1. Acid Rain

3. Acid Rain
pH value – the measure of the acidity and alkalinity of a solution, range from 0 to 14
pH 7 is neutral
pH>7 = alkaline
pH<7 = acidic
Natural rain in Hong Kong is about pH 6.
Natural rain in Central Europe is pH 4.3,
N. Europe, N. America and Japan is 3.5

4. Situation Acid rain(Acid deposition) Acid rain: pH > 5.5
Wet deposition: acidic rain, fog, hail and snow
Dry deposition: acidic gases and particles
Acid rain: pH > 5.5
Normal rain ~ pH 5.5 (CO2 dissolves in rain water  weak Carbonic acid)
Acid rain can be as acidic as vinegar and lemon juice
One of the Global Problems
Widely spread (Prevailing winds disperse the pollutants far away from the sources)
problem between national borders or frontier

5. What is the acid rain ?
Acid Rain is caused when sulphur dioxide (SO2) and nitrogen oxides (NOx) chemically react with other substances in the atmosphere to form acidic compounds.Sunlight increases the reaction rate.
They fall to the earth in wet and dry form.

6. Causes of acid rain [2] Main acid rain causing chemical Acid Rain
Nitric Oxides
(nitric oxide NO
& nitric dioxide NO2)
Sulfur dioxide
SO2
Sulfuric acid
H2SO4
Nitric acid
HNO3
Acid Rain

7. Where do air pollutants come from ?
Oil refineries,
the use of coal in the production of electricity,
from base-metal smelting,
and from fuel combustion in vehicles.

8. Causes of acid rain [3] - sources
Industry -- emission of acidic gases (e.g. smelting plant & power plant)
Natural source
of sulfur dioxide --
Volcanic Eruption
Transportation --
source of acidic gases,
mostly nitric oxides

9. Causes of acid rain [4] Chemical Process in Atmosphere
dissolution
2H+ + SO42-
H+ + NO3- O3
energy O2
NOx
SO2
H2SO4
HNO3
oxidation

10. Effects of Acid Rain the acidification of lakes and streams
forest damage
decay of buildings and paint
an increase in public health problems

11. LAKES AND STREAMS an acidity of between 6 and 8.
Acid rain can cause a pH of as low as 3 in some places.
cause to kill certain aquatic plant and animal life.
Increase concentration of mercury, aluminium, manganese, lead and zinc in water.
Norway and Sweden suffered most because no chalk and limestone (Geology)

12. Effects of acid rain [2] - water bodies
When the water bodies is acidified, most of the aqueous species cannot survive and so the biodiversity decreases
Lake - can be acidified easily as low water flow

13. This chart shows the different levels of acidity that certain lifeforms can handle.

14. FORESTS
Acid rain causes direct damage to trees at high elevations, especially the red spruce. As shown in this picture from the EPA, large areas of forests have died. This occurs mainly in the very severe cases of acid rain, those causing a pH of 4 or less. Acidic soil causes the leaching of the nutrients from soil

15. Effects of acid rain [3] - forests
Plant injury
Soil acidified
Further affect plant reproduction and growth
Massive injury of plants by acid rain

16. MATERIALS damage certain materials ( limestone and marble)
dissolves calcium carbonate in the stone
forming crystals with stone and break apart stone

17. Effects of acid rain [4] - materials
Status worn out by acid rain
Marbles eroded by acid rain

18. PUBLIC HEALTH ~ also the contamination of edible fish. And crops
~ affect through both the water and the atmosphere.
the pH of soil decreases,
~ the mobility of metallic compounds ( aluminum and
mercury) increase
~ make them easily transported into the water system
~ lead to the contamination of not only the water
~ also the contamination of edible fish. And crops

19. Effects of acid rain [5] - human health
Effects are usually indirect
lung cancers, bronchitis, emphysema and asthma
caused by inhalation

20. Acid Rain in the United States and Canada
Acid rain is a large problem in the Eastern U.S. and Canada.This is mainly because emissions rise high into the atmosphere and are carried by the strong winds from the West, falling out with precipitation in the East.

21. Prevention: Reduce acidic gases emission [1]
Good practice in fossil fuels combustion
low sulphur coal used in power plants
scrubbers used to remove sulphur dioxide from exhaust gas
catalytic converters in vehicles reduce nitrogen oxides emission

22. Prevention: Reduce acidic gases emission [2]
Application of clean energy resources
nuclear power, hydropower, wind and geothermal energy
high combust-efficient biomass fuel used in vehicles
Wind-powered electricity plant

23. Mitigation: Restore damaged environment
Liming
neutralize acidity in lakes and streams
however, not effective in damaged soil and watershed
expensive

24. Improvements ~set up some regulations / law
~use Calcium carbonate / lime to neutralize the lakes and streams

25. Local actions 1984 Sweden $25 million to neutralize lakes
1985 USA 3-7 billions to control
Encourage the industries to install some environmental facilities such as scrubber, electrostatic precipitator or using low sulphur content diesel, washing coal before use by tax break or by subsidization.

26. Individual actions Energy consumption is the main cause
energy conservation help to avoid the problem

27. Is acid rain a serious problem in Hong Kong?
Serious in some districts because of factories and acidic rain may have been emitted from the factories or brought from China causing pipelines rusting, paint peeling, kills trees and causing people suffer from respiratory diseases (bronchitis and asthma).
However, Hong Kong has few historical building and sculptures.
No large lakes or rivers with big fish populations.
Little farming, no large forest.

28. To what extent do you think that acid rain in Hong Kong is caused by nearby territories, for example, mainland China?
If acid rain in Hong Kong is caused partly by China, who should bear the responsibility and costs of combating it, and how would you justify your view?
What would be the likely difficulties encountered in negotiation with China?

29. Discussion What are the natural sources of acid rains?
How acid rains affect economic and agricultural activities?
Can you show some evidences about buildings being destroyed by acid rain?
Use of the nuclear power is a way to reduce the problem of acid rain, but is nuclear power an environmentally friendly fuel?
What are some actions that individual can take to conserve energy & to reduce the problem of acid rain?
Referring to section 1.1 Air Pollution, what is the trend of concentration of sulphur dioxide and nitrogen dioxide in Hong Kong? What is the implication of the trend on the problem of acid rain in Hong Kong?

30. International Efforts
Convention on Long-range Transboundary Air Pollution, adopted on , entered into force on
Protocol to the 1979 Convention on Long-range Transboundary Air Pollution on Long-term Financing of the Cooperative Programme Monitoring and Evaluation of the Long-range Transmission of Air Pollutions in Europe (EMEP), adopted on
Protocol to the 1979 Convention on Long-range Transboundary Air Pollution on the Reduction of Sulphur Emisssion or their Transboundary Fluxes by at least 30%, adopted on

31. Relevant websites Acid Rain 2000(
U.S. Environmental Protection Agency - Acid Rain Program (
The site of Environment Canada - Atlantic Region (
EcoNet's Acid Rain Resources (

32. THE END