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Fig. 4. Smoke belching from an electric utility company stack blankets an entire area.

James R. Jones, combustion engineer, Peabody Coal Company, Inc.; Harry Perry, Director of Coal Research, Bureau of Mines, U.S. Department of the Interior; and Dr. L. A. Ripperton, Associate Professor of Air Hygiene, University of North Carolina. This diverse group of panelists was moderated by T. T. Frankenberg, consulting mechanical engineer, American Electric Power Service Corporation, and R. L. Ireland of the Consolidation Coal Company, Inc., Cleveland, Ohio. Many of the following facts and figures were presented at this symposium.

Coal, CO, SO:, and temperature inversion. At the present time, coal is used for the production of about 55 percent of the electric power in the United States, and electric generation represents almost half of the total domestic market for coal. And, although nuclear energy will be used increasingly for power production, estimates projected to the year 2000 indicate that the electric utility industry will require about 40 percent of the total available energy--the equivalent of 1.6 million tons of bituminous coal. Of this amount, coal is expected to account for at least 600 000 tons, even at the optimum rate of nuclear power introduction. This level of coal use would be 25 percent more than the total amount of coal mined in the United States in 1964. These statistics indicate the continuing importance of coal in providing a significant portion of the nation's total energy requirements.

Realistically speaking, any restrictions on the use of coal for electric generation would have a serious economic impact on the welfare of the coal-producing regions of the United States, and it would impose cost penalties for present and future power generation.

Air pollution, however, presents one of the most serious threats to the coal industry in the fulfillment of its predicted future as a source of fuel for electric generation. The 2000-MW conventional steam-electric power plants, presently in the design stages, will consume about 20 000 tons of coal per day. This could mean that, in addition to a large volume of carbon monoxide being produced through incomplete combustion, between 700 and 800 tons of sulfur would be burned to produce an intolerable level of sulfur dioxide.

In the vicious cycle wherein urban population densities are increasing, the quantities of energy required in our burgeoning economy will also spiral upward. At some predictable time it will be necessary to decrease the quality of coal used for electric generation as the reserves of high-grade fuel dwindle. And, since the lower-grade bituminous coals contain a higher sulfur content, the problem of air pollution control will be intensified.

Temperature inversion is a meteorological phenomenon which, when occurring over large cities, can have very serious consequences. Essentially, temperature inversion is a perverse atmospheric condition in which the air temperature increases with height above the earth's surface. Normally, temperature decreases with height in the lower atmosphere up to the troposphere, and then the temperature increases in the stratosphere. The rate of decrement, or lapse rate, is about 3.3°F per 1000 feet of altitude.

Inversions are caused by radiative cooling of a lower air layer, subsidence heating of an upper layer, or the advection of warm air over cooler air or of cool air under warmer air. Radiative exchange between the earth's sur

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contamination. In addition to London, the industrial midland cities of Birmingham, Manchester, Sheffield, and Liverpool suffer from the same malady. With the advent of the megalopolis and vast urban industrial sprawls, air pollution is no longer the exclusive property of any one country—it is rapidly becoming a worldwide menace. Later in this article we will discuss in detail the individual air pollution problems of five American cities and what efforts-if any, are being made to remedy the conditions.

The Fig. 5 bar graph dramatically indicates the major air contaminants and quantities emitted per year in the United States, while Fig. 6 shows the amount of suspended dusts and other particulates in relation to urban population classifications. Note that there is a steady rise in the number of particulates with every increase in population classification. Mining, meteorology, and medicine

An entire session at the recent American Power Conference in Chicago clearly indicated that air pollution has become a prime interdisciplinary concern to both the electric utilities and industry. The participants in the panel discussion on this subject included Dr. Bertram D. Dinman, Associate Professor of Preventive Medicine at Ohio State University; Francis E. Gartrell, Assistant Director of Health, Tennessee Valley Authority; Abraham Gerber, secretary of the System Development Committee, American Electric Power Service Corporation;

Pollen

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Industrial dust and ash

Sulfur oxides

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Emissions in the United States, millions of tons per year Fig. 5. Horizontal bar graph showing principal major air contaminants that are emit. ted per year in the United States.

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face and the atmosphere on clear nights cools the ground and the adjacent layer of air. This makes the adjacent layer colder than the layers immediately above, and thereby creates a ground inversion that can vary from a few feet to a few thousand feet in thickness.

Radiative cooling of the top of a cloud bank or dust layer can also create an inversion. In this case, the sinking air warms at the adiabatic lapse rate of 5.5°F per 1000

cet, and this sinking air can produce a layer warmer than the layer of air that is immediately adjacent to the earth's surface.

Cool air that displaces warmer air, such as air that blows from a cool ocean onto a warmer land, can cause a pronounced inversion that persists as long as the flow continues. Similarly, warm air may flow over a cold surface layer, especially one trapped in a valley, and this may cause an inversion. The episodes of acute air pollution in the Meuse River Valley of Belgium, in 1930; in

Donora, Pa., in 1948; and in London, England, in 1952 were caused by this latter phenomenon.

Inversions effectively suppress vertical air movement and cause an atmospheric stagnation in which smoke and other volatile contaminants cannot rise from the earth's surface. Persistent inversions have been experienced in Los Angeles, New York, London, and other industrial metropolises. Under such conditions, lethal layers of sulfur dioxide, soot, carbon monoxide, ozone, and nitrous oxide can become statically entrapped for days at a time.

Climatological factors. There are meteorological and climatological factors that influence the action of airborne, volatile chemicals. The most common of these variables are temperature, wind velocity and turbulence, humidity, atmospheric pressure, and intensity and duration of sunlight.

