20 Jul 2022
20