Task 6. Skim the text and tell what the general idea of the text is.

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Air pollution is of public health concern on several scales: micro, meso, and macro. Microscale problems range from those covering less than a centimeter to those the size of a house or slightly larger. Meso-scale air pollution problems are those of a few hectares up to the size of a city or a country. Macro-scale problems extend from countries to states, nations, and in the broadest sense, the globe. Indoor air pollution results from products used in construction materials, adequacy of general ventilation, and geophysical factors that may result in exposure to nat­urally occurring radioactive materials. Industrial and mobile sources contribute to meso-scale air pollution that contaminates the ambient air that surrounds us out­doors. Macro-scale impacts include transport of ambient air pollutants over large distances and global impact. Examples of macro-scale impacts include acid rain and ozone pollution. Global impacts of air pollution result from sources that may poten­tially change the upper atmosphere. Examples include depletion of the ozone layer and global warming. While micro- and macro-scale effects are of concern, our focus will predominately be on meso-scale air pollution.

To investigate and describe the environmental effects of any air pollutant emitted by stationary or mobile sources that may adversely affect human health or the environment the National Ambient standards (NAAQS) were established. These standards for the ambient air are divided into primary and secondary according to criteria pollutants (CO, lead, No2, ozone, particulate matter, SO2). They were developed on health based criteria. The pri­mary standard was established to protect human health with an “adequate margin of safety.” The secondary standards are intended to prevent environmental and property damage. Using a risk-based approach regulations for hazardous air pollutants (HAPs) were established. Seven hazardous air pollutants were regulated: asbestos, arsenic, benzene, beryllium, mercury, vinyl chloride, and radionuclides.

There are three basic units of measure used in reporting air pollution data: micrograms per cubic meter (g/m³), parts per million (ppm), and the micron ()

or, prefer­ably, its equivalent, the micrometer (m). Micrograms per cubic meter and parts per million are measures of concentration. Both /m³ and ppm are used to indicate the concentration of a gaseous pollutant. However, the concentration of particulate matter may be reported only as g/m³. The m is used to report particle size.

EFFECTS OF AIR POLLUTANTS. Five mechanisms of deterioration have been attributed to air pollution: abrasion, deposition and removal, direct chemical attack, indirect chemical attack and electrochemical corrosion.

Solid particles of large enough size and traveling at high enough speed can cause deterioration by abrasion. With the exception of soil particles in dust storms and lead particles from automatic weapons fire, most air pollutant particles either are too small or travel at too slow a speed to be abrasive.

Small liquid and solid particles that settle on exposed surfaces do not cause more than aesthetic deterioration. For certain monuments and buildings this form of deterioration is in itself quite unacceptable. For most surfaces, it is the cleaning process that causes the damage.

Solubilization and oxidation/reduction reactions typify direct chemical attack. Frequently, water must be present as a medium for these reactions to take place. Sulfur dioxide and SO₃ in the presence of water react with limestone (CaCO₃) to form calcium sulfate (CaSO₄) and gypsum (CaSO₄∙2H₂O). Both CaSO₄ and CaSO₄∙2H₂O are more soluble in water than CaCO₃, and both are leached away when it rains. The tarnishing of silver by H₂S is a classic example of an oxidation/reduction reaction.

Indirect chemical attack occurs when pollutants are absorbed and then react with some component of the absorbent to form a destructive compound. The compound may be destructive because it forms an oxidant, reductant, or solvent. Further, a compound can be destructive by removing an active bond in some lattice structure. Leather becomes brittle after it absorbs SO₂, which reacts to form sulfuric acid because of the presence of minute quantities of iron. The iron acts as a catalyst for the formation of the acid. A similar result has been noted for paper.

Oxidation/reduction causes local chemical and physical differences on metal surfaces. These differences, in turn, result in the formation of microscopic anodes and cathodes. Electrochemical corrosion results from the potential that de­velops in these microscopic batteries.

Moisture, temperature, sunlight, and posi­tion of the exposed material are among the most important factors that influence the rate of deterioration.

