Environmental Unit 7

COMPOSITION
% in
component importance to life on Earth
atmosphere
- Growth of plants.
nitrogen (N2) 78%
- Mostly comes from volcanic eruptions
- Produced by photosynthesis
oxygen (O2) 21%
- Used in respiration.
- Can create an inert atmosphere that protects
argon (Ar) 0.93 materials from reacting with oxygen or other gases.
- an inert or noble gas
- Used by plants in photosynthesis
carbon dioxide - Greenhouse gas.
0.04%
(co2) - cycled through photosynthesis, respiration and
burning of fossil fuels
- Source for precipitation
water vapour 0.03% (other - Provides most of the natural greenhouse gases
(H2O) gases too) - Vital for existence of life.

Carbon Dioxide 200 years Number of year gases stay in the

atmosphere
Methane 12-17 years

CFCs 1000 years

Nitrous Oxides 114 years

The natural balance of gases in the atmosphere is maintained by various cycles such as the nitrogen
cycle or the carbon cycle. Human activities can alter the composition in many ways. Carbon dioxide is
added by burning fossil fuels and deforestation. Growing rice and keeping cattle both increase
methane levels. We can also reduce some gasses by afforestation or realizing ozone destroying CFCs

STRUCTURE OF THE ATMOSPHERE

- Atmospheric pressure drops with altitude
- Temperature variations are more difficult to predict
- Separated into four levels based on changes in temperature.
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  Troposphere:
Height: From the surface to 8 to 14.5 km
t°: Decreases with height at 6.5 °C/km.
Features: The most dense part of our
atmosphere. Contains almost all
atmospheric water vapour and most of
our weather.

 Stratosphere
Height: 14.5 - 50 km
t°: Stable, then increases with altitude due
to the ozone layer ( -50 ° to 0 °)
Features: A zone of dry, thin air that is cold
and clear. It contains the ozone layer
which absorbs and scatters incoming solar
radiation and protecting us from harmful
UV radiation.

 Mesosphere
Height: 50 - 85 km
Temperature: Decreases with altitude to about -80 °C.
Features: The coldest layer of the atmosphere. Ice clouds form here that are visible at sunset.
Meteors burn up in this layer.

 Thermosphere
Height: 85 - 600 km
Temperature: Rises continually up to 1000 °C
Features: This layer is so thin, that although the air molecules are hot, to us it would be freezing. The
International Space Station orbits in this layer. The lower part is where highly energy charged particles
from the sun strike the atmosphere and form the beautiful aurora seen in polar regions.

 Exosphere
Height: 600 - 10 000 km
Temperature: Highly variable; too little air to measure
accurately.
Features: This is the uppermost part of our atmosphere which merges into space. This is where many
satellites orbit the Earth.
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NATURAL GREEN HOUSE EFFECT
The greenhouse gases absorb energy from the sun, creating a natural greenhouse effect that warms
the Earth's surface. This makes Planet Earth habitable for life. Without these gases the average
temperature of the Earth's surface would be -18°C, instead of today's average of -15°C.

GREEN HOUSE GASES:

o Carbon dioxide 65%
o Methane 17%
o CFCs 12%
o Nitrous oxides6%

ATMOSPHERIC POLLUTION AND ITS CAUSES

 Occurs when the atmosphere contains gases and substances in harmful amounts.
 Primary pollutants are the ones which directly pollute the atmosphere.
 When the primary ones go under chemical reactions the resulting compounds are secondary
pollutants
Primary pollutants Secondary pollutants
- Carbon monoxide - Ozone
- Sulphur dioxide - Nitrogen dioxide
- Nitrogen oxides - Sulphuric acid

SMOG
Smog is a mixture of smoke (from burning coal) and fog.
causes:
• coal emissions • forest fires
• industrial emissions of volatile • photochemical reactions
organic compounds (VOCs) • temperature inversions.
• vehicle emissions 
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PHOTOCHEMICAL SMOG
 is caused by photochemical reactions between sunlight, nitrogen oxides and VOCs.
 The nitrogen oxide is emitted from vehicle exhausts, burning coal and from industrial
processes in factories.
 VOCs are organic chemicals that easily enter the surrounding air, for example, from petrol,
paints and cleaning products.
 The sunlight causes a reaction and the creation of ground level ozone, which at this level is
harmful to humans.

