The atmosphere is described as a gaseous envelope surrounding earth. The earth’s atmosphere contains gases essential to plant and animal life.

The layer of the atmosphere next to the earth where the temperature decreases with elevation is the troposphere. Above that is the stratosphere, where the temperature of the air increases with height. Between the two is a transition zone, the tropopause, where there is no change in temperature with elevation. Absorption of the sunlight’s short wavelength radiation by the ozone and oxygen in the stratosphere causes the temperature to rise.

The mesosphere is the layer above the stratosphere, and the temperature declines with height in that layer. Above the mesophere, cosmic radiation causes ionization and results in an increase in temperature from absorption of the energy.

Composition of the Earth’s Atmosphere
Nitrogen	78.09
Oxygen	20.95
Argon	0.93
Carbon dioxide	0.03

Solar Energy Solar Calculator

Our solar system has the sun at its center and eight planets orbiting about it. The earth, the third planet, is about 150 million kilometers (93 million miles) from the sun. Thermonuclear reactions (fusion of atomic nuclei) in the sun provide the light and heat for our solar system, resulting in a surface temperature on earth ranging from 88ºC to 58ºC, with a mean at 100C. This temperature range is significant because over much of the earth water is in a liquid state, a necessary condition for life as we know it.

The range of all possible wavelengths is called the electromagnetic spectrum. This spectrum contains radiation of short and long wavelengths and includes visible light. Visible light is an emission of radiant energy with an electromagnetic wavelength in the range detectable by the human eye (0.4-0.7 micron). Red is the longest wavelength seen by the human eye; violet, the shortest. Black is an absence of light, and white is a mixture of all detectable wavelengths. The longer wavelengths (over 0.7 micron) include infrared radiation (like the heat from a stove that can be felt but not seen); radio waves; and radiation from radar and microwave ovens. The shorter wavelengths (less than 0.4 micron) include ultraviolet (UV) light, X-rays, and gamma rays.

Persons exposed to short wavelength radiation may experience undesired effects to their health. A limited exposure to ultraviolet light can cause sunburn. Prolonged exposure to sunlight for many years may cause skin cancer. Ultraviolet radiation is sometimes used to kill microorganisms in air and water, and X-rays and gamma rays can damage and destroy all kinds of cells.

The sun warms the surface of the ocean and evaporates water. Each gram of water evaporated represents 580 calories of heat waiting to be released when the vapor condenses. The buildup of heat in the late summer makes the area ripe to produce thunderstorms. When this tendency for storms is combined with a cyclonic weather system moving through the area, the thunderstorms may be so intense as to release sufficient heat to warm the air over a large area. The rising warm air creates a local low-pressure area, and air flows around and inward toward the low-pressure center. The spiraling of air inward causes the speed to increase. The center of the hurricane, the eye, is calm, and there the skies are nearly clear. As the moist air rises, condensation releases energy that further warms the air, increasing the speed of circulation. This brings in more moist air which releases more energy, and in this manner the system expands.

Photosynthesis Photosynthesis

Photosynthesis uses the energy of light to make the sugar, glucose. A chemical equation for photosynthesis is:

                                6 CO₂ + 12 H₂O +      light     → C₆H₁₂O₆ + 6 O₂ + 6 H₂O
                         carbon dioxide + water + light energy → glucose + oxygen + water

    Photosynthesis occurs in two stages. In the first phase light-dependent reactions capture the energy of light and use it to make high-energy molecules. During the second phase, the light-independent reactions use the high-energy molecules to capture carbon dioxide (CO₂) and lead to the formation of glucose.
     In the light-dependent reactions one molecule of chlorophyll absorbs one photon and loses one electron. This electron allows the start of a flow of electrons that is used for the synthesis of ATP. The chlorophyll molecule regains the lost electron by taking one from a water molecule and releases oxygen gas as a waste product.
    In the Light-independent or dark reactions an enzyme captures CO₂ from the atmosphere and forms glucose.
    Photosynthesis may simply be defined as the conversion of light energy into chemical energy by living organisms. It is affected by its surroundings and the rate of photosynthesis is affected by the concentration of carbon dioxide, light intensity and the temperature.

