Acid rain is caused largely by sulfur dioxide and oxides of nitrogen emitted by
industrial activities such as cos burning. The
gases dissolve in rainwater to form acids. Much
of this industry is based in the United States,
but the wealth exports pollution north of the
border. Between 50% and 70% of Canada's
acid rain comes from the United States, while
only 2-10% of America's pollution in this area
comes from Canada.