Vapor is spreading in the atmosphere, and return to earth surface in the form of rain, snow, and other kinds of rain. In the atmosphere, water molecules react with air pollution such as carbon dioxides that dissolve with water and later on forming rain, it produces low carbonate acid. Consequently, rainwater which is usually normal becomes acid. Air pollutant, especially sulphur dioxide and nitrogen dioxide, increase the acidity of rainwater.
With the existence of sunlight, these pollutants react with water and oxygen in the air, forming sulphate acid and nitrate acid. So, acid rain is rain or snow which acidity is higher than unpolluted rainwater. Sulphur is released, mostly by the activity of manufacturing industries using coal burning, and energy from plants. The main source of nitrogen oxide is moke from motor vehicles. In some cities and industrial areas, the amount of released pollutant to the air is so huge that the rain and snow become so acid like vinegar; even fog and morning dew can be so acid as a result of air pollution. Unpolluted rainwater has pH around 5.6 – 5.7. Rain which has pH lower than 5.6 is considered as acid rain.
THE IMPACT OF ACID RAIN
Acid rain dissolves calcium, potassium, and other valuable nutrients from the soil surface. Since the nutrients from the soil have been washed out by acid rain, the soil becomes infertile. The lost of these nutrients can cause deaths to trees. Acid rain also damages plant tissues, disturbs its growth and disturb nitrogen fixation. A lot of trees in forests die because of acid rain. Acid rain also, influence a lake ecosystem. Acid rain which falls flow, through a river flow, makes the pH level in the ecosystem decrease below normal. The changing of acidity in the lake disturbs the lake ecosystem.