<P> The principal cause of acid rain is sulfur and nitrogen compounds from human sources, such as electricity generation, factories, and motor vehicles . Electrical power generation using coal is among the greatest contributors to gaseous pollutions that are responsible for acidic rain . The gases can be carried hundreds of kilometers in the atmosphere before they are converted to acids and deposited . In the past, factories had short funnels to let out smoke but this caused many problems locally; thus, factories now have taller smoke funnels . However, dispersal from these taller stacks causes pollutants to be carried farther, causing widespread ecological damage . </P> <P> Combustion of fuels produces sulfur dioxide and nitric oxides . They are converted into sulfuric acid and nitric acid . </P> <P> In the gas phase sulfur dioxide is oxidized by reaction with the hydroxyl radical via an intermolecular reaction: </P> <Dl> <Dd> SO + OH → HOSO </Dd> </Dl>

In the united states the highest levels of acid rainfall occurs in