2. Definition of Acid Rain
• Precipitation that has a pH of less than that of
natural rainwater.
• It is formed when sulphur dioxides and
nitrogen oxides, as gases or fine particles in
the atmosphere, combine with water vapour
and precipitate as sulphuric acid or nitric
acid in rain, snow, or fog.
3. Causes of Acid Rain
• Natural Sources
– Emissions from volcanoes
and from biological
processes that occur on the
land and in the oceans
contribute acid-producing
gases to the atmosphere.
– Effects of acidic deposits
have been detected in
glacial ice thousands of
years old in remote parts of
the globe.
4. Causes of Acid Rain
• The principal cause of acid rain is from human
sources
–Industrial factories, power-generating
plants and vehicles.
–Sulphur dioxide and oxides of nitrogen are
released during the fuel burning process
(i.e. combustion)
5. • When water vapour condenses, or as the
rain falls, gases (SO2 and NO) dissolve in
the water to form sulphuric acid (H2SO4)
and nitric acid (HNO3).
7. Acid Deposition
• Acid deposition consists of delivery
of acid substances or precursors,
principally sulfur and nitrogen oxides,
acids, from the atmosphere to the
earth surface
• Wet deposition- rain
• Dry deposition- aerosols, particulate.
8. Deposition of NOx and SO2
• Wet deposition
–Rain, snow, fog
–SO2 and NOx form HNO3 and H2SO4
–Soluble gasses that dissolve in
raindrops
–causing acid rain
• Dry deposition
–Particulates and aerosols absorbed by
plants or deposited on surfaces
–Ammonia and sulfur form ammonium
sulfate (in form of aerosols). Land
directly on surfaces.
9. Acid Rain Distribution
Water
•Lakes, streams and oceans.
•Most effected lake areas are in mountainous regions.
Land
•Areas of thin soil display more effects from acid rain
as there is little or no buffering of the acid.
Vegetation
•The leaves of trees and plants are stripped off by acid
rain.
•Most effected are trees at high elevation which are
constantly surrounded by acidic clouds.
Others
•Metals, paints and stone exposed to acid rain are
corroded.
•Sulfate particles responsible for the poor visibility.
10. • Forests affected by Acid Rain
• Northeast US
• Canada
• Northern Europe
• Asia
Natalie Maida
Source: EPA,
geocities
11. Affected Areas
• Canada
– Acid rain is a problem in Canada
– Water and soil systems lack natural alkalinity such
as lime base
• Cannot neutralize acid
– Canada consists of susceptible hard rock such as
granite
• Do not have the capacity to effectively neutralize
acid rain
12. Affected Areas
• Industrial acid rain is a substantial problem in
China, Eastern Europe and Russia.
• Acid rain from power plants in the Midwest United
States has also harmed the forests of upstate New
York and New England.
• This shows that the effects of acid rain can spread
over a large area, far from the source of the
pollution.
13. It kills micro-organisms
present in the soil.
It poisons plants
It damages metals and
limestone
It kills fish
14. Effects of Acid Rain
• The ecological effects of acid rain can also be seen
in the water environments. Acid rain flows to water
sources after falling on land, buildings, and roads.
• Lakes and streams become acidic when the water
itself and its surrounding soil cannot buffer the acid
rain enough to neutralize it.
• In areas where buffering capacity is low, acid rain
also releases aluminum from soils into lakes and
streams; aluminum is highly toxic to many species
of aquatic organisms.
•Harmful to aquatic life
15. • Acidification of freshwater greatly affects fish
populations.
• A decrease in pH is often paired with an increase in
toxic metals like aluminum and mercury.
• A decrease in pH and elevated aluminum
concentration will increase fish mortality, decrease
fish growth, decrease egg production and embryo
survival, and result in physiological impairment of
adult fish.
• Aluminum in the water can precipitate onto fish gills,
which would inhibit diffusion and result in respiratory
stress.
16. • Soft bodied animals like leeches, snails, and crayfish
die with a very little change in acidity, which is often an
indicator of acidification.
• Acid rain is extremely detrimental to amphibian
populations.
• Most amphibians lay their eggs in small, shallow
ponds which receive most of their water from rainfall.
• A very small amount of acidic rainfall would kill any
embryos in these small ponds.
17. Effects of Acid Rain
• Harmful to vegetation
– Increased acidity in soil
– Leaches nutrients from soil, slowing plant growth
– Leaches toxins from soil, poisoning plants.
– Creates brown spots in leaves of trees, impeding
photosynthesis.
– Allows organisms to infect through broken leaves
19. Acid rain and tree
• Acid rain does not directly kill trees.
• Acidic water dissolves the nutrients and minerals in
the soil and washes them away before trees.
• Acid rain also releases toxic substances such as
aluminum into the soil which in very small amounts are
very harmful to trees.
• Trees high up in the mountains are more at risk to
receive acid, from acidic clouds and fog.
• The trees are often bathed in these clouds, which eats
away at the waxy protective coating on the leaves.
• After this occurs, the leaves cannot perform
photosynthesis and the trees are left unhealthy, weak,
and usually die from disease or from insect attacks.
21. Acid Rain and Buildings
•Many buildings are made
of concrete and or stone.
•The building technically
“weathers” very fast, or
Non technically “crumbles”.
•Accelerates weathering in
metal and stone structures
Eg. Parthenon in Athens,
Greece; Taj Mahal in
Agra, India
Europe
22. Effects of Acid Rain
• Affects human health
–Respiratory problems, asthma, dry coughs,
headaches and throat irritations.
–Leaching of toxins from the soil by acid rain
can be absorbed by plants and animals.
When consumed, these toxins affect
humans severely.
–Brain damage, kidney problems, and
Alzheimer's disease has been linked to
people eating "toxic" animals/plants.
23. Preventive Measures
• Reduce amount of sulphur dioxide and
oxides of nitrogen released into the
atmosphere
–Use less energy (hence less fuel burnt)
–Use cleaner fuels
–Remove oxides of sulphur and oxides of
nitrogen before releasing
• Flue gas desulphurization
24. Preventive Measures
• Use cleaner fuels
– Coal that contains less sulphur
– Natural Gas
• Flue Gas Desulphurisation (FGD)
– Removes sulphur dioxide from flue gas (waste
gases)
– Consists of a reaction tower equipped with a fan
that extracts hot smoky stack gases from a power
plant into the tower
– Lime or limestone (calcium carbonate) in slurry
form is injected into the tower to mix with the stack
gases and reacts with the sulphur dioxide present
25. Preventive Measures
• (continued)
– Produces pH-neutral calcium
sulphate that is physically
removed.
– Sulphates can be used for
industrial purposes
26. Preventive Measures
• Use other sources of electricity
• i.e. nuclear power,
• hydro-electricity,
• wind energy,
• geothermal energy,
• and solar energy.
27. Can We Do Anything About Acid
Rain?
• YES! We can all take small actions to
help solve the problem
• We can help by:
–using our cars less
–conserving electricity