Absorption and Radiation of Energy

An object exposed to solar radiation of any wavelength will absorb energy and warm up. Of course, depending on the characteristics of the material, some radiant energy is reflected. White snow reflects most of the radiation in the visible range. A black body is an almost perfect absorber, of light, and emitter, of heat.

A warmed object, in turn, reradiates electromagnetic energy. Since the electromagnetic spectrum of the radiant energy emitted depends on the absolute temperature of the radiating body, more of the radiation emitted from extremely hot bodies will be in the shorter wavelengths; colder bodies will emit more radiant energy in the longer wavelengths. A wood-burning stove emits infrared radiation even though it may not be obvious just by looking at it that it is hot. An incandescent lamp is so hot at the filament that it emits visible light as well as invisible radiant energy. Most of the solar radiation is in the visible light spectrum.

Ozone Ozone Layer Ozone Ozone Destruction

If all the short wavelength radiation reached the earth’s surface, it is doubtful if higher life forms, including human beings, could survive. In the upper atmosphere, about 15 to 50 kilometers above the earth’s surface, the energy in sunlight causes oxygen molecules (O₂) to dissociate to form atomic oxygen (O). Atomic oxygen in the presence of sunlight and other particles combines with oxygen molecules (O₂) to form ozone (O₃). The ozone selectively absorbs the portion of solar radiation in the short wavelength range, thus preventing most of the ultraviolet, X, and gamma radiation from reaching the earth’s surface. The radiation reaching lower levels is thereby limited to those wavelengths longer than 0.3 micron.

When products discharged into the atmosphere are stable—that is, they do not readily degrade—their effects are cumulative. So while it is difficult to imagine a little squirt of hair spray changing the world, billions of squirts can make a difference if the propellant is a stable fluorocarbon. Over time the fluorocarbons diffuse over the earth and up to the stratosphere. At altitudes above 25 kilometers the fluorocarbons will degrade as they absorb solar energy, releasing some chlorine atoms. The chlorine in turn reacts with ozone, depleting the ozone concentration. The ozone layer in the upper atmosphere might be irreversibly depleted by this reaction. As with other global issues, an international strategy is necessary to deal with this problem. Sweden, Canada, Norway, and the United States have taken actions to control the use of fluorocarbons as aerosol propellants.

Ozone* is a highly reactive gas consisting of 3 oxygen atoms (O3). Ozone is frequently mentioned in the news these days. You may hear "the ozone layer is being depleted; don’t use products containing CFCs that harm the protective ozone layer". Next you hear "the air quality index is high today due to ozone pollution; ground level ozone causes breathing difficulties for sensitive population groups." So which is it - good or bad? The answer is both! The protective ozone layer in the upper atmosphere is very different from ground level ozone pollution, also known as photochemical smog.

The ozone layer in the stratosphere occurs more than 10 miles above the surface of the earth. This thin, high altitude, shield protects the earth from the sun’s ultraviolet rays. The ozone molecules block many of the harmful rays. The thicker the ozone layer, the greater the protection. Scientists know that chlorofluorocarbons (CFCs) deplete the ozone layer. Chlorofluorocarbons are lowering the average concentration of ozone in the stratosphere. This stratospheric ozone blocks UV-B radiation to the earth' s surface. UV-B causes sunburn, cataracts and skin cancer. We can protect the ozone layer by stopping production of all ozone-depleting chemicals. Many countries have banned CFCs and the Montreal Protocol and other agreements have reduced emissions of CFCs. Use of CFCs is decreasing, but the chemical can still be found in many air conditioning and refrigerant systems, industrial processes such as plastic foams and in cleaning solvents. CFCs were also previously used as propellants in spray cans. Scientists predict there will be increased numbers of people with skin cancer and depressed immune systems as the size of the ozone layer decreases. There could also be reduced crop yield, an increase in ground level smog, and reductions in oxygen producing microorganisms in the oceans.

Ozone that occurs at ground level - where people breathe - can be a very serious problem. In the Great Lakes region, ground level ozone is a warm-weather phenomenon which develops through the reaction of sunlight with nitrogen oxides and volatile organic compounds (VOCs). Ozone can occur hundreds of miles from where VOCs and nitrogen oxides are emitted into the atmosphere: it’s not just a big city problem. Ozone damages crops, forests, and materials such as plastics and rubber. Adverse health effects include eye irritation, decreased vision, increased asthma and chronic lung disease incidence, coughing, dizziness, nausea, and reduced heart and lung capacity. People who exercise heavily during periods of elevated ozone levels are included in the most sensitive category. Many scientists believe the air quality health standards for ground level ozone provide little margin of safety and need to be strengthened to reflect current ozone research.

