What is the gas which causes acid rain when fossil fuels are burned?

Answer 1

Acid rain will usually contain one or two types of acid formed from gasses that occur in the atmosphere.

Volcanic eruptions and man burning sulphur containing fossil fuels (eg coal) will put Sulphur Dioxide (SO2) into the atmosphere. SO2 will react with water droplets in the air to produce dilute Sulphuric Acid. This will then come down with the rain as 'acid' rain.

The air also contains naturally Carbon Dioxide (CO2) and this gas too reacts with water in the air to form Carbonic Acid (H2CO3), a week acid which will be present in rain. Man burning carbon containing fossil fuels will add to the CO2 in the atmosphere.

It is also possible to form acid rain form other gases (Oxides of Nitrogen and Hydrogen Chloride gas) if these get in the atmosphere. However, when people use the term 'Acid Rain' they usually mean the SO2 variety as the acid is much stronger and on many occasions it is caused by man made pollution.