BSCI 124 Lecture Notes
Undergraduate Program in Plant Biology, University of Maryland
LECTURE 38 - Atmosphere and the Environment
I. THE ATMOSPHERE
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A. The atmosphere is a thin layer of gasses that envelope the earth (picture).
It is composed of gasses held close to the Earth by gravity and the thermal
movement of air molecules
B. The major gasses in the atmosphere are nitrogen (78%), oxygen
(21%), argon (0.9%), and carbon dioxide (0.03%). The atmosphere also contain
trace amounts of numerous other elements and compounds
C. The atmosphere
is divided into several layers:
200 km
100 Thermosphere
80
70 Mesosphere
50
30 Stratosphere
10 Troposphere
0
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1. Thermosphere - layer greater than 90 km
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a. the hottest layer of the atmosphere (can reach 1300-1800 degrees Celsius);
heat from absorption of solar radiation by oxygen molecules
2. Mesosphere - layer about 70-80 km
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a. atmosphere reaches coldest temperatures (about -90 degrees Celsius)
3. Stratosphere - layer about 20-50 km
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a. where commercial jets fly
b. has a steady wind (but no turbulence or other weather)
c. temperature increases with altitude because ozone gas absorbs ultraviolet
radiation creating heat
4. Troposphere - layer closest to Earth's surface; extends up to about
8-18 km (depending on location)
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a. weather
occurs in the troposphere; area that gets smog pollution
b. contains abut 75% of the total mass of the atmosphere
c. maximum air temperatures of this layer occur near the surface (air
temperature drops with increasing height at a rate of 6.5 degrees Celsius
per 1000 meters
II. FOSSIL FUELS
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1. Coal (solid organic material) - formed from Carboniferous Period (300-350
million years ago) when most of the land was low and swampy; trees (horsetails,
ferns, club mosses, gymnosperms) died but were covered over before they
were decomposed - little oxygen for decomposition; over time, heat and
pressure ---> peat and later ---> coal
2. Oil and natural gas (liquid and gaseous organic material) - Actual
process is not well understood, but organisms that contributed to oil and
natural gas were probably planktonic
B. Environmental
effects of burning fossil fuels - the release into the atmosphere of
particulates including:
1. sulfur dioxide - from burning fossil fuels, mostly coal in power plants
2. carbon monoxide - about 90% in the atmosphere is from natural sources,
and 10% comes mainly from fires, automobiles, and other sources of incomplete
burning of organic compounds
3. nitrogen oxides - from automobiles and power plants that burn fossil
fuels
4. hydrocarbons - about 80% from natural sources, and 20% primarily
from automobiles
III. ENVIRONMENTAL CONSEQUENCES OF BURNING FOSSIL FUELS
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A. Acid rain
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1. cause
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a. acid rain is the acidic depositions that occur near or downwind of areas
where there are major emissions of sulfur dioxide and nitrogen oxides
b. in the atmosphere they are transformed by reactions with oxygen
and water to form sulfuric and nitric acids
c. they fall from the atmosphere in the rain
d. review these national maps of acid rain from the National Atmospheric
Deposition Program/National Trends Network:
2. effects
B. Global
climate change - probably the most pressing environmental problem
today
1. causes
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a. greenhouse effect: carbon dioxide and other greenhouse gases (nitrogen
oxides, ozone, CFCs, and methane) released into the atmosphere from human
activities trap the infrared wavelengths of radiant energy so that the
heat is not dispersed into space
b. works like insulation
-
1) review short wave and long wave radiation (long wave = infrared = heat)
- example - park your car in the summer sun with windows rolled up; your
car ends up like a oven, the glass traps the heat inside
c. carbon dioxide
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1) carbon dioxide is a trace gas (less than 1%) in our atmosphere
2) natural biological source is respiration; natural sink (what removes
the gas) is photosynthesis
3) until 150-200 years ago carbon dioxide in = carbon dioxide out
4) Why
is carbon dioxide increasing?
