The Earth is a unique planet in our Solar System. Due to the natural combination of gases in the atmosphere, the atmosphere captures some of the heat from the Sun. Without the atmosphere daily surface temperatures would vary between 1000C and -1500C! With our unique atmosphere, the daily temperature fluctuations are much smaller and the result is an average surface temperature of 330C (Johnston, Gostelow, King, 2000, pp 483). The phenomenon of the thermal blanket of the atmosphere has been occurring for millions of years and is now known as the Greenhouse Effect.

Nearly all the energy the Earth receives comes from the Sun. Of all the forms of heat transfer, the only form that can transmit heat through space (a vacuum) is radiation. Radiation is heat energy in the form of electromagnetic waves. There are different types of radiation, but heat is only transferred by thermal radiation. (Cengel, Boles, 1994, pp97 – 100).

Everything at a temperature above –273oC (0 Kelvin) emits thermal radiation. The temperature of the object determines the wavelength of the electromagnetic waves. The higher the temperature of an object, the smaller the electromagnetic waves are. The Sun, which has a surface temperature of about 6000K emits wavelengths between 0.2 and 5.0 mm. On the other hand the Earth typically has a surface temperature of about 300K. The Earth emits thermal radiation of wavelengths between 4.0 - 100mm (Halliday, Resnick Walker, 1994 pp E7-1 – 7-5).

The importance of the different radiation wavelengths is they determine how the Earth’s ‘blanket’ of atmosphere behaves. What scientists have found is that certain gases in the atmosphere retain the heat emitted from the Earth’s surface. These same gases allow some of the Sun’s heat through. These gases are known as the Greenhouse Gases (GHG). In recent history the presence of GHG has increased, which is causing more heat to be retained. This effect is called Global Warming. Without greenhouse gases, we would find it very hard to live. The average surface temperature would be -18 oC! The trouble is, all the artificial (anthropogenic) pollution is upsetting the fine natural balance, hence the Global Warming (Colls, 1997, pp 253 – 255).

Based on ‘Global Climate Models’ the impact of Global Warming has been predicted. Melting ice-caps and thermal expansion of the oceans will cause rises in sea levels. This will impact on low lying countries and islands. Weather patterns will change globally, by varying degrees, including more tropical cyclones and droughts. The follow on effects will be damaging to many aspects of life, including natural ecosystems, agriculture, forestry, fisheries and health (Diesendorf, Hamilton, 1997, pp 199).

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The radiation paths that contribute to the greenhouse effect (Halliday, Resnick, Walker, 1993, pp E7-4)

Greenhouse gases (GHG) have occurred naturally for millions of years, allowing the Greenhouse Effect to support life on the Earth’s surface. Naturally occurring greenhouse gases include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3), and water vapour (Diesendorf, Hamilton, 1997, pp 99). Anthropogenic greenhouse gases include the naturally occurring greenhouse gases but also halocarbons, (Chloroflourocarbons [CFC]), hydrocarbons and aerosols. One negative, yet important characteristic of greenhouse gases is long lifetimes, maximising the impact of anthropogenic pollution sources (Colls, 1997, pp 261 – 264).

Air Pollution is the introduction by humankind of substances or energy that damages living creatures, resources and environments. Sulphur dioxide (SO2), nitrogen oxides (NO, NO2), carbon monoxide (CO) and ozone (O3) among others have proven health effects in certain quantities. Understandably air pollution mostly affects the breathing system and lungs in humans. Changes in breathing capacity, asthma, lung infections and lung tissue damage are results of exposure to air pollution (Colls, 1997 pp 225 – 236). Another consequence of air pollution is acid rain. Acid rain is a combination of the sulphur and water in the atmosphere. The sulphur dioxide oxidises into sulphur trioxide, which dissolves in water to produce sulphuric acid. This affects not only the living creatures, but damages the forests and water systems. Acid rain has lasting effects on many artificial structures too (Brown, Lemay, Bursten, 1994, pp 230 – 677).

It has been known for some time that air pollution is mainly derived from burning fossil fuels. Fossil fuels have formed over millions of years from the decomposition of plants and animals. Fossil fuels are a family of energy sources including coal, oil, petroleum and natural gas. These fossil fuels are primarily made up of organic compounds (sulphur, nitrogen and oxygen) and hydrocarbons (chemical compounds that contain only carbon and hydrogen).

To harness the energy of fossil fuels, a process called combustion is used. Combustion involves burning the hydrocarbons, then they react with oxygen gas (O2) to form carbon dioxide (CO2) and water (H2O). In a real situation the reaction takes place in air, not just oxygen and the hydrocarbons are not totally burnt. The heat of the combustion reaction enables the organic compounds to react with excess oxygen gas to produce various polluting gases (NO, NO2, SO3). The incomplete combustion forms carbon monoxide. From these products, secondary pollutants are produced in the atmosphere, including ozone (O3) and sulphur dioxide (SO2) (Brown, Lemay, Bursten, 1994 pp72 – 165).

In Australia the majority of air pollution stems from the use of fossil fuels powering the motor vehicle (Table 1). These statistics are reflected on a global scale (Table 2). To make the biggest impact on pollution contributions, solutions involving motor vehicles would be the logical place to start. Solution include;

• alternative energy vehicles
• public transport
• reducing motor vehicle use
• reducing traffic congestion
• improving motor vehicle efficiency
• financial incentives

Major obstacles to these solutions include cost and convenience. Alternative energy vehicles, particularly electric vehicles (EV) represent a realistic solution for urban transport. They can readily be adapted to existing infrastructure, using the existing power grid with renewable energy. This would make a massive difference in the amount of pollution generated. Electric vehicles are a developing technology that will become cheaper over time. With more development they can become more effective over longer distances. The attractive feature of this solution is that it can make a huge difference, while maintaining a high level of convenience.

References

• Johnston, S., F., Gostelow, J., P., King, J., W., 2000, “Engineering & Society”, Prentice Hall, New Jersey, pp483.
• Diesendorf, M., Hamilton, C., 1997, “Human Ecology Human Economy”, Allen & Unwin, Sydney, pp 99 - 199 .
• Colls, J., 1997, “Air Pollution An Introduction”, E & FN SPON, London, pp 5 – 264.
• Aplin, G., Mitchel, P., Cleugh, H., Pitman, A., Rich, D., 1995, “Global Environmental Crises, An Australian Perspective” Oxford University Press, Melbourne, pp 15 – 257.
• Halliday, D., Resnick., R., Walker, J., 1993, “Fundamentals of Physics” 4th Edition, John Wiley & Sons, New York, pp E7-1 E7-7.
• Cengel, Y., A., Boles, M., A., 1994, “Thermodynamics, An Engineering Approach” 2nd Edition, McGraw Hill, New York, pp 97 – 100.
• Brown, T.,L., Lemay, H., E., Bursten, B., E., 1994, “Chemistry The Central Science” 6th Edition, Prentice Hall, New Jersey, pp 72 – 677.