"Why not build a giant fan to blow all the ground level ozone into the stratosphere to patch up the ozone layer?" Unfortunately, solutions to our ozone problems are not that simple. But there is something we all can do to reduce the ozone problem ...

· Drive less, consolidate trips, walk, bicycle, use mass transit

· Purchase fuel efficient vehicles

· Keep vehicles tuned up; repair faulty emission control equipment

· Keep paint cans and solvent products tightly sealed when not in use

· Don’t burn refuse

· Support environmentally conscious manufacturers and products

· REDUCE, REUSE, RECYCLE

Climate Climate Currents Climate

Climate is commonly considered to be the weather averaged over a long period of time. The Intergovernmental Panel on Climate Change definition is: “the “average weather”, or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. The classical period is 30 years, as defined by the World Meteorological Organization. These quantities are most often surface variables such as temperature, precipitation, and wind.”

When Alfred Wegener proposed a theory of continental movement, he thought that apparent changes in climate (revealed by fossils and other signs found on continents) could be explained by continental migration to higher latitudes. He believed it was more likely that the continents moved rather than the basic air circulation patterns changed. The forces which control air movement, on first appraisal, seem to be beyond society’s ability to control. Even though the amount of energy generated by the sun is beyond our control, we can change the composition of the atmosphere in ways that will determine the amount of sunlight energy that will reach the earth and be retained.

Ocean currents redistribute heat and influence climate and vegetation especially along coastal areas. Dissolved oxygen and nutrients are distributed by currents to aquatic organisms. Upwelling of water containing oxygen support large populations of phytoplankton, zooplankton, fish and fish eaters. Normal current upwelling can be affected by climate pattern changes such as El Nine-Southern Oscillation or ENSO. The upwelling suppression decreases coastal fish populations and a strong ENSO can trigger extreme weather over two-thirds of the world. The earth's average temperatures or climate can be affected by Atmospheric Greenhouse Gases and the Ozone layer. Greenhouse gases trap heat radiating to the atmosphere and radiate the heat back to earth's surface. Normal levels of greenhouse gases make the earth's surface comfortable for life; however material or human induced global warming could have disastrous consequences for many forms of life.

Carbon Dioxide and Oxygen Cycle Carbon Cycle and Oxygen Cycle

The temperature of the earth remains relatively constant because the solar energy absorbed by the earth is radiated back into space. Water vapor absorbs radiation strongly at 5 to 7 microns and above 12 microns. Carbon dioxide absorbs best between 4 and 5 microns and above 14 microns. Most of the incoming solar radiation is able to pass through air containing carbon dioxide and water vapor because most of its electromagnetic energy is in the shorter wavelengths. However, as the earth radiates heat back into space, the shift to the longer wavelengths puts the radiation in a range readily absorbed by water vapor and carbon dioxide. Therefore, any increase in the carbon dioxide content of the atmosphere may result in more of the outgoing earth radiation being absorbed in the air and a warming of the earth’s atmosphere. This warming effect has become widely known as the greenhouse effect, even though a greenhouse behaves quite differently.

Variations in the carbon dioxide concentration in the atmosphere have the potential to generate climatic change. Increasing rate of combustion of fossil fuels (oil, coal, and gas) in the United States and elsewhere and combustion of fuels, volcanic activity, and decomposition of vegetation put carbon dioxide into the air. The increase in carbon dioxide concentration is about one-half the amount expected from the rate of burning fuel. Several natural processes seem to be moderators. The oceans dissolve carbon dioxide and it is stored as carbonates and bicarbonates. An increase in carbon dioxide in the air acts as a stimulant in plant growth and thus more carbon is fixed in plant parts. Carbon fixed in marine organisms is deposited in the ocean when the organism dies, effectively removing that carbon from any cycle.

