Smelting and refining of sulfur-bearing metal ores and the combustion of fossil fuels for transportation, power generation, and heating produce sulfur dioxide and nitrogen oxide. These emissions combine with atmospheric water vapour to produce corrosive nitric and sulfuric acid, which fall as rain, fog, or snow, or spread as gases and particles. Acid precipitation has long been a problem in the Boreal Shield, particularly in Ontario and Quebec, where rock, water, and soil cannot neutralize acid. The fallout damages forests, and kills lakes and streams. Winds waft emissions far from their sources.
Some acid rain that falls in Canada comes from industries in the midwestern United States. Canada, however, sends some of its acid rain to the eastern United States. In 1991, the two countries signed an accord to cut emissions. But a decade later, experts claimed 56 percent of Canada’s lakes were still acidified; 11 percent were in worse condition. By 2010, about 800,000 square kilometres in eastern Canada may still receive harmful levels of acid rain.
The animation begins with a diagram showing a three-quarter drawing of a partially wooded slope, which also has a lake and a river. As the narration proceeds, industrial buildings appear, which emit gases from smokestacks. Labels and arrows show how the emissions mix with atmospheric clouds and water and form acid rain and snow, and how acids leach through soils into groundwater.
Acid precipitation has long been a problem in the Boreal Shield. Sulfur dioxide and nitrogen oxide are by-products of smelting and refining certain metal ores and of fossil fuel combustion for transportation, power generation, and heating.
These emissions combine with atmospheric water vapour to produce corrosive nitric and sulfuric acid. The acid may then fall as rain, fog, or snow, or spread as gases and particles. Winds can carry emissions far from where they originated.
These emissions are particularly problematic in Ontario and Quebec, where rock, water, and soil are unable to neutralize acid. Instead, acid can leach through the soil and into the water table. The fallout damages forests, makes soil too acidic for organic growth, and devastates lakes and streams.