Clean Air Act Reduces Acid Rain In Eastern United States

"Pennsylvania has long been recognized as the acid rain capital of the country," says James A. Lynch, professor of forest hydrology, school of forest resources. "The pollutants that cause acid rain come from local sources and sources located in the Midwest and affect a wide region up into New England.

"However, since implementation of phase one of title VI of the Clean Air Act of 1990, acid rain concentrations in the North Eastern U.S. have decreased by as much as 20 percent," Lynch recently told attendees at the Pennsylvania Acidic Deposition Conference, University Park, Pa.

Acid rain is caused by sulfur dioxide and nitrogen oxides produced when fuels burn. The source of most sulfur dioxide is high-sulfur coal burned in power plants. Controlling this source of sulfur dioxide production can have a major impact on acid rain in Pennsylvania and other regions of the Northeast.

Unfortunately, only 30 percent of the nitrogen oxides causing acid rain come from power production. Automobiles generate another 30 percent and the agricultural sector contributes an additional 25 to 30 percent. Lightening strikes and biological processes produce the remaining nitrogen naturally. Consequently, it is much more difficult to control and regulate nitrogen oxides.

In 1995, Phase one of the Clean Air Act Amendments of 1990 took effect for 110 electrical utilities. Most of these power plants were in the Eastern U.S. with a few plants located west of the Mississippi River. The act specified a reduction of sulfur dioxide emissions of 10 million tons, based on 1980 levels. Reduction at the 110 utilities affected by phase one were set at 2.3 million tons.

"The actual reduction was about 3.9 million tons," says Lynch. "Some companies are actually making money by increasing their reduction because they can sell their excess emission permits to other sulfur dioxide producers."

Reduction of nitrogen oxides began in 1996, but a reduction of only two-tenths of a million tons was expected and realized. Because of the wider variety of sources of nitrogen, nitrogen oxides are more difficult to regulate and reduce.

Acid rain forms when sulfur dioxide and nitrogen oxides in the atmosphere combine with water to form sulfuric acid and nitric acid, respectively. These acids, mixed with rainwater, fall to Earth as acid rain, snow or fog and can acidify lakes and streams in the Northeast. This can affect a wide variety of other terrestrial and aquatic ecosystems as well as cultural and material resources.

Lynch calculated the pre 1995 baseline for acid deposition using data from the National Atmospheric Deposition Program. His baseline includes precipitation samples collected weekly between 1983 and 1994 from approximately 200 sites across the U.S. NADP measures samples for acidity, sulfate and nitrate concentrations. Lynch compared this baseline data with data collected in 1995 and 1996.

"Looking at sulfate concentrations, there is a 20 to 25 percent reduction of sulfate in precipitation samples over a wide region of the northeastern United States," says Lynch. "There is also a 20 to 25 percent reduction in the acidity of rainwater over this same region."

The almost one-to-one correlation between sulfate deposition and acidity is too strong to be a coincidence, according to Lynch. The Clean Air Act Title VI appears to have reduced acid rain levels in the Northeast.

The Penn State researcher admits that some reductions in acidity in northern New England are probably a direct result of similar environmental controls in Canada's southeastern provinces.

A severe drought in some portions of the Southeast apparently caused higher sulfate and nitrate concentrations during 1995 and 1996. With less precipitation, concentrations increase, but do not necessarily suggest an increase in total sulfate or nitrate deposition. Lynch is currently looking at 1997 data to determine if sulfate and nitrate deposition remains at 1995 and 1996 levels.