United States Environmental Protection Agency
Clean Air Status and Trends Network
Weekly rural air chemistry and dry deposition at United States monitoring sites since 1987. Filter packs exposed for a week are analysed for sulphate, nitrate, ammonium, sulphur dioxide and nitric acid, and dry deposition fluxes are computed from those concentrations and a modelled deposition velocity. The network exists to measure the acidifying and nutrient inputs reaching land and water from the air, and it holds the record of their decline after the Clean Air Act amendments.
Rights
- Commercial reuse
- Yes
- Redistribution
- Yes
- Derivative use
- Yes
- Attribution required
- No
- Restrictions
- Applies to material authored by US federal agencies. Third-party material carried within a federal product may be separately protected.
- Terms last checked
- 27 August 2026
Access and coverage
- Publisher
- United States Environmental Protection Agency
- Website
- https://www.epa.gov/castnet
- Geographic coverage
- United States — rural monitoring sites
- Temporal coverage
- 1987 onwards
- Resolution
- Monitoring site, weekly
- Update frequency
- weekly
- Formats
- csv, zip
- Bulk download
- Available
- Registration required
- No
- Cost to Hydrionis
- Free
- Domains
- atmospheric
What Hydrionis holds from this publisher
The publisher’s own coverage is above. This is what Hydrionis has actually taken from it, at the subjects it measures — gauges, boreholes, reservoirs or places.
1,426,840
Values held
1,132
Series, each one measurement at one place
123
Subjects measured
1987–2026
Period actually held, not the publisher’s span
What is measured
- Dry ammonium deposition · kg/ha
- Dry nitric acid deposition · kg/ha
- Dry particulate nitrate deposition · kg/ha
- Dry sulphate deposition · kg/ha
- Dry sulphur dioxide deposition · kg/ha
- Nitric acid in air · µg/m³
- Particulate ammonium in air · µg/m³
- Particulate nitrate in air · µg/m³
- Particulate sulphate in air · µg/m³
- Sulphur dioxide in air · µg/m³
How current it is
- Partial record held
- EPA CASTNET offers more than Hydrionis currently holds. The newest value here covers 2026-05; the gap is a deliberate limit on what has been collected, not a limit on the source. CASTNET publishes filter-pack chemistry, dry deposition, hourly ozone, meteorology and site metadata. Hydrionis holds five measured concentrations and their five modelled dry deposition fluxes at sites with at least 200 weekly records. Ozone and meteorology are not held: Hydrionis has no water pathway for the first and holds weather from elsewhere. Wet deposition is measured by a separate network with a different access route and is not held, so no total deposition figure is available here.CASTNET publishes filter-pack chemistry, dry deposition, hourly ozone, meteorology and site metadata. Hydrionis holds five measured concentrations and their five modelled dry deposition fluxes at sites with at least 200 weekly records. Ozone and meteorology are not held: Hydrionis has no water pathway for the first and holds weather from elsewhere. Wet deposition is measured by a separate network with a different access route and is not held, so no total deposition figure is available here.
Hydrionis products built from it
Where this publisher’s data reaches a reader. Each has its own page, with its licence and how to cite it.