Fossil fuels combustion, problems with

Selection of pollution control methods is generally based on the need to control ambient air quaUty in order to achieve compliance with standards for critetia pollutants, or, in the case of nonregulated contaminants, to protect human health and vegetation. There are three elements to a pollution problem a source, a receptor affected by the pollutants, and the transport of pollutants from source to receptor. Modification or elimination of any one of these elements can change the nature of a pollution problem. For instance, tall stacks which disperse effluent modify the transport of pollutants and can thus reduce nearby SO2 deposition from sulfur-containing fossil fuel combustion. Although better dispersion aloft can solve a local problem, if done from numerous sources it can unfortunately cause a regional one, such as the acid rain now evident in the northeastern United States and Canada (see Atmospheric models). References 3—15 discuss atmospheric dilution as a control measure. The better approach, however, is to control emissions at the source. 

Another problem associated with fossil fuel combustion is the greenhouse effect, which brings up critical environmental concerns. 

Acid rain. Lakes in some areas of the world are now registering very low pH s because of excess acidity in rain. This was first noticed in Scandinavia and is now prevalent in eastern Canada and the northeastern U.S. Normal rainfall is 5.6 (because of CO2 in the air forming H2CO3). However, excessive use of fossil fuels (especially coal) with high sulfur and nitrogen content cause sulfuric and nitric acids in the atmosphere from the sulfur dioxide and nitrogen oxide products of combustion. Some rain in the Adirondack Mountains of upper New York State has been measured with a pH of 3.0. This problem is not specific to the chemical industry but should be of concern to all of us. 

It has been observed in the past that the rate of emission of these trace metals into the atmosphere is low due to their low volatility. However, with the advent of large-scale metal mining and smelting as well as fossil-fuel combustion in the twentieth century, the emission rate of these metals has increased dramatically. As most of these emissions are released into the atmosphere where the mammals live and breathe, we see a great increase in the occurrence of health problems such as lead (Pb) poisoning, cadmium (Cd) Itai-itai disease, chromium (Cr), and nickel (Ni) carcinogenesis. 

Acidic precipitation is a growing environmental problem. Acid rain, snow or fog is formed when oxides of sulfur and nitrogen from fossil fuel combustion are oxidized in the atmosphere by ultra-violet light and ozone to give sulfuric and nitric acids. These acids then mix with atmospheric water to form acidic precipitation. Since the normal pH of atmospheric water is 5.6-5.7, precipitation having a pH below 5.6 is termed acid rain (J, ). 

Fireside additives have been developed primarily to combat fouling in fossil fuel combustion, but more recently, the technology has been transferred to problems associated with other fuels, e.g. industrial domestic and agricultural waste. Additives have also been used to overcome corrosion and acidic emissions, but a discussion of these problems is outside the scope of this book except where they may affect heat transfer. 

We can learn from history that all kinds of persons were interested in the subject from a philosophical perspective and/or with respect to the application of techniques (engineering) but always motivated by the specific problems (e. g. pollution) of their era. We also hold deep respect for our scientific ancestors for their brilliant conclusions, based on scientific experiments with very simple techniques and limited quantitative measurements. The great interest in historical data from the era before fossil fuel combustion lies in determining background concentrations, in other words, the natural reference concentrations for assessing the human-influenced changes in chemical air composition. The endeavor remains to learn from previous studies to ask the appropriate open questions and draw the right conclusions for further studies. 

It is remarkable that basically all sub-global air pollution problems (dust and smoke, sulfur and nitrogen pollution) in connection with fossil fuel combustion have been (or can be) solved by end-of-pipe technologies. Hence, the last and apparently insoluble problem remains CO2 emissions and the subsequent increase in the greenhouse effect. CCS technology is another end-of-pipe approach and far from any sustainable chemistry. But it seems the only practical way to start the abatement of CO2 emissions. 

A third problem associated with fossil fuel combustion is acid rain. The nitrogen oxides and sulfur oxides emitted into air make rain acidic. This acidic rain falls into lakes and streams and makes them acidic as well (see Section 14.11). Some species of aquatic life cannot tolerate the increased acidity and die. Acid rain also affects forests and building materials. Again, good legislation— specificaUy the Clean Air Amendments of 1990— have addressed add rain, and sulfur oxide emissions have been decreasing in the United States over the past 20 years. We can expect to see the positive effects of these reductions in lakes and streams in the coming years. 

Nuclear fission is used to generate electricity without the harmful side effects associated with fossil fuel combustion. Yet nuclear power has its own problems, namely the potential for accidents and waste disposal (8.7). Will the United States build a permanent site for nuclear waste disposal Will we turn to nuclear power as the fossil fuel supply dwindles away How many resources will we put into the development of fusion as a future energy source These are all questions that our society faces as we begin this new millennium. 

The other major problems associated with fossil fuel use stem from the products of combustion. The chemical equations shown for fossil fuel combustion all produce cartxM dioxide and water. However, these equations represent the reactions under ideal conditions and do not account for impurities in the fuel, side reactions, and incomplete combustion. When these are taken into account, we can identify three major awiron-mental problems associated with the emissitxis of fossil fuel combustion air pollution, acid rain, and global climate change. We discussed acid rain in Chjpter 3 (see Chemistry in the Environment Acid Rain in Section 3.6). Here we will address air pollution and global climate change, which we first touched on in Section 4.1. 

The two most important environmental hazards faced by humankind today are air pollution and global warming. Both have a direct link with our current overdependence on fossil fuels. Pollutants produced from combustion of hydrocarbons now cause even more health problems due to the urbanization of world population. The net increase in environmental carbon dioxide from combustion is a suspect cause for global warming, which is endangering the Earth—the only known place to support human life. In addition, the import of expensive hydrocarbon fuel has become a heavy burden on many countries, causing political and economic unrest. 

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