Warming or cooling of the atmosphere is important because it could influence vast climatic changes, such as glacial recession or expansion. In recent history the temperature of the earth increased from the 1800s to the 1940s, but it has decreased since the 1940s by 0.3⁰C. There is no indication that this fluctuation is associated with pollution. Short-term increases or decreases in temperature of about 2⁰C over a period of a decade have been experienced without great ecological changes. We know that glacial periods are associated with accumulation of snow over thousands of years and that there appear to be cyclical interglacial periods when glaciers melt and retreat. The cause of these cycles is not clear. At present, some scientists think we are nearing the end of an interglacial cycle. Perhaps a warming of the atmosphere will delay the next glacial period. However, more cloud cover and more particles in the air could reflect heat, increasing cooling tendencies. These trends and their influences will be debated for some time.

We can slow possible global warming by reducing global CO₂ emissions, natural gas emits smaller amounts of CO₂than coal or other high carbon fuels, phase out government subsidies for fossil fuels, and phase in carbon taxes, trade and sell emission permits in global marketplaces, halt deforestation and plant massive reforestation projects. The cheapest way to reduce CO₂ emissions is to improve energy efficiency and produce less carbon dioxide.

Greenhouse Gases and the Kyoto Protocol Major Greenhouse Gasses from Human Activities

Greenhouse Analogy: Energy from the sun in the form of some ultraviolet and visible light (short wavelength) passes through the glass of the greenhouse. As the light strikes various surfaces in the greenhouse and they are heated. These surfaces in turn re-radiate the heat in the form of infrared radiation (long wavelength). However, the IR radiation is blocked from escaping by the glass. IR is not able to pass through the glass, hence the greenhouse air heats up fairly dramatically. The greenhouse gases have the same property as the glass towards the IR radiation. Think of the greenhouse gases acting as an invisible glass shield around the earth.

The "stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous interference with the climate system is the purpose of the Kyoto Protocol. The Intergovernmental Panel on Climate Change has predicted an average global rise in temperature of 1.4°C to 5.8 °C between 1990 and 2100). Current estimates indicate that even if successfully and completely implemented, the Kyoto Protocol will reduce that increase by somewhere between 0.02 °C and 0.28 °C by the year 2050

Both presidents Clinton and Bush oppose the Kyoto Protocol because it exempts 80 percent of the world, including major population centers such as China and India, from compliance, and would cause serious harm to the U.S. economy. The Senate's vote, 95-0, shows that there is a clear consensus that the Kyoto Protocol is an unfair and ineffective means of addressing global climate change concerns. Bush supports a comprehensive and balanced national energy policy that takes into account the importance of improving air quality. Consistent with this balanced approach, He intends to work with the Congress on a multi-pollutant strategy to require power plants to reduce emissions of sulfur dioxide, nitrogen oxides, and mercury. Any such strategy would include phasing in reductions over a reasonable period of time, providing regulatory certainty, and offering market-based incentives to help industry meet the targets.

Heat Islands

Human activities can modify the weather in unintentional ways. On a small scale, brick, concrete, and other construction materials in urban areas absorb and hold the sun’s heat. Heating, air conditioning, and generation of electricity result in waste heat; consequently in large urban areas acting as heat islands. The air circulation pattern between urban and rural areas is similar to the sea breezes induced by convection currents when the atmosphere is relatively stable. When there is a wind, the pattern resembles a plume moving downwind from a huge smokestack. This localized pattern of air circulation transports urban air pollutants, such as auto exhaust and the resulting ozone and other oxidants, to rural areas. In addition to the heat island effect urban areas also experience increased fog and precipitation associated with particulate matter discharged into the air, especially from burning coal. As London has eliminated air pollution, the weather has changed to more days of sunshine and fewer of dense fog.

Cloud Seeding

Intentional efforts to modify the weather are directed at dispersing fog, suppressing hail and lightning, inducing rainfall, and reducing the intensity of tornadoes and hurricanes. Rain is induced in moist air when drops or ice crystals become sufficiently large to begin falling. Cloud seeding with silver iodide crystals is a method which provides a nucleus for freezing super cooled cloud droplets, which then leads to the growth of precipitation-sized particles. Cloud seeding efforts have been controversial. The effectiveness of seeding is debatable, although some investigators think that 10 percent or more additional precipitation may be induced. In addition, there are serious legal and political questions. Clouds seeded over South Dakota were followed by 0.3 meter of rain that caused a flash flood in Rapid City, killing many people. Thus indicating that the potential hazard is real. Other efforts to dissipate the force of hurricanes by seeding have raised questions about the desirability of interfering with one of the ways that heat accumulations at the equator are rapidly dispersed toward the poles. Some meteorologists fear drastic climatic changes if hurricanes are suppressed.

