Coal, fuel oil and natural gas which are found underground are the hydrocarbons that are referred to as fossil fuels. The term fossil fuel is rooted in the fact that the three natural underground energy sources were formed over very long periods from the remains of animals and plants. Although the term ‘fossil fuels’ also includes other hydrocarbons originating from natural resources that are not the remains of animals or plants, this type of energy sources is called mineral fuels.
Indeed, “the utilization of fossil fuels has enabled large-scale industrial development and largely supplanted water-driven mills, as well as the combustion of wood or peat for heat.” (Wikipedia Encyclopeadia, 2006) However, like many of other utilization matter fossil fuels have their undesirable effects that have to be addressed seriously in order that the problems are combated.
The main concern for scientists and other authorities dealing with problems of pollution is the air pollution caused by the burning of fossil fuels and the impact on the environment and the health of people.
In this paper the air pollution caused by burning fossil fuels will be studied under of the following headings:
A. Chemistry of Combustion
B. Air Pollution Caused by Fossil Fuel Combustion
C. Measures Taken to Combat the Air Pollution
A. Chemistry of Combustion
Combustion is a chemical reaction between a fuel (e.g. fossil fuel) and an oxidant (e.g. atmospheric oxygen. This chemical reaction normally results in producing heat and light. However, it is important to point out that not every oxidation process produces heat. For example, corrosion is an oxidation process but it does not produce heat. The chemical oxidation process in burning fossil fuels occurs at a rate fast enough to produce heat. This type of oxidation is what we refer to as combustion. That is why the term combustion is applied to exothermic processes.
The chemical process of a complete combustion is detailed in the following quote from Wikipedia Online Encyclopaedia:
“In a complete combustion reaction, a compound reacts with an oxidizing element, and the products are compounds of each element in the fuel with the oxidizing element. For example:
A simpler example can be seen in the combustion of hydrogen and oxygen, which is a commonly used reaction in rocket engines:
The result is simply water vapour.”
However, in real world uses of combustion it is not always a complete combustion. For fossil fuels to burn the combustion takes place as a result of the ambient air oxygen (O2) combining with the fossil fuel in the presence of a spark. Then the resulting fuel gas will contain nitrogen. That is to say that nitrogen is the largest part of the resultant fuel gas when combustion uses the ambient air oxygen.
“In reality, combustion processes are never perfect or complete. In flue gases from combustion of carbon (as in coal combustion) or carbon compounds (as in combustion of hydrocarbons, wood etc.) both unburned carbon (as soot) and carbon compounds (CO and others) will be present. Also, when air is the oxidant, some nitrogen will be oxidized to various, mostly harmful, nitrogen oxides (NOx).” (Wikipedia Online Encyclopaedia)
Therefore, for the real world combustions there are a number of types that I am going to summarize:
This type is the ‘fire’ type of combustion which results in large amounts of heat and light. This type is typical to the internal combustion engines.
In contrast to the rapid ones which normally take place at high temperatures , the slow ones are take place at low temperatures. A typical example is respiration.
In this type of combustions the reactant (e.g. fossil fuel) should burn in oxygen leaving a limited number of products. Therefore, hydrocarbons that burn in oxygen (other than ambient air oxygen) will only produce carbon dioxide and water. On the other hand hydrocarbons burning in air results in products that include nitrogen. It should be pointed out here that complete combustion is difficult to achieve in real world uses of combustion. Indeed: “In reality, as actual combustion reactions come to equilibrium, a wide variety of major and minor species will be present. For example, the combustion of methane in air will yield, in addition to the major products of carbon dioxide and water, the minor products which include carbon monoxide, hydroxyl, nitrogen oxides, monatomic hydrogen, and monatomic oxygen.” (Wikipedia Online Encyclopaedia)
In this type of combustion flows are turbulent. Since this turbulence helps in mixing the fuel and oxidizer this type is most common in industry e.g. turbines and diesel engines.
While complete combustion is achieved by ensuring adequate supply of oxygen, the incomplete combustion occurs when the supply of oxygen is not adequate as it happens normally for fuels burning in air. Here the reactant (whether it is fossil fuel or other) will burn in oxygen but will result in a number of products. These are: carbon dioxide, water, carbon monoxide, and a number of compounds such as nitrogen oxides. This is the most common type of combustion and is characterized by the production of large amounts of by-products. These, for example, in burning fuel in automobiles results in by-products that affect health and damages the environment.
Hydrocarbons and other fossil fuels are mainly utilized in today’s world as fuels. Therefore, a summary of types of fuels is in order at this stage:
a- Liquid fuels
A liquid does not burn until it is heated to a certain temperature and becomes vapour. This certain temperature above which it burns is called its flash point which is defined as “the lowest temperature at which it can form an ignitable mix with air. It is also the minimum temperature at which there is enough evaporated fuel in the air to start combustion.” (Wikipedia Online Encyclopaedia)
b- Solid Fuels
In this type of fuel combustion comprises three phases which are distinct and overlapping:
– Pre-heating phase: this the stage when the fuel is being heated to bring its temperature up to the flash point. Subsequently is the fire point when flammable gases are being evolved.
– Distillation phase or gaseous phase when the flammable gas mixes with oxygen and is ignited. The result is, of course, heat and light.
