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Acid Rain in New England

A Brief History

Boott Mill, Lowell, MA - Photographed by Ian Cohen - Click for a larger image.

Acid rain was first observed in the mid 19th century, when some people noticed that forests located downwind of large industrial areas showed signs of deterioration. The term “acid rain” was coined in 1872 by Robert Angus Smith, an English scientist. Smith observed that acidic precipitation could damage plants and materials.

Acid rain was not considered a serious environmental problem until the 1970s. During that decade, scientists observed the increase in acidity of some lakes and streams. At the same time, research into long range transport of atmospheric pollutants such as sulfur dioxide, indicated a possible link to distant sources of pollution. Many power plants use coal with a relatively high concentration of sulfur as fuel. Scientists realized that sulfur dioxide emitted from many of these plants could be transported to the Northeast. When we began to see acid rain as a regional, rather than a local, problem, the federal government had to become involved.

In 1980, the U.S. Congress passed an Acid Deposition Act. This Act established a 10-year research program under the direction of the National Acidic Precipitation Assessment Program (NAPAP). NAPAP looked at the entire problem. It enlarged a network of monitoring sites to determine how acidic the precipitation actually was, and to determine long term trends, and established a network for dry deposition. It looked at the effects of acid rain and funded research on the effects of acid precipitation on freshwater and terrestrial ecosystems, historical buildings, monuments, and building materials. It also funded extensive studies on atmospheric processes and potential control programs.

In 1991, NAPAP provided its first assessment of acid rain in the United States. It reported that 5% of New England Lakes were acidic, with sulfates being the most common problem. They noted that 2% of the lakes could no longer support Brook Trout, and 6% of the lakes were unsuitable for the survival of many species of minnow. Subsequent Reports to Congress have documented chemical changes in soil and freshwater ecosystems, nitrogen saturation, decreases in amounts of nutrients in soil, episodic acidification, regional haze, and damage to historical monuments.

Meanwhile, in 1990, the US Congress passed a series of amendments to the Clean Air Act. Title IV of these amendments established a program designed to control emissions of sulfur dioxide and nitrogen oxides. Title IV called for a total reduction of about 10 million tons of SO2 emissions from power plants. It was implemented in two phases. Phase I began in 1995, and limited sulfur dioxide emissions from 110 of the largest power plants to a combined total of 8.7 million tons of sulfur dioxide One power plant in New England (Merrimack) was in Phase I. Four other plants (Newington, Mount Tom, Brayton Point, and Salem Harbor) were added under other provisions of the program. Phase II began in 2000, and affects most of the power plants in the country. Click here to see a list of affected power plants in New England.

Emissions of nitrogen oxide and nitrogen dioxide, generally called NOx, have been reduced by a variety of programs required under the Clean Air Act. NOx is emitted by anything burning fuel, such as power plants, large factories, automobiles, trucks, and construction equipment.

In New England, between 1990 and 2000, we have seen a 25% decrease in NOx emissions from all sources (from approximately 897,000 tons to 668,000 tons). Between 2000 and 2006, NOx emissions from Acid Rain affected power plants in New England have further decreased by more than 31,000 tons. During that same period, SO2 emissions from those power plants have decreased by 54% (from approximately 211,000 tons to 96, 500 tons).

During the 1990s, research has continued, and we are gradually developing a better understanding of acid rain and its effects on the environment. We are looking more closely at soil chemistry, and are seeing how acid rain has changed the balance of calcium, aluminum, and other elements.

The success of the Acid Rain Program has led to consideration of other programs based on setting an emissions cap. The NOx budget program which began in 1999, places a limit on NOx emissions from power plants and some other sources during the warmer months of the year. Its purpose is to control ground level ozone, but it will have some effect on acid rain also. Massachusetts, New Hampshire, and Connecticut have designed their own programs to further limit emissions of NOx and SO2. Connecticut's rule contributed to a 68% decrease in SO2 emissions from large sources from 2001 to 2002.

On March 10, 2005, EPA issued the Clean Air Interstate Rule (CAIR). This rule provides states with a solution to the problem of power plant pollution that drifts from one state to another. CAIR will permanently cap emissions of SO2 and NOx in the eastern United States. When fully implemented, CAIR will reduce SO2 emissions in 28 eastern states and the District of Columbia by over 70 percent and NOx emissions by over 60 percent from 2003 levels.

We have made significant progress in reducing acid rain, but we still have much work to do.

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