the sulfur dioxide which is in the air from the burning of coal

Yep - that's why it is called "acid rain".

Dave

Here is a link that might be useful: What is Acid Rain

The pH of distilled water is between 5 and 6 because CO2 forms carbonic acid, which is a weak acid but still corrosive enough that distilled water lines in labs are glass coated.

Rain is similar even without the sulfur and nitric acid pollution. The pollution is a much stronger acid though.

would be interesting to know if the icelandic volcano eruption has contributed to this.