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Acid rain is rain that is unusually acidic. In other words, it is rain that has high levels of hydrogen ions (low pH). Acid rain can have harmful effects on plants, animals, and on humans. Acid rain is caused when gaseous compounds of ammonium, carbon, nitrogen, and sulphur are released into the atmosphere. The wind carries the gases high into the sky. There the compounds react with the water in the atmosphere and acids are made.
Acid rain is caused by sulphur dioxide mixing with the atmosphere caused by human activity.
Scientists have realised that humans are resposible for giving out most of the compounds that cause acid rain. People started producing acid rain gases when they started building factories and power stations. The buildings burns coal or oil and this causes the acid rain gases. Governments have tried since the 1970s to reduce the amount of sulfuric oxide being released into the Earth's atmosphere. They have had good results so far. However, it is expensive to clean the smoke from factories and power stations. Great Britain still produces about five million tonnes of these gases every year. China produces eighteen million tonnes. The United States of America produces more than twenty million tonnes.
Acid rain can also be caused naturally. For example, it can be caused by nitrogen compounds can be split by the energy from lightning strikes, and volcano eruptions can release sulfur dioxide into the atmosphere.
Acid rain poisons rivers and lakes. Fish and other animals cannot live in acid water. It is also bad for buildings as the acid damages the stone. The acid makes it erode away (crumble away.) Many of the world's oldest and most famous buildings and monuments are in danger because of acid rain.
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