40 CFR § 1065.369 - HO, CO, and CO interference verification for photoacoustic alcohol analyzers.

---
identifier: "/us/cfr/t40/s1065.369"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 1065.369 - HO, CO, and CO interference verification for photoacoustic alcohol analyzers."
title_number: 40
title_name: "Protection of Environment"
section_number: "1065.369"
section_name: "HO, CO, and CO interference verification for photoacoustic alcohol analyzers."
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"
---


# 1065.369 HO, CO, and CO interference verification for photoacoustic alcohol analyzers.

(a) *Scope and frequency.* If you measure ethanol or methanol using a photoacoustic analyzer, verify the amount of H<sub>2</sub>O, CO, and CO<sub>2</sub> interference after initial analyzer installation and after major maintenance.

(b) *Measurement principles.* H<sub>2</sub>O, CO, and CO<sub>2</sub> can positively interfere with a photoacoustic analyzer by causing a response similar to ethanol or methanol. If the photoacoustic analyzer uses compensation algorithms that utilize measurements of other gases to meet this interference verification, a correct result depends on simultaneously conducting these other measurements to test the compensation algorithms during the analyzer interference verification.

(c) *System requirements.* Photoacoustic analyzers must have combined interference that is within (0.0 ±0.5) µmol/mol. We strongly recommend a lower interference that is within (0.0 ±0.25) µmol/mol.

(d) *Procedure.* Perform the interference verification by following the procedure in § 1065.375(d), comparing the results to paragraph (c) of this section.

[79 FR 23770, Apr. 28, 2014, as amended at 89 FR 29801, Apr. 22, 2024]