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a) burning fossil fuels
b) deforestation - has been estimated that 25-30% of carbon dioxide
being added to the atmosphere is due to deforestation; from burning the
forests and removing the carbon sinks
5) see this figure
from W.H. Freeman Publishing
2. effects
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a. 2030 - doubling of CO2 projected (since
beginning of Industrial Revolution) resulting in surface air temperature
changes (see
chart)
b. 3-8 degree F temperature
increase in the next 100 years
1) 1997
warmest year of the century
2) 1997-98
warmest winter on record
3) 1998
- each month January through May has set a new all-time record
high global
temperature
4) 1998
warmest year of the millennium
c. rise in sea level = flooding of coastal areas and islands; loss
of land (1 foot rise will cause 10 mile loss in Florida) - warmer water
expands, ice melts
d. increase in severity and frequency of storms in coastal areas
e. expanding deserts in interior of continents (U.S. grain belt) and
a loss of water resources
f. loss of species diversity
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1) many species are already under stress from other causes; this will push
them over the brink
2) will trees be able to migrate fast enough to keep pace with the
change in climate? - climate change too rapid
g. changes in agriculture due to environmental change (see the CIESIN
link)
h. humans living along coastal areas (Bangladesh and Egypt) or in drought
areas will become environmental refuges; where will they go?
i. there may also be an increase
in human diseases with the spread of the tropics and tropical diseases
and the effects of increased temperature on the human body
3. solutions
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a. developed nations must cut back on emissions (20% of population consumes
80% of world's resources)
b. develop alternative, non-polluting energy sources (solar and solar
hydrogen, wind) - only nuclear can presently supply large amounts of energy
c. plant trees (plants use CO2)
d. develop energy-efficient products and conserve energy; example-
fluorescent light bulbs - use energy conservation measures
e. develop mass transit and reduce automobile use
f. involve developing nations in global climate change efforts
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1) during 1990s, 96% of population growth will occur in developing nations
2) as developing countries become industrialized, they will emit large
quantities of greenhouse gases
IV. THE OZONE PROBLEM
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A. Ozone (O3) - a form of oxygen
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1. It is naturally created in the Stratosphere when ultraviolet radiation
breaks down the oxygen molecule (O2) into
two individual oxygen atoms. Each of these atoms combines with an O2
molecule to form ozone
B. Essential in one part (stratosphere) and a pollutant in another
part of the atmosphere (troposphere)
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1. Ozone
shield - the stratosphere (layer above the troposphere) is the location
of ozone shield
-
a. ozone in stratosphere forms naturally- oxygen reacts with incoming ultraviolet
(UV) radiation (from sun) to form ozone - pollution is breaking down faster
than replenished
b. stratospheric ozone blocks
much of the UV from penetrating to Earth's surface - reflects it out;
approximately 99% of all ultraviolet solar radiation is absorbed or screened
out in the ozone layer
c. ozone depletion
in the stratosphere (see
TOMS image)
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1) cause
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a) ozone is broken down by human-made pollutants. Primary cause chlorofluorocarbons
(CFCs) - used as propellants in aerosol cans, as coolants in a.c. and refrigerators,
as foam for insulation and packaging, as sterilizers for hospitals
b) also caused by halons (in many fire extinguishers), methyl chloroform
(used to degrease metals), and carbon tetrachloride (used to manufacture
pesticides and dyes)
c) all contain chlorine
2) effect
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a) 1 atom of chlorine can destroy 100,000 ozone molecules
b) initially observed over South Pole and later over North pole; ozone
is also thinning everywhere else including North America (see map
here)
c) tropospheric ozone doesn't replenish stratospheric ozone
d) decrease in stratospheric ozone results in an increase in surface
UV levels
3) effects of high levels of UV
2. Smog - ozone
in troposphere formed by human activities (click
here to see ozone map for different regions, orwith
animation)
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a. cause
b. effects
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1) plants - at low concentrations can reduce plant growth rates and at
higher concentrations can kill plant tissues and entire plants
2) animals - the effects on animals involves reduced visibility and
health
problems (eye irritations and aggravate respiratory illnesses)
3) Climate - Involved in global climate change (tropospheric ozone
is a greenhouse gas)
Other Sites of Interest
The effects
of acid rain on forests Acid Rain
Acid rain program
- EPA
Global change data Global
Warming ;
Greenhouse
effect
Ozone
The ozone hole, a multimedia
tour
The science
of ozone depletion - EPA
The
Ozone Layer
Graphing
stratospheric ozone
Smog
The
air that we breathe
Global map
Global
mapping datasets
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BSCI 124 main page
Last revised: 6 April 1999 - Browning
Update Dec 13, 2000 - Straney