Air Quality 1

The Air Components A person may survive many days without food, or few days without water, but without air a person could not exist long enough to walk 100 feet. The air that humans must have is an odorless, colorless mixture of natural gases, roughly 78% nitrogen and 21% oxygen. The remaining 1% is mostly argon (0.93%), carbon dioxide (0.032 %), and traces of neon, helium, ozone, xenon, hydrogen, methane, krypton, and varying amounts of water vapor. When any thing else is added, it becomes air pollution. 2

Sources of air Pollution Some natural sources of air pollution are forest fires, dust storms, and volcanic eruptions. Anthropogenic air pollution, that produced by humans, also may affect human health adversely. Some sources are smoke from chimneys, gases from septic tanks, odors from cooking food, and fumes, gases, vapor and particles released from paint, household cleaner, hair sprays and so on. Industrial pollution is created by the release of sulfur dioxide (SO 2 ), carbon dioxide (CO 2 ), carbon monoxide (CO), nitrogen oxides (NO and NO 2 ) and other gases, vapors and fumes, where industry is making the cars, closing, cleaning agents, furniture, and other products we purchase. This is in addition to the emissions from coal and oil burning electric power plants. 3

photochemical smog Air pollutants are created in agricultural where our food is grown. For example, crop yields are increased greatly when insecticides and herbicides are used to rid from pests. Transportation contributes to the pollution problem and accounts for approximately 50% of all air pollution. Carbon monoxide (CO) is the major source of air pollution generated by transportation. Now catalytic convertors installed on automobiles have reduced CO emissions from this source significantly. Carbon monoxide (CO) is the result of incomplete combustion of products; in contrast, complete combustion produces Carbon dioxide ( CO 2 ). Nitrogen oxides and hydrocarbons are additional byproducts of the combustion of petroleum products to produce what is called photochemical smog, a major problem in large cities. 4

Health effects of air pollution Epidemiological studies indicate that high levels of air pollutants contribute to or cause a number of respiratory conditions such as:- Asthma, chronic bronchitis, lung cancer and heart disorders. 5

Air Pollution Control Input control 1.Reduce the need for energy. 2.Enhance fuel-dependent units such as gas engines. 3.Recycle resources and prevent loss of metals and chemicals into the environment. 4.Reduce our dependency upon fossil fuels. 5.Find new nonpolluting sources of energy (e.g., wind, tidal, and solar energy). 6.And others. 6

Output control 1. Remove pollutants after combustion by using scrubbers and electrostatic precipitators. 2. Improve catalytic conversion in automobiles. 3- Support improved methods of emission control. 4- And others. 7

Some Air Quality Phenomena 1) Acid Precipitation Emission of sulfur dioxide (SO 2 ) - that comes from burning coal and other fuels containing sulfur - converts to acid (sulfuric acid) in the atmosphere and falls to the earth as acid precipitation (acid rain). Similarly, emission of nitrogen oxides transform into acid and falls to the earth as acid precipitation. The nitrogen oxides are produced from the high temperature combustion of fossil fuels, such as in cars, in which the nitric oxides are oxidized to nitrogen oxides, which further oxidizes and dissolves in water droplets at the atmosphere to form nitric acid. These acids depress the pH of the soil, lakes, rivers, and other natural resources after precipitation as rain or snow. 8

2) The Greenhouse Effect The earth’s temperature remains relatively constant because some of the solar energy absorbed by earth eventually is radiated back into space. Nowadays, however, the heat is not being radiated back into space as it once was, and thus the earth is undergoing a warming trend. This warming is caused mainly by CO 2 and water vapor in the air. 9

The world produces more CO 2 each year as the population growth. Burning fossil fuels in automobiles, Coal-fired electric plants, and the like produces more CO 2. Thus, more CO 2 remains in the air each year. Water vapor and CO 2 absorb radiation. Hence, more and more radiation is absorbed and trapped in the atmosphere. This causes an increase in the earth’s temperature, termed the greenhouse effect. 10

A greenhouse lets in sunlight through its glass. The light warms the inside, and the glass prevents the heat from escaping. Like the glass, CO 2 and water vapor in the atmosphere absorb the long-wavelength heat radiated by the earth. The greenhouse effect causes much concern because of the possible repercussions of global warming. 11

Global warming has a possible harmful effect: Glaciers and ice fields in polar regions would melt, causing a projected rise in the average sea level of about 2.4 meters by 2100, thus possibly causing flooding of coastal cities and industrial areas. 12

3) Ozone Layer Depletion The main cause of the depletion of the ozone layer is chlorofluorocarbon (CFCs). The chlorofluorocarbon are propellants used in products such as hair spray, bathroom cleaners, and other aerosol products. Chlorofluorocarbons can be found in the production of foam coffee cups, egg cartons, building insulation and others. CFCs contain chlorine. When the CFCs reach 10 to 20 miles into the atmosphere, chlorine is released when the CFCs molecular bonds break down. Once released, the chlorine takes a molecule from an atom of ozone. Ordinary oxygen, which has no sun-blocking properties, is left. 13

The major concern with the depletion of the ozone layer is that the increase in ultraviolet light will reach the surface, increasing the incidence of skin cancer and cataracts. 14