Environmental Impacts of Acid Deposition
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Introduction
In the early 1970's, acid deposition was identified as a serious ecological threat to New York State's waters and forests. The primary emissions responsible for acid deposition are sulfur dioxide (SO2) and oxides of nitrogen (NOx) from the combustion of fossil fuels which are transformed and transported downwind before they are deposited. Acid deposition is of particular concern to New York State because of important and sensitive ecosystems which lie immediately downwind of the largest mid-western utilities burning fossil fuels and emitting SO2 and NOx emissions in North America.
An ecosystem is considered sensitive to acid deposition when it lacks adequate soil buffering capacity to counter the acids deposited to it. Sensitive ecosystems include the Adirondack Mountains, the Catskill Mountains and the Hudson Highlands.
Acid deposition also damages building materials by eroding the ornamental facades, statuary and other vulnerable edifices that are an important part of our heritage. In addition to being the main ingredient in acid rain formation, SO2 also leads to sulfate formation; acidic particles that can cause respiratory problems in humans.
In 1984, the "State Acid Deposition Control Act" (SADCA) required the reduction of SO2 emissions from existing sources and further NOx emission controls on new sources in New York State. SADCA also required the Department of Environmental Conservation (DEC) to set an Environmental Threshold Value (ETV) for sulfate deposition. The ETV was set at 20 kilograms per hectare. The Department established the New York State Acid Deposition Network to determine levels of actual deposition in the state for comparison to the ETV and to measure any changes in deposition that might occur as a result of the control program.
Clean Air Act
The Clean Air Act Amendments of 1990 contained important provisions to control acid deposition by reducing the amounts of SO2 and NOx emitted to the air. By 1995, a national reduction of approximately 3.5 million tons of SO2 emissions was expected, and a reduction of approximately 10 million tons is expected by the year 2000. A study released December 5, 1995 by the United States Environmental Protection Agency (EPA) estimated that 31 eastern states where sulfates are a significant problem would realize health benefits valued between $3 billion and $11 billion in 1997. In 2010, when control provisions are fully implemented, the report estimates that annual health benefits in the United States will range between $12 billion and $40 billion. Reductions in premature deaths account for about 88 percent of the total health benefits, while reductions in the number of new cases of chronic bronchitis accounts for another 9 percent.
Monitoring in the Future
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Future monitoring of acid deposition will determine if the emission reductions projected over the next decade will yield corresponding reductions in acid deposition. Even though large changes in deposition are expected, only one of the five national acid deposition networks that existed in the 1980s remains. This is the National Acid Deposition Program (NADP), and sampling at some stations in this network has already been discontinued. The New York network is increasingly important because it covers important areas of the state such as the western Adirondacks not previously addressed by the national networks. In addition to the traditional remote and rural monitoring sites, the network has several urban and suburban monitors which provide useful data for study of materials damage. Without the network, there would be no accurate means for establishing whether needed reductions in acid deposition are in fact occurring.
The network measures not only the "wet" deposition described in this report, but also continuously monitors SO2 with a sensitivity of one part-per-billion at selected sites. These rural SO2 measurements are not made by any other network. It is expected that measured SO2 concentrations will be very sensitive to changes in emissions and give the earliest indication of any benefits which may result from the new emission controls.
NOx Impact
Recent studies indicate that nitric acid may be more important to the acidification of sensitive ecosystems than was previously thought. In addition to the monitoring of "wet" deposition of nitrate that the network is currently performing, monitoring of atmospheric concentrations of other nitrogen compounds is also in the network plan. This would include monitoring of NOx, nitric acid and possibly some other nitrogen compounds such as peroxyacetyl nitrate (PAN). As with SO2, changes in emissions may be easier to detect with these compounds than with the wet deposition of nitrate. It appears that NOx emissions will increase in the next decade from a variety of emission sources. As such, there is increasing interest in monitoring nitrogen deposition. It is hoped New York State can add measurements of the gas-phase portion of the nitrogen chemistry to its network in the future.
More about Environmental Impacts of Acid Deposition:
- Environmental Impacts of Acid Deposition: Lakes - This picture shows the damage done by acid deposition to a lake in the Adirondacks.
- Environmental Impacts of Acid Deposition: Trees - This picture shows the damage done by acid deposition to the trees on this Adirondack mountainside.