 Photochemical smog can become a significant threat to human health when it accumulates due to
Temperature inversion (weather condition when the air temperature increases with altitude rather
than decreasing.)
 The smog may be thick enough to block out the Sun, which gives rise to the 'dustbin lid
effect.
 The conditions needed for a temperature inversion include:
- high air pressure (anticyclone), which causes the upper air to sink
- calm conditions resulting from high pressure (winds will disperse smog)
- valleys surrounded by steep-sided hills, which trap the smog.

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ACID RAIN
 precipitation with a pH value of less than 7.
 Acid rain comes in two main forms: dry deposition and wet deposition
 Wet deposition:
1) Burning of fossil fuels in factories and power stations release sulphur dioxide and
nitrogen oxides.
2) Vehicle emissions add further nitrogen oxides.
3) When these gases mix and react with the water vapour in the atmosphere, they form
weak solutions of nitric and sulphuric acid.
4) Prevailing winds carry them.
5) They eventually fall to Earth as acid rain.

 Dry deposition occurs when substances mix with dust particles to become acidic.

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OZONE DEPLETION
 The layer of ozone in the stratosphere shields the Earth from harmful ultraviolet B radiation.
 Ozone reacts and is broken down by chemicals such as chlorine. (One atom of chlorine can break
down more than 1 000 000 ozone molecules.)
 One major cause of ozone depletion is the use of chlorofluorocarbons (CFCs).
 High in the atmosphere, the CFCs react with sunlight and form chlorine, which destroys ozone.
 The greatest depletion of ozone can be found in the polar regions. There the region's low
temperatures speed up the conversion of CFCs to ozone-damaging chlorine.

THE ENHANCED GREENHOUSE EFFECT

 Created by the addition of greenhouse gases into the atmosphere by human activities
 More heat is retained in the atmosphere.

 Increased temperature of the Earth's surface leads to global warming and climate change.

Greenhouse gas Human activities that increase their abundance

of carbon dioxide Burning of fossil fuels; Deforestation.
Cattle and rice production; Coal mine ventilation; Deforestation;
methane
Decomposition of waste (landfill sites).
CFCs Aerosol sprays; Fire extinguishers; Refrigeration; Air conditioning.
Nitrogen Oxides Vehicle exhausts; Chemical fertilizers.
Tropospheric ozone Chemical reactions involving nitrogen oxides and unburnt fuel vapours.
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IMPACTS OF ATMOSPHERIC POLLUTION

Pollutant impact

 Irritation of eyes and throat;

 Respiratory diseases, like asthma;
Smog  Fine particles are carried into the lungs, leading to lung cancer, strokes and
heart attacks;
 Breathing difficulties.

 Acidification of groundwater, making the water undrinkable;

 It can cause diarrhea and stomach
 Upset if the water is consumed;
 Aluminum leached from the soil to groundwater;
Acid rain  Acidification of groundwater damages tree roots
 Crop yields decline;
 Nutrients like calcium are leached out of the soil;
 Fish die as acidity levels increase;
 Limestone buildings are chemically weathered.

 Higher levels of ultraviolet radiation cause sunburn, skin cancers, retina

damage and cataracts;
Ozone  Extra ultraviolet radiation limits the reproduction of phytoplankton, affecting
Depletion the entire food web;
 Changes in the biochemical composition of some plant leaves make them less
attractive as food.

 Melting of ice sheets, glaciers and permafrost causes a rise in sea levels;
 Damage to low-lying countries from flooding;
 Forced migration as people lose their homes and farmland from rising sea
Climate
levels;
change
 Loss of biodiversity, habitat or extinction if animals and plants can’t adapt;
 Increased droughts could lead to desertification and famine;
 Sea-level rise leads to the loss of coastal land and increased erosion.