# 1065.272 Nondispersive ultraviolet NO analyzer.
(a) *Application.* You may use a nondispersive ultraviolet (NDUV) analyzer to measure NO<sub>X</sub> concentration in raw or diluted exhaust for batch or continuous sampling. We generally accept an NDUV for NO<sub>X</sub> measurement, even though it measures only NO and NO<sub>2</sub>, since conventional engines and aftertreatment systems do not emit significant amounts of other NO<sub>X</sub> species. Measure other NO<sub>X</sub> species if required by the standard-setting part. Note that good engineering judgment may preclude you from using an NDUV analyzer if sampled exhaust from test engines contains oil (or other contaminants) in sufficiently high concentrations to interfere with proper operation.
(b) *Component requirements.* We recommend that you use an NDUV analyzer that meets the specifications in Table 1 of § 1065.205. Note that your NDUV-based system must meet the verifications in § 1065.372 and it must also meet the linearity verification in § 1065.307.
(c) *NO*<sub>2</sub>*-to-NO converter.* If your NDUV analyzer measures only NO, place upstream of the NDUV analyzer an internal or external NO<sub>2</sub>-to-NO converter that meets the verification in § 1065.378. Configure the converter with a bypass to facilitate this verification.
(d) *Humidity effects.* You must maintain NDUV temperature to prevent aqueous condensation, unless you use one of the following configurations:
(1) Connect an NDUV downstream of any dryer or chiller that is downstream of an NO<sub>2</sub>-to-NO converter that meets the verification in § 1065.378.
(2) Connect an NDUV downstream of any dryer or thermal chiller that meets the verification in § 1065.376.
[70 FR 40516, July 13, 2005, as amended at 73 FR 59323, Oct. 8, 2008; 76 FR 57442, Sept. 15, 2011; 79 FR 23761, Apr. 28, 2014]