Moisture, in the form of humidity, is essential for most of the mechanisms of deterioration to occur. Metal corrosion does not appear to occur even at relatively high SO₂ pollution levels until the relative humidity exceeds 60 percent. On the other hand, humidity above 70 to 90 percent will promote corrosion without air pollutants. Rain reduces the effects of pollutant-induced corrosion by dilution and washing away of the pollutant.

Higher air temperatures generally result in higher reaction rates. However, when low air temperatures are accompanied by cooling of surfaces to the point where moisture condenses, then the rates may be accelerated.

In addition to the oxidation effect of its ultraviolet wave lengths, sunlight stimulates air pollution damage by providing the energy for pollutant formation and cyclic reformation. The cracking of rubber and the fading of dyes have been attributed to ozone produced by these photochemical reactions.

The position of the exposed surface influences the rate of deterioration in two ways. First, whether the surface is vertical or horizontal or at some angle affects deposition and wash-off rates. Second, whether the surface is an upper or lower one may alter the rate of damage. When the humidity is sufficiently high, the lower side usually deteriorates faster because rain does not remove the pollutants as efficiently.

Effects on Health. It is difficult at best to assess the effects of air pollution on human health. Personal pollution from smoking results in exposure to air pollutant concentrations far higher than the low levels found in the ambient atmosphere. Occupational exposure may also result in pollution doses far above those found outdoors. Tests on rodents and other mammals are difficult to interpret and apply to human anatomy. Tests on human subjects are usually restricted to those who would be expected to survive. This leads us to a question of environmental ethics. If the allowable concentration levels (standards) are based on results from tests on rodents, they would be rather high. If the allowable concentration levels must also protect those with existing cardiorespiratory ailments, they should be lower than those resulting from the observed effects on rodents.

The standards must protect the most sensitive responders. The sensitive populations are those with heart and circulatory ailments, chronic pulmonary disease, developing fetuses, and those with conditions that cause increased oxygen demand, such as fever.

We know relatively little about the specific effects of the HAPs at the low levels normally found in ambient air. Most of the information on the direct human health effects of hazardous air pollutants (also known as air toxics) comes from studies of industrial workers. Exposure to air toxics in the work place is generally much higher than in the ambient air. We know relatively little about the specific effects of the HAPs at the low levels normally found in ambient air. The HAPs (Lead (Pb), Nitrogen dioxide (NO₂), photochemical oxidants, Sulpher Oxides and total suspended particles) were identified as causal agents for a variety of diseases. For example, asbestos, arsenic, benzene, coke oven emissions, and radionuclides may cause cancer. Beryllium primarily causes lung disease but also affects the liver, spleen, kidneys, and lymph glands. Mercury attacks the brain, kidneys, and bowels. Other potential effects from the HAPs are birth defects and damage to the immune and nervous systems.

Waste minimization. The best and first step in any air pollution control strategy should be to minimize the production of pollutants in the first place. Since a large proportion of air pollutants re­sults from the combustion of fossil fuels, an obvious approach to waste minimization is to conserve energy. Modern technology has yielded more efficient furnaces that improve fuel use, but simple measures such as turning off the lights in unoccupied rooms, turning down the heat at night and, in factories, during weekends and holi­days, can have a dramatic impact. Because of the interrelationship between energy consumption and water supply, water conservation also reduces air pollution. In a similar manner, building smaller, lighter automobiles reduces air pollution because less fuel is burned to propel them, but alternatives such as mass transit, walking, and bicycles can contribute significantly to reduced fuel consumption. Alternative sources of energy such as solar, wind, and nuclear also reduce air pollution emissions. (Nuclear power, of course, has a series of pollution problems that may outweigh the benefits of reduced air pollution.)

The chlorofluorocarbon destruction of the ozone layer can only be resolved by waste minimization. Preventing the escape of CFCs from refrigeration systems, the use of alternative propellants for spray cans, and similar measures are the only ones that will be successful, since control devices make no sense. Waste minimization is, in fact, the method of control. In a similar fashion, the production of ozone in the lower atmosphere can only be reduced by minimizing the release of and the production of NO*. Reduced use of solvents and the substitution of water-based paints for solvent-based paints are examples of methods to reduce hydrocarbon release.

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