---
kind: "section"
citation: "40 C.F.R. § 50.7"
title: "40"
number: "50.7"
heading: "National primary and secondary ambient air quality standards for PM 2.5 ."
url: "https://uscodex.org/cfr/40/50.7"
---

# §50.7. National primary and secondary ambient air quality standards for PM 2.5 .

- (a) The national primary and secondary ambient air quality standards for particulate matter are 15.0 micrograms per cubic meter (µg/m 3) annual arithmetic mean concentration, and 65 µg/m 3 24-hour average concentration measured in the ambient air as PM2.5 (particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers) by either:
  - (1) A reference method based on appendix L of this part and designated in accordance with [part 53](/cfr/40/part53.md) of this chapter; or
  - (2) **An equivalent method designated in accordance with part 53 of this chapter.**
- (b) The annual primary and secondary PM2.5 standards are met when the annual arithmetic mean concentration, as determined in accordance with appendix N of this part, is less than or equal to 15.0 micrograms per cubic meter.
- (c) The 24-hour primary and secondary PM2.5 standards are met when the 98 th percentile 24-hour concentration, as determined in accordance with appendix N of this part, is less than or equal to 65 micrograms per cubic meter.

## Notes

### Amendments

[62 FR 38711, July 18, 1997, as amended at 69 FR 45595, July 30, 2004]

### Authority

Authority: 42 U.S.C. 7401, et seq.

### Source

Source: 36 FR 22384, Nov. 25, 1971, unless otherwise noted.

### Amendments

[62 FR 38711, July 18, 1997, as amended at 69 FR 45595, July 30, 2004]