Air pollution can be defined as the presence in the outdoor or indoor atmosphere of one or more gaseous or particulate contaminants in quantities, characteristics and duration such as to be injurious to human, plant or animal life or to property, or which unreasonably interferes with the comfortable enjoyment of life and property.Air pollution problems may vary greatly with the geography, demography and the socio-economic profile of a region, which will determine the source and emission rate of the pollutant. The climate and topography a region will influence the distribution and atmospheric processes of the pollutant and ultimately its effect on the environment and human health.
Carbon dioxide (CO2): Carbon dioxide is not by definition an air pollutant but a natural component of the atmosphere. Increasing emissions of CO2 in the atmosphere over the past 100 years resulted in global warming by the following process: CO2 is transparent to short-wave solar radiation but absorbs infrared radiation and traps it in the lower atmosphere. This phenomenon is known as the "green house effect".
Carbon monoxide (CO): Carbon monoxide is one of the most common and widely distributed air pollutants. There is evidence to suggest that global emissions of CO have risen in line with the massive growth of motor vehicle numbers and mileage. Concentrations inside motor cars often exceed those in the surrounding atmosphere. Forest clearance, savanna burning and the oxidation of methane are the other sources of CO.
Sulphur dioxide (SO2): Man-made emissions include fossil fuel combustion, power plants and industries. Natural emissions form from soil, plants, the burning of biomass, marine biogenic sea spray and volcanoes.
Particulate matter: On a global scale particulate matter is one of the most prevailing atmospheric pollutant. Natural sources include wind blown dust, sea spray, pollen, forest fires and volcanoes. The following are some of the natural and man-made emissions for the different particulate matter:
Hydrocarbons: Petrol and Diesel fuel consists of a large number of hydrocarbons. Aromatic hydrocarbons are added to petrol to aid refining. In some countries large quantities of alcohol or ethanol are added to petrol which give rise to large numbers of Volatile Organic Compounds (VOCs).
Nitrogen Oxides (NOx): They are significant pollutants on both local and regional scale. NOx emissions result from fossil fuel combustion and half of these man-made emissions are from mobile sources. Natural production is from bacterial action in soils, lightning and forest fires.
Photochemical Smog: Nitrogen oxide and other primary pollutants react under certain climatic conditions to form secondary pollutants such as NO2, O3 and peroxyacyl nitrates (PANs). These photochemical oxidants in combination with various organic compounds are referred to as "photochemical smog".