Air pollution is mostly caused by human activities. Exhaust fumes from motor vehicles are one of the main pollutants. They contain greenhouse gasses which are thought to contribute to global warming. They also contain substances such as sulphur and nitrogen oxides that can cause damage to our lungs. Very large amounts of pollutions are produced as a result of more and more industries. In many countries industrial pollution is now controlled, but it still causes a large amount of damage to our health and the environment in many developing countries. Another recent form of pollution came from parts of Asia where they were burning down the rainforests to clear the land for farming.