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Acid Rain and Mercury

Monitoring Pollutants in Rain

The DEP, under cooperative agreement with Penn State, has maintained the Pennsylvania Atmospheric Deposition Monitoring Network since 1981. The purpose of this program is to determine how much acid rain is falling in Pennsylvania for environmental assessment purposes. Parameters monitored include pH, sulfate, nitrate, ammonium, chloride, calcium, magnesium, potassium, sodium, and specific conductance. Starting in 1997, measurements were made of the amount of mercury in rain. The DEP currently supports 17 acid rain and13 mercury monitoring sites.

Acid Rain Information

Acid rain has been in the headlines for a number of years. It's effects on forests and soils, streams and lakes, fish and other organisms, materials, and human health have been well documented. Title IV of the Clean Air Act has successfully reduced two of the major pollutants that cause acid rain that are emitted from large stationary sources. But more needs to done before the environment can recover.


  • Acid Rain Monitoring Sites and Data
    See a map of acid rain monitoring sites in Pennsylvania. Visit a site to get more information including raw acid rain data in a text format.


  • EPA's Acid Rain Program
    EPA's goal is to achieve significant environmental and public health benefits through reductions in emissions of sulfur dioxide and nitrogen oxides, the primary causes of acid rain.
    The nation's primary source for data on dry acidic deposition and rural, ground-level ozone. Operating since 1987, CASTNET is used in conjunction with other national monitoring networks to provide information for evaluating the effectiveness of national emission control strategies.


    Alliance for Aquatic resource Monitoring

Mercury in Rain

Mercury is emitted into the air primarily by large coal-fired power plants. Mercury in the air is usually of little direct concern. But when mercury is washed from the air by rain into our streams and lakes, it is transformed to a highly toxic form that can build up in fish. People are then exposed to mercury by eating fish.


  • Fish Consumption Advisory
    Mercury in the environment can accumulate in fish. Refer to the advisory on which fish are safe to eat.