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transportation can BE simply defined as the movement of people, goods, and services from one place to another. Its system consists of the fixed facilities, flow entities, and control systems that permit the free flow and efficient movement of people and goods from place to place across geographical boundaries. Basically, there exist three forms of transportation: the road, water, and air transport.

The road transport systems are made up of the vehicular transport system and the rail transport system. The vehicular transport system comprises the different grades, sizes, and types of automobiles, and the rail transport system comprises the train systems of transportation. Water transportation also comprises the different shapes and sizes of water vehicles, known primarily as ships, boats, ferries, canoes, and so on. Air transport, in turn, comprises the different grades, shapes, and sizes of airplanes and helicopters.


Each one of these means of transportation runs on fossil fuels of crude oil distillates and coal, apart from modern train systems in developed countries, which may run on automated power. These fuels are subjected to internal cycles of combustion, giving gaseous by-products of carbon dioxide (CO2), carbon monoxide, and sulphur dioxide. Methane and nitrous oxide are also emitted by cars. World over, the greenhouse gas contribution of transportation is very high as a result of factors that include an increase in the number of vehicles, volume of passengers, and freight traffic. The percentage contribution of CO2 from transportation alone varies from state to state and country to country. In 1990, Japan's contribution was put at about 19 percent, and that of the United States surprisingly doubled between 1960 and 2001. Specifically, it is reported that emissions of CO2 in the United States jumped from 2 billion metric tons in 1960 to almost 5.7 billion metric tons in 2001, accounting for over a 100 percent increase, with over 20 percent of this emission linked to transportation. Transportation is also reported to account for 40 percent of volatile organic compounds, 77 percent of carbon monoxide, and 49 percent of nitrogen oxide emissions in the United States. In Canada, also, it is reported that transportation is the largest single anthropogenic source of outdoor air pollution. On average, each of the several million vehicles registered across the country emits approximately 5 tons of air pollutants and gases annually. This trend in record is the same for all industrialized nations and several developing nations, such as Nigeria in West Africa, because of an increased population and a rapid rate of economic growth, bringing about increased use of automobiles and other means of transportation. This increase has brought with it increasing emissions of air pollutants and greenhouse gases because of the type of engines in use and the nature of the fuels in place.

In general, it is reported that combustion engines emit nitrogen oxides (NOx), carbon monoxide, and unburned hydrocarbons capable of chemical transformation in the atmosphere, creating other gaseous matter such as ozone. Ozone is a triatomic molecule consisting of three atoms of oxygen; it is an allotrope of oxygen but is much less stable. Its instability makes it a strong oxidizing agent, having the ability to decompose to oxygen in the atmosphere within 30 minutes. In its physical undiluted state, at standard temperature and pressure, it is a pale blue, odorless gas. In the troposphere, ozone acts as a greenhouse gas and has a radiative forcing of about 25 percent that of CO2. Around the Earth's surface, it poses a regional air pollution problem damaging human health and agricultural crops.

More so, residual fuel oils, particularly the heavy oil used aboard ships, contain sulphur, which reacts with atmospheric water and oxygen to produce sulfate particles and sulphuric acids, also known as acid rain. It lowers soil and freshwater pH, resulting in damage to our natural environment, and also causes chemical weathering. Its ability to increase the reflection of part of the sunlight that should come into the Earth's surface creates a cooling effect. Road traffic on its own is a major contributor to environmental degradation and global warming. It clearly provides the largest net contribution to warming through its large emissions of CO2 and significant emissions of ozone and soot. Soot particles emitted by diesel engines have the ability to absorb sunlight, thus heating up the climate. Total warming from road traffic is reported to be about 0.19 Watts per sq. m. (W/m2), forming about 7 percent of the total climate forcing, as a result of an increased concentration of ozone, soot, and greenhouse gases.

Air traffic, as a sector in the transportation industry, also shows a trend toward increased environmentally unfriendly emissions. Airplanes fly in the upper edges of the atmosphere, where the air is rarefied and the planes release large quantities of greenhouse gases. CO2, the main constituent in the exhaust gases, slowly descends into the lower altitude. However, the large number of planes flying across the sky has caused the average amount of these greenhouse gases to increase. CO2 and other greenhouse gases get cut up in the stratosphere, where they become much more potent than at the Earth's surface, blocking radiant energy from reaching the planet. Thus, the global warming effect of air traffic pollution in the stratosphere is very high. In addition, the NOx emitted have an especially large effect on ozone formation. A more recent research report on air traffic suggests that the occurrence of ice clouds, called cirrus clouds, at flying altitudes is increasing in areas with heavy air traffic because the trails of vapor left by aircraft at high altitude under certain meteorological conditions can expand. These clouds, found at altitudes of between 5 and 7.5 mi. (8 and 12 km.), have a warming effect on the climate because their greenhouse effect is stronger than their cooling effect through the reflection of light. This is a result of the low temperatures at this height.

