Acid rain is a rain or any other form of precipitation that is
unusually acidic, meaning that it possesses elevated levels of
hydrogen ions (low pH). It can have harmful effects on plants,
aquatic animals and infrastructure. Acid rain is caused by
emissions of sulfur dioxide and nitrogen oxide, which react with
the water molecules in the atmosphere to produce acids.
Governments have made efforts since the 1970s to reduce the
release of sulfur dioxide into the atmosphere with positive results.
Nitrogen oxides can also be produced naturally by lightning strikes
and sulfur dioxide is produced by volcanic eruptions. The chemicals
in acid rain can cause paint to peel, corrosion of steel structures
such as bridges, and erosion of stone statues.
Combustion of fuels produces sulfur dioxide and nitric oxides. They are converted into
sulfuric acid and nitric acid.
Gas phase chemistry:
In the gas phase sulfur dioxide is oxidized by reaction with the hydroxyl radical via an
SO2 (g) + OH → HOSO2
Which is followed by:
HOSO2 + O2 (g) → HO2 (l) + SO3
In the presence of water, sulfur trioxide (SO3) is converted rapidly to sulfuric acid:
SO3 (g) + H2O (l) → H2SO4 (aq)
Nitrogen dioxide reacts with OH to form nitric acid:
NO2 + OH → HNO3
Chemistry in cloud droplets:
When clouds are present, the loss rate of SO2 is faster than can be explained by gas
phase chemistry alone. This is due to reactions in the liquid water droplets.
Sulfur dioxide dissolves in water and then, like carbon dioxide, hydrolyses in a series
of equilibrium reactions:
• SO2 (g) + H2O → SO2·H2O
• SO2·H2O H+ + HSO3
• HSO3− H+ + SO32−
There are a large number of aqueous reactions that oxidize sulfur from S(IV) to S(VI),
leading to the formation of sulfuric acid. The most important oxidation reactions are
with ozone, hydrogen peroxide and oxygen (reactions with oxygen are catalyzed
by iron and manganese in the cloud droplets).
• Burning coal. Oil and natural gas in power stations
makes electricity, giving off sulphur dioxide gas.
• Burning petrol and oil in vehicle engines gives off
nitrogen oxides as gases.
• These gases mix with water vapour and rainwater
in the atmosphere producing weak solutions of
sulphuric and nitric acids – which fall as acid rain.
People probably couldn't live without electricity! Therefore coal will continue to be
burnt. Also, electricity and energy are constantly being overused.
Think of it this way: every time you turn on a light switch or the television set without
really needing to, you're indirectly contributing to the acid rain problem.
Acid rain can travel long distances.
Often it doesn’t fall where the gas is produced. High chimneys disperse (spread) the
gases and winds blow them great distances before they dissolve and fall to Earth as
Soil biology and chemistry can be seriously damaged by acid rain. Some microbes are
unable to tolerate changes to low pH and are killed.
Acid rain is an extremely destructive form of pollution,
and the environment suffers from its effects. Forests,
trees, lakes, animals, and plants suffer from acid rain.
The needles and leaves of the trees turn brown and fall
off. Trees can also suffer from stunted growth; and have
damaged bark and leaves, which makes them vulnerable
to weather, disease, and insects.
All of this happens partly because of direct contact
between trees and acid rain, but it also happens when
trees absorb soil that has come into contact with acid
rain. The soil poisons the tree with toxic substances that
the rain has deposited into it.
Lakes: are also damaged by acid rain. Fish die off, and that
removes the main source of food for birds. Acid rain can even kill
fish before they are born when the eggs are laid and come into
contact with the acid.
Fish usually die only when the acid level of a lake is high; when
the acid level is lower, they can become sick, suffer stunted
growth, or lose their ability to reproduce.
Also, birds can die from eating "toxic" fish and insects.
Acid rain dissolves the stonework and mortar of buildings (especially
those made out of sandstone or limestone).
It reacts with the minerals in the stone to form a powdery substance
that can be washed away by rain.
Currently, both the railway industry and the
aeroplane industry are having to spend a lot of
money to repair the corrosive damage done by acid
rain. Also, bridges have collapsed in the past due to
acid rain corrosion.
Humans can become seriously ill, and can even die from
the effects of acid rain. One of the major problems that
acid rain can cause in a human being is respiratory
Many can find it difficult to breathe, especially people
who have asthma. Asthma, along with dry coughs,
headaches, and throat irritations can be caused by the
sulphur dioxides and nitrogen oxides from acid rain.
Acid rain can be absorbed by both plants (through soil
and/or direct contact) and animals (from things they eat
and/or direct contact). When humans eat these plants or
animals, the toxins inside of their meals can affect them.
Brain damage, kidney problems, and Alzheimer's disease
has been linked to people eating "toxic" animals/plants
Research carried out in North America in 1982, revealed
that sulphur pollution killed 51,000 people and about
200,000 people become ill as a result of the pollution
• Ride your bike
• Tell your friends and family about pollution
• Make sure your parents get pollution checks on their cars
Ride the school bus
Learn more; stay up to date
• Join a group to stop pollution
Encourage your parents to carpool to work
• Switch off lights, fan, heat, etc. when you leave the room