What is Acid Rain?
Acid rain is a result of air pollution. When
any type of fuel is burnt, lots of different
chemicals are produced. The smoke that comes
from a fire or the fumes that come out of a
car exhaust don't just contain the sooty grey
particles that you can see - they also contains
lots of invisible gases that can be even more
harmful to our environment.
stations, factories and cars all burn fuels
and therefore they all produce polluting gases.
Some of these gases (especially nitrogen oxides
and sulphur dioxide) react with the tiny droplets
of water in clouds to form sulphuric and nitric
acids. The rain from these clouds then falls
as very weak acid - which is why it is known
as "acid rain".
How acidic is acid rain?
Acidity is measured using a scale called the
pH scale. This scale goes from 0 to 14. 0 is
the most acidic and 14 is the most alkaline
(opposite of acidic). Something with a pH value
of 7, we call neutral, this means that it is
neither acidic nor alkaline.
strong acids will burn if they touch your skin
and can even destroy metals. Acid rain is much,
much weaker than this, never acidic enough to
burn your skin.
Rain is always slightly acidic because it mixes
with naturally occurring oxides in the air.
Unpolluted rain would have a pH value of between
5 and 6. When the air becomes more polluted
with nitrogen oxides and sulphur dioxide the
acidity can increase to a pH value of 4. Some
rain has even been recorded as being pH2.
Vinegar has a pH value of 2.2 and lemon juice
has a value of pH2.3. Even the strongest recorded
acid rain is only about as acidic as lemon juice
or vinegar and we know that these don't harm
us - so why do we worry about acid rain?
The Effects of Acid Rain
Acid rain can be carried great distances in
the atmosphere, not just between countries but
also from continent to continent. The acid can
also take the form of snow, mists and dry dusts.
The rain sometimes falls many miles from the
source of pollution but wherever it falls it
can have a serious effect on soil, trees, buildings
all over the world are dying, fish are dying.
In Scandinavia there are dead lakes, which are
crystal clear and contain no living creatures
or plant life. Many of Britain's freshwater
fish are threatened, there have been reports
of deformed fish being hatched. This leads to
fish-eating birds and animals being affected
also. Is acid rain responsible for all this?
Scientists have been doing a lot of research
into how acid rain affects the environment.