Two-thirds of the sulfur dioxide that pollutes the air is produced by

Power plants.

Explanation:

When power plants start the burning coal process, the chemical bonds carrying its carbon atoms are brake down and releasing energy also carrying heavy metals such as lead, mercury, and cadmium into the atmosphere.

When the sulfur which is present in coal reacts with oxygen it produces sulfur dioxide and they the ability to combines with other lethal toxic molecules that are found in the atmosphere and form small, acidic particulates that can cause several diseases in humans.