This essay investigates a chemical issue faced in society today of a social or environmental nature. By exploring two different perspectives of the issue conclusions are formed based on the collated information using appropriate chemical terms where necessary (e.g. chemical equations).
In recent times largely populated cities are becoming increasingly susceptible to photochemical smog. Toxic grey fog is produced by transport, factories and other high pollution producing industries which are concentrated in one particular area. This essay highlights how pollution is produced, reduced and what we can do.
Photochemical smog is the result of primary and secondary pollutants, such as carbon monoxide (CO), nitric oxide (NO), ozone (O3) and sulphuric acid (H2SO4), concentrated in one area. These pollutants are toxic to humans and other organisms, reducing oxygen levels in the air. Extended exposure can lead to irritation of the eyes and respiratory system and even death.
Primary pollutants are molecules that are directly emitted into the atmosphere (Morton, B. Essen. Wrkbk.). Transportation, a common producer of primary pollutants, is proportionally the reason why large cities, such as Milan (Italy), Mexico City (Mexico) and Linfen (China), experience a haze during the day (http: (2)). In a car’s internal combustion chamber reactions taking place create energy. If oxygen supply is limited incomplete combustion occurs, less energy is released, and unwanted molecules form. Examples of primary pollutants are carbon monoxide, carbon (fine particle soot) and unburnt hydrocarbons.
The combustion of cyclohexane, a fuel constitute used in cars:
C6H12(l) + 9O2(g) 6CO2(g) + 6H2O(l) ∆H = -3916 kJ mol -1
Incomplete combustion, its effect on heat energy, and the pollutants produced:
C6H12(l) + 6O2(g) 6CO(g) + 6H2O(l) ∆H = -2224 kJ mol -1
C6H12(l) + 3O2(g) 6C(s) + 6H2O(l) ∆H = -1558 kJ mol -1
A general formula showing incomplete combustion:
Petrol + air (oxygen/nitrogen) CO2 + CO + C + NOx + H2O + unburnt hydrocarbons
(Morton, B. Essen. Wrkbk.)
Secondary pollutants are formed due to photochemical reactions taking place between primary pollutants, air and ultraviolet radiation (sunlight). Examples of common secondary pollutants include nitrogen dioxide (NO2), atomic oxygen (O), ozone (O3), aldehydes and peroxyacyl nitrates (PAN) (Morton, B. Essen. Wrkbk.). Nitrogen dioxide creates what is visible as the brown smog. Most other primary and secondary pollutants are colourless (Stanley, R. Discovering Chem.).
How the primary pollutant nitric oxide (NO) can be converted into secondary pollutants:
2NO(g) + O2(g) 2NO2(g) … when nitric oxide mixes with oxygen in the atmosphere nitrogen dioxide may form.
NO2(g) + hv NO(g) + O(g) …this highly reactive nitrogen dioxide in the atmosphere splits after absorbing solar radiation...