Air Pollution and Control

Air pollution: It is defined as the excessive concentration of foreign matter in the air which adversely affects the well being of individual or causes damage to the property. It also affects plants, animals and buildings.

SOURCES OF AIR POLLUTION:

• Natural sources of air pollution
• Man-made sources of air pollution

NATURAL SOURCES OF AIR POLLUTION:

• Products from atmospheric reactions (chemical reactions like oxidation, combination, polymerization, photochemical reactions etc.)
• Aerosols-Particulates : Aerosols are finely divided solid or liquid particles of microscopic size held suspended - and dispersed in atmosphere. They cause visibility reduction, soiling of surfaces, corrosion etc.

The various types of aerosols are:

1. Dust
2. Smoke
3. Mists
4. Fog
5. Haze
6. Fumes.

• Micro-organisms: infect plants and animals.
• Pollens: Pollens arc the small grains from the anthers of flowers which may cause allergic reactions.
• Radioactive minerals:
•  Volcanic ash and gases:
• Gases and odour from swamps and marshy lands.

MAN-MADE SOURCES AIR POLLUTION:

• Combustion of fuels: (CO2), (SO2), (NO2),etc. accumulate ¡n the atmosphere.
• Industries: Emit undesirable gases (SO2, CO2, NO2, NH3, CO.
• Thermal Power Plants: Mainly they emit Sulphur dioxide.
• Automobiles: Exhaust contain carbon monoxide (CO), methane, un-burnt carbon CO is the main source of air pollution in congested cities.
• Agricultural activities: Crop spraying and field burning.
• Nuclear Power Plants: Emit various radioactive substances

 CLASSIFICATION OF AIR POLLUTANTS:

According to the manner ¡n which they are formed they are classified as:

• Primary air pollutants
• Secondary air pollutants.

Primary air pollutants: They are those which are emitted directly from the identifiable sources.

• Particulate matter such as dust and aerosols
• Pollens
• Sulphur compounds (SO2, SO3, H2S)
• Nitrogen compounds (NO, NO2, NH3)
• Carbon monoxide (CO) and carbon dioxide (CO2)
• Photochemical oxidants
• lead
• Hydrocarbons
• Radioactive materials
• Halogen compounds                                                                                                               (Hydrogen fluoride. hydrochloric acid)

Secondary air pollutants: They are those which are formed in the atmosphere as a result of interaction between two or more primary air pollutants or by reactions with the normal atmospheric constituents with or without photo activation. These are more harmful.

• Sulphuric acid
• Ozone 
• Formaldehyde
• Peroxy-acetyl - nitrate (PAN)
• Photochemical smog