Air Circulation And Weather Patterns Graphic - Global Cloud Patterns

Air circulation patterns are influenced by a complex array of factors. A major influence is the absorption and release of heat by the atmosphere, land masses, and bodies of water. When the sun shines, the temperature of oceans and lakes rises more slowly than that of land. When there is no sunshine, as at night, the temperature of the water bodies falls more slowly. Wind and wave action may act to mix the water so that heat absorbed at the surface is distributed downward in the water to a depth of as much as 100 meters. However, heat penetrates the ground to very shallow depths. Because land heats and cools more rapidly than water and the heat storage in land is limited by the shallow depth of penetration, adjacent bodies of water tend to moderate the local temperature on shore by absorbing large quantities of heat in hot weather and releasing it in cold weather.

Land temperatures change rapidly while ocean temperatures are relatively constant, with the result that the ocean is cooler than the land in the daytime and warmer at night. These conditions favor the movement of air associated with sea breezes in the morning and land breezes in the evening. Furthermore, prevailing winds induce ocean currents, which carry warmed water from the equator toward the poles. At the poles their stored heat is released, thereby distributing heat over the earth. Also, the heat stored in the oceans in the summer is released to the atmosphere in the winter. Both of these actions moderate the climate.

Places where circulating air warms and rises tend to be areas of low pressure (lows), and where the air cools and subsides, areas of high pressure (highs). Winds occur when air moves from high pressure to low pressure areas. Because of the influence of the earth’s rotation (Corollas effect), air flows clockwise around highs (anticyclones) and counterclockwise around lows (cyclones) in the Northern Hemisphere. Near the ground, surface friction tends to reduce the Corollas effect, resulting in a spiral flow outward away from the anticyclone (high-pressure system) and inward toward the center of cyclone (low-pressure system).

These basic systems of air motion not only influence weather patterns, but also affect the distribution of air pollutants. For example, when a high-pressure system is stationary over Bermuda, the basic clockwise air motion will tend to sweep air pollutants along the eastern seaboard of the United States from Richmond, Washington, Baltimore, Philadelphia, and New York City to the New England area.

Warm and Cold Fronts

The development of cyclonic air circulation systems and the movement of high- and low-pressure systems across the country may cause relatively warm (less dense) air to move over cooler (denser) air. The intersection of these dissimilar air masses is a warm front. If the warm air is uplifted, rain may be produced. Warm air is also uplifted at ground level where the leading edge of relatively cooler air moves in under warmer air, as with a cold front. This also causes shower activity.

Clouds associated with rainstorms or approaching storms are formed in layers and are called stratiform clouds. Thin, feathery clouds known as cirrus clouds appear at a high level (6-18 kilometers) and are often an indication of an approaching storm. Cirrostratus clouds form a thicker layer at a high level. Altostratus, a middle-level (2-6 kilometers) cloud, appears as a uniform white or gray layer and is thick to the point of obscuring the sun. Nimbostratus clouds are low (0-4 kilometers) clouds in a uniform gray layer from which rain falls.

Jet Streams

Jet streams are normally thousands of kilometers long, more than a hundred kilometers wide, and a few kilometers thick, and they move at a speed in excess of 30 meters per second. In both hemispheres, the surface air temperature is relatively uniform over wide areas except for a sharp change in horizontal temperature gradient at the boundary between cold polar air and warm tropical air, which is called the polar front. Blowing from the west, the two polar front jet streams meander around the earth above these polar fronts. Another jet stream flows above the subtropical high-pressure belt during the winter season only. In the hemisphere experiencing winter, a polar-night jet stream develops at a height of 32 to 48 kilometers at middle to high latitudes due to equatorial and polar temperature differences in the stratosphere. Jet streams tend to narrow at places where their speeds are extremely high, becoming jet maximums.

