What is Environmental Thermodynamics?
R. F. Mueller
Aluminum cans are collected from roadsides and transported to a recycling center. A helicopter is used to fly junk out of a wilderness area. Does nature come out ahead in these "cleanup" activities?
Hydrogen is frequently proposed as the clean fuel of the future. Does this make sense?
A tractorcade is formed to protest the demise of the family farm. How does this rank as appropriate symbolism?
A newly hired pollution control engineer for an industrial firm makes $200,000 a year, buys a large house in the suburbs and drives to work. How is this person's life style related to the firm's pollution control efforts?
Increasingly environmentalists feel a need to reevaluate a variety of proposals and actions once thought to be non- controversial or beneficial to the environment. In this deeper analysis they inevitably confront concepts of thermodynamics, a science whose very name my strike fear into those not technically oriented. Yet, the assimilation of the central ideas of thermodynamics is not only crucial but fairly easy for anyone smart enough to be an environmentalist in the first place.
Before we discuss environmental thermodynamics we need to define what thermodynamics as such is. We find first of all that its subject matter is energy conversion. A thermodynamic process occurs each time one form of energy is converted into another, which includes every material process, including mental activity. A common industrial thermodynamic process, for example, is the conversion of the chemical energy of fuels into heat energy of combustion, and this heat is in turn converted to mechanical or electrical work. All natural processes also have a thermodynamic aspect and the behavior of such diverse objects as minerals, stars and life itself cannot be understood without it.
The most important contribution of thermodynamics is in determining whether a given conceivable process is possible or not.. Thermodynamics answers this question by making use of its famous first and second laws. The first is the law of the conservation of energy, while the second implies the impossibility of constructing a perpetual motion machine or the spontaneous transfer of heat from a low to a high temperature reservoir by a cyclic process. The latter also involves the concept of entropy. Although energy is a quite well understood concept, that of entropy is less so. A simple way to understand entropy is to consider it as an index of disorder or the absence of order. Disordered or high entropy states occur with the highest probability because there are relatively more ways to achieve them. Thus, there are many more ways to disorder (shuffle) a deck of cards than to place it in an ordered array.
A fundamental concept of thermodynamics is that of "system" vs. "surroundings". We may, for example, be interested in a particular system consisting of a chemical fuel, oxygen to burn it, and the combustion products, carbon dioxide and water. But the total behavior of this system cannot be understood without reference to the surroundings, with which it may exchange both energy and matter. This concept is particularly important to us because "surroundings" is here synonymous with "environment."
The first law of thermodynamics is simply one of bookkeeping and expresses the fact that energy is always conserved or that any process must yield as much energy, albeit in different form, as was put into it in the first place. Thus, the total number of calories in the heat, sound waves, air pollution, etc. produced by a machine must equal the chemical energy-also in calories-placed in the fuel tank. Strangely, this simple relation is widely ignored, particularly by pollution control experts, who almost invariably fail to take into account all significant energy inputs into their particular technology, and by certain industry propagandists who are promoting some wasteful technology.
By contrast, the second law is the very antithesis of conservation, since it expresses the spontaneous creation of entropy or disorder that drives the process. Here the key word is spontaneous, since any independent process that is possible must be thermodynamically spontaneous, which, in this sense, means any process that does not require help from an outside energy source. The second law states that in such a process the total entropy (of system plus surroundings) always increases. If the total entropy change for any conceivable process is negative, we can be sure that it is impossible in practice unless outside energy is brought to bear.
There is another concept of thermodynamics known as "free energy". It is actually energy only in a formal sense, since it simultaneously incorporates both the energy and entropy of the system. It is directly and simply related to the total entropy and like it is an index of the possibility or impossibility of any process we might conceive of. Unlike total entropy, however, it decreases during a spontaneous process. Free energy turns out to be a convenient way to characterize pollutants of all kinds, since these always have more of it than their degradation products. For example, under Earth surface conditions there is a marked decrease in free energy when the pollutant carbon monoxide is converted to carbon dioxide and subsequently, by reaction with calcium oxide, to harmless carbonate minerals (limestone). It is a fact that virtually all materials useful to modern society carry a heavy burden of free energy-and ordinary energy as well-which they acquire as a necessary part of the manufacturing process, or which they possess in nature, as is the case with fuels. It is this "excess" free energy that gives all our favorite gadgets and trinkets such great potential as pollutants. It also forges a link of inevitability between energy in all its technological forms and the resulting pollution.
It should be obvious at this point that thermodynamics must have important practical as well as philosophical implications for environmentalists. It is sometimes implied that entropy and free energy are mysterious and vague concepts of no use in practical affairs. Some readers may be surprised to learn that numerical values of both quantities are regularly tabulated and used in everyday calculations vital to industry and every branch of science. The philosophical side of thermodynamics stands out in the characteristic of spontaneity of all independent energy transformations, since, if the process is truly spontaneous, it must contain uncontrollable elements. We should then ask ourselves to what extent technologists really control any of the energetic processes they set in motion.
As powerful as thermodynamics is, it shares with other successful theories the characteristic of strict limitations. Since it depends for its success on the statistics of large numbers, it cannot be used to predict the behavior of individual or small numbers of atoms or molecules. Nor does it explicitly contain time as part of its structure, so that it cannot predict when or how rapidly a process will occur.
