Modification of a conventional photolytic converter for improving aircraft measurements of NO<sub>2</sub> via chemiluminescence

Abstract

Abstract. Nitrogen oxides (NOx≡NO+NO2) are centrally involved in the photochemical processes taking place in the Earth's atmosphere. Measurements of NO2, particularly in remote areas where concentrations are of the order of parts per trillion by volume (pptv), are still a challenge and subject to extensive research. In this study, we present NO2 measurements via photolysis–chemiluminescence during the research aircraft campaign CAFE Africa (Chemistry of the Atmosphere – Field Experiment in Africa) 2018 around Cabo Verde and the results of laboratory experiments to characterize the photolytic converter used. We find the NO2 reservoir species MPN (methyl peroxy nitrate) to produce the only relevant thermal interference in the converter under the operating conditions during CAFE Africa. We identify a memory effect within the conventional photolytic converter (type 1) associated with high NO concentrations and rapidly changing water vapor concentrations, accompanying changes in altitude during aircraft measurements, which is due to the porous structure of the converter material. As a result, NO2 artifacts, which are amplified by low conversion efficiencies, and a varying instrumental background adversely affect the NO2 measurements. We test and characterize an alternative photolytic converter (type 2) made from quartz glass, which improves the reliability of NO2 measurements in laboratory and field studies.

Nitrogen oxides in the free troposphere: implications for tropospheric oxidants and the interpretation of satellite NO2 measurements

“…The horizontal bars show the interquartile ranges of the measurements in each 1 km altitude bin. Nussbaumer et al, 2021;Bourgeois et al, 2022), and we find that the ratio of NO / NO * 2 (NO * 2 ≡ NO 2 + HNO 4 + MPN) in GEOS-Chem matches the NO / NO 2 ratio for the P-CL NO 2 measurements (Fig. 1c, f).…”

“…Accurate in situ measurements of NO 2 in the free troposphere are challenging because of low NO 2 concentrations and interferences from labile non-radical NO x reservoirs (HNO 4 , N 2 O 5 , and organic nitrates) when sampling at cold temperatures (Bradshaw et al, 1999;Browne et al, 2011;Reed et al, 2016;Nussbaumer et al, 2021). Current techniques to measure NO 2 in situ involve either (i) the conversion of NO 2 to NO by photolysis followed by measurement of NO through chemiluminescence (photolysischemiluminescence or P-CL; Walega et al, 1991;Ryerson et al, 2000;Bourgeois et al, 2022) or (ii) the direct measurement of NO 2 through laser-induced fluorescence (LIF; e.g., Thornton et al, 2000;Matsumoto et al, 2001;Javed et al, 2019), cavity ring-down spectroscopy (Osthoff et al, 2006), or cavity-enhanced differential optical absorption spectroscopy (Platt et al, 2009).…”

“…Accurate in situ measurements of NO 2 in the free troposphere are challenging because of low NO 2 concentrations and interferences from labile non-radical NO x reservoirs (HNO 4 , N 2 O 5 , and organic nitrates) when sampling at cold temperatures (Bradshaw et al, 1999;Browne et al, 2011;Reed et al, 2016;Nussbaumer et al, 2021). Current techniques to measure NO 2 in situ involve either (i) the conversion of NO 2 to NO by photolysis followed by measurement of NO through chemiluminescence (photolysischemiluminescence or P-CL; Walega et al, 1991;Ryerson et al, 2000;Bourgeois et al, 2022) or (ii) the direct measurement of NO 2 through laser-induced fluorescence (LIF; e.g., Thornton et al, 2000;Matsumoto et al, 2001;Javed et al, 2019), cavity ring-down spectroscopy (Osthoff et al, 2006), or cavity-enhanced differential optical absorption spectroscopy (Platt et al, 2009). Intercomparisons of NO 2 instruments have generally found agreement among the different techniques at high (> 1 ppbv -parts per billion by volume) NO 2 concentrations (Thornton et al, 2003;Fuchs et al, 2010;Sparks et al, 2019;Bourgeois et al, 2022) but poor agreement in free tropospheric conditions, where NO 2 concentrations are below 50 pptv (parts per trillion by volume) and close to the instrument detection limits (Gregory et al, 1990a;Sparks et al, 2019).…”

Ozone Formation Sensitivity to Precursors and Lightning in the Tropical Troposphere Based on Airborne Observations

“…Nitric oxide was measured with the chemiluminescence instrument (CLD 790 SR, ECO Physics, Dürnten, Switzerland) NOAH (Nitrogen Oxides Analyzer for HALO) with a detection limit of 5 pptv (1 min) and an uncertainty of 6%. The instrument is described in detail in Tadic et al (2020) and Nussbaumer, Parchatka, et al (2021). Ozone was measured with the FAIRO instrument, as described in Section 2.2.1.…”

Data Quality Enhancement for Atmospheric Chemistry Field Experiments via Sequential Monte Carlo Filters

“…This site has been used before for field campaigns and is described in more detail in Crowley et al (2010) and Sobanski et al (2016). NO and NO 2 were measured via a photolysis-chemiluminescence detector described in Tadic et al (2020) and Nussbaumer et al (2021). j NO2 was calculated from actinic flux measurements by a spectral radiance detector (MetCon GmbH) (Bohn and Lohse, 2017).…”