Over the course of a few decades, researchers turned their attention toward what was rapidly becoming an issue not only in industrial regions, but in airsheds across the globe. Since international borders mean nothing to moving air masses, acid rain also became a political issue. Tensions between the U.S. and Canada escalated, specifically because the environmental damage seen in southern Canada was linked to emissions originating in the industrial sectors of the U.S.
The Push for Cleaner Air
Federal legislation around air pollution had existed since the mid-1950s in the U.S. and paved the way for the Clean Air Act of 1963. The landmark legislation was a major step forward, and in the following decades, continual public concern led to Congress amending the Act to set air quality standards, launch monitoring programs and expand enforcement. By the 1980s, political and societal pressure regarding the issue of acid rain surged, and further amendments to the Clean Air Act in 1990 directly addressed sulfur dioxide pollution from manufacturing, requiring emissions be cut by over 50%. The Environmental Protection Agency already had authority to regulate vehicle emissions; further tightening of fuel regulations and personal vehicle emissions led to a continual decline in nitrogen oxides and sulfur dioxide in urban areas. (The agency continues to make progress in improving air quality and as of April 2023 proposed new regulations on vehicle emissions.) Under the combination of these new regulations, both sulfur and nitrogen emissions in the airshed plummeted from their record-high levels. Ecosystems, and government relations, began the long road to recovery—although the U.S.-Canadian relationship mended itself much faster than the acidified habitats.
Since laws and regulations were improved to reduce pollution, forests and lakes throughout southern Canada and the mid-Atlantic have rebounded significantly. Challenges remain, though; although low sulfur fuels have made acid rain less of an environmental threat in the region, emissions from other sources remain a concern. The Chesapeake Bay is surrounded by dense, urban areas and large-scale agriculture, which continue to emit nitrogen oxides from vehicles and fertilizers. Even with tougher standards, an estimated 25% of nitrogen-based pollution in the watershed is entering it through the atmosphere.