discharge of acidic effluents onto neutral or slightly alkaline land where the acidic components precipitate

emissions of sulphur oxides and nitrogen oxides from thermal power plants and burning of fossil fuels; these oxides dissolve in atmospheric water vapour and fall back on earth as acid rain

natural carbon dioxide released during respiration of living organisms dissolves in water, forming carbonic acid which is the chief contributor to acidity in rain water

chloro-fluoro-carbons readily react with various chemicals near the earth’s surface, producing acidic intermediates which cause acid precipitation.