Jump to main content.


The Acid Rain Challenge

Table of Contents

Acid Rain

Acid deposition, more commonly known as acid rain, occurs when emissions of SO2 and NOX from power plants, vehicles, and other sources react in the atmosphere (with water, oxygen, and oxidants) to form various acidic compounds. These acidic compounds then fall to earth in either a wet form (rain, snow, or fog) or a dry form (gases and particles) and can harm aquatic and terrestrial ecosystems (particularly forests); affect human health; impair visibility; and damage automotive finishes, buildings, bridges, monuments, and statues.

Key Commitments of the Acid Rain Annex

Both the United States and Canada have been successful in reducing SO2 and NOX emissions and thus, mitigating the impact of acid rain on each side of the border. Despite these achievements, however, further efforts are needed to restore all damaged ecosystems to their pre-acidified conditions.

Commitments and Progress: SO2 Emission Reductions

CANADA:

Figure 1. Canadian SO2 Emissions from Acid Rain Sources, 1980–2006

Figure 1. Canadian SO2 Emissions from Acid Rain Sources, 1980–2006
Source: Environment Canada, 2008

1 One tonne is equal to 1.1 short tons.

UNITED STATES:

Figure 2. U.S. SO2 Emissions from Acid Rain Program Electric Generating Units, 1980–2007

Figure 2. U.S. SO2 Emissions from Acid Rain Program Electric Generating Units, 1980–2007
Source: EPA, 2008

Preventing Air Quality Deterioration and Protecting Visibility

Under the Acid Rain Annex, Canada and the United States have recognized the importance of preventing air quality deterioration and protecting visibility from sources that could cause significant transboundary air pollution. In October 2007, a joint U.S.-Canada visibility workshop was held in Research Triangle Park, North Carolina. The U.S. Environmental Protection Agency (EPA), the U.S. Federal Land Managers, and Canadian government representatives came together to review the history of the U.S. visibility program and to share information and lessons learned from joint analyses, discuss international transport, and investigate future collaboration.

Commitments and Progress: NOX Emission Reductions

CANADA:

UNITED STATES:

Figure 3. NOX Emission Trends for All Acid Rain Program Units, 1990–2007

Figure 3. NOX Emission Trends for All Acid Rain Program Units, 1990–2007
Source: EPA, 2008

Consultation and Notification Concerning Significant Transboundary

Air Pollution Since 1994, Canada and the United States have regularly notified each other concerning potential new sources and modifications to existing sources of transboundary air pollution within 62 miles (100 km) of the U.S.–Canada border. Since publication of the 2006 United States–Canada AQA Progress Report, Canada has notified the United States of eight additional sources, for a total of 52 Canadian notifications. The United States has notified Canada of nine additional sources, bringing the total number of U.S. notifications to 56. More information is available on the government Web sites of each country at:

Canada:
www.ec.gc.ca/cleanair-airpur/ CAOL/canus/canus_applic_e.cfm

United States:
www.epa.gov/ttn/gei/ uscadata.html

Acid Deposition Trends

Both nations use wet deposition (rain or snow) data to assess how the atmosphere is responding to decreasing or increasing emissions of sulfur and nitrogen. Figures 4 and 5 show the U.S.–Canada spatial patterns of wet sulfate and wet nitrate deposition, respectively, for 1990 and 2005. The pattern from 1990 to 2005 illustrates that significant reductions occurred in wet sulfate deposition in both the eastern United States and much of eastern Canada. Reductions in wet nitrate deposition have generally been more modest than for wet sulfate deposition.

Figure 4. Annual Sulfate Wet Deposition

Figure 4. Annual Sulfate Wet Deposition

Figure 5. Annual Nitrate Wet Deposition

Figure 5. Annual Nitrate Wet Deposition
Source: National Atmospheric Chemistry (NAtChem) Database (www.msc-smc.ec.gc.ca/natchem/index_e.html) and the National Atmospheric Deposition Program (NADP)

Top of page

 


Local Navigation


Jump to main content.