Overview of Air Pollution, The Chemistry Behind Pollution - page 2
Keywords: Environmental Studies
By Vickiduduu on 10/11/2007
Level: Foundation Degree
Page Number: 2 of 5 pages: 1 2 3 4 5
are anthropogenic; however oxides of Sulphur can be given off naturally, from the bacterial action in soils for example or upon the eruption of a volcano. The Sulphur dioxide and other gases dissolved in magma underneath the earths crust bubble through the magma and force it through the top of the volcano explosively, releasing not only the magma but the gases too.
Once the oxides of Sulphur reach the earth’s troposphere there are a whole host of reactions which can occur to form secondary pollutants and harm the environment. The most problematic secondary pollutant arising from oxides of Sulphur is acidification of precipitation. Acid precipitation is the term used to describe rainfall with a pH of less than normal (5.6), the reactions that occur to produce acid precipitation can happen in the liquid
water droplets of clouds, which can then fall to earth as acidified rain. This is because oxides of Sulphur dissolve in water and can then hydrolyse producing weak acidic solutions.
Sulphur dioxide + water → sulphurous acid + hydrogen
SO2 + 3H2O→ H2SO3 + 2H2
Sulphur trioxide + water → sulphuric acid
SO3 + H2O → H2SO4
Acid precipitation has been monitored for many years and it has been found to consist of on average only 65% dilute sulphuric acid, so what is the other 35% made from? Studies have found that acid precipitation contains dilute nitric acid as well. Similarly to Sulphuric acid, Nitric acid is formed from Oxides of Nitrogen reacting with water in the cloud droplets.
Nitrogen dioxide + water → Nitric acid + hydrogen
2NO2 + 2H2O → 2HNO3 + H2
As with Sulphur, Oxides of Nitrogen are released into the atmosphere through industrial processes where Nitrogen containing fuels are used. Nitric Oxide is usually formed from the combustion of these fuels, which once released readily oxidise to form Nitrogen dioxide. NOx are the main culprit in the formation of photochemical smog. This is the cause of reduced visibility levels in heavily populated areas. Photochemical smog is the secondary pollutant formed when Nitrogen dioxide reacts further with O2 molecules in the air.
At high concentrations of NO2, and when sunlight is present, an oxygen atom can split from the NO2 molecule.
Sunlight
NO2 NO + O
This O atom can now react with O2 molecules in the air to form O3, as this is a more energetically favourable state for O, then the O3 builds up at ground level However, Nitric oxide has
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