PARENT SESSION
Symposium 8: Ecosystem response and recovery: Assessing the 1991 Canada-US Air Quality Agreement
Organized by: RA Haeuber, R Birnbaum, and K Timoffee
Tuesday, August 9, 1:30 PM - 5:00 PM, Meeting Room 517 B, Level 5, Palais des congrès de Montréal
Sulfur and nitrogen deposition across eastern North America.
Vet, Robert*,1, Lear, Gary2, Narayan, Julie1, Ro, Chul-Un1, Shaw, Mike1, 1 Environment Canada, Toronto, ON, Canada2 United States Environmental Protection Agency, Washington, DC, USA
ABSTRACT- Sulfur and nitrogen deposition patterns across eastern North America are presented based on wet, dry and total deposition estimates from the Canadian Air and Precipitation Monitoring Network (CAPMoN) and the U.S. Clean Air Status and Trends Network (CASTNET). The deposition estimates provide a basis for understanding the atmospheric loading of sulfur and nitrogen to ecosystems in both eastern Canada and the eastern U.S.A. As well, they provide an opportunity to assess the atmospheric response to SO2 and NOx emission changes agreed to under the 1991 Canada-U.S. Air Quality Agreement and the Canadian and US domestic emission control programs. Wet deposition of sulfur in eastern North America decreased markedly in the late 1990s in response to major emission reductions in both countries. Between the five-year periods 1990-1994 and 1996-2000, total SO2 emissions in eastern North America decreased by 21% while total wet deposition decreased by 15%. These changes acted as the main driver for ecosystem response and recovery throughout the area. During the same two periods, NOx emissions and nitrogen wet deposition changed minimally. As an atmospheric input into ecosystems, dry deposition has traditionally been very difficult to estimate -- certainly much more difficult than wet deposition. This analysis combines CAPMoN and CASTNET dry deposition estimates for sulfur and nitrogen and assesses the importance of dry deposition compared to wet deposition across the broad area of eastern North America. Current estimates suggest that dry depoisition of sulfur and nitrogen is roughly equivalent to wet deposition in the high emission areas of eastern Canada and the eastern USA and drops to approximately 25% in the more remote areas of the north and south. Dry, wet and total (wet+dry) deposition patterns across eastern North America will be shown and CAPMoN and CASTNET dry deposition estimates will be compared at a collocated site.
Key words: acid deposition, wet and dry deposition, atmospheric deposition, emissions and deposition