How does air pollution lead to acid rain?
Some factories and industries burn sulphur to release sulphur dioxide into the air. For example, during preparation for the contact process.
This sulphur dioxide then reacts with oxygen in the air to form sulphur trioxide.
(During the contact process, which is the industrial preparation of sulphuric acid, this takes place at high temperature and pressure and in the presence of a Vanadium pentoxide catalyst.).
Both of these products can react with water in the atmosphere when it rains to form acid rain, sulphurous acid or sulphuric acid.
This acid rain can erode away metals etc.