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Research Efforts on the Effects of Air Pollution

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Health Effects


Between 2003 and 2007, Health Canada carried out two research programs to characterize air pollution exposure and human health issues under the Canadian portion of the Border Air Quality Strategy, coordinated with research in the United States. The research programs pertain to the Great Lakes Basin Airshed and the Georgia Basin-Puget Sound International Airshed. Further information on these studies can be found at <www.hc-sc.gc.ca/ewh-semt/air/out-ext/great_lakes-grands_lacs-eng.php> and <www.pyr.ec.gc.ca/airshed/index_e.htm>, respectively.


EPA conducts human health and exposure research as part of the Clean Air Research Program. The research conducted in this program includes studies focused on the Detroit–Windsor area, located within the PEMA. More information on these studies can be found at <www.epa.gov/dears/> and <www.epa.gov/dears/studies.htm>.

Photo of lake and sky.Aquatic Effects

In a recent study, Canadian and U.S. scientists analyzed trends in acidification of lakes and streams in eight regions of the northeastern United States and southeastern Canada. The scientists looked at data from 1990 to 2004, which approximately parallels the existence of the U.S.–Canada AQA.

One of the strongest trends found in this analysis was for sulfate, an acidic compound that is formed when SO2 emissions combine with water, oxygen, and oxidants in the atmosphere. After sulfate is formed in the atmosphere it can fall back to earth and acidify surface waters such as lakes and streams, making it difficult for acid-sensitive aquatic organisms to survive. The results of this analysis indicate that U.S. and Canadian SO2 emission reductions included in the AQA commitments have resulted in obvious, significant, and substantial declining sulfate trends in all but one of the regions examined.

Critical Loads and Exceedances

The critical load of acid deposition is defined as the maximum deposition that an ecosystem can assimilate without significant long-term harmful effects. For environmental impacts related to acidification, deposition of both nitrogen and sulfur compounds can contribute to a critical load exceedance.


In the 2004 Canadian Acid Deposition Science Assessment, for the first time in North America, new and combined critical load estimates were generated for sulfur and nitrogen acid deposition.


In the United States, the critical loads approach is not an officially accepted approach to ecosystem protection. However, recent activities within federal and state agencies, as well as the research community, indicate that critical loads might be emerging as a useful ecosystem protection and program assessment tool.

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