How the acid rain happens?

Answer 1

Coal is made from trees that died long ago and were covered with dirt that turned to rock. Coal contains the same inorganic elements as trees and in the same percentages. One of those elements is sulphur. When coal burns, it produces a lot of carbon dioxide and a little bit of sulphur dioxide. Power plants and refineries can use scrubbers to remove sulphur dioxide from smoke or they can let it go into the atmosphere. When the sulphur dioxide reaches the atmosphere, it slowly turns into sulphur trioxide. When a molecule of sulphur trioxide meets with a molecule of water vapor, it forms a molecule of sulphuric acid, an extremely powerful acid. This joins other molecules of water to create dilute sulphuric acid. This falls as rain, acid rain.

Petroleum also contains sulphur but the sulphur is generally removed in the refining process.