40 CFR § 1065.277 - NH measurement devices.

---
identifier: "/us/cfr/t40/s1065.277"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "40 CFR § 1065.277 - NH measurement devices."
title_number: 40
title_name: "Protection of Environment"
section_number: "1065.277"
section_name: "NH 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"
---


# 1065.277 NH measurement devices.

(a) *General 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.

(b) *Instrument types.* You may use any of the following analyzers to measure NH<sub>3</sub>:

(1) Nondispersive ultraviolet (NDUV) analyzer.

(2) Fourier transform infrared (FTIR) analyzer. Use appropriate analytical procedures for interpretation of infrared spectra. For example, EPA Test Method 320 (see § 1065.266(c)) and ASTM D6348 (incorporated by reference, see § 1065.1010) are considered valid methods for spectral interpretation.

(3) Laser infrared analyzer. Examples of laser infrared analyzers are pulsed-mode high-resolution narrow-band mid-infrared analyzers, modulated continuous wave high-resolution narrow band near and mid-infrared analyzers, and modulated continuous-wave high-resolution near-infrared analyzers. A quantum cascade laser, for example, can emit coherent light in the mid-infrared region where NH<sub>3</sub> and other nitrogen compounds can effectively absorb the laser's energy.

(c) *Sampling system.* Minimize NH<sub>3</sub> losses and sampling artifacts related to NH<sub>3</sub> adsorbing to surfaces by using sampling system components (sample lines, prefilters and valves) made of stainless steel or PTFE heated to (110 to 202) °C. If surface temperatures exceed ≥130 °C, take steps to prevent any DEF in the sample gas from thermally decomposing and hydrolyzing to form NH<sub>3</sub>. Use a sample line that is as short as practical.

(d) *Interference verification.* Certain species can positively interfere with NDUV, FTIR, and laser infrared analyzers by causing a response similar to NH<sub>3</sub>. Perform interference verification as follows:

(1) Perform SO<sub>2</sub> and H<sub>2</sub>O interference verification for NDUV analyzers using the procedures of § 1065.372, replacing occurances of NO<sub>X</sub> with NH<sub>3</sub>. NDUV analyzers must have combined interference that is within (0.0 ±2.0) µmol/mol.

(2) Perform interference verification for FTIR and laser infrared analyzers using the procedures of § 1065.377. Use good engineering judgment to determine interference species. Note that interference species, with the exception of H<sub>2</sub>O, are dependent on the NH<sub>3</sub> infrared absorption band chosen by the instrument manufacturer. Determine interference species under this paragraph (d)(2) that are appropriate for each NH<sub>3</sub> infrared absorption band, or you may identify the interference species based on the instrument manufacturer's recommendations.

[89 FR 29797, Apr. 22, 2024]