Development of a broadband cavity-enhanced absorption spectrometer for simultaneous measurements of ambient NO 3 , NO 2 , and H 2 O

• Published in: Atmospheric Measurement Techniques
• Main Authors: W. Nam, C. Cho, B. Perdigones, T. S. Rhee, K.-E. Min
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2022
• Subjects: Environmental engineering; TA170-171; Earthwork. Foundations; TA715-787; Arctic; Arctic Ocean
• Online Access: https://doi.org/10.5194/amt-15-4473-2022; https://doaj.org/article/0f16f2dc7ac24031ad8cf74d957d8b5e

We describe the characteristics and performances of our newly built broadband cavity-enhanced absorption spectrometer for measurements of nitrate radical ( NO 3 ), nitrogen dioxide ( NO 2 ), and water vapor ( H 2 O ). A customized vibration-resistance cavity layout incorporated with N 2 purging on high-reflection mirror surfaces was implemented with a red light-emitting diode (LED) as a light source. In general, this system achieved over 40 km (up to 101.5 km) of effective light path length at 662 nm from a 0.52 m long cavity. For accurate NO 3 measurement, the measured absorption spectrum of H 2 O was used for simultaneous concentration retrievals with the other species instead of being treated as interferences to be removed or corrected prior to NO 3 detection. Synthesized N 2 O 5 crystals under atmospheric pressure were used for performance tests of linear response and transmission efficiency. From the standard injection experiments of NO 3 , NO 2 , and H 2 O , high linearities were observed ( R 2 ≥0.9918 ). The total NO 3 transmission efficiency through the system was determined to be 81.2 % ( ±2.9 , 1 σ ) within the residence time of 2.59 s. The precisions (1 σ ) of NO 3 , NO 2 , and H 2 O in 1 Hz measurement from a single pixel on the charge-coupled device (CCD) were 1.41 pptv, 6.92 ppbv, and 35.0 ppmv with uncertainties of 10.8 %, 5.2 %, and ≥20.5 %, respectively, mainly from the errors in the literature absorption cross-section. The instrument was successfully deployed aboard the Korean icebreaker R/V Araon for an expedition conducted in the remote marine boundary layer in the Arctic Ocean during the summer of 2021.