From Earth Science Information Partners (ESIP)

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Data System Name: CASTNET
Data System URL:
Contact Person: Gary Lear
Contact e-mail:


About the Data System (Purposes, Audience)

The Clean Air Status & Trends Network (CASTNET) is a rural, regional monitoring network designed primarily to measure seasonal and annual average concentrations and depositions over many years. CASTNET measurements are used to track long-term temporal and spatial trends due to changes in air quality. Data is used to assess the environmental impacts as a result of the U.S. EPA’s emission reduction programs (in particular, the Acid Rain Program (ARP) and the NOx Budget Trading Program (NBP)). In the future, CASTNET is expected to serve as an assessment tool for the Clean Air Interstate Rule (CAIR). Data measured from the CASTNET network is used by universities, ecologists, tribes, as well as federal regulators, as it is the only national long-term, regional, rural monitoring network.


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Developed from the National Dry Deposition Network (NDDN), CASTNET was established in 1991 under the Clean Air Act Amendments. CASTNET provides nationwide data for determining relationships between changes in emissions and any subsequent changes in air quality, atmospheric deposition, and ecological effects. The network has been a key assessment tool for tracking changes in SO2, NOx and O3 after implementation of the Acid Rain Program, NOx State Implementation Plan, and the NOx Budget Trading Program.



List of Publications, Papers, Presentations

Data System Scope

Data Content

Datasets Served

All data can be found/downloaded on the CASTNET website at, while real-time ozone concentrations from 35 sites are submitted to AirNow and can be viewed on the AirNow website.


Weekly samples – SO2, HNO3, SO42-, NO3-, NH4+, Ca2+, Mg2+, K+, Na+ and Cl-

1-hr samples – Ozone, temperature (2m & 9m), wind speed, wind direction, sigma theta, solar radiation, relative humidity, precipitation, surface wetness

Spatial - Temporal Coverage

CASTNET sites are located throughout the United States, with the best spatial coverage in the East. Many CASTNET sites have been collecting data for 15+ years. The filter pack collects weekly samples of particulate and gaseous data while the ozone monitor records hourly averages at each site.



Real-time ozone measurements being sent to AirNow determine “ozone action days” or days when it is unhealthy for children, elderly and those with weak respiratory systems to go outside. CASTNET data is used for ecological health studies, less so for human health.

Forecasting and Reanalysis

CASTNET data from 35 sites are currently submitted to AIRNow. The remainder of network sites are planned for submission in 2008.

Model/Emissions Evaluation

CASTNET has been and is continuing to be used as an assessment tool for emission reduction programs such as the Acid Rain Program and the NOx Budget Trading Program. CASTNET data is also used extensively for validation and development of atmospheric models, including CMAQ.

Characterization, Trends, Accountability

More than 50 CASTNET sites have been collecting data consistently for over 15 years and are used extensively for determining trends in air chemistry and deposition. CASTNET data is used by the EPA as an accountability tool for regulated emissions reductions programs.


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Data System IT

Primary/Official Store for Some data

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Data Consolidation/integration

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Providing Data Access to users/externals

All data is provided on the CASTNET website after it is QA’ed. Ozone data is provided to the public through the CASTNET website and AirNow

Data Processing

Data is managed in an Oracle 10g database


Concentration maps for the Eastern and CONUS regions are shown on the CASTNET website. Deposition trends plots, changes in meteorology, and ozone concentrations are shown for each site on the CASTNET website. Additional publications with supporting visualization and analysis are also available on the website.

Decision Support (e.g. some integration into user business process)

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End-to-End Integration

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Other DS Values

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Data Access and/or Output Interoperability

Data is available within the EPA firewall via SQL*Net and ODBC drivers. Data are available via the Web as prepackaged data sets and a data query wizard.

Reusable Tools and Methods

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Security Barriers and Solutions

Database is behind EPA firewall.

User Feedback Approach

Comments via EPA’s web site comments.

Other Architecture

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User Provided Content

Agency Details

  • CASTNET is run through EPA’s Clean Air Markets Division. Presently there are a total of 84 operational sites. EPA sponsors 59 sites, including several operated by tribal and local authorities, US Forest Service, and USDA. The National Park Service sponsors 25 sites which are located in national parks or designated Class-I areas.
  • CASTNET also has a partnership with the National Atmospheric Deposition Program/National Trends Network (NADP/NTN). To calculate total deposition (wet+dry) NADP/NTN operates a wet deposition sampler at or near almost every CASTNET site.
  • CASTNET runs a collocated site at Egbert, Ontario in collaboration with Canadian Air and Precipitation Monitoring Network (CAPMoN)