Coal-fired power stations release sulphur dioxide, especially those burning lignite coal. This gas, together with nitrous oxides from vehicle exhausts, reacts with water in the air to form weak acids. These acids create acid rain — rain that has a lower pH than normal. Acid rain erodes and damages the outside of buildings and statues, especially than made of limestone.
Acid rain falling on conifer forests in mountainous areas of Scandinavia, North America and central Europe has caused long—term damage to the trees. The soils become more acid and this causes toxic compounds, such as aluminium, to be released. The first signs of damage are a tree’s needles turning brown and whole branches dying. Increased acidity in the soil damages trees’ roots, and this reduces their ability to take up water and nutrients. The trees become more vulnerable to frost and disease. Eventually, they die.
Lakes are also vulnerable. The acidic rainwater drains off soils into the lake, causing it to become more acid. Aluminium in the water causes the gills of fish to produce more mucus, and this prevents them from obtaining sufficient oxygen from the water. In extreme cases, all life in the water may die.