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Environmental Monitoring to Assess Program Results
To evaluate the results of emission reduction programs, EPA tracks, assesses, and reports on trends and conditions in the environment. EPA uses data collected from long-term monitoring networks such as the Clean Air Status and Trends Network (CASTNET), the National Atmospheric Deposition Program/National Trends Network (NADP/NTN), and the Long-Term Monitoring (LTM) and Temporally Integrated Monitoring of Ecosystems (TIME) programs. These complementary monitoring networks provide information on a variety of indicators necessary for tracking temporal and spatial trends in regional air quality, acid deposition, and environmental change in ecosystems sensitive to acid rain.
Clean Air Status and Trends Network (CASTNET)
CASTNET provides atmospheric data on the dry deposition component of total acid deposition, ground-level ozone, and other forms of atmospheric pollution. Established in 1987, CASTNET now consists of over 80 sites across the United States. EPA’s Office of Air and Radiation operates most of the monitoring stations; the National Park Service (NPS) funds and operates approximately 30 stations in cooperation with EPA. Many CASTNET sites have a continuous 20-year data record, reflecting EPA’s commitment to long-term environmental monitoring.
National Atmospheric Deposition Program/National Trends Network (NADP/NTN) 
NADP/NTN is a nationwide, long-term network tracking the chemistry of precipitation in order to assess the environmental response to emission reductions. NADP/NTN provides data on hydrogen (acidity as pH), sulfate, nitrate, ammonium, chloride, and base cations. The network is a cooperative effort involving many groups, including the State Agricultural Experiment Stations, U.S. Geological Survey, U.S. Department of Agriculture, EPA, NPS, the National Oceanic and Atmospheric Administration (NOAA), and other governmental and private entities. NADP/NTN has grown from 22 stations at the end of 1978 to more than 250 sites spanning the continental United States, Alaska, Puerto Rico, and the Virgin Islands.
Long-Term Monitoring (LTM) and Temporally Integrated Monitoring of Ecosystems (TIME) Program
The LTM and TIME programs are designed to assess the ecological response to emission reductions by tracking trends in the chemistry of lakes or streams in regions sensitive to acid deposition. LTM and TIME monitor a total of 145 lakes and 147 streams, representing all of the major acid-sensitive regions of the northern and eastern United States (New England; Adirondack Mountains; northern Appalachian Plateau, including the Catskill Mountains; and the Ridge/Blue Ridge Provinces of Virginia). These programs measure a variety of important chemical characteristics, including acid neutralizing capacity (ANC), pH, sulfate, nitrate, major cations (e.g., calcium and magnesium), and aluminum.