# Ozone Transport Region (CAA 184, 40 CFR 81.457)

The Ozone Transport Region of the Clean Air Act, where a source of 50 tons a year of volatile organic compounds is a major source, as if the area were in moderate ozone non-attainment, even where the air meets the standard.

## Source

| Fact | Value |
| --- | --- |
| Publisher | U.S. Congress (Clean Air Act section 184) and EPA (40 CFR 81.457) |
| Product | Ozone Transport Region (statutory boundary, as of 2022-03-14) |
| Source | [https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-81/subpart-E/section-81.457](https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-81/subpart-E/section-81.457) |
| Category | Hazard |
| Period | The boundary as of 2022-03-14 (40 CFR 81.457) |
| Refresh cadence | None (statutory table in the code) |
| Geographies | County, from the statute's list as codified; a metro is the population-weighted mean of its counties', so it reads as the share of its population in the region. |
| Availability | Available |
| Cadastre key | `ozone-transport-region` |

## Licence and attribution

| Fact | Value |
| --- | --- |
| Licence | Public domain (U.S. statute and regulation) |
| Terms | [https://www.law.cornell.edu/uscode/text/42/7511c](https://www.law.cornell.edu/uscode/text/42/7511c) |
| 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. Congress (Clean Air Act section 184) and EPA (40 CFR 81.457), Ozone Transport Region (statutory boundary, as of 2022-03-14)**.

## 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 |
| --- | --- | --- | --- |
| `ozone_transport_region` | Population in the Ozone Transport Region (share) | share (0-1): a county is 1 inside the Ozone Transport Region, 0 outside, and a Maine county only partly inside counts by its listed towns' share of its population (ACS); a metro is the population-weighted mean of its counties' (a 50 tpy VOC major-source threshold applies in the region) | population-weighted county mean |

## Known gaps and caveats

- Ten whole states (CT, DE, MD, MA, NH, NJ, NY, PA, RI, VT), the District of Columbia and ten Virginia counties and cities of the Washington metro, and only listed towns of Maine since 2022.
- A Maine county only partly inside counts by its listed towns' share of its population (ACS 5-year, by county subdivision). Chebeague Island, split from Cumberland town in 2007, is not in the rule's list and counts as outside.
- Being in the region tightens VOC and NOx permitting; it is not a non-attainment designation.

## See also

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