– Charcoal phase or solid phase when “the output of flammable gases from the material is too low for persistent presence of flame and the charred fuel does not burn rapidly anymore but just glows and later only smoulders.” (Wikipedia Online Encyclopaedia)
B- Air Pollution Caused by Fossil Fuel Combustion
A number of air pollutants are harmful for human beings by its direct effect on their health or its effect on the environment. In most of the areas over the globe the air pollutants are mainly the products of combustion whether it is from space heating, power generation or from the use of motor vehicles. It is also pointed out that the problems resulting from these sources is not confined to the immediate vicinity of these sources but are capable of traveling long distances and reacting chemically in the atmosphere. This process of further chemical reaction is responsible the secondary pollutants such as acid rain or ozone. The adverse effects of burning fossil fuels are numerous and here we are going to address the most common and the most environment and health threatening ones.
1. Flue Gas Emissions from Fossil Fuel Combustion
Fossil fuels that are combusted with ambient air, containing about 79% volume gaseous nitrogen which is not combustible, release a number of gases in the atmosphere. These include mainly nitrogen, and carbon dioxide. In addition it also releases small amounts of nitrogen oxides (NOx), sulphur dioxide (SO2) and particular matter.
Most of the flue gas emissions come from large power plants, furnaces in large refineries and petrochemical plants. A point of interest here is the fact that flue gas generated by coal combustion is 10% higher than that generated by natural gas combustion.
2. Pollution from Electricity Generation (Coal)
Production of electricity is effected by converting other forms of energy into electricity. In many countries including the USA, electricity is generated by burning fossil fuels. Obviously the process of burning fossil fuels is never completely clean, but a major source of environmental pollution.
3. Pollution from Automobiles (Gasoline Combustion)
Gasoline, one of the useful products of petroleum, when combusted gives off products. Since combustion here is incomplete the emissions out of the exhaust pipe react with atmospheric components other than oxygen in addition to reactions of impurities release gases that are not healthy.
Thus the main sources of pollution here are carbon dioxide and water. However, it is argued that carbon dioxide and water, both necessary for life on earth, are beneficial rather than being harmful. However, it is obvious that too much of a useful thing can as a result of existing in excess ca be a problem.
4. Global Warming
The term global warming is equivalent to more general one of ‘climate change’. It is also described as the increase in the average temperature of the earth’s atmosphere recently.
“The Earth’s average near-surface atmospheric temperature rose 0.6 ± 0.2 Celsius (1.1 ± 0.4 Fahrenheit) in the 20th century. The prevailing scientific opinion on climate change is that “most of the warming observed over the last 50 years is attributable to human activities.” (Wikipedia Online Encyclopaedia)
Global warming is know to be effected by interference of humans, e.g. combustion of fossil fuels and also by some other causes. However, it is established that the primary causes are the human induced causes. The release of increased amounts of carbon dioxide and other greenhouse gases have the greatest effect.
“The predicted effects of global warming are many and various, both for the environment and for human life. These effects include sea level rise, impacts on agriculture, reductions in the ozone layer, increased intensity and frequency of extreme weather events, and the spread of disease. In some cases, the effects may already be manifest, although it is difficult to attribute specific natural phenomena to long-term global warming. In particular, the relationship between global warming and hurricanes is still being debated.” (Wikipedia Online Encyclopaedia)
C- Measures Taken to Combat Air Pollution
Air pollution is one of the problems that have been receiving a lot of planned attention involving scientists and other professionals. Despite the dangers expected and the varying attention given to the problem throughout the world the pollution problem is being handled appropriately.
The problem seem to be diminishing in the economically developed countries. This achievement has materialized as a result of changing fuel-use patterns, and the increase in use of cleaner fuel such as natural gas and the effective policies implemented to control smoke and emissions. Even in the developing countries long term changes in air pollution is being effected.
“In both developed and developing countries, the major threat to clean air is now posed by traffic emissions. Petrol- and diesel-engined motor vehicles emit a wide variety of pollutants, principally carbon monoxide (CO), oxides of nitrogen (NOx), volatile organic compounds (VOCs) and particulates, which have an increasing impact on urban air quality.” (McGinlay, 1997)
While there is considerable improvement in controlling domestic and industrial pollutant sources, the problem traffic pollution is worsening worldwide and more seriously in developing countries where there a great increase in the vehicle fleets imported combined with problems of infrastructure, poor maintenance for transport machinery and poor control of engine emissions.
The most effective control of air pollution caused by fossil fuel combustion is the policies implemented to control the problem. These are mainly legislations defining the problem and the required action.
Conclusions of this paper can be summarized in the following:
1. Fossil fuel burning has been an effective vehicle for advancing the industry and technology and effecting the many facilities of today.
2. Simultaneous with the advantages of fossil fuel burning there have been serious problems of pollution resulting from the use of fossil fuel burning.
3. The reaction of governments and other professional bodies to combat the problem has been adequate and successful to date and is expected to continue.
1. Wikipidea, the free online encyclopaedia – downloaded on 23 October 2006 from: http://en.wikipedia.org/wiki/Fossil_fuel
2. Fossil Fuel Information – downloaded on 23 October 2006 from: www.fossilfuel.info
3. Jim McGinlay (1997) – The Chemistry of Atmospheric Pollutants – downloaded on 23 October 2006 from: http://www.aeat.co.uk/netcen/airqual/kinetics/