How do human activities affect acid rain?

The main cause is Sulfur in the atmosphere. Sulfur is an impurity in oil and coal. Modern methods of burning and refining have greatly reduced the amount of sulfur being put into the atmosphere, in countries where such actions are encouraged.

When the sulfur gets into the atmosphere, it creates low concentration sulfuric acid. As an experiment, try cutting up an onion. That also will put sulfur into the air, and low concentration sulfuric acid will develop right on your eyes. It's enough to make you cry.