Composition of the Atmosphere
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
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 uses the energy of light to make
the sugar, glucose. A chemical equation for photosynthesis is:
+ 12 H2O
+ light →
C6H12O6 + 6 O2
+ 6 H2O
light energy →
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
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
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.
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.
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.
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.
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.
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.
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 ...
consolidate trips, walk, bicycle, use mass transit
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
environmentally conscious manufacturers and products
REDUCE, REUSE, RECYCLE
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.
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 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
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.
can slow possible global warming by reducing global CO2 emissions, natural gas emits smaller
amounts of CO2 than 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
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
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
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
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.
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 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
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,
and New York City to the New
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.
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
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
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 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
transport pollutants many miles from their source, causing effects such as
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
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.
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.
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.
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
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.
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
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
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.
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
Bag houses consist of long sleeves or
bags made of fabric that will withstand high temperatures. As the air stream
enters the sleeve and coats the fabric with particles, the particles are
filtered out as the air passes through the fabric. As the coating builds up,
the system becomes more efficient, but resistance to air flow increases.
Ultimately, the sleeve has to be taken out of service to be blown or shaken
clean. The temperature in the bag house has to be higher than the dew point of
water or any vapors in the air stream to prevent condensation. Bag houses are
used in conjunction with other systems, like cyclones. Efficiencies approach
those of electrostatic precipitators, but bag houses are more effective in
removing very fine particles from the air.
Scrubbers can be simple screens of
water spray that will knock some of the large part home. As particles collect
on the fabric, filtering of fine particles becomes more efficient, but
resistance to air flow increases. The sleeves are then shaken to cause
particles to fall into a hopper.
are composed of two sections, a charging section and a collection section. The
charging section uses ionizer wires to impart a positive charge to the incoming
smoke, fume, and dust particles. The charged particles are then drawn into a
secondary electric field where they are collected on a series of metal plates.
Clean air is then recirculated back into the air.
While most efforts in recent
years have been directed at meeting ambient air quality standards, the Clean
Air Act also covers air pollutants that are considered to present special
health hazards. The EPA has proposed or issued standards for seven hazardous
air pollutants: asbestos, mercury, beryllium, vinyl chloride, benzene,
radionuclides, and arsenic. Other substances under consideration for
designation as hazardous air pollutants are polycyclic organic matter, cadmium,
ethylene dichloride, perchloroethylene, acrylonitrile, methylene chloride,
methyl chloroform, toluene, and trichloroethylene. At present there is no
system for monitoring airborne carcinogens.
biodiversity, biomes and life zones certainly illustrate how everything is
connected. There are three viewpoints concerning global warming; Global warming
is not a threat, Wait until we have more
information before we take action, Take informal action before there is
overwhelming scientific knowledge to justify acting. Some say we should take
actions needed to slow global warming even if there is no threat because of the
environmental and economic benefits. Carbon dioxide emissions need to be
reduced along with other air pollutants.
The quickest and easiest way is to use energy more efficiently.
determines whether a biome is a desert, grassland or forest. Characteristic types of natural, undisturbed
plant communities are adapted to a biome's climate. Precipitation is the major limiting factor
along with temperature and soil type to produce tropical, temperate, or polar
deserts, grasslands and forests. Most
biomes will blend into one another in ecotones or transition zones. Microclimates, soil variations and natural or
man-made disturbances can cause variations in biomes. Climate and vegetation can vary with latitude
can be created by mountains that interrupt surface winds and storm
patterns. The leeward side of the
mountain has less precipitation which is called the rain shadow effect. Large clusters of vegetation such as forests
take up and release water and break up wind patterns. Cities, also, have distinct microclimates
that absorb and hold heat and break up wind flow.
The earth’s unique
oxygen-rich atmosphere, which is necessary for mammal respiration, evolved as a
result of plant photosynthesis. Now human activities, particularly the
combustion of fossil fuels and the destruction of forests, may increase the
carbon dioxide concentration enough to alter the earth’s heat balance. Other
human activities may deplete ozone in the upper atmosphere, with the result
that ultraviolet and ionizing radiation normally absorbed by ozone could reach
the earth. Increased skin cancer or worse results are possible consequences.
The basic air circulation
disperses and transports pollutants. During periods of temperature inversions,
however, pollutants are not dispersed but are concentrated in a particular
area. Pollutants, by absorbing or reflecting solar energy, could alter weather
patterns drastically. So far, attempts to modify the weather, such as cloud
seeding, have been controversial. On the other hand, especially in urban areas,
some human activities have produced unintentional small- and large-scale
effects. Examples are urban heat islands, an increase in carbon dioxide, and
The future of human beings
is related to the condition of the atmosphere because life, food supplies, and
ways of life are bound to the weather. Community air quality standards have
been set for suspended particulate matter, sulfur oxides, carbon monoxide,
hydrocarbons, nitrogen oxides, ozone, and lead. The last five are associated
especially with auto exhaust. Upon exposure to sunlight, hydrocarbons and
oxides of nitrogen will undergo photochemical reactions to form ozone and other
oxidants. Carbon monoxide is produced when there is insufficient oxygen to
complete combustion. Particulate and sulfur dioxide emissions are associated
with stationary combustion, principally processes using high-sulfur coal.
Acid deposition is a problem
of global proportions. It has damaged forests, lakes, and other ecosystems in
Europe and eastern North America. More
recently, evidence of acid deposition has been found in the western United States.
two main factors that determine climate are an area's temperature and the
distribution and amount of precipitation.
Different climates are caused mostly by global air circulation patterns. Air circulation over the earth's surface is determined
solar output changes due to tiny changes in the earth's orbit around the sun
2. uneven heating
of the earth's surface with the equatorial area being hot, the polar regions cold and temperate areas
having intermediate average temperatures
3. opposite seasonal changes in the
northern and southern hemisphere to the earth's tilted axis
4. the earth
rotating on its axis deflect winds (moving air masses) to the right in the northern hemisphere and to the left
in the southern hemisphere. These huge convection cells move heat and water
from one area to another.
5. properties of
air and water affect climate and global air circulation
the equator, moisture evaporates from the ocean, expands as moist, hot air and
moves in upward spirals which cool and release moisture and the heat radiates
into space. (Low Pressure) Cooler drier air sinks and creates an area of
high pressure. The movement of water,
air and heat, vertically and place to place leads to different climates and
Department of Environmental Quality