<P> There are a large number of aqueous reactions that oxidize sulphur from S (IV) to S (VI), leading to the formation of sulphuric acid . The most important oxidation reactions are with ozone, hydrogen peroxide and oxygen (reactions with oxygen are catalyzed by iron and manganese in the cloud droplets). </P> <P> Wet deposition of acids occurs when any form of precipitation (rain, snow, and so on .) removes acids from the atmosphere and delivers it to the Earth's surface . This can result from the deposition of acids produced in the raindrops (see aqueous phase chemistry above) or by the precipitation removing the acids either in clouds or below clouds . Wet removal of both gases and aerosols are both of importance for wet deposition . </P> <P> Acid deposition also occurs via dry deposition in the absence of precipitation . This can be responsible for as much as 20 to 60% of total acid deposition . This occurs when particles and gases stick to the ground, plants or other surfaces . </P> <P> Acid rain has been shown to have adverse impacts on forests, freshwaters and soils, killing insect and aquatic life - forms as well as causing damage to buildings and having impacts on human health . </P>

Where does the chemical content of the acid rain came from