Jet streams maximums are always associated with strong fronts in the lower atmosphere. In the Northern Hemisphere, areas of low-pressure air will be to the left and areas of high-pressure air to the right of a jet stream. Air tends to ascend in the low-pressure area and descend in the high-pressure area. Thus, the jet streams are involved in horizontal transport and vertical mixing of ozone and air pollutants.

Cyclonic Air Movements

The sun warms the surface of the ocean and evaporates water. Each gram of water evaporated represents 580 calories of heat waiting to be released when the vapor condenses. The buildup of heat in the late summer makes the area ripe to produce thunderstorms. When this tendency for storms is combined with a cyclonic weather system moving through the area, the thunderstorms may be so intense as to release sufficient heat to warm the air over a large area. The rising warm air creates a local low pressure area, and air flows around and inward toward the low-pressure center. The spiraling of air inward causes the speed to increase. As the moist air rises, condensation releases energy that further warms the air, increasing the speed of circulation. This brings in more moist air which releases more energy, and in this manner the system can expand.

A tornado is another type of cyclone, but is much smaller in diameter than a hurricane. Tornadoes are about 100 meters to 1 kilometer in diameter, with wind speeds exceeding 200 meters per second. In addition to damage caused by wind speed or by propelling objects through the air, there is very low pressure in the center of a tornado which causes buildings to explode. Tornadoes usually form over land when cooler, drier air moves rapidly over warm, moist air. This creates an unstable condition, and the rising warm air creates a turbulent situation. The condensation of the water vapor releases energy to warm the air more and to speed up the circulation. Although tornadoes may occur at any time, they are frequently spawned in the spring when there is a maximum temperature differential between the cold and warm air masses. They are also associated with severe thunderstorms and may be produced on the fringes of large hurricanes.

Not all cyclonic systems are as violent as hurricanes and tornadoes. The vast majority of cyclones are the low-pressure systems that produce a great deal of the weather. High-pressure systems (anticyclones) are usually characterized by fair weather because the descending air becomes warmer as air pressure increases and any droplets evaporate. Wind speeds and mixing depths are usually lower in anticyclones. Because there is less rapid dispersion and diffusion, higher concentrations of pollution are usually associated with the highs.

Because intense storms like hurricanes and tornadoes often endanger human life and property, hazard management systems have evolved to deal with them. These management systems involve procedures for forecasting and warning, hazard protection, and disaster relief and recovery

Air Pollution The Human Body and Pollution

Air pollution can affect the earth’s heat balance and modify climate and weather patterns. Atmospheric conditions also influence the severity of air pollution. Sunlight produces photochemical smog, and atmospheric inversions can cause pollutants to accumulate in dangerous concentrations. Wind can transport pollutants many miles from their source, causing effects such as acid deposition.

With the use of coal for power in industry and locomotives, smoke became a nuisance in many cities. After conditions became so bad you could barely discern the sun at midday, Pittsburgh pioneered in attacking the smoke problem, mainly by restricting the burning of soft coal.

Near the beginning of this century, acid fumes from a smelter at Copper Hill, Tennessee, completely denuded the land in the area, creating a “devil’s playground” of barren eroded hills. Other forms of air pollution have since been found to affect all kinds of vegetation.

Thermal Inversions

In the 1940s another type of air pollution was recognized in the Los Angeles area. This form of air pollution was most severe on sunny days, when there were also temperature inversions. Vegetation damage was observed in 1944, and as the problem became more severe, eye irritation caused tearing. In the 1950s it was demonstrated that auto exhaust gases, when irradiated by sunlight, formed compounds that had oxidizing and irritating qualities. This chemical soup was called photo-chemical smog. Major air pollution episodes resulting in human deaths have involved an interaction of atmospheric stratification referred to as an inversion, which places a “lid” over the polluted area and prevents dispersion of the pollutants.

Under normal conditions, the temperature of air declines with height, but under conditions of zero or low wind an inversion might occur, a condition where a band of warmer air overlays cooler air. Such inversions may be caused by any of several conditions. When the sun sets, the ground cools more rapidly than the air. Nocturnal cooling of air next to the ground frequently leaves a layer of warmer air immediately above. A nocturnal inversion breaks up when the early morning sun warms the earth, heating the air next to it On a larger scale, the overrunning of cooler air by a warmer air mass or the subsidence of a warmer air mass over a layer of cooler air causes an inversion that will not break up until the weather system changes. Also, a wedge of cooler air may move in underneath warmer air.

