# EPA Class I areas

EPA's boundaries of the Class I areas under the Clean Air Act: the national parks and wilderness areas whose air the prevention-of-significant-deterioration (PSD) program protects most. A new major source that may affect one faces Class I increment and air-quality-related-value review and notice to the federal land manager; 100 km is the customary screening distance in EPA and land-manager guidance, so nearness is a cue for how involved air permitting will be.

## Source

| Fact | Value |
| --- | --- |
| Publisher | U.S. Environmental Protection Agency, OAQPS (from NPS, USDA Forest Service, FWS and BIA boundaries) |
| Product | Class I areas under the Clean Air Act (mandatory federal and tribal) |
| Source | [https://www.epa.gov/visibility/regional-haze-program](https://www.epa.gov/visibility/regional-haze-program) |
| Category | Hazard |
| Period | The layer's last data edit (EPA ArcGIS service) |
| Refresh cadence | Quarterly |
| Geographies | County and metro. The distance is from each county's centroid, and a metro's is the population-weighted mean of its counties'; the count and the area share within 100 km are measured for counties and metros directly (a metro's share is its counties' weighted by area). |
| Availability | Available |
| Cadastre key | `epa-class-one-areas` |

## Licence and attribution

| Fact | Value |
| --- | --- |
| Licence | Public domain (U.S. federal government work) |
| Terms | [https://www.arcgis.com/home/item.html?id=86b6748fb99544eeb49ca9e5a1d12d99](https://www.arcgis.com/home/item.html?id=86b6748fb99544eeb49ca9e5a1d12d99) |
| Register status | Production approved; licence open |
| Allowed uses | `evaluation`, `internal`, `public_display`, `derived_analytics`, `redistribution`, `bulk_export`, `public_geometry` |

This source requires no credit line beyond naming the publisher. Cite it as **U.S. Environmental Protection Agency, OAQPS (from NPS, USDA Forest Service, FWS and BIA boundaries), Class I areas under the Clean Air Act (mandatory federal and tribal)**.

## Measures

The key is the measure's identifier in Cadastre. A measure stored for the metro itself is read as stored; **Rule from counties** is how a metro is assembled from its counties where it is not (see [Methodology](https://getcadastre.com/docs/methodology)).

| Key | Label | Unit | Rule from counties |
| --- | --- | --- | --- |
| `class1_nearest_km` | Distance to the nearest Class I area (km) | km from the county's centroid to the nearest of the 158 mandatory Class I federal areas (national parks and wilderness areas of 1977; tribal Class I areas not counted), 0 inside one; a metro is the population-weighted mean of its counties'; a screening cue for PSD Class I review, not a permitting finding | population-weighted county mean |
| `class1_areas_within_100km` | Class I areas within 100 km | areas: how many of the 158 mandatory Class I federal areas (national parks and wilderness areas of 1977; tribal Class I areas not counted) lie within 100 km of any part of the county or metro; a screening cue for PSD Class I review, not a permitting finding | Not assembled from counties: a metro has a value only where one is stored for the metro itself |
| `class1_within_100km_area_share` | Area within 100 km of a Class I area (share) | share of the area (0-1) within 100 km of one of the 158 mandatory Class I federal areas (national parks and wilderness areas of 1977; tribal Class I areas not counted); a metro is its counties' shares weighted by area; a screening cue for PSD Class I review, not a permitting finding | Not assembled from counties: a metro has a value only where one is stored for the metro itself |

## Known gaps and caveats

- Distance to a Class I area is a screening cue, not a PSD applicability finding: that depends on the source's size, emissions and modeling.
- The measures count the 158 mandatory Class I federal areas (the 156 of 40 CFR 81 subpart D and the two where visibility is not an important value); the seven tribal Class I areas are stored but not counted.
- A county's distance is from its centroid, not from a particular site; a large county can be much nearer or farther at its edges.
- Boundaries are simplified to about 50 m before distances are measured.

## See also

- [All datasets](https://getcadastre.com/docs/datasets)
- [Rights and attribution](https://getcadastre.com/docs/rights)
- [Data freshness](https://getcadastre.com/docs/freshness)