WHAT GOES UP... MUST COME DOWN

As April showers roll around so do the nasty reminders of acid rain levels in Canada. The most common pollutants which acidify rain are sulphur dioxide and nitrogen oxide. Sulphur dioxide (SO2) is generally a byproduct of industrial processes and burning of fossil fuels. Ore smelting, coal-fired power generators, and natural gas processing are the main contributors. We find, for instance, U.S. SO2 emissions were measured at 16.8 million tonnes, a full six times greater than Canada's 2.7 million total tonnes. But the sources of SO2 emissions from the two countries are quite different. While 61% of Canada's emissions come directly from industrial sources, 66% of the U.S.' emissions are from the electrical utilities. More than half of the acid deposition in eastern Canada originates from emissions in the United States. Areas such as Muskoka-Haliburton and Quebec City receive about three-quarters of their acid deposition from the United States. The main source of NOX emissions is the combustion of fuels in motor vehicles, residential and commercial furnaces, industrial and electrical-utility boilers and engines, and other equipment. Canada's largest contributor of NOX is the transportation sector, which accounted for approximately 60% of all emissions.. By comparison, U.S. NOX emissions are 10 times more than Canada's. The influence of transboundary flows of air pollutants from the United States into Canada is significant. Overall about 24% of the regional-scale ozone episodes that are experienced in the United States occur simultaneously in Ontario. An analysis of ozone concentrations at four sites in extreme southwestern Ontario taking wind factors into account provides an estimate that 50 to 60% of the ozone at these locations is of U.S. origin. Acid rain is a problem in eastern Canada because many of the water and soil systems in this region lack natural alkalinity, such as a lime base, and cannot neutralize acid naturally. Provinces that are part of the Canadian Precambrian Shield, like Ontario, Quebec, New Brunswick and Nova Scotia, are hardest hit because their water and soil systems cannot fight the damaging consequences of acid rain. In fact, more than half of Canada consists of susceptible hard rock (i.e., granite) areas that cannot neutralize the effects of acid rain. If the water and soil systems were more alkalineas in Western Canada they could neutralize or "buffer" against acid rain naturally. In Western Canada, acid rain is not a big problem yet but could always become one if we are not careful. Historically, lower levels of industrialization relative to eastern Canada combined with natural factors such as eastwardly moving weather patterns and resistant soils (i.e., soils better able to neutralize acidity), have preserved much of Western Canada from the ravages of acid rain. However, not all areas in Western Canada are naturally protected. Lakes and soils resting on granite bedrock, for instance, cannot neutralize precipitation. These districts include areas of the Canadian Shield in northeastern Alberta, northern Saskatchewan and Manitoba, and parts of western British Columbia. Lakes in these areas are as defenseless to acid rain as those in northern Ontario. They must be shielded from exposure to acid rain if not environmental damage could be swift and serious.