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.
Power
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. Acid rain is precipitation containing higher than normal amounts of nitric and sulfuric acid. Acid
rain forms from both natural and man-made sources. Volcanoes and
decaying vegetation can form sulfur dioxide and nitrogen oxides.
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.
Very strong acids will burn if they touch your skin and can even destroy
metals. Acid rain is much, much weaker than this; it is 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.
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 and water. In the 1970s the effects of acid
rain were seen at their worst.
Forests all over the world were dying... in Scandinavia the fish were
dying; lakes were crystal clear but contained no living creatures or
plant life. Many of Britain's freshwater fish were threatened their
eggs were damaged and deformed fish were being hatched . This in turn
led to to fish-eating birds and animals also being affected.
Forests
It
is thought that acid rain can cause trees to grow more slowly or even
to die but scientists have found that it is not the only cause. The same
amount of acid rain seems to have more effect in some areas than it
does in others.
As
acid rain falls on a forest it trickles through the leaves of the trees
and runs down into the soil below. Some of it finds its way into streams
and then on into rivers and lakes. Some types of soil can help to
neutralise the acid - they have what is called a "buffering
capacity".Other soils are already slightly acidic and these are
particularly susceptible to the effects of acid rain.
Acid rain can effect trees in several different ways.It may:
• dissolve and wash away the nutrients and minerals in the soil
which help the trees to grow such as potassium, calcium and magnesium
• cause the release of harmful substances such as aluminium into the soil and waterways which further affects wildlife.
• wear away the waxy protective coating of leaves, damaging them
and preventing them from being able to photosynthesise properly.
A combination of these effects weakens the trees which means that they
can be more easily attacked by diseases and insects or injured by bad
weather. It is not just trees that are affected by acid rain, other
plants may also suffer.
Lakes and rivers
It
is in aquatic habitats that the effects of acid rain are most obvious.
Acid rain runs off the land and ends up in streams, lakes and marshes -
the rain also falls directly on these areas.
As the acidity of a lake increases, the water becomes clearer and the
numbers of fish and other water animals decline. Some species of plant
and animal are better able to survive in acidic water than others.
Freshwater shrimps, snails, mussels are the most quickly affected by
acidification followed by fish such as minnows, salmon and roach. The
roe and fry (eggs and young) of the fish are the worst affected, the
acidity of the water can cause deformity in young fish and can prevent
eggs from hatching properly and fish struggle to take in oxygen.
The
acidity of the water does not just affect species directly, it also
causes toxic substances like aluminium to be released into the water
from the soil, harming fish and other aquatic animals.
Buildings
According
to the Environmental Protection Agency, "acid rain" refers to a mixture
of wet and dry deposition (deposited material) from the atmosphere
containing higher than normal amounts of nitric and sulfuric acids.
Apart from its adverse effects on the ecosystem, acid rain degrades
stone monuments, especially those built out of limestone or marble.
Color Change
o Fading
and tarnishing of color are the most common effects of acid rain. The
milky white marble of the Taj Mahal in India is turning pale.
Pock Marks
o Acid
rain causes pock marks in various marble structures, thereby marring
their appearance. The marble columns of the Capitol building in
Washington D.C have developed such pock marks.
Disintegration of Parts
o As
a result of exposure to acid rain, parts of several monuments are
falling off. Some of the pieces of the Acropolis of Athens, Greece have
begun falling off and a total structural collapse is possible in future.
Total Disappearance
o Sometimes the damage of acid rain on monuments is irreversible. Acid rain is erasing most of the
Dampier rock art complex in Australia, and it is estimated that by the
middle of the 21st century, most of this art will disappear completely.
Monetary Implications
o Continuous
erosion of monuments from acid rain is a global problem. In order to
preserve these heritage sites, governments spend huge sums of money on
their renovation.
Where is it coming from?
Until relatively
recently air pollution has been seen as a local issue. It was in
southern Scandinavia in the late 1950's that the problems of acid rain
were first observed and it was then that people began to realise that
the origins of this pollution were far away in Britain and Northern
Europe. One early answer to industrial air pollution was to build very
tall chimneys. Unfortunately all this does is push the polluting gases
up into the clouds allowing emissions to float away on the wind. The
wind carries the pollution many hundreds of miles away where it
eventually falls as acid rain. In this way Britain has contributed at
least 16% of the acid deposition in Norway. Over ninety percent of
Norway's acid pollution comes from other countries. The worst European
polluters re Germany, UK, Poland and Spain. In 1994 each of them
produced over a million tons of sulphur emissions. Governments have
since admitted that acid rain is a serious environmental problem and
many countries have taken steps to reduce the amount of sulphur and
nitrogen emissions, but they are still a problem.
Restoring the damage done by acid rain
Lakes and rivers can have powdered limestone added to them to
neutralise the water - this is called "liming". Liming, however, is
expensive and its effects are only temporary - it needs to be continued
until the acid rain stops. The people of Norway and Sweden have
successfully used liming to help restore lakes and streams in their
countries.
A major liming programme has been taking place in Wales where 12,000 km
of its waterways were acidified. In 2003 liming of the river Wye led
to a return of the salmon which had completely disappeared in 1985.
However, other parts of Wales have taken longer to recover and there are
still no signs of life.
Recently a more positive side of acid rain has been noted as it can be
very effective at reducing the natural production of methane, a
“greenhouse gas” approximately 23 times more powerful than carbon
dioxide, especially in wetland areas.
What can be done?
Reduce emissions:
•
Burning fossil fuels is still one of the cheapest ways to produce
electricity so people are now researching new ways to burn fuel which
don't produce so much pollution.
• Governments need to spend more money on pollution control even if it does mean an increase in the price of electricity.
• Sulphur can also be 'washed' out of smoke by spraying a mixture of water and powdered limestone into the smokestack.
• Cars are now fitted with catalytic converters which remove three dangerous chemicals from exhaust gases
Find alternative sources of energy
• Governments need to invest in researching different ways to produce energy.
• Two other sources that are currently used are hydroelectric and
nuclear power. These are 'clean' as far as acid rain goes but what other
impact do they have on our environment?
• Other sources could be solar energy or windmills but how reliable
would these be in places where it is not very windy or sunny?
• All energy sources have different benefits and costs and all theses
have to be weighed up before any government decides which of them it is
going to use.
Conserving resources
• Greater
subsidies of public transport by the government to encourage people to
use public transport rather than always travelling by car.
• Every individual can make an effort to save energy by switching off
lights when they are not being used and using energy-saving appliances -
when less electricity is being used, pollution from power plants
decreases.
• Walking, cycling and sharing cars all reduce the pollution from vehicles.
