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Air Pollution PDF Print E-mail

 Air pollution can be defined as the presence in the outdoor or indoor atmosphere of one or more gaseous or particulate contaminants in quantities, characteristics and duration such as to be injurious to human, plant or animal life or to property, or which unreasonably interferes with the comfortable enjoyment of life and property.Air pollution problems may vary greatly with the geography, demography and the socio-economic profile of a region, which will determine the source and emission rate of the pollutant. The climate and topography a region will influence the distribution and atmospheric processes of the pollutant and ultimately its effect on the environment and human health.

Sources

Carbon dioxide (CO2): Carbon dioxide is not by definition an air pollutant but a natural component of the atmosphere. Increasing emissions of CO2 in the atmosphere over the past 100 years resulted in global warming by the following process: CO2 is transparent to short-wave solar radiation but absorbs infrared radiation and traps it in the lower atmosphere. This phenomenon is known as the "green house effect".

Carbon monoxide (CO): Carbon monoxide is one of the most common and widely distributed air pollutants. There is evidence to suggest that global emissions of CO have risen in line with the massive growth of motor vehicle numbers and mileage. Concentrations inside motor cars often exceed those in the surrounding atmosphere. Forest clearance, savanna burning and the oxidation of methane are the other sources of CO.

Sulphur dioxide (SO2): Man-made emissions include fossil fuel combustion, power plants and industries. Natural emissions form from soil, plants, the burning of biomass, marine biogenic sea spray and volcanoes.

Particulate matter: On a global scale particulate matter is one of the most prevailing atmospheric pollutant. Natural sources include wind blown dust, sea spray, pollen, forest fires and volcanoes. The following are some of the natural and man-made emissions for the different particulate matter:
a. Fine particulate matter (up to 2 ?m): Combustion, gas particles condensation and conversions mainly from from SO2 and NOx.
b. Large particles (2 -100 ?m): They are usually natural particles or industrial dust.
c. Black elemental carbon particles: Diesel vehicle emissions and Coal use.
d. Toxic trace metals in the particulate fraction: Potentially toxic trace metals such as As, Pb, Cd and Hg from metals melting and coal combustion.
e. Lead in the particulate fraction: Forms from using Lead (Pb) as an anti-knock petrol additive, paint pigment and in the manufacturing of batteries.
f. Polynuclear (Polycyclic) aromatic hydrocarbons (PAH): A large group of organic compounds with two or more benzene rings formed by pyrolytic processes resulting from incomplete combustion and are very often absorbed on to particulate matter. Shipping, heavy industry, biomass burning, heating with coal are the other sources of man-made emissions. Carbonization is the principle natural source.

Hydrocarbons: Petrol and Diesel fuel consists of a large number of hydrocarbons. Aromatic hydrocarbons are added to petrol to aid refining. In some countries large quantities of alcohol or ethanol are added to petrol which give rise to large numbers of Volatile Organic Compounds (VOCs).

Nitrogen Oxides (NOx): They are significant pollutants on both local and regional scale. NOx emissions result from fossil fuel combustion and half of these man-made emissions are from mobile sources. Natural production is from bacterial action in soils, lightning and forest fires.

Photochemical Smog: Nitrogen oxide and other primary pollutants react under certain climatic conditions to form secondary pollutants such as NO2, O3 and peroxyacyl nitrates (PANs). These photochemical oxidants in combination with various organic compounds are referred to as "photochemical smog".
Human Impact
Most atmospheric pollutants pose a risk to human health. Health effects vary according to the intensity and duration of exposure and health status of the population exposed. In recent years, a growing body of scientific evidence has indicated that indoor air can be more seriously polluted than outdoor air, even in cities with relatively poor air quality. People spend approximately 90% of their time indoors, therefore it is likely that the risk to the health may be greater due to air pollution indoors. The most susceptible members are the very young, the elderly and the chronically ill who spends the longest periods indoors.

Environmental Impacts
It is now generally accepted that the increase in atmospheric CO2 together with other green house gases, CH4, N2O, O3 and CFCs leads to an increase in average global temperature. This will alter global weather patterns, ocean currents with an expected rise of mean sea level 30 to 50 cm by the year 2050. Thus, effecting world agriculture and marine ecosystems. Other impacts include the deposition of many air pollutants in the marine environment and the atmospheric oxidation and hydrolysis of others to form acidic precipitation. Many gaseous pollutants also inhibit plant growth and development and cause direct damage to various structures and materials.

Control Strategies
Strategies for controlling air pollution depends upon national and regional authorities setting air quality and emission standards. By requiring adherence to such a set of performance standards governments can encourage industry to develop new and better technologies.

 


 

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