2. ACID RAIN???
(acid deposition)
• Refers to the deposition of wet
and dry acidic components.
• Unpolluted rain - slightly acidic pH
of about 5.2(carbon dioxide and water in
the air react together to form carbonic acid,
a weak acid), but polluted rain
contains other chemicals.
• The extra acidity in rain comes
from the reaction of primary air
pollutants, primarily sulphur oxides
and nitrogen oxides, with water in
the air to form strong acids (like
sulphuric and nitric acid).
3. HISTORY
Since the Industrial Revolution, emissions of sulphur dioxide and nitrogen oxides
to the atmosphere have increased.
Robert Angus Smith(1852) was the first to show the relationship between acid
rain and atmospheric pollution in Manchester, England. Though acidic rain was
discovered in 1852, it wasn't until the late 1960s that scientists began widely
observing and studying the phenomenon. From then until now, acid rain has
been an issue of intense debate among scientists and policy makers.
The term "acid rain" was generated in 1972.
Occasional pH readings in rain and fog water of well below 2.4 have been
reported in industrialized areas.
The problem of acid rain not only has increased with population and industrial
growth, but has become more widespread.
4. CAUSES
• primary causes of acid rain are sulphur dioxide and nitrogen oxides.
• Most sulphur dioxide comes from power plants that use coal as their fuel.
These plants emit 100 million tons of sulphur dioxide, 70% of that in the
world.
• Automobiles produce about half of the world's nitrogen oxide. As the
number of automobiles in use increases, so does the amount of acid rain.
Power plants that burn fossil fuels also contribute significantly to nitrogen
oxide emission. Fires, volcanic eruptions, bacterial decomposition, and
lightening also greatly increase the amount of nitrogen oxide on the planet.
5. Acid Deposition
• Wet deposition
Occurs when any form of
precipitation (rain, snow, sleet, fog
and cloud water, dew) removes
acids from the atmosphere and
delivers it to the Earth's surface.
• Dry deposition
Occurs in the absence of
precipitation (acidifying particles
and gases). This occurs when
particles and gases stick to the
ground, plants or other surfaces.
6. Adverse Effects
Countries that are developed have the most severe acid rain problems.
As the undeveloped nations begin to industrialize, acid rain will
increase greatly.
Acid rain has adverse effects on:
Surface waters and aquatic animals
• kills adult fishes and eggs may not get hatched
• biodiversity is reduced
• has eliminated insect life and some fish species,(including the brook trout in
some lakes, streams, and creeks in geographically sensitive areas, such as the
Adirondack Mountains of the United States)
Soils
• microbes are unable to tolerate changes, enzymes of these microbes are
denatured (changed in shape so they no longer function), ruins plant nutrients,
hurting plants' ability to survive and to give life to other organisms.
7. (conti.)
Forests and other vegetation
Human health
• cause illness and premature deaths such as cancer and other
diseases
Other adverse effects
• cause damage to certain building materials and historical monuments.
8. Affected Areas
• most of Europe
(particularly Scandinavia
with many lakes with
acidic water containing no
life and many trees dead)
• many parts of the United
States (states like New
York are very badly
affected)
• South Western Canada
• South Eastern coast of
China and Taiwan
9. Incidences
• Third of China 'hit by acid rain', 27 August
2006,25.5 million tonnes of sulphur dioxide
were spewed out, mainly from the country's
coal-burning factories -up 27% from
2000.Emissions of sulphur dioxide were
double the safe level.
In some areas, rainfall was 100% acid rain.
Due to these increased emissions one-third of
China's territory was affected by acid rain,
posing a major threat to soil and food safety.
• In Japan, an acid rain incident occurred in
1973 where people complained of irritation to
the skin or eyes, and this occurred with a
drizzling rain.
10. Prevention Methods
• Technical solutions
In the United States, many coal-burning power plants
use Flue gas desulphurization (FGD) to remove sulphur-
containing gases from their stack gases. An example of
FGD is the wet scrubber which is commonly used in the
U.S. and many other countries.( A wet scrubber, shown in the
figure is basically a reaction tower equipped with a fan that extracts
hot smoke stack gases from a power plant into the tower.) And
also, they use coal with a low sulphur content
Automobile emissions control reduces emissions of
nitrogen oxides from motor vehicles.
• International treaties
International treaties on the long range transport of
atmospheric pollutants have been agreed e.g. Sulphur
Emissions Reduction Protocol under the Convention on
Long-Range Tran boundary Air Pollution.
