Unit 8 Acid rain, smog and global warming
Unit 8
Acid rain, smog and global
warming
Unit 8 Acid rain, smog and global warming
Are there acids in the air?
Acid rain is also called “acid precipitation” (snow, rain, fog,
and dry particulate acidic depositions).
Sulphur dioxide is emitted primarily from stationary
sources such as power plants that burn fossil fuels.
Sulphur dioxide  H2O
Sulphuric acid
Nitrogen oxides are emitted from both stationary
and transportation-related sources.
Nitrogen oxides  H2O
Nitric acid
Unit 8 Acid rain, smog and global warming
Are there acids in the air?
We use the pH scale to describe the strength of an acid. The scale
is a numerical one from 0 to 14.
Battery
acid
Pure rain
(5.6)
Distilled
water
Ammonia
ACID RAIN
Acidic
Neutral
Basic
Pure rain has a pH of about 5.6 while distilled water a pH of 7,
which is neutral.
Acid rain is defined as precipitation which has a pH of below 5.6.
Unit 8 Acid rain, smog and global warming
Areas most affected by acid rain
N

Arctic Ocean
Europe
North
America
Asia
Atlantic Ocean
Pacific Ocean
Africa
Indian
Ocean
South
America
Australasia
Areas most affected by acid rain
km
Unit 8 Acid rain, smog and global warming
How acid rain is formed?
Sulphur dioxide
Nitrogen oxides
Moisture + sulphur
dioxide + nitrogen
oxides
Acid rain
Motor vehicle
Power station
Factory
Unit 8 Acid rain, smog and global warming
Are there acids in the air?
Acid rain affects industrial areas and the
neighbouring regions around them.
Buildings and statues are damaged
Unit 8 Acid rain, smog and global warming
Are there acids in the air?
Acid rain affects farming and forested areas.
Trees are particularly sensitive to acid rain.
The acid deposition weakens the trees
and affects their nutrient uptake.
Unit 8 Acid rain, smog and global warming
Effects of acid rain
Air pollution usually forms
high in the clouds
Air pollution creates acid rain
Streams are polluted
by acid rain
Animals and fishes are
seriously affected
Unit 8 Acid rain, smog and global warming
Acid rain in China
40% of the area of China
is now affected by acid
rain.
These provinces lose about
$3.7 billion worth of farm
products annually because
of acid rain.
More than 1.28 million
hectares of forest are also
affected.
Jiangsu, Zhejiang and five other
coastal provinces are the most
seriously affected area.
Unit 8 Acid rain, smog and global warming
What is smog?
Smog is a layer of brown haze covering a city caused by
pollutants reacting with sunlight.
Pollutants such as
hydrocarbons, dust,
smoke, nitrogen
dioxide and ozone
react with sunlight
to give air a hazy
appearance.
Smog
Unit 8 Acid rain, smog and global warming
What is smog?
A city with a large population, a lot of factories, thousands of
motor vehicles, light winds and plenty sunshine is ideal for the
formation of smog.
Unit 8 Acid rain, smog and global warming
How smog is formed?
Sunlight
Ozone
Still air
Gases, dust, smoke
Gases
Motor vehicle
Power
station
Factory
Unit 8 Acid rain, smog and global warming
What is smog?
Los Angeles on the
western coast of USA is
seriously affected by
smog.
Unit 8 Acid rain, smog and global warming
What is smog?
Sydney
New York City on the eastern coast of USA
and other big cities are also affected by smog.
Santiago
Unit 8 Acid rain, smog and global warming
What is smog?
Exhaust gas from vehicles
on a windless day is the
main cause of the formation
of smog in Hong Kong.
China is also seriously affected by smog,
especially in those big cities.
Unit 8 Acid rain, smog and global warming
What is ozone?
Ozone (O3) is a gas made up of oxygen. It is a
pollutant gas which has a sharp smell.
How ozone is formed?
 It is formed
when sunlight
or lightning
strikes oxygen.
 It is formed
Sunlight
Ozone
when nitrogen
dioxide reacts
with sunlight.
Lightning
Nitrogen
dioxide
Oxygen
Ozone
Unit 8 Acid rain, smog and global warming
What is global warming?
Greenhouse gases
There are gases in the
atmosphere which trap
heat and keep the earth’s
surface warm.
Most of the greenhouse
gases have increased
rapidly in quantity in
the atmosphere except
water vapour.
CFCs 12%
5%
Nitrogen oxides
Methane 15%
Carbon dioxide
60%
The major greenhouse gases
Unit 8 Acid rain, smog and global warming
Greenhouse gases
Carbon dioxide and
nitrogen oxides are
produced in the
burning of fossil
fuels.
Methane is
produced in rice
farming and
cattle rearing.
Unit 8 Acid rain, smog and global warming
Things that give off CFCs
CFCs are used as coolants in air-conditioners,
refrigerators and as aerosol propellants.
Spray can
Air-conditioner
Fast food
plastic foam
container
Computer
Motor vehicle
Refrigerator
Unit 8 Acid rain, smog and global warming
What is global warming?
The heat-trapping process the “greenhouse effect” has resulted
in a rise in world temperature -- global warming.
Water vapour, carbon
dioxide, methane,
nitrogen oxides, CFCs
Greenhouse gases trap heat
Heat reflected back
to Earth’s surface
Earth surface
Sun
Unit 8 Acid rain, smog and global warming
What is global warming?
Ozone hole
 The ozone layer
protects us from
ultraviolet radiation
from the sun.
Too much ultraviolet
radiation causes
cancer in people and
animals.
Unit 8 Acid rain, smog and global warming
The “hole” in the Antarctic
Since the late 1970s, scientists have found that ozone in the
atmosphere above the Antarctic has been decreasing.
The layer of ozone above it becomes so thin that a “hole”
develops over the continent.
 The percentage of ozone in the Antarctic ozone layer is rapidly
declining.
Unit 8 Acid rain, smog and global warming
Terms to learn
Acid rain (酸雨) -- rain that is acidic because it has mixed
with acidic gases sulphur oxides and nitrogen oxides. It has a
pH of below 5.6.
Smog (煙霧) -- a layer of brown haze covering a city caused
by pollutants reacting with sunlight.
Greenhouse effect (溫室效應) -- the process in which
greenhouse gases trap sun’s heat, leading to the rise in world
temperature.
Global warming (全球增溫) -- the rise in world temperature
as a result of the greenhouse effect.