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Air pollution is the appearance of air contaminants in the atmosphere that can create a harmful environment to human health or welfare, animal or plant life, or property . In the United States, air pollution is mainly the result of industrialization and urbanization. In 1970, the Federal Clean Act was passed as Public Law 91-604. The objective of the act was to protect and enhance the quality of the US air resources so as to promote public health and welfare and the productive capacity of its population. The Act required that the administrator of the US Environmental Protection Agency (EPA) promulgate primary and secondary National Ambient Air Quality Standards (NAAQS) for six common pollutants. NAAQS are those that, in the judgment of the EPA administrator, based on the air quality criteria, are requisite to protect the public health (Primary), including the health of sensitive populations such as asthmatics, children, and the elderly, and the public welfare (Secondary), including protection against decreased visibility, damage to animals, crops, vegetation, and buildings. These pollutants were photochemical oxidants, particulate matter, carbon monoxide, nitrogen dioxides, sulfur dioxide, and hydrocarbons.

Desulfurization removes elemental sulfur and its compounds from solids, liquids, and gases. Predominantly, desulfurization involves the removal of sulfur oxides from flue gases, compounds of sulfur in petroleum refining, and pyritic sulfur in coal cleaning. This chapter discusses the following topics:

“Carbon sequestration” refers to a portfolio of activities for the capture, separation and storage or reuse of carbon or CO. Carbon sequestration technologies encompass both the prevention of CO emissions into the atmosphere as well as the removal of CO already in the atmosphere.

Nitrogen oxides (NO) and sulfur oxides (SO) emissions are primary contributors to acid rain, which is associated with a number of effects including acidification of lakes and streams, accelerated corrosion of buildings, and visibility impairment. Among the various nitrogen oxides emitted from stationary combustion; nitrogen oxide (NO), nitrous oxide (NO), and nitrogen dioxide (NO) are stable, and NO predominates (over 90%). In health effects, NO can irritate the lungs and lower resistance to respiratory infection. In the area of ozone nonattainment, NO and volatile organic compounds (VOCs) react in the atmosphere to form ozone, a photochemical oxidant and a major component of smog. Atmospheric ozone can cause respiratory problems by damaging lung tissue and reducing lung function .

Heavy metals are elements that are located in the periodic table from groups III to VI and periods 4 or greater. The elements have high atomic weight greater than sodium and high specific gravity (i.e., usually greater than 5.0 g/cm). In addition, the elements have high thermal conductivity and are characterized by malleability and ductility. There are 65 elements listed in the periodic table that can be defined as heavy metals based on the above definitions. Approximately 30 metals, either in elemental forms, in salts, or in organometallic compounds, have been used by industry. Heavy metals in the wastes will not be directly exposed to the atmosphere. Thermal or vaporization processes enhance heavy metal exposure into the atmosphere. Unlike organic compounds, metals cannot be completely destroyed by the thermal process. The thermal process can only oxidize the majority of metals to particulate matter. Only a small amount of volatile metals having a boiling point lower than the thermal/combustion operation temperature will be vaporized. Metals, such as arsenic, barium, beryllium, chromium, cadmium, lead, mercury, nickel, and zinc, are of great concern in waste incineration and coal combustion because of their presence in many wastes and because of possible adverse health effects from human exposure to emissions .

Ventilation is defined as the process of supplying air to, or removing it from, any enclosed space by natural or mechanical means. Such air may or may not be conditioned. There are at least five effects resulting from human occupancy of unventilated or poorly ventilated rooms: (1) a decrease in the oxygen content in air, (2) an increase in the carbon dioxide content in air, (3) a release of odor-causing organic compounds from the skin, clothing, and mouths of the occupants, (4) an increase in humidity owing to the moisture in the breath and evaporation from the skin, and (5) an increase in the room temperature owing to the heat generated in the body processes .

Indoor air pollution has occurred since prehistoric times when people moved to live indoors and fire was brought into closed shelters for cooking and space heating . Today, indoor air pollution caused by burning of traditional solid fuels such as woodfuel, agricultural residues, and dried animal dung in unvented cookstoves in rural areas of developing countries is not much different from that of the past. Problems associated with indoor air pollution, however, have developed a new dimension, because of energy-efficient measures (tightly constructed buildings, increased insulation, and reduced ventilation) implemented since the early 1970s in response to the oil crisis. Tightly constructed buildings, for instance, reduce the amount of fresh air for dilution and for purging out of pollutants, which, in turn, builds up high levels of toxic substances indoors. The fact that indoors air quality is not an exact reflection of the ambient air quality was recognized only recently. Scientific evidence has indicated that the air within homes and other public and office buildings can be more seriously polluted than the outdoor air. Public concern about indoor air pollution effects on health has thus attracted expanded research on the topic.

Humans perceive odors by chemical stimulation of the chemoreceptors in the olfactory epitheliurn located in the nose. Odorants are the chemicals that stimulate the olfactory sense. This interaction between sensory cells and volatile molecules, which produces a nerve impulse, enables humans to detect and differentiate between different odors and to detect odor intensity.

Human beings are exposed to two sources of radiation in the environment: natural and man-made. Natural sources include radioactive radon, radioisotopes with a long half-life, such as potassium in the body, cosmic rays (energetic γ-rays and particles from the sun and interstellar space), and some rocks. Various sources of artificial radiation include medical X-rays, nuclear medicine for cancer treatment, and some consumer products containing radioisotopes. Natural sources of radiation account for 82% of total exposure for humans. A common radioactive element is radium, one of whose decay products, radon, poses health concerns. Radon emanates from rock, soil, and underground water as a gas. In the solar system, various radioisotopes of radon gas form from decay of radioactive uranium and thorium elements found naturally. The contributing effects from natural and man-made radiation sources on human beings is shown in Fig. 1.

The discharge of water at elevated temperatures is often described as . It is produced by industries such as electric power plants, pulp and paper mills, chemical facilities, and other process industries that use and subsequently discharge water. Even if the discharged water is merely elevated in temperature, allowing it to return to streams, rivers, lakes, and other waters can dramatically alter the native environment.