS

Primary pollutants

Pollutants that are emitted directly from identifiable sources are produced by natural events such as dust storms and volcanic eruptions, and human activities such as emission from vehicles, industries, pesticides etc...these are called primary pollutants.

There are five primary air pollutants that together contribute about 90% of global air pollution. These are carbon oxides, nitrogen oxides, sulfur oxides, volatile organic compounds are mainly  hydrocarbons and suspended particulate matter.

Secondary pollutants

Pollutants that are produced in the atmosphere when certain chemical reactions take place among the primary pollutants are called secondary pollutants. Examples sulfuric acid, nitric acid, carbonic acid,etc..

MAJOR AIR POLLUTANTS

Carbon monoxide

That is a colourless,odorless organic materials such as natural gas, coal or wood are incompletely burnt.

Sulfur oxides

That are produced when sulfur containing fossil fuels are burnt.

Nitrogen oxide

That are found in vehicular exhausts. Nitrogen oxides are significant, they are involved in the production of secondarybair pollutants such as ozone.

Hydrocarbons

Hydro carbons are a group of compounds consisting of carbon hydrogen atoms. They are evaporate from fuel supplies or remnants of fuel that did not burn completely. Hydrocarbons are washed out of the air when it rains and run in to surface water.They causes an oily film on the water surface.

                                                   

Particulates

They are small pieces of solid materials such as smoke particles and ash from industries. They dispersed in to the atmosphere. The effects of particulates causing cancer in human beings.

Lead

It is a major air pollutant. It is largely emitted by vehicles. Leaded petrol is the primary source of airborne lead emission in Indian cities.

Acid deposition

Sulphur dioxide and nitrogen oxides are transported by prevailing winds they form secondary pollutants such as nitric acid vapour,droplets of sulfuric acid and particles of sulphate and nitrate salts.

 These chemicals are accumulate on the earth`s surface in two forms such as wet form(as acid rain,snow,fog and cloud vapour) and dry form(acidic particles).The resulting mixture is called acid deposition. Commonly called acid rain.

Acid deposition has many harmful effects especially when the PH falls below 5.1 for terrestrial system and below 5.5 for aquatic system.

It causes human respiratory diseases such as bronchitis and asthma, which can cause pre-mature death.Acid deposition can damage foliage that causes weakening of trees.

                                              

Chlorofluro carbons (CFC)

Ozone a variant of oxygen is present throughout the atmosphere. It is  acts as a filter, absorbing harmful wave lengths of ultraviolet radiation(UV).Without the radiation shield, more U.V radiation would reach the earth surface, and would damage plants and animal life and greatly increase the risk of skin cancer and eye diseases..The widespread use of Chloro Fluro Carbons are highly stable compounds used in aerosol propellants refrigeration, foam blowing and industrial solvent's could damage the ozone shield.