Moreover, the various gases emitted by engines of transportation units pose serious challenges to the environment. CO2, the most popular of the greenhouse gases, is a colorless, odorless gas with a covalent bond between its atomic constituents. It is the most potent greenhouse gas, being highly atmospherically stable and having a life of over a hundred years, with a strong ability to absorb radiations below the visible light spectrum, thus trapping heat attempting to escape from the Earth's surface and causing an increase in the temperature of the planet's surface. It has a radiative forcing of 1.5 W/ m2 and is regarded as the most powerful greenhouse gas because of its long atmospheric stability period.

The presence of a ton of CO2 put into the atmosphere thus has a deleterious environmental warming effect for over a hundred years. With the increasing anthropogenic emission of this gas from transportation and other sources, the global warming effect of CO2 on the environment has never been ignored. It is heavily concentrated in the atmosphere.

Methane (NH4), in contrast, is a covalent compound, colorless and odorless. It is not as stable as CO2 but has a stronger effect as a greenhouse gas than CO2. Its stability period in the Earth's atmosphere is 10 years. It absorbs infrared radiation and affects tropospheric ozone. Methane may not be as popular a greenhouse gas as carbon dioxide, but its effects on the climate are stricter than it, and methane has been rated the second most potent greenhouse gas, after CO2, with the exception of water vapor because of its short life and the quantity of it found in the Earth's atmosphere.

Another gas emitted from the burning of fossil fuels is nitrous oxide. It is a colorless, nonflammable, sweet-smelling gas having two nitrogen and one oxygen atoms covalently bonded together. When released into the atmosphere, nitrous oxide is the third largest greenhouse gas contributor to global warming, and has more effect than an equal amount of CO2. It is reported that nitrous oxide is 296 times stronger a greenhouse gas than CO2. It attacks ozone in the stratosphere, increasing the amount of ultraviolet light entering the Earth's surface. This ultraviolet light has deleterious effects on the human immune system, as well as the eye, and on the skin. It causes sunburn, inflammation, immunosup-pression, tanning, and the accelerated aging of the skin.


Other gaseous pollutants from transportation (mentioned earlier) are carbon monoxide and sulphur dioxide. Carbon monoxide is a colorless, odorless, and tasteless gas, formed by the thermal composition of excess carbon with oxygen. It is made up of a carbon atom covalently bonded to an oxygen atom. It is also released from the exhaust of motor vehicle engines, having gone through an incomplete internal combustion process of burning excess fossil fuels in the presence of oxygen. It is a toxic air pollutant. Its reaction in the atmosphere with some atmospheric constituents like the hydroxyl radical (OH-) can increase the amounts of atmospheric methane and tropospheric ozone, thus causing an indirect forcing effect. It has the ability to combine with oxygen in the atmosphere to give CO2, thereby contributing to greenhouse effects and global warming. Apart from this environmental degradation, CO has deleterious effects on human health.

Exposure to excess carbon monoxide can lead to heart and respiratory problems and has an effect on pregnancy, the central nervous system, and the heart—to mention a few adverse effects. Sulphur dioxide, in contrast, is a covalently bonded chemical compound made up of an atom of sulphur and two atoms of oxygen. It is anthropogenically produced from the combustion of coal and petroleum, which is commonly used by cars. It is a colorless gas with the smell of burning sulphur and is able to undergo serial combination to form sulphuric acid, which is an acid rain with corrosive tendencies found in the atmosphere. Sulphur dioxide is also toxic and has caused damage to humans in times past. However, its effects as a regulatory measure on the global warming effects of the greenhouse gases is limited by its lifespan on the Earth's surface, which is not more than a week.

With the present system of transportation still in use the world over, the rate of emissions of these harmful gases will continue to be on the increase, and their deleterious effects will become severe, as anthropogenic emissions of CO2, methane, and nitrous oxide from industry and transportation are among the major causes of global warming. Gaseous pollutants of carbon monoxide and sulphur dioxide also contribute to dangerous effects on humans and the environment. However, various reports of the Intergovernmental Panel on Climate Change exist, each pointing to the damaging effects of such greenhouse gases as carbon dioxide, methane, and nitrous oxide. The contribution of transportation to the emission of these gases is high, and determining what must be done to reduce these emissions must be a global exercise that involves scientific contribution. Transportation effects on global warming and environmental pollution cannot be reduced without a redesign of the present system of engines vis-à-vis the available fuel systems. The emissions from modes of transportation can only increase as the numbers of vehicles, airplanes, ships, and other transport units migrating from one place to another increase.

sEE ALso: Automobiles; Climate Change, Effects; Tourism.

BIBLIoGRAPHY. M. Myhre, E.J. Highwood, K.P. Shine, and F. Stordal, "New Estimates of Radiative Forcing due to Well Mixed Greenhouse Gases," Geophysical Research Letters (v.25/14, 1998); J.R. Partington, A Short History of Chemistry, 3rd ed. (Dover Publications, 1989); C.N. Sawyer, P.L. McCarty, and G.F. Parkin, Chemistry for Environmental Engineering and Science, 5th ed. (McGraw-Hill, 2003); M. Wang, The Greenhouse Gases, Regulated Emissions and Energy Use in Transportation (GREET) Version 1.5 (Center for Transportation Research, Argonne National Laboratory, 1999).

Ajayi Oluseyi Olanrewaju Covenant University

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