The presence of substances that are not part of the natural composition of the atmosphere, which could be harmful to living organisms even in small concentrations, is called air pollution.
Due to natural processes or human activities, gases other than oxygen and other solid substances increase in the atmosphere. It reduces the air quality in several cities across the globe. Gases like SO2, nitrites, CO2, and other gaseous compounds, along with particulate pollutants, are common pollutants. Here are the air pollutants and its types.
Sources of Air Pollution
Air pollutants can have natural sources and also arise due to human activities.
Natural Sources of Air Pollution
Pollens, dust arising due to volcanic activity, desert storms, etc and hydrocarbons released by vegetation, etc, are common air pollutants. Gases arising due to volcanic activity and volcanic ash are other examples.
Air Pollution Due to Human Activities
- Industrial wastes from petroleum refineries are a major source of SO2, NO2, etc.
- Cement factories and other similar companies cause dust particles in the air that commonly cause various health issues.
- Similarly, acid fumes from chemical industries also contribute to air pollution.
- Thermal power station uses coal that releases CO, NO2, SO2, aldehydes, and hydrocarbons.
- Automobile exhaust releases toxic gases and unburnt hydrocarbons into the air. Moreover, lead oxides, esters, and aldehydes are also released.
Air Pollutants and Its Types
Air pollutants are mainly classified into gaseous and particulate pollutants.
Gaseous Pollutants
Gaseous pollutants include the sulphur oxides, hydrogen sulphides, carbon monoxide, and any other gas that pollutes the air.
- Sulphur oxides and hydrogen sulphides arise due to the decomposition of organic matter and volcanic eruptions. Combustion of sulphur-containing fuels like coal also contributes.
- Carbon monoxide is released from gasoline engines, defective furnaces that burn coal.
- Nitrogen oxides are released by anaerobic bacterial decomposition of nitrogenous compounds, lightning and forest burning. Automobile exhausts, power generators, burning of organic wastes, nitrogenous fertilisers and explosives are other sources.
- Photochemical smog: Usually, the ultraviolet light reduces atmospheric NO2 into NO and oxygen. This oxygen reacts with O2 to form O3, ozone. Ozone reacts with NO to regenerate NO2 and O2. Instead of this cyclic process, the oxygen released from NO2 reacts with hydrocarbons to form radicals- highly reactive intermediates. These radicals react with NO2 and oxygen to form more ozone molecules and other secondary pollutants. This is called phorochemical smog.
- Ozone: Lightning flashes, reaction of UL light on NO2 and oxygen, vertical flux of stratospheric ozone, etc generate more amount of ozone.
- Flurocarbons are generated by active volcanoes, petroleum mining, steel plants, blast furnaces, etc.
- Hydrocarbons are released by natural gas, decomposition or organic matter, volatile emissions from plants, etc.
- Hydrogen chloride is released from the combustion of coal, plastics, paper, spillage from chemical plants, etc.
- Ammonia is released from refrigerators, explosives, dyes, varnishes, etc.
- Tobacco smoke generates nicotine and other carcinogens.
Particulate Pollutants
- Fluorides from volcanoes and petroleum products
- Lead from automobile exhaust, lead-lined cookware, etc.
- Mercury in soil and rocks arises into the air from paints, fungicides, cosmetics, etc.
- Zinc from zinc oxide fumes from scrap zinc refineries.
- Cadmium from industries of fertilisers, pesticides, etc.
- Potassium salts from potash mines.
- NaCl is used in ice removal.
- Agricultural chemicals such as insecticides, pesticides and fertilisers.
- Particulate matter or suspended particles from industries and black soot.
- Grinding and abrasions cause dust particles.
- Inorganic dust, silica, and heavy metals.
- Organic dust from cotton textiles, ginning, coir, jute, sawdust, etc.
References
- Shukla, R.S. and Chandel, P.S. (2001) Plant Ecology. S. Chand and Company Ltd., New Delhi.
- Verma, P.S., Agarwal, V.K. (1999). Cell Biology, Genetics, Molecular Biology, Evolution, and Ecology. New Delhi: S.Chand Co.(Pvt) Ltd.
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