Jordan, NickGarner, Natasha MMatchett, Laura CTokarek, Travis WOsthoff, Hans DOdame-Ankrah, Charles AGrimm, Charles EPickrell, Kelly NSwainson, ChristopherRosentreter, Brian W2021-06-232021-06-232020-08-03Jordan, N., Garner, N. M., Matchett, L. C., Tokarek, T. W., Osthoff, H. D., Odame-Ankrah, C. A., … Rosentreter, B. W. (2020). Potential interferences in photolytic nitrogen dioxide converters for ambient air monitoring: Evaluation of a prototype. Journal of the Air & Waste Management Association, 70(8), 753–764. doi:10.1080/10962247.2020.1769770http://hdl.handle.net/1880/11352710.11575/PRISM/46084Mixing ratios of the criteria air contaminant nitrogen dioxide (NO2) are commonly quantified by reduction to nitric oxide (NO) using a photolytic converter followed by NO-O3 chemiluminescence (CL). In this work, the performance of a photolytic NO2 converter prototype originally designed for continuous emission monitoring and emitting light at 395 nm was evaluated. Mixing ratios of NO2 and NOx (= NO + NO2) entering and exiting the converter were monitored by blue diode laser cavity ring-down spectroscopy (CRDS). The NO2 photolysis frequency was determined by measuring the rate of conversion to NO as a function of converter residence time and found to be 4.2 s-1. A maximum 96% conversion of NO2 to NO over a large dynamic range was achieved at a residence time of (1.5 ± 0.3) s, independent of relative humidity. Interferences from odd nitrogen (NOy) species such as peroxyacyl nitrates (PAN; RC(O)O2NO2), alkyl nitrates (AN; RONO2), nitrous acid (HONO), and nitric acid (HNO3) were evaluated by operating the prototype converter outside its optimum operating range (i.e., at higher pressure and longer residence time) for easier quantification of interferences. Four mechanisms that generate artifacts and interferences were identified as follows: direct photolysis, foremost of HONO at a rate constant of 6% that of NO2; thermal decomposition, primarily of PAN; surface promoted photochemistry; and secondary chemistry in the connecting tubing. These interferences are likely present to a certain degree in all photolytic converters currently in use but are rarely evaluated or reported. Recommendations for improved performance of photolytic converters include operating at lower cell pressure and higher flow rates, thermal management that ideally results in a match of photolysis cell temperature with ambient conditions, and minimization of connecting tubing length. When properly implemented, these interferences can be made negligibly small when measuring NO2 in ambient air.engUnless otherwise indicated, this material is protected by copyright and has been made available with authorization from the copyright owner. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.https://creativecommons.org/licenses/by-nc/4.0NO2 measurementphotolytic conversionperformanceinterferencesjournal articleEGP515261-17http://dx.doi.org/10.1080/10962247.2020.1769770