All rain is slightly acidic, but the term Acid Rain is used to describe rain that has mixed with a range of industrial pollutants and become far more acidic that it could normally become.
Air borne pollutants such as sulphur dioxide, nitrogen oxides and assorted hydrocarbons react in the air with sunlight and water to form nitric acid, sulphuric acid and assorted other mineral acids and ammonium salts.
Unfortunately, nature does not provide a water filter in the atmosphere that is able to remove most of these pollutants and the result creates an acidic water can be carried thousands of miles by the wind before it falls to earth as rain, snow, fog or as dry particles which settle out due to gravity.
The biggest source of the 'acid rain' chemicals that pollute the atmosphere is the burning of fossil fuels. Fossil fuels were created from organic ( animal and plant ) material that died millions of years ago. The original material was full of carbon, and it's decay created sulphur, so the coal, oil and gas we burn today are rich in hydrocarbons and sulphur.
We burn these fuels in power stations to make electricity, in factories and oil refineries to make plastics and similar products, and in our vehicles which produce huge amounts of nitrogen and carbon gasses.
In recent years there have been some efforts to reduce the amount of pollutants that we pump into the air, but these efforts have been too small and too late to stop vast amounts of damage occurring across the world. Even though we know that acid rain is dangerous to us and the planet, we still produce all the chemicals that cause it.
In some parts of the world scientists have recorded rain that was more acidic than vinegar. Animals, plants, and even some rocks cannot survive when they come into contact with something so acidic. In Greece, the famous Parthenon is being dissolved by the rain that lands on the rocks from which it is made. In India, the Taj Mahal is suffering the same problem.
This photograph shows a small section of masonry from a church in northern France.
The rock was originally a smooth pillar like structure forming part of the outside decoration of the building. Over the last hundred years or so, acidic rain water has constantly dripped onto the rock from a rain gutter several meters above it.
The acidic rain has slowly dissolved away those parts of the rock that were richest in calcium carbonate, leaving behind the more resistant areas. Whilst this sort of weathering can give a building an attractive 'weathered' appearance it can also be a serious threat to the structure .Weakened building stone can lead to sections of the structure falling off, waterproof roofing starting to leak, and even result in major collapses.
Next time you visit a church or similar old building, take a close look at the outside stonework. Many buildings will have undergone repairs, giving you an opportunity to see both weathered sections and new replacements that show how the stonework would have looked when it was new.
Graveyards are also good hunting grounds for evidence of acid rain weathering; with dates on stones it's even possible to see how long it takes for a rock to weather!
In Sweden, over 18,000 lakes have become so acidic due to acid rain that all the fish have died. Some success has been achieved by dumping vast quantities of rocks like limestone into the lakes, because these rocks destroy the acid, but for most of the lakes it will be many years after we stop producing acid rain before the water returns to normal.
In what used to be called West Germany the government discovered that more than 70,000 square kilometers of forests had died because of acid rain. In the old East Germany, the damage was even worse due to factories creating much more pollution. It is not always the country that produces the pollution that suffers from the acid rain. For example, industrial pollution from the United Kingdom is blown across the sea and falls as acid rain over Norway and Sweden.
Acid rain is not just a European problem; it occurs around the world. In North America thousands of lakes along the eastern coast are so acidic that fish cannot survive any longer, and at least 10 percent of the lakes in the Adirondack region have a pH value of five or less. ( A pH of 7 is neutral, pure water. Lower values are acidic, higher values are alkaline. )
In the Appalachian Mountains a World Resources Institute report in the late 1980's stated that the acidity of clouds on the mountains was 100 times greater than it would be if it wasn't polluted. In consequence, trees were dying.
With all this damage, why do we still produce so much pollution and continue tolerating acid rain? Well, it's basically because governments don't consider it important enough. They believe that other things are more important, such as making sure that industry continues to grow and that the prices of goods are kept as low as possible. Making factories cleaner costs money, and unless everyone does it, the clean factories wont be able to make goods as cheaply as the dirty ones,and will make less money.
Developed countries also make huge profits from the exploitation and sale of the fuels that produce the pollution. The technology exists to run all our cars and lorries on other 'cleaner' fuels, but the oil companies wouldn't want that to happen, and neither would the governments that tax the oil companies!
The USA and Britain have both been particularly active in blocking and watering down a range of international agreements to reduce atmospheric pollutants.
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update to this statement was on:
March 26, 2013
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