Many natural and pollutant gases dissolved in the air are nonmetal oxides.
CO2, SO2, NO2.
Nonmetal oxides are acidic.
CO2 + H2O H2CO3
2 SO2 + O2 + 2 H2O 2 H2SO4
Processes that produce nonmetal oxide gases as waste increase the acidity of the rain.
Natural—volcanoes and some bacterial action.
Man-made—combustion of fuel.
Weather patterns may cause rain to be acidic in regions other than where the nonmetal oxide is produced.