Photochemical Somog - Assignment Example

Topic: Photochemical Smog Photochemical smog is a type of air pollution that develops when primary pollutants (nitrogen oxides and volatile organic compounds mainly created from fossil fuel combustion) interact under the presence of sunlight leading to accumulation and high concentration of ozone in atmosphere and produces a mixture of hundreds of different and toxic chemicals known as secondary pollutants((aldehydes, peroxyacetyl nitrates. The major component is produced as a secondary chemical reaction in the air and not by a direct source such as car.

An interesting issue is the development of photochemical smog – a question that has been considered by a number of scientists. To gain a better insight into this matter I will seek to discuss the chemical reactions causing the formation of such a hazardous condition. Having being canvassed with the chemistry of photochemical smog, the primary culprits known as ‘smog pollutants’ will be highlighted; succeded by the details about their harmful effects. Every problem is solution-borne and so is the photochemical smog.

Before concluding with the essay I would like to focus on the possible solutions that can help minimize the formation of photochemical smog. Researches have shown several topographical and meteorological factors also influence the conditions of the formation of photochemical smog. Topographically, areas situated in valleys experience more smog as compared to plains. Hills and mountains surrounding them cause restriction in air movement, increasing the concentration of air pollutants. Temperature inversion is yet another meteorological factor that can enhance the severity of a photochemical smog condition.

During day the air near the surface is heated and as it warms, it rises, carrying the pollutants with it to higher altitudes. However, if a temperature inversion develops pollutants get trapped close to the ground surface causing the reduction in atmospheric mixing and therefore reduce the vertical dispersion of pollutants. In unpolluted atmosphere ozone (O3) is consumed by nitrogen oxide, producing nitrogen dioxide naturally (Save the Earth, Save the Future 2007). O3+NO >NO2+O2 The presence of volatile organic compounds in atmosphere provides an alternate pathway for nitrogen oxide to produce nitrogen dioxide.

In this process ozone is not consumed hence, its concentration is increased to toxic level. NO+Volatile organic compounds>NO2+other products Nitrogen dioxide can absorb ultraviolet light energy from the visible portion of sunlight and is photo-degraded into nitric oxide and an atom of oxygen. NO2+sunlight >NO+O The atomic oxygen (O) then reacts immediately with oxygen (O2) producing ozone (O3) which has high oxidizing properties. O+O2>O3 Ozone produced can again react with hydrocarbons and produce noxious aldehydes.

O3+hydrocarbons>aldehydes In a series of reactions nitrogen dioxide can also react with radicals from volatile organic compounds in the presence of sunlight to form toxic products such as peroxyacetyl nitrates (PAN). NO2+O2+hydrocarbons> products such as PAN (CH3CO-O2-NO2) (in the presence of sunlight) The amount of production of nitrogen oxides through natural processes such as lightning and chemical reaction between nitrogen mono oxide and oxygen is limited. Industrial fumes and toxic chemicals of vehicular emissions can be accounted to raise the levels of nitrogen oxides in the air.

The pale blue gas ozone (O3) exists in stratosphere of our atmosphere and is constantly created and destroyed maintaing an eco-balance. Ozone can also be formed in the lower altitudes by reactions between nitrogen oxides and hydrocarbons under sunlight (photolysis), or by electric sparks which occur in automobiles, thus crossing the threshold level of ozone concentration. In cars and other vehicles incomplete combustion of the fuel leave unburnt hydrocarbons in the gaseous exhaust one of the primary causes in the formation of Volatile Organic Compounds (VOCs).

Petrol and other organic solvents such as paints; aerosol sprays; disinfectants are volatile in nature and therefore, produces harmful hydrocarbons when left unattended and exposed to air. This secondary pollutant Peroxyacetyl Nitrates (PAN) is formed from other pollutants by chemical reaction of nitrogen dioxide and volatile organic compounds. Photochemical smog can cause severe headaches, eye, nose and throat irritations, impaired lung function, coughing and wheezing. Even more importantly, it reduces visibility.

The pollutants pose a serious threat to our health by decreasing immunity towards infections. Temperature inversion near the surface of earth may cause trapping of pollutants in high concentrations .Such situations not only respiratory irritants, but is also cancer causing agents-carcinogens. Apart from affecting health photochemical smog inhibits plant growth leading to the loss of crops. Deteriorate fabrics and rubber; damage plastics. In the house hold front fabrics and rubber get deteriorated because of the smog.

It is impossible to control the ultraviolet rays from the sun on a large scale therefore; we have to try to reduce the emissions of oxides of nitrogen and volatile organic compounds (Wang and Milford 2001).Fuel quality standards for petrol and diesel should be improved ensuring the availability of quality fuels with reduced content of benzene, sulfur and polyaromatic hydrocarbons. The vapor pressure of the gasoline sold during summer can be significantly reduced. Thus reduces evaporation of hydrocarbons and a further decrease in the formation of ozone and photochemical smog.

Reduction in emissions from motor vehicles can be achieved through encouraging public transport, pooling car, walking or cycling for short distances. Solar panels use the sunlight to produce energy and pollution created is very little. Hence, we should encourage installing solar panels at household. It can therefore be inferred from the above discussion that though human beings cannot alter the topographical or meteorological factors affecting smog formation, yet they can help minimize the hazard by generating self-awareness towards lessening the formation of some of the pollution-causing agents.

References “Save the Earth, Save the Future” Virtual centre for Environmental Technology Exchange http://www.apec-vc.or.jp.Web 2007. Wang Lihuaand, Milford Jana B. (2001) “Reliability of Optimal Control Strategies for Photochemical Air Pollution” Environmental Science & Technology. 35 (6), pp1173-1180.Print.