Thermal reactions, involving the corrosion of materials,

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will approximately double in rate for each 18°F rise in temperature. While temperature is not usually considered to have an effect on photochemical reactions, recent research has indicated that photochemical oxidant production and the rate of photooxidation of hydrocarbons are accelerated by increased temperature in synthetic smog. And there is evidence to indicate that eye irritants could also be increased in the atmosphere by the elevation of air temperature.

It is known that when the air temperature is raised, the respiratory rates of humans and animals are increased, And the toxic effects of many pollutants are affected by temperature changes. For example, in one experiment, the lethal dose of ozone for rats in a temperature environment of 90°F was 2.6 ppm for a 4-hour exposure; while at 75 °F, the lethal dosage for a 6-hour exposure was 6-8 ppm. This would seem to indicate that the permissible levels of air pollution should be revised in accordance with seasonal mean temperatures.

Humidity can influence the effects of air pollution. Its presence often causes more rapid corrosion of metals by certain chemical substances. Many acidic gases, such as sulfur dioxide, nitrous oxide, hydrogen sulfide, and chlorine, are much more corrosive in atmospheres that contain high humidity than they are in the presence of drier air. And since humidity directly affects the heat transfer between humans and their environment, it will, in turn, influence the effect of exposure on humans.

High wind velocity and air turbulence are generally teneficial because pollutants are dispersed and diluted more rapidly

It is known that sunlight is an important factor in the effects of air pollution since eye irritants, plant toxins, and ozone are formed in the air by photochemical reactions. Air pollution experts are aware, for instance, that some types of soot deposited on motor vehicles will damage the lacquer in the presence of sunlight. If the soot is removed, however, before sunlight can touch the finish, no damage will result.

Atmospheric pressure has a relevant influence in air pollution. The oxygen pressure in the air decreases as the height above sea level is increased. The immediate physiological effect of increased altitude is a more rapid blood flow rate, then, the involuntary rate of respiration increases. As the body adapts to the new atmospheric environment, the concentration of blood hemoglobin rises. The ambient pressure in populated areas of the United States varies somewhat more than 0.2 atmosphere (assuming that 1.0 atmosphere equals about 15 psi). For relative comparison, the instantaneous rate for a given concentrauon of air contaminant may be expressed as dxdı - K. At a higher elevation, such as Denver, Colo., with a pressure approximately 0.8 of that at sea level, the instantaneous rate would be dxdı = 0.64K, or 36 percent slower. Therefore, pressure considerations are important in establishing standards that are designed to prevent the formation of secondary pollutants that are synthesized by either photochemistry or oxidation from primary contaminants.

Medically, a dim view. Sulfur dioxide is increasingly emerging as a prime villain in the air pollution drama. This contaminant is a major by-product of fossil-fuel combustion from the lower grade fuel oils and coal.

London's smog, a true smoke suspension in fog, has for many centuries been a prime example of traditional air

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pollution. Because England imports limited quantities of high-grade fossil fuels, the typical London "pea souper" consists mainly of sulfur compounds, particularly SO2, which are produced by the combustion of bituminous coal, low-grade heating oil, acid manufacture, ore smelting, and other industrial manufacturing processes.

In the United States, New York and Chicago have record quantities of So, in their atmospheres that are second only to London's. In all, about 60 percent of the American population is exposed to continuous peril from atmospheric contaminants (see Fig. 7). And it does not require a medical opinion to suggest that pollutants capable of corroding metal, darkening white paint (Fig. 8), disintegrating stone, dissolving nylon hose, and cracking rubber are somewhat less than beneficial to human lung tissue. There is ample circumstantial evidence to link air pollution with asthma, pneumonia, tuberculosis, pulmonary emphysema, lung cancer, and even the common cold. In 1962, the chairman of a panel of medical experts at the National Conference on Air Pollution Control stated: “The evidence that air pollution contributes to the pathogenesis of chronic respiratory disease is over. whelming."

During the symposium on the clean air problem at the recent American Power Conference, Dr. Dinman, in his opening statement, gave a concise description of the pathological effects of sulfur dioxide:

"To understand the effects of So, on health, it is neces

sary to delineate those mechanisms whereby sulfur oxides alter human function. On a mechanistic basis, we may conceive of air conduction tubes (the tracheobronchial tree) as a series of interconnecting ducts. These ducts have the unusual capacity of changing their crosssectional area. This is accomplished by contraction of circumferentially aligned muscles. Thus, given a proper stimulus at certain receptions in the wall of this air conduction system, input from these receivers arrives at the brain. A flow of impulses, in turn, is transmitted to these surrounding muscles, which leads to their contraction with a decrease in cross-sectional area.

"The consequences of such decrease in cross-sectional area are apparent. Consider that a fixed volume of air per unit time must be available for oxygen extraction by the blood. Therefore, an increase in velocity is the only method whereby this fixed volume may be moved through this attenuated system. Obviously, the energy required per unit time to obtain this work function is increased. In individuals who have cardiac disease, these increased demands are met with difficulty and subsequent deterioration. Another complication stems from one other consequence of SO, or so, (sulfur trioxide) or H2SO. (sulfuric acid) impingement on the lining of the gas-blood exchange surfaces. Impingement of these irritant polar compounds stimulates the release of a diluent at such asfected surfaces. While this dilution increases pH toward normal levels, at the same time it imposes a thickened barrier to gas transfer across the membrane. Since this barrier is but a few hundred microns thick, this imposes no significant load on gas transfer in the normal person.

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