Mistress of moon
19-04-2006, 03:02 PM
Air pollution
Air pollution occurs when wastes dirty the air. Artificially created wastes are the main sources of air pollution. They can be in the form of gases or particulates (tiny particles of liquid or solid matter). Such wastes result chiefly from the burning of fuel to power motor vehicles and to heat buildings. They also come from industrial processes and the burning of solid wastes. Natural pollutants (impurities) include dust, pollen, and soil particles.
The rapid growth of population and industry, and the increase in the number of motor vehicles and aeroplanes, has made air pollution an increasingly serious problem in many big cities since the 1950's. The air over these cities often becomes so filled with pollutants that it harms the health of people. Air pollution also harms plants, animals, fabrics, building materials, and the economy.
Chief sources of air pollution
Cities that have many coal-burning furnaces and power plants tend to have higher sulphur oxide levels. Cities with more industry tend to have high levels of organic compounds. But in most western cities, car exhausts account for most of the nitrogen oxide and carbon monoxide in the air.
Weather conditions called thermal inversions may enable pollutants to build up over a certain area. A thermal inversion occurs when a layer of warm air settles over a layer of cool air that lies near the ground. This prevents pollutants from rising and scattering, and causes them to collect near the ground. The thermal inversion continues until rain or wind breaks up the layer of stationary warm air, allowing the impurities to rise.
Forms of transportation, such as aeroplanes, cars, ships, and trains, are a leading source of air pollution. Exhaust from engines contains various kinds of harmful pollutants. Such pollutants include carbon monoxide gas, hydrocarbons (compounds of hydrogen and carbon), and nitrogen oxides (compounds of nitrogen and oxygen). Nitrogen oxides in the air help produce a form of oxygen called ozone. Ozone reacts with hydrocarbons to form a type of air pollution known as smog.
Fuel combustion for heating homes, office buildings, and factories sharply increases the level of air pollution in urban areas. Furnaces that burn coal or fuel oil give off nitrogen oxides, particulates, and sulphur oxides (compounds of sulphur and oxygen). Electricity generating stations that use these fuels also release such pollutants into the atmosphere.
Industrial processes contribute significantly to air pollution. Industries give off various types of pollutants. For example, factories that produce aluminium expel fluoride dust. Oil refineries discharge ammonia, hydrocarbons, organic acids, and sulphur oxides into the atmosphere. Industrial plants that produce plastic foams are a major source of chlorofluorocarbons (CFC's), compounds of chlorine, fluorine, and carbon.
Burning of solid wastes creates a very visible form of air pollution--thick, black smoke. The burning of leaves, refuse, scrap cars, and other solid wastes is prohibited in some areas.
Other sources of air pollution include chemical sprays, forest fires, and structural fires. Pollution also results from the burning of forest, bush, and grass to clear land for farming.
Effects of air pollution
Health. When people breathe polluted air, the impurities often remain in their lungs. These impurities can worsen such respiratory ailments as asthma and bronchitis. Laboratory tests have associated some pollutants with the formation of cancer, pneumonia, and emphysema. In London in 1952, about 4,000 people died of respiratory diseases during a "killer smog." A total of more than 600 people died as a result of thermal inversions that occurred in New York City in 1953 and 1963. By the late 1980's, such cases of killer smog became rare, due to the introduction of tougher emissions standards and better monitoring.
Agriculture. Air pollution causes severe damage to crops and livestock in countries with heavy industries and crowded roads. Plants will not grow alongside many roads in these countries because vehicle exhaust fumes kill them. Air pollution can damage fruit, vegetable and grain crops.
Atmosphere. Some pollutants are not poisonous but can cause damage by altering the earth's atmosphere. For example, the amount of carbon dioxide in the atmosphere has been increasing since the early to mid-1800's, chiefly as a result of the burning of coal, oil, and other carbon-containing fuels. Carbon dioxide allows sunlight to reach the earth and warm its surface, but it prevents some surface heat from escaping out of the atmosphere. This process, called the greenhouse effect, may produce significant climatic changes, which could destroy many kinds of plants and animals. Chlorofluorocarbons (CFC's) break down the layer of ozone in the earth's upper atmosphere. This layer protects plants and animals from harmful ultraviolet rays .
Other effects. Most materials deteriorate faster when exposed to the pollutants present in the air. Concrete and stone are dissolved by air pollutants. Metals corrode faster than usual. Plastics, rubber, and fabrics are also damaged by air pollutants.
Air pollution is closely related to other forms of pollution. Sulphur dioxide and nitrogen oxides can react with water droplets in the air to produce acid rain. Acid rain pollutes lakes and streams and, in high concentrations, can harm soil fertility .
Control of air pollution
Air pollution from such stationary sources as factories, furnaces, incinerators, and power stations can be reduced in several ways. For example, a plant can install equipment designed to limit the amount of pollutants given off. It can change to a method of manufacture or of burning fuel that causes less air pollution. Or the plant can switch to a cleaner fuel. In some cases, plants must use a combination of these steps to reduce air pollution.
Controlling the pollution emitted by cars and trucks involves changing the way engines operate, changing the ingredients in fuel, and adding pollution control devices to the vehicle. Manufacturers and refiners are working in all of these areas to find good ways of controlling pollution. In addition, research is underway to develop alternative engines that are driven by electricity, methanol, natural gas, steam, or other energy sources that create less air pollution.
Increasingly, national and local governments are passing laws and setting requirements designed to control pollution. They issue information on the effects of air pollutants and the techniques available for controlling them. They set goals called air quality standards for achieving clean air. They then must enforce control measures to meet the goals. Governments may act directly against polluters if they fail to obey the regulations.
The control measures include emission standards, which restrict the amount of pollution from factories and other sources of pollution. Governments also set emission standards for motor vehicles. In many countries, to meet these emission standards, new cars must be equipped with control devices called catalytic converters.
International agreements can also help to reduce air pollution. The 1987 Montreal Protocol on Substances That Deplete the Ozone Layer was ratified by more than 150 countries. As a result of the protocol, most industrialized countries had stopped producing and importing CFC's by 1996. Many developing countries aimed to freeze CFC consumption in 1999 and to phase it out completely by 2010.
ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ
Pollution
INTRODUCTION Pollution, contamination of the environment by man-made substances or energy that have adverse effects on living or non-living matter. This contamination of air, water, or soil materials interferes with human health, the quality of life, or the natural functioning of ecosystems. In simple terms, pollution can be seen as the wrong substance in the wrong place in the wrong quantities at the wrong time. This implies that harm is caused to the environment, and if the same substance is present at levels too low to cause harm, then it can be considered as contamination. Many substances that can be pollutants also occur naturally, in which case they are not classified as pollution. However, other pollutants result entirely from human activity, such as most toxic organic compounds and artificial forms of radioactivity , particularly from nuclear waste. TYPES OF POLLUTION Pollution can be categorized according to the medium in which it occurs: atmospheric pollution (seeAir Pollution), freshwater and sea pollution (see Water Pollution), or land pollution (see Solid Waste Disposal). However, transfers can occur in both directions between the atmosphere, water, and the land, with consequences for both the spread of pollution and its effects. For example, the emission of sulphur dioxide-caused by the combustion of fossil fuels such as gas, petroleum, and coal-into the air can result in the acidification of soils and lakes when it reaches the Earth's surface (see Acid Rain). Pollution can also be classified on the basis of the type of pollutant, such as pesticides (seePest Control) and other persistent toxic organic compounds, heavy metals, radioactivity, human and animal effluent, and toxic gases. The most familiar forms of pollution result from the chemical properties of the substances concerned, but the physical properties may also be important, for example ionizing radiation, noise pollution, and excessive heat. Water pollution arises from the discharge of industrial, agricultural, and human wastes into freshwaters, estuaries, and seas. This may result in the poisoning of aquatic organisms or the depletion of oxygen owing to excessive growth of micro-organisms (anthropogenic eutrophication), which makes less of the water habitable for fish. Metal pollution and toxic organic compounds are of concern for human and environmental health as a result of discharges to water, air, and the terrestrial environment. Air pollution can result in adverse effects on health, crops, natural ecosystems, materials, and visibility. The major concerns over air pollution are acidification of soils and waters with its detrimental affects on animal and plant life, and the impact of traffic-derived pollutants on health in cities (see Traffic Pollution). On a global scale air pollution probably represents the greatest problem of all, with greenhouse gases (such as carbon dioxide) resulting in global warming and synthetic chlorine compounds (chlorofluorocarbons) depleting the stratospheric ozone layer. Nuclear waste is a further modern environmental concern, which poses a problem not just for the present generation, but for future generations as the waste remains radioactive for thousands of years. TRENDS IN POLLUTION Trends in pollution are difficult to determine accurately, particularly on a world scale. The best-documented trend is the global increase in carbon dioxide at a rate of about 0.5 per cent per year. Overall, there is a trend for decreasing levels of pollutants in the developed world, but the opposite in many developing countries as they rapidly industrialize. For example, it has been predicted that sulphur dioxide emissions will fall by 63 per cent in Europe from 1990 to 2010, while they will rise in China by 118 per cent. The reductions in the developed world result largely from environmental legislation, which has led to the introduction of control measures and cleaner technology. Examples are the introduction of more advanced waste-water treatment processes, shifts to cleaner fuels, and the recycling of potential contaminants. See also Conservation; Oil Pollution; and Environmentalism. المصدر "Pollution," Microsoft® Encarta® Encyclopedia 2000. © 1993-1999 Microsoft Corporation. All rights reserved
مسامحة ع القصوووور
ريد روز