When no inversion exists, a discharge of warm gases from a smokestack will be buoyed upward and dispersed by the wind. However, when there is an inversion, there is little if any horizontal air motion. The stack discharge rises until it encounters the inversion layer, whereupon it ceases rising. Inversions lead to a concentration of pollutants discharged into the atmosphere. The pollutants accumulate at the inversion level, gradually spreading out horizontally in all directions and diffusing downward. Since the concentration of pollutants will be a maximum at the inversion layer, this is not good for persons who live on upper floors in high-rise buildings if that is the level of the inversion layer. The concentrations at ground level can also exceed safe limits during an inversion with deadly results.

Human Body and Pollution Name that Poison

The toxicity of two different substances can cause different effects even though the concentrations and duration of exposure are identical and the test animals exposed are as nearly alike as possible. The difference in effect is caused by toxicity. Toxicity is commonly measured by how much of a substance kills 50 percent of exposed animals, a quantity called LD50. The National Institute of Occupational Safety and Health publishes a list of toxic substances and their known toxic effects.

Individual susceptibility depends on the person’s health history. People with lung and heart ailments are most affected by air pollutants, as are the very young and the aged. Individuals who are allergic to certain substances are sensitive to lower exposures and have worse reactions when exposed to those substances.

We are also aware that greater reaction is produced when a person is exposed to two or more of certain substances simultaneously than when exposed to either substance alone. This effect is called synergism. Such combined effects have been noticed in community air pollution episodes where the concentration of a pollutant in the air appears to cause adverse reactions at levels below those observed in laboratory experiments.

As scientists link some 60 to 90 percent of cancer to environmental stimuli, air pollutants become suspect. More lung cancer occurs among persons living in urban and industrial areas than among those in rural areas and among persons raised in areas of high air pollution than among those in areas of low pollution. However, cancer cannot definitely be attributed to air pollution on this basis alone.

Air Pollution Effect on Vegetation

Air pollution effects on plants can best be seen near the source of pollution. For example, tree foliage along turnpikes is damaged in a band where fumes from diesel truck exhaust touch the leaves. Cement dust deposited on leaves, when moistened, will form incrustations; other dusts plug the leaf openings, or stomata. Where ozone levels are high, pine needles turn brown and die (necrosis). Sulfur oxides can cause acute injury, resulting in tissue drying to an ivory color or darkening to a reddish brown. Just as some pollutants can damage plants, deposits of arsenic, lead, and fluoride on leaves or grass can poison grazing animals. Pollutants also reach plants through the soil. Cement dust makes soil more alkaline and acid rain makes it less so. A soil that is too acid will be completely barren. Vegetation injury in the Los Angeles area was first attributed to photochemical smog. Since then, ozone has been identified as the major culprit. Ozone possibly causes more damage to vegetation in the United States, trees, flowers, and crops, than any other air pollutant.

Types of Air Pollution

There are many point sources of air pollution that cause hazards or concern to immediate neighbors: metal fumes from a smelter, smoke from the boiler of a dry cleaning plant, smoke from burning leaves, and smoke and odors from backyard barbecues. An accumulation of pollution emitted from many point sources, or a few large ones, can affect the air quality of an entire region.

A serious problem has been pollution from increasing numbers of autos, trucks, buses, and other mobile sources. Also contributing to region wide air pollution are heavily traveled highways, and shopping centers and sports and amusement centers. Government programs aimed at controlling these sources of air pollution in the United States began with cities and states. With passage of the Clean Air Act, the federal programs became dominant.

Particulates are produced by burning coal which creates unburned or incompletely burned particulates of carbon (smoke and soot) and solid residue (fly ash). More complete combustion results when there is adequate air and mixing of combustion gases above the burning coal bed. Oil will also produce particles, but not to the same extent as coal. However, an inadequate air supply to burning oil will produce soot, a process sometimes done intentionally to make lamp black. Substituting natural gas for coal and oil would eliminate particulate emission problems from combustion, but because it is scarce it is reserved for home heating and manufacture of synthetic materials. Similarly, nuclear plants do not have these air pollution problems, but people have other concerns about using nuclear fuel. The social and economic costs and benefits, including environmental impacts, need to be evaluated in order to choose the best fuel system. Dusts, another form of particulate matter, are produced from a variety of manufacturing processes which involve grinding and crushing or the handling of dusty materials, cement plants, asphalt plants, foundries, and so on. Construction and demolition make dust which can blow away (fugitive dust). Particles from combustion and dusts from manufacturing and processing can be captured by simple air cleaning equipment. Among the most used are cyclones, scrubbers, bag houses, and electrostatic precipitators.

