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Acid Rain. What is acid rain?. Any ppt →pH value < 5.6 → acid rain. Introduction. 1) Wet deposition → acidic rain, fog + snow a) Rainout: incorporation of materials into cloud drops b) Washout: when materials below the

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what is acid rain
What is acid rain?

Any ppt

→pH value < 5.6

→ acid rain


1) Wet deposition

→acidicrain, fog + snow

a) Rainout: incorporation of materials into

cloud drops

b) Washout: when materials below the

cloud are swept out by rain

or snow as it falls

2) Dry deposition

→ acidic gases + particles

a) Atmospheric pollutants directly contact with

the ground, vegetation and buildings

b) Gravitational settling

causes of acid rain
Causes of acid rain

Main sources

1) Sulphur dioxides (SO2)

a) Natural

- volcanoes

- sea spray

- rotting of vegetation +

plankton (浮游生物)

b) Human

→ burning of fossil fuels

(coal, oil + natural gas) in

power plants +


→ releases sulphur into the


→ combines with oxygen

→ SO2

so 2 emissions from canada the usa in 1998
SO2 Emissions from Canada & the USA in 1998

e.g. In 1998, U.S.’ SO2

emissions were 6

times greater than


2) Nitrogen oxides (NOX)

→ combustion of fossil fuels in motor vehicles, residential and commercial furnaces, industrial and electrical-utility boilers and engines


a) In HK, 8500 tonnes of SO2, 43200 tonnes of NO2& 5900 tonnes of particulates are emitted annually from the fleet of some 424000 licensed vehicles

b) In UK, power stations are responsible for 71% of SO2, 32% ofNO233% ofCO2emission

nox emissions from canada the usa in 1998
NOx Emissions from Canada & the USA in 1998

e.g. In 1998, by comparison,

U.S. NOX emissions was

11 times more than



formation of acid rain
Formation of acid rain


→mixed with moisture

→sulphuric acid (H2SO4)&

nitrate acid(HNO3)

→dissolved in rain

→falls onto the ground as acid rain

area affected by acid rain
Area affected by acid rain

West Europe

East N. America

SE China


1)↑no. of cities


3)↑power plants



→ pollutants are produced

regional pollution in scandinavia
Regional pollution in Scandinavia

∵↑level of industrialization in UK

→↑emission of SO2

→ Westerlies blow the pollutants from the

west of U.K. to Scandinavia and the rest

of Europe

→Scandinavia has been receiving acid rain

for at least a century

effects of acid rain
Effects of acid rain

A. Positive effects (local and short term)

1) improves visibility

2) dissolves some of the atmospheric pollutants poisonous to plants and animals

3) washes away dust on the leaves of the urban plants and revitalize photosynthesis

4) cools the hot concrete surface

B) Negative effects

1) Aquatic ecosystem

↑ lake acidification

→ fish kills

 stock depletion

e.g.In Sweden, 14,000 lakes cannot support sensitive aquatic life and 2,200 show no signs of life at all.

2) Forest destruction

Acid rain causes release of metals, e.g. Al, from soil

→ rots plant roots,

attacks leaves

→ forest are destroyed

e.g. a) In UK, 70% of beech trees + 80% of yew trees have

been hit by acid rain.

b) 54% of all trees in Germany

have been hit by acid rain.

c) In some Chinese provinces

like Maocaoba, over 90% of the pine trees are dead.

3) Crop yield drops

∵↑ acidity

e.g. Acid rain in China causes $260 million in crop damages in the Hunan province alone.

4) Human health

→contaminated fish + drinking water supplies passed on to

people through the food chain


a) Sweden, 1000 lakes with high concentration of mercury esp. Pregnant women’s fetuses (胎兒) are sensitive to mercury poisoning

b) Sweden, drinking water with high levels of copper causes diarrhea (腹瀉 ) in young children →harms liver, kidneys

c) Norway, aluminum from acid rain  pre-smile dementia (痴呆)

d) N. America & Canada, in 1982, 51000 people die from Sulfur pollution

e) Others: respiratory problems, asthma(哮喘), dry coughs + brain damage

5) Material and visibility

→ corrodes buildings, monuments,

bridges and highways

→ reducing the life expectancy

of properties + infrastructure


a) In Europe, structures like The Acropolis in Greece and

Renaissance buildings in Italy, as well as several churches and

cathedrals have suffered visible damage.

b) In the Yucatan peninsula in Mexico, and in places in South America, ancient Mayan Pyramids are being destroyed by acid rain.



1) Legislation


a) In HK , Air Pollution Control Regulation (Fuel Restriction) has been very successful + SO2 have been reduced by about 40% on average.

b) In HK, between 1992-97, emissions of SO2+ NOx were reduced by banning the use of high sulphur fuels, using natural gas for power generation. As a result, the total amount of SO2 emitted was reduced by 54 % in 1992 -97, and NOx emitted was educed by 44 % in 1992 -97.


2) Economic Emission Strategy


In USA, the Emission Trading Policy (1982) sold

the right to pollute

But, strict controls

→ ↑ production costs may drive industries to area

where there is less control

3) Installation of advanced anti-pollution equipments


Power plants in H.K. have adopted flue-gas

desulphrization to↓SO2 emission by 90% and water

injection techniques to↓Nox emission by 75%

4) Education

i) encourage people to adopt waste reduction

and recycling programmes should be launched

→ ↓pollutants emitted from incineration

ii) encouragement and promotion towards

environmental conservation

5) Transport

i) Construct mass transport system which is more

efficient + uses cleaner fuel

e.g. MTR, KCR

ii) Encourage drivers to turn off engine while waiting

iii) Encourage drivers to install catalytic converter to reduce NOx emission

e.g. By the end of 1998, 75% of petrol cars were fitted with 3-way catalytic converters and using unleaded petrol

iv) Encourage people to use unleaded petrol, LPG and


e.g. No diesel taxi will be allowed after 2006

v) Encourage people to use public transport instead of

driving their own car

6) Better and proper city planning

i) Highly polluting industries should be separated

from residential zones by buffer.

ii) Highly polluting industries should be relocated to

less populated areas.

iii) Highly polluting industries must be carefullt sited

e.g. Power plants in Tsing Yi, Lamma I sland + Tap

Shek Kok are all located at the western side of

H.K., which are the downwind sides of the urban

area since the prevailing wind is easterly

Yet, it is sometimes criticized that the city

planners are simply shifting pollution problem

from one part of the city to the other.


Whether it is effective, depends on:

1) availability of capital

2) advanced technology

3) inter-departmental coordination

4) cooperation among government,

industrialists and