40 CFR § 1065.257 - HO measurement devices.

---
identifier: "/us/cfr/t40/s1065.257"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 1065.257 - HO measurement devices."
title_number: 40
title_name: "Protection of Environment"
section_number: "1065.257"
section_name: "HO measurement devices."
chapter_name: "ENVIRONMENTAL PROTECTION AGENCY"
subchapter_number: "U"
subchapter_name: "AIR POLLUTION CONTROLS"
part_number: "1065"
part_name: "ENGINE-TESTING PROCEDURES"
positive_law: false
currency: "2026-03-24"
last_updated: "2026-03-24"
format_version: "1.1.0"
generator: "[email protected]"
authority: "42 U.S.C. 7401-7671q."
regulatory_source: "70 FR 40516, July 13, 2005, unless otherwise noted."
cfr_part: "1065"
---


# 1065.257 HO measurement devices.

(a) *Component requirements.* We recommend that you use an analyzer that meets the specifications in § 1065.205. Note that your system must meet the linearity verification in § 1065.307 with a humidity generator meeting the requirements of § 1065.750(a)(6).

(b) *Measurement principles.* Use appropriate analytical procedures for interpretation of infrared spectra. For example, EPA Test Method 320 (see § 1065.266(b)) and ASTM D6348 (incorporated by reference, see § 1065.1010) are considered valid methods for spectral interpretation. You must use heated analyzers that maintain all surfaces that are exposed to emissions at a temperature of (110 to 202) °C.

(c) *Instrument types.* You may use any of the following analyzers to measure H<sub>2</sub>O:

(1) Fourier transform infrared (FTIR) analyzer.

(2) Laser infrared analyzer. Examples of laser infrared analyzers are pulsed-mode high-resolution narrow band mid-infrared analyzers and modulated continuous wave high-resolution narrow band near or mid-infrared analyzers.

(d) *Interference verification.* Certain compounds can interfere with FTIR and laser infrared analyzers by causing a response similar to water. Perform interference verification for the following interference species:

(1) Perform CO<sub>2</sub> interference verification for FTIR analyzers using the procedures of § 1065.357. Use good engineering judgment to determine other interference species for FTIR analyzers when performing interference verification. Consider at least CO, NO, C<sub>2</sub>H<sub>4</sub>, and C<sub>7</sub>H<sub>8</sub>. Perform interference verifications using the procedures of § 1065.357, replacing occurances of CO<sub>2</sub> with each targeted interference species. Determine interference species under this paragraph (d)(1) that are appropriate for each H<sub>2</sub>O infrared absorption band, or you may identify the interference species based on the instrument manufacturer's recommendations.

(2) Perform interference verification for laser infrared analyzers using the procedures of § 1065.375. Use good engineering judgment to determine interference species for laser infrared analyzers. Note that interference species are dependent on the H<sub>2</sub>O infrared absorption band chosen by the instrument manufacturer. For each analyzer determine the H<sub>2</sub>O infrared absorption band. Determine interference species under this paragraph (d)(2) that are appropriate for each H<sub>2</sub>O infrared absorption band, or you may identify the interference species based on the instrument manufacturer's recommendations.

[89 FR 29795, Apr. 22, 2024]