4. Regional impacts: risks to health and ecosystems

4.1 Acid rain

The term acid rain refers to the fallout of substances that acidify ecosystems: wet deposits of pollutants incorporated into precipitation (rain, snow, fog, etc.), dry deposits of gases and particles. The pollutants that cause acid rain are sulfur and nitrogen compounds. These gases undergo chemical changes in the air to form acids or their salts, which are found in clouds and precipitation. These compounds also settle on the ground, after undergoing chemical transformation, in the form of dry deposits of gas or dust. Other pollutants...