Air Pollution

Introduction

Air Pollution, addition of harmful substances to the atmosphere resulting in damage to the environment, human health, and quality of life. One of many forms of pollution, air pollution occurs inside homes, schools, and offices; in cities; across continents; and even globally. Air pollution makes people sick—it causes breathing problems and promotes cancer—and it harms plants, animals, and the ecosystems in which they live. Some air pollutants return to Earth in the form of acid rain and snow, which corrode statues and buildings, damage crops and forests, and make lakes and streams unsuitable for fish and other plant and animal life.

Pollution is changing Earth's atmosphere so that it lets in more harmful radiation from the Sun. At the same time, our polluted atmosphere is becoming a better insulator, preventing heat from escaping back into space and leading to a rise in global average temperatures. Scientists predict that the temperature increase, referred to as global warming, will affect world food supply, alter sea level, make weather more extreme, and increase the spread of tropical disease.

 

II. Major Pollutant Sources

1. human activity: burning fossil fuels—natural gas, coal, and oil—to power industrial processes and motor vehicles. Among the harmful chemical compounds this burning puts into the atmosphere are carbon dioxide, carbon monoxide, nitrogen oxides, sulfur dioxide, and tiny solid particles—including lead from gasoline additives—called particulates. 
2. Decomposing garbage in landfills and solid waste disposal sites emits methane gas, and many household products give off VOCs.
   
3. Natural sources.

•  forest fires emit particulates and VOCs into the atmosphere.
• Ultrafine dust particles, dislodged by soil erosion when water and weather loosen layers of soil, increase airborne particulate levels.
• Volcanoes spew out sulfur dioxide and large amounts of pulverized lava rock known as volcanic ash. A big volcanic eruption can darken the sky over a wide region and affect the Earth's entire atmosphere.

Unlike pollutants from human activity, however, naturally occurring pollutants tend to remain in the atmosphere for a short time and do not lead to permanent atmospheric change.

 

III. Local and Regional Pollution

Local and regional pollution take place in the lowest layer of the atmosphere, the troposphere, which at its widest extends from Earth's surface to about 16 km (about 10 mi).  If the load of pollutants added to the troposphere were equally distributed, the pollutants would be spread over vast areas and the air pollution might almost escape our notice. Pollution sources tend to be concentrated, however, especially in cities.

In the weather phenomenon known as thermal inversion, a layer of cooler air is trapped near the ground by a layer of warmer air above. When this occurs, normal air mixing almost ceases and pollutants are trapped in the lower layer. Local topography, or the shape of the land, can worsen this effect—an area ringed by mountains, for example, can become a pollution trap.

A. Smog and Acid Precipitation

Smog is intense local pollution usually trapped by a thermal inversion. Burning gasoline in motor vehicles is the main source of smog in most regions today.

Powered by sunlight, oxides of nitrogen and volatile organic compounds react in the atmosphere to produce photochemical smog. Smog contains ozone. Ozone in the lower atmosphere is a poison—it damages vegetation, kills trees, irritates lung tissues, and attacks rubber. When the ozone level is high, other pollutants, including carbon monoxide, are usually present at high levels as well.

In the presence of atmospheric moisture, sulfur dioxide and oxides of nitrogen turn into droplets of pure acid floating in smog. These airborne acids are bad for the lungs and attack anything made of limestone, marble, or metal. Oxides of nitrogen and sulfur dioxide pollute places far from the points where they are released into the air. Carried by winds in the troposphere, they can reach distant regions where they descend in acid form, usually as rain or snow. Such acid precipitation can burn the leaves of plants and make lakes too acidic to support fish and other living things.

For the very young, the very old, and people who suffer from asthma or heart disease, the effects of smog are even worse: It may cause headaches or dizziness and can cause breathing difficulties. In extreme cases, smog can lead to mass illness and death, mainly from carbon monoxide poisoning.

1948- the steel-mill town of Donora, Pennsylvania, intense local smog killed 19 people.

952- London, about 4,000 people died (London Fogs) in 1962 another 700 Londoners died.

IV. Global Scale Pollution

Air pollution can expand beyond a regional area to cause global effects. The stratosphere is the layer of the atmosphere between 16 km (10 mi) and 50 km (30 mi) above sea level. It is rich in ozone, the same molecule that acts as a pollutant when found at lower levels of the atmosphere in urban smog. Up at the stratospheric level, however, ozone forms a protective layer that serves a vital function: It absorbs the wavelength of solar radiation known as ultraviolet-B (UV-B). UV-B damages deoxyribonucleic acid (DNA) increasing the risk of such problems as cancer in humans. Because of its protective function, the ozone layer is essential to life on Earth.

