---
kind: "section"
citation: "40 C.F.R. § 1066.615"
title: "40"
number: "1066.615"
heading: "NO X intake-air humidity correction."
url: "https://uscodex.org/cfr/40/1066.615"
---

# §1066.615. NO X intake-air humidity correction.


You may correct NOX emissions for intake-air humidity as described in this section if the standard-setting part allows it. See [§ 1066.605(c)](/cfr/40/1066.605.md?p=c) for the proper sequence for applying the NOX intake-air humidity correction.

- (a) For vehicles at or below 14,000 pounds GVWR, apply a correction for vehicles with reciprocating engines operating over specific test cycles as follows:
  - (1) Calculate a humidity correction using a time-weighted mean value for ambient humidity over the test interval. Calculate absolute ambient humidity, H, using the following equation:
  - (2) Use the following equation to correct measured concentrations to a reference condition of 10.71 grams H2O vapor per kilogram of dry air for the FTP, US06, LA-92, SC03, and HFET test cycles:
- (b) For vehicles above 14,000 pounds GVWR, apply correction factors as described in [40 CFR 1065.670](/cfr/40/1065.670.md).

## Notes

### Amendments

[80 FR 9121, Feb. 19, 2015, as amended at 81 FR 74207, Oct. 25, 2016]

### Authority

Authority: 42 U.S.C. 7401-7671q.

### Source

Source: 79 FR 23823, Apr. 28, 2014, unless otherwise noted.

### Amendments

[80 FR 9121, Feb. 19, 2015, as amended at 81 FR 74207, Oct. 25, 2016]