Air Pollution

Degradation of air quality and natural atmospheric conditions constitute air pollution. As air pollutant may be a gas or particulate matter (i.e. suspended aerosols composed of solids and liquids). Concentration of atmospheric pollutants depends mainly on the total mass emitted into the atmosphere, and the atmospheric conditions that affect their fate and transport. Most of the air we breathe is elemental O₂and N₂. About 1 percent is composed of other constituents, such as CO₂ and water vapor. A small part of this 1 percent may, however, be air pollutants, including gases and particulate matter. Even such a small concentration may be extremely harmful to life and property.

Natural sources of air pollution include pollen, dust and smoke (from forest fire and volcanic ash) which are emitted into the atmosphere. Anthropogenic air pollutants enter the atmosphere from fixed and mobile sources. Fixed sources include large factories, electrical power plants, mineral smelters and different small-scale industries, while mobile sources include at sorts of transport vehicles moving by road, rail or air.

Air pollutants can be classified into two categories, viz. primary and secondary air pollutants. Primary pollutants enter the atmosphere directly from various sources. Secondary pollutants are formed during chemical reactions between primary air pollutants and other atmospheric constituents, such as water vapor. Generally, these reactions occur in the presence of sunlight.

Primary Air Pollutants

Amongst the primary air pollutants, most important are particulate matter, carbon monoxide (CO), hydrocarbons (HCs), sulphur dioxide (SO₂), and nitrogen oxides (NOx).

Control of Air Pollution

Important preventive strategies to control air pollution are:

1. Suitable fuel selection (example: fuel with low sulphur content) and its efficient utilization to reduce pollutant level in emission.

2. Modifications in industrial processes and/or equipments to reduce emissions.

3. Correct selection of manufacturing site and zoning for industrial set up to disperse pollution sources. The most common methods of eliminating or reducing pollutants to an acceptable level include destroying the pollutant by thermal or catalytic combustion, changing the pollutant to a less toxic form, or collecting the pollutant by use of equipment to prevent its escape into the atmosphere.