Environmental thermodynamics, like its familiar counterparts, is concerned with energy conversions and flows. Rather than being confined to individual machines or wholly natural processes, however, it is concerned with the interactions of technology and the natural world. As such it is very much concerned with human behavior and life styles. Thus, technological energy flows are involved in their entirety, from initial production, through consumption, and to eventual radiation into space. Unlike industrial thermodynamics, it does not stop with the evaluation of inputs and outputs of useful work energy and products, but follows these products and accompanying waste through all the devious paths and interactions in the biosphere, its organisms and humankind itself. Consequently, it is the science peculiarly suited to casting light on questions such as those posed earlier as well as generalizations such as "clean" or "soft" technological energy. Most significant, perhaps, is that it enables us to raise and answer important questions.
Now let us return to our examples stated at the beginning of this piece. We note first that rejecting something (cans, bottles, refuse) into the environment is a relatively spontaneous process (by any definition of the word!) because the rejected material represents a highly disordered and hence probable state. As in the case of a deck of cards, there are many more ways to throw things away than to reclaim them in an ordered array. Also, reclaiming them requires a substantial input of energy. When aluminum companies speak of the energy advantage of reclaimed aluminum cans over new cans made from ore, they do not consider the "throw away entropy" involved, since many of these cans are picked up from roadsides. The energy cost of overcoming this entropy could be greatly reduced by mandatory recycling for metal content of the cans. It might be further reduced by retaining and cleaning the cans, thus saving their "form energy" as well. However, in this alternative the energy cost of cleaning would have to be balanced against the cost of re-melting and re-forming. For similar reasons a heavy penalty is paid for a relatively small return in cleaning up a wilderness area by machine. The only good solution is not to pollute in the first place.
The same reasoning also applies to toxic chemical dumps. The greatest benefit of such legislation as "superfund" may be not in cleaning up existing dumps, which simply leads to more pollution, but in suppressing the type of industrial development which inevitably results in some form of pollution despite best efforts to control it.
The question regarding presumed benefits of hydrogen as a fuel can be answered by reference to ordinary thermodynamic tables. Sources of hydrogen are natural hydrocarbons and water. Exploitation of the former is through thermochemical technologies by which heat is used to drive chemical reactions that yield hydrogen. In the case of a water source, electrolytic or photolytic processes separate the hydrogen from the oxygen in the water molecule. In all cases a huge expenditure of energy is required to separate hydrogen from the other constituents. This energy would likely come from a large, readily available source such as the highly polluting fossil or nuclear power plants. However, even if solar power were used for this purpose, it can be shown that this energy form would also require a highly polluting infrastructure and would degrade to pollution-prone forms on use.
Similarly, the favorite tactic of the American Agricultural movement should not impress environmentalists who demand consistency in their symbolism. It has been convincingly argued (1) that a major source of difficulties experienced by today's farmers is overproduction, which depends upon over-mechanization ( well symbolized by large tractors!), resulting in debt, soil degradation, etc. A technology that can't work with heavy inputs of fossil fuels and solar energy can scarcely claim thermodynamic efficiency, or indeed, any kind of efficiency.
Our last example, that of the pollution control engineer, is of greatest interest here, since it represents the officially sanctioned and endorsed solution to industrial pollution. Also, many environmentalists would consider the creation of this job as not only a desirable response on the part of industry, but as a positive economic spin-off of pollution control. Yet, the total cultural ramifications of technology-based, energy intensive pollution control strategies are seldom given a thought by industry, government or their critics. Some light is cast on the underlying factors here by an important study of energy analysts B. Hannon and R. A. Herendeen (2) , who showed how total family energy use by consumers rises directly with income in an almost straight line relation. Given the correspondence between technological energy and pollution previously identified here, it is clear that our affluent pollution control engineer must contribute a significant increment of pollution and that this is multiplied by other newly created jobs, not only in industry, but in the state and federal agencies as well. Add this culturally-derived pollution to that produced by the primary production and the pollution control technology itself, and we see at least the potential of a serious circularity. Finally, it must also be remembered that by the first law the original pollution energy is usually not eliminated by control devices, but is only transformed or diverted elsewhere. It is unfortunate that neither industry nor government has so far been inspired enough by thermodynamic reasoning to seriously consider these problems.
At this point I wouldn't blame the reader for being discouraged at the apparent proclivity of thermodynamics to dash water on everyone's fondest hopes. But if thermodynamic considerations are hard on naive pollution control efforts, they will probably turn out to be lethal to many of our most environmentally destructive technologies, old and new, particularly if free energy outflows from them into the environment are taken into account. This goes particularly for such examples as the automobile-centered transportation system, stream modification projects, nuclear power, and lately, the synfuels industry. Although none of these monstrosities has ever been subject to full analysis, their thermodynamic weaknesses are beginning to be revealed in economic terms. As Georgescu-Roegen (3) has suggested, accounting properly for all the energy and material flows in such technologies would require a drastic revision in our economic system. Thus thermodynamics becomes a powerful and even necessary instrument of social change that we should welcome.
The New Farm 3,12, 1981.
Science 168, 95, 1975.
Southern Economic Journal 41, 347, 1975.