---
kind: "section"
citation: "40 C.F.R. § 1065.659"
title: "40"
number: "1065.659"
heading: "Removed water correction."
url: "https://uscodex.org/cfr/40/1065.659"
---

# §1065.659. Removed water correction.

- (a) If you remove water upstream of a concentration measurement, x, correct for the removed water. Perform this correction based on the amount of water at the concentration measurement, xH2O[emission]meas, and at the flow meter, xH2Oexh, whose flow is used to determine the mass emission rate or total mass over a test interval. For continuous analyzers downstream of a sample dryer for transient and ramped-modal cycles, you must apply this correction on a continuous basis over the test interval, even if you use one of the options in [§ 1065.145(e)(2)](/cfr/40/1065.145.md?p=e-2) that results in a constant value for xH2O[emission]meas because xH2Oexh varies over the test interval. For batch analyzers, determine the flow-weighted average based on the continuous xH2Oexh values determined as described in [paragraph (c)](#c) of this section. For batch analyzers, you may determine the flow-weighted average xH2Oexh based on a single value of xH2Oexh determined as described in paragraphs [(c)(2)](#c-2) and [(3)](#c-3) of this section, using flow-weighted average or batch concentration inputs.
- (b) Determine the amount of water remaining downstream of a sample dryer and at the concentration measurement using one of the methods described in [§ 1065.145(e)(2)](/cfr/40/1065.145.md?p=e-2). If you use a sample dryer upstream of an analyzer and if the calculated amount of water remaining downstream of the sample dryer and at the concentration measurement, xH2O[emission]meas, is higher than the amount of water at the flow meter, xH2Oexh, set xH2O[emission]meas equal to xH2Oexh. If you use a sample dryer upstream of storage media, you must be able to demonstrate that the sample dryer is removing water continuously (i.e., xH2Oexh is higher than xH2O[emission]meas throughout the test interval).
- (c) For a concentration measurement where you did not remove water, you may set xH2O[emission]meas equal to xH2Oexh. You may determine the amount of water at the flow meter, xH2Oexh, using any of the following methods:
  - (1) Measure the dewpoint and absolute pressure and calculate the amount of water as described in [§ 1065.645](/cfr/40/1065.645.md).
  - (2) If the measurement comes from raw exhaust, you may determine the amount of water based on intake-air humidity, plus a chemical balance of fuel, DEF, intake air, and exhaust as described in [§ 1065.655](/cfr/40/1065.655.md).
  - (3) If the measurement comes from diluted exhaust, you may determine the amount of water based on intake-air humidity, dilution air humidity, and a chemical balance of fuel, DEF, intake air, and exhaust as described in [§ 1065.655](/cfr/40/1065.655.md).
- (d) **Perform a removed water correction to the concentration measurement using the following equation—**

## Notes

### Amendments

[73 FR 37335, June 30, 2008, as amended at 76 FR 57462, Sept. 15, 2011; 79 FR 23804, Apr. 28, 2014; 86 FR 34566, June 29, 2021]

### Authority

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

### Source

Source: 70 FR 40516, July 13, 2005, unless otherwise noted.

### Amendments

[73 FR 37335, June 30, 2008, as amended at 76 FR 57462, Sept. 15, 2011; 79 FR 23804, Apr. 28, 2014; 86 FR 34566, June 29, 2021]