1) acidifying deposition 2) acid rain a fallout of substances from the atmosphere, e.g. through rain, snow, fog, or dry particles, that have the potential to increase the acidity of the receptor medium; they are primarily the result of the discharge of gaseous sulphur oxides and nitrogen oxides from the burning of coal and oil, e.g. in electricity generation, smelting industries and transport; acid rain is the result of the combination of these gases in the air with vapour GRM: n. (1,2) Note: acidifying deposition can be responsible for acidification of lakes, rivers and groundwater, with resulting damage to fish and other components of aquatic ecosystems, and for damage to forests and other harmful effects on plants; precipitation is naturally acid as a result of the absorption of carbon dioxide from the atmosphere