# co-nonattainment-serious — Clean Air Act "major source" emission thresholds by pollutant and area classification

For co-nonattainment-serious, which major-source test is Part D Title I nonattainment major stationary source; pollutant or pollutant class is carbon monoxide; area classification (if applicable) is Serious; threshold (tons per year) is 50; definition heading is Major source means any stationary source, recorded from its source on 2026-08-19; source re-checked 2026-09-09.

- **Row ID:** co-nonattainment-serious _(our reading, not quoted from the source)_
- **Which major-source test:** Part D Title I nonattainment major stationary source _(our reading, not quoted from the source)_
- **Pollutant or pollutant class:** carbon monoxide _(verified: appears in the quote below)_
- **Area classification (if applicable):** Serious _(verified: appears in the quote below)_
- **Threshold (tons per year):** 50 _(verified: appears in the quote below)_
- **Definition heading:** Major source means any stationary source _(verified: appears in the quote below)_

## What the source says

> For carbon monoxide nonattainment areas: (A) That are classified or treated as classified as “Serious,” and (B) in which stationary sources contribute significantly to carbon monoxide levels as determined under rules issued by the Administrator, sources with the potential to emit 50 tpy or more of carbon monoxide; and

## Source

- https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-70/subpart-A/section-70.2

Last verified: 2026-09-09. Review by: 2027-02-15.
Part of [Clean Air Act "major source" emission thresholds by pollutant and area classification](https://referencesource.org/clean-air-act-major-source-thresholds/).