---
kind: "section"
citation: "40 C.F.R. § 50.3"
title: "40"
number: "50.3"
heading: "Reference conditions."
url: "https://uscodex.org/cfr/40/50.3"
---

# §50.3. Reference conditions.


All measurements of air quality that are expressed as mass per unit volume (e.g., micrograms per cubic meter) other than for particulate matter (PM2.5) standards contained in §§ [50.7](/cfr/40/50.7.md), [50.13](/cfr/40/50.13.md), [50.18](/cfr/40/50.18.md), and [50.20](/cfr/40/50.20.md), and lead standards contained in [§ 50.16](/cfr/40/50.16.md) shall be corrected to a reference temperature of 25 (deg) C and a reference pressure of 760 millimeters of mercury (1,013.2 millibars). Measurements of PM2.5 for purposes of comparison to the standards contained in §§ [50.7](/cfr/40/50.7.md), [50.13](/cfr/40/50.13.md), [50.18](/cfr/40/50.18.md), and [50.20](/cfr/40/50.20.md), and of lead for purposes of comparison to the standards contained in [§ 50.16](/cfr/40/50.16.md) shall be reported based on actual ambient air volume measured at the actual ambient temperature and pressure at the monitoring site during the measurement period.


## Notes

### Amendments

[89 FR 10365, Dec. 19, 2024]

### Authority

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

### Source

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

### Amendments

[89 FR 10365, Dec. 19, 2024]