Atmospheric Pollution

Atmospheric pollution means the contamination of air by harmful gases, smoke and tiny solid particles. The main air pollutants are carbon monoxide (from incomplete burning of fuel), sulphur dioxide (from burning coal and oil), oxides of nitrogen (from vehicle engines and lightning), hydrogen sulphide, unburnt hydrocarbons, chlorofluorocarbons (from refrigerators and aerosols) and suspended particulate matter such as dust, soot and smoke. These come mostly from vehicles, factories, power stations and the burning of fossil fuels. Each pollutant harms health or the environment in its own way.

When sulphur dioxide and oxides of nitrogen are released into the air, they are oxidised and dissolve in the water droplets of clouds. Sulphur dioxide turns into sulphur trioxide, which reacts with water to form sulphuric acid; nitrogen oxides form nitric acid. This rain, with a pH below 5.6, is called acid rain. It corrodes metals and marble buildings (the Taj Mahal is at risk), makes lakes and soil acidic, kills fish and damages forests and crops.

High up in the stratosphere a layer of ozone (O3) absorbs most of the Sun's harmful ultraviolet rays, acting as Earth's sunscreen. Chlorofluorocarbons rise into this layer, and ultraviolet light splits off chlorine atoms from them. Each chlorine atom breaks apart many ozone molecules, thinning the layer and creating the 'ozone hole'. More UV then reaches the ground, causing sunburn, premature ageing, skin cancer and eye cataracts, and harming crops and sea life.

Carbon dioxide and certain other gases let sunlight in but trap the heat the warm Earth gives back, just as glass traps heat inside a greenhouse. This natural warming keeps the Earth livable, but burning more and more fossil fuels and cutting forests has raised carbon dioxide levels sharply. The extra trapping causes global warming: rising temperatures, melting glaciers, rising sea levels and changing climate. Controlling pollution with scrubbers, catalytic converters, cleaner fuels and planting trees helps protect the atmosphere.