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Clean Air Markets

Environmental Monitoring

Long-term environmental monitoring is critical for assessing the effectiveness of regulatory programs implemented to reduce emissions of multiple pollutants from coal-fired power plants and other stationary and mobile sources in the U.S.  EPA’s Clean Air Markets Division (CAMD) runs  two long-term environmental monitoring programs, the Clean Air Status and Trends Network (CASTNET) and the Long-Term Monitoring (LTM) Program, and contributes to a complementary long-term program run by the National Atmospheric Deposition Program Exit (NADP). For more than 30 years, CASTNET, LTM, and NADP collectively have provided data used to evaluate changes in air quality, atmospheric deposition, and water quality in lakes and streams. The consistent, high-quality data these monitoring programs continue to offer are the cornerstone for tracking the extent to which emissions reductions are having their intended effects on improving human and ecosystem health, particularly as shifts in the energy sector and changes in the environment continue to occur.


Monitoring Networks

  • Clean Air Status and Trends Network (CASTNET): CASTNET is a national monitoring program established to assess trends in pollutant concentrations, atmospheric deposition, and ecological effects due to changes in air pollutant emissions. The CASTNET Data Download page provides raw measurement data as well as prepackaged data sets available for download.

  • The Long Term Monitoring (LTM) program: LTM tracks changes in surface water chemistry in response to changing air emissions and acid deposition. Data are available for download on the data section of the LTM page.

  • The National Atmospheric Deposition Program Exit (NADP): is a cooperative effort between many different groups, including federal, state, tribal and local governmental agencies; educational institutions; private companies; and non-governmental agencies. NADP provides wet deposition of sulfur, nitrogen, and mercury to complement the dry deposition estimates provided by CASTNET as well ambient concentrations of ammonia and mercury.

Frequent Questions

How do I cite CAMD Environmental Monitoring Data?

CAMD suggests the following citations for CASTNET & LTM data:

U.S. Environmental Protection Agency Clean Air Markets Division
Clean Air Status and Trends Network (CASTNET)
[Data table(s) accessed (i.e., Hourly Ozone, Annual Total Deposition)]
Available at
Date accessed: [month day, year]

U.S. Environmental Protection Agency Clean Air Markets Division
EPA Long-Term Monitoring of Acidified Surface Waters
Version 1.0
DOI: 10.23719/1518546 
Date accessed: [month day, year]

Monitoring Partners

The following links exit the site Exit

  • The Canadian Air and Precipitation Monitoring Network (CAPMoN): Environment & Climate Change Canada supports CAPMoN, a program similar to CASTNET and NADP. CAPMoN measures long-term regional trends in atmospheric pollutants in both air and precipitation. Data can be found on the CAPMoN website.

  • The National Park Service (NPS) supports thirty CASTNET sites in National Parks, Class 1 areas, and National Monuments to evaluate air quality, visibility, and critical load exceedances within the federal boundaries. 

  • The Bureau of Land Management Wyoming State Office (BLM-WSO) supports several CASTNET sites in Wyoming in partnership with the Wyoming Air Resources Monitoring System (WARMS).

  • The Shenandoah Watershed Study and Virginia Trout Stream Sensitivity Study (SWAS-VTSSS): The program is a monitoring and research network focused on mountain streams in western Virginia. They collect Virginia stream water quality data used for the LTM program. 

  • The Vermont Department of Environmental Conservation (VT DEC): VT DEC has been monitoring the chemistry of low-ionic strength lakes in Vermont since the winter of 1980. They collect Vermont lake water quality data used for the LTM program. 

  • The University of New Hampshire (UNH): UNH collects New Hampshire and Maine lake water quality data used for the LTM program.

  • The United States Geological Survey (USGS) New York Water Science Center:  USGS monitors trends in surface water quality by nesting a few intensively-monitored stations within a network of more numerous but less frequently sampled stations. They collect Catskills stream water quality data used for the LTM program.

  • The Adirondack Long Term Monitoring Program (ALTM): ALTM collects Adirondacks lake water quality data used for the LTM program.