Transcript Acid Rain

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
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
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 +
factories
→ releases sulphur into the
air
→ combines with oxygen
→ SO2
SO2 Emissions from Canada & the USA in 1998
e.g. In 1998, U.S.’ SO2
emissions were 6
times greater than
Canada's.
2) Nitrogen oxides (NOX)
→ combustion of fossil fuels in
motor vehicles, residential and
commercial furnaces, industrial
and electrical-utility boilers and
engines
e.g.
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%
of NO2 33% of CO2 emission
NOx Emissions from Canada & the USA in 1998
e.g. In 1998, by comparison,
U.S. NOX emissions was
11 times more than
Canada's.
.
Formation of acid rain
SO2 + NOX
→mixed with moisture
→sulphuric acid (H2SO4) &
nitrate acid(HNO3)
→dissolved in rain
→falls onto the ground as acid rain
Area affected by acid rain
East N.
America
West Europe
SE China
Reasons
1)↑no. of cities
2)↑population
3)↑power plants
4)↑industries
5)↑traffic
→ pollutants are produced
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
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
e.g.
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
e.g.
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.
Solution
1) Legislation
Examples:
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
e.g.
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
e.g.
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
bio-diesels
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.
Conclusion
Whether it is effective, depends on:
1) availability of capital
2) advanced technology
3) inter-departmental coordination
4) cooperation among government,
industrialists and
citizens