By putting a high electric charge on a wire, electrostatic precipitators create a charge on particles in the air-stream. A grounded plate is placed between the wires to collect charged particles, which slide down the plates to a hopper at the bottom for withdrawal. This system works very well on particles that become electrically charged, like carbon. Its efficiency depends on the amount of energy put in the charge, the number of precipitators in the series, and the temperature of the air-stream. Sometimes electrostatic precipitators are used after cyclones. Under some conditions, overall collection efficiencies as high as 99 percent can be achieved. Again, the collection is more efficient for larger particles than for those in the respirable range.

Particles discharged from volcanoes or from industrial smokestacks can restrict the amount of sunlight reaching the earth. This phenomena could lead to a cooling of the earth’s atmosphere and possibly reduce or eliminate the Summer thus affecting the crops. The eruption of Tambora in 1815, which killed 12,000 people, discharged 80 cubic kilometer of rock fragments into the atmosphere. Some of the small particles remained in the stratosphere and circled the earth affecting the average temperature. The following year, known as the “Year Without Summer,” affected crops in northern parts of the United States, causing reduced yields.

Sulfur oxides and particulate matter are thought to be a principal cause of deaths in air pollution episodes and a continuing cause of bronchitis and emphysema in lesser concentrations, there is great concern about sulfur oxides. Some oxides of sulfur are emitted by smelters, oil refineries, and paper mills, but community pollution is usually caused by burning fuel that contains sulfur. When such fuel is burned, most of the sulfur converts to sulfur dioxide and a small fraction converts to sulfur trioxide. Sulfur dioxide is partly oxidized to sulfur trioxide by photochemical processes, and moisture will convert sulfur trioxide to sulfuric acid. Sulfur dioxide can be controlled by switching to a low-sulfur fuel such as natural gas. But, because it is scarce, natural gas is no longer practical for power plants. Furthermore, low-sulfur coal and oil (with less than one percent sulfur) is in limited supply.

Carbon Monoxide is the major source of community pollution in the internal combustion engine. Carbon monoxide is absorbed through the lungs and reacts with the hemoglobin of the blood to form carboxyl hemoglobin (CO Hb). Hemoglobin has an affinity for carbon monoxide that is 200 times stronger than for oxygen, preventing oxygen from reaching body tissues. Absorption increases with carbon monoxide concentration, duration of exposure, and ventilation rate of lungs, which varies with exercise. However, carbon monoxide is expired and an equilibrium is reached after a period of exposure. Cigarette smokers have a carboxyl hemoglobin level of about 5 percent, contrasted with non-smokers at 0.5 percent. Nonsmokers exposed to similar concentrations had visual acuity impairment and had trouble estimating time. From this evidence it appears that there might be no safe threshold for carbon monoxide exposure. Carbon monoxide is a special problem for street traffic and tunnel police officers and for underground garage personnel. Ventilation can help persons who work in tunnels and garages. Traffic police in Tokyo have been equipped with gas masks and oxygen supplies.

Nitrogen Cycle

Oxides of nitrogen (NO₂) and hydrocarbons (HC) undergo chemical reactions with each other and other compounds when exposed to sunlight. These photochemical reactions produce strong oxidizing agents or oxidants, chiefly ozone. While ozone in the upper atmosphere is beneficial, high concentrations near the ground are undesirable. The complex mixture of pollutants generated in this way is called photochemical smog. The operation of internal combustion engines is so designed as to be an ideal producer of nitrogen oxides, although this is not the only source.

Lead Sources of airborne lead are primarily smelters and automobile exhaust. Smelters may be a problem for nearby residents. Lead concentrations due to auto exhaust will be greatest near heavily traveled streets and highways.

Devices Used by Industry to Remove Air Borne Pollution