A. Ozone Depletion

Several pollutants attack the ozone layer. Chief among them is the class of chemicals known as chlorofluorocarbons (CFCs). CFC molecules are virtually indestructible until they reach the stratosphere. Here, intense ultraviolet radiation breaks the CFC molecules apart, releasing the chlorine atoms they contain. These chlorine atoms begin reacting with ozone, breaking it down into ordinary oxygen molecules that do not absorb UV-B. The chlorine acts as a catalyst—that is, it takes part in several chemical reactions—yet at the end emerges unchanged and able to react again. A single chlorine atom can destroy up to 100,000 ozone molecules in the stratosphere. Other pollutants, including nitrous oxide from fertilizers and the pesticide methyl bromide, also attack atmospheric ozone.

B. Global Warming

Humans are bringing about another global-scale change in the atmosphere: the increase in what are called greenhouse gases. Like glass in a greenhouse, these gases admit the Sun's light but tend to reflect back downward the heat that is radiated from the ground below, trapping heat in the Earth's atmosphere. This process is known as the greenhouse effect.

Scientists predict that increases in these gases in the atmosphere will make the Earth a warmer place. They expect a global rise in average temperature of 1.4 to 5.8 Celsius degrees (2.5 to 10.4 Fahrenheit degrees) in the next century.

Global warming will have different effects in different regions. A warmed world is expected to have more extreme weather, with more rain during wet periods, longer droughts, and more powerful storms. Although the effects of future climate change are unknown, some predict that exaggerated weather conditions may translate into better agricultural yields in areas such as the western United States, where temperature and rainfall are expected to increase, while dramatic decreases in rainfall may lead to severe drought and plunging agricultural yields in parts of Africa, for example.

Warmer temperatures are expected to partially melt the polar ice caps, leading to a projected sea level rise of 9 to 100 cm (4 to 40 in) by the year 2100. A sea level rise at the upper end of this range would flood coastal cities, force people to abandon low-lying islands, and completely inundate coastal wetlands. For many of the world's plant species, and for animal species that are not easily able to shift their territories as their habitat grows warmer, climate change may bring extinction.

V. Indoor Air Pollution

Indoor pollutants include tobacco smoke; radon, an invisible radioactive gas that enters homes from the ground in some regions; and chemicals released from synthetic carpets and furniture, pesticides, and household cleaners. When disturbed, asbestos, a nonflammable material once commonly used in insulation, sheds airborne fibers that can produce a lung disease called asbestosis.

Pollutants may accumulate to reach much higher levels than they do outside, where natural air currents disperse them. Indoor air levels of many pollutants may be 2 to 5 times, and occasionally more than 100 times, higher than outdoor levels. These levels of indoor air pollutants are especially harmful because people spend as much as 90 percent of their time living, working, and playing indoors. Inefficient or improperly vented heaters are particularly dangerous.

VI. Pollution Cleanup and Prevention

Pollution is controlled in two ways: with end-of-the-pipe devices that capture pollutants already created and by limiting the quantity of pollutants produced in the first place.

End-of-the-pipe devices include catalytic converters in automobiles and various kinds of filters and scrubbers in industrial plants. In a catalytic converter, exhaust gases pass over small beads coated with metals that promote reactions changing harmful substances into less harmful ones.

The choices people make in their daily lives can have a significant impact on the state of the air. Using public transportation instead of driving, for instance, reduces pollution by limiting the number of pollution-emitting automobiles on the road. During periods of particularly intense smog, pollution control authorities often urge people to avoid trips by car.

Indoor pollution control must be accomplished building by building or even room by room. Proper ventilation mimics natural outdoor air currents, reducing levels of indoor air pollutants by continually circulating fresh air. After improving ventilation, the most effective single step is probably banning smoking in public rooms. Where asbestos has been used in insulation, it can be removed or sealed behind sheathes so that it won't be shredded and get into the air. Sealing foundations and installing special pipes and pumps can prevent radon from seeping into buildings.

New efforts to control air pollution will be necessary as long as these trends continue.

Source: http://miosh.net/articles/ (OSH Articles)

 

Sekretariat EOSH____2010

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