Pollution And Environmental Problems

An immediate mental association with "environment" is "pollution." Yet what constitutes a pollutant is not easily stated. One tends to associate the term with materials produced by human activity that enter the environment with harmful effects especially on living organisms—for example, SO2 from combustion of sulfur-containing fuels, or hydrocarbons that contribute to smog. However, these and other "pollutants" would be present even in the absence of humans, sometimes in considerable amounts. We will consider a "pollutant" to be any substance not normally present, or present in larger concentrations than normal. One type of source commonly associated with pollution consists of industrial plants, especially chemical, but also factories using organic solvents, heavy metals, and so on. Another source is mining, including waste rock dumps and smelters. Waste disposal dumps are yet another source; materials can be released from these dumps. Military bases, training, and testing facilities may be sources of pollution from heavy metals as well as explosives residues. Fuel storage facilities, airports, and on a smaller but more widespread scale, gasoline stations may pollute through spills or leaking tanks. Power plants and incinerators may emit pollutants to the atmosphere, while automobiles and other internal combustion engines provide a delocalized but abundant source.

Although any discussion of the environment must consider pollution, this will not be our primary aim. Rather, we will be concerned with some of the more important chemical principles that govern the behavior of the physico-chemical environment and the interactions of its various facets.

Among the controversial topics as this book is written are global warming and ozone depletion. The chemistry of these phenomena is discussed in some detail later in this book (Chapters 3 and 5), but an introduction to them at this point may give a useful illustration of environmental problems. With respect to global warming, some aspects are beyond scientific dispute, some are highly probable, and some are still uncertain. There is no question that introduction of carbon dioxide and some other gases into the atmosphere will increase heat retention, and that the atmospheric concentration of carbon dioxide has been increasing. It is also well established that introduction of some (but not all) particulate material into the upper atmosphere will reflect solar energy and lead to cooling. What is in question is how much of the introduced materials will be removed by natural processes, what the relative heating and cooling effects will be, and other details that need to be understood before a quantitative prediction of the net result can be made. It is almost certain that the average temperature of the earth's surface has increased in the last few years, and likely that at least part of this increase is due to human activity, but natural variabilty makes the latter conclusions less certain. Also uncertain are collateral changes in atmospheric circulation, rainfall, and ocean currents that could accompany an increase in global average temperature. There are two primary responses to these uncertainties. One is the attitude that if there is any doubt, one can ignore the potential problem and continue business as usual. The other is to assume the worst and advocate massive changes at once, whatever the costs involved. An intermediate response, "Make the changes that have moderate cost but move in the right direction," is often overlooked.

Ozone destruction in the stratosphere by chlorofluorocarbons, as discussed in Chapter 5, was clearly shown to be inherent in the chemistry of the atmosphere long before its observed decrease caused responsive action to be taken. Even then, many people refused to accept that human activities could have a deleterious effect and used uncertainties in the details of the destruction mechanism to argue against the need for controls. Some still do.

Other responses to environmental problems are to focus on potential benefits, which is a perfectly valid thing to do if all the implications are understood. For example, it has been pointed out that global warming may have beneficial effects by permitting agricultural activity in the Arctic regions, but do the soils in these regions have the necessary characteristics to support domestic plant growth? Will the possible increase in productivity in the Arctic balance possible losses elsewhere? What about changes in patterns of precipitation that may accompany temperature changes? It is also pointed out that massive environmental changes, including higher temperatures, have occurred naturally, so that anthropogenic changes do not involve anything new. This ignores the rate of change: changes that human activity can bring about may take place much more rapidly than those arising from natural causes, although knowledge of details is generally inadequate to predict time scales. For example, people could adjust to the conversion of, say, Wisconsin or Provence to a desert over a thousand years, but the same change in a few decades would be disastrous to the people involved.

Two human activities that are strongly connected with environmental chemistry in general and pollution in particular are energy production and waste disposal, as discussed in Chapters 15 and 16, respectively. Aspects of the chemistry of these activities will be considered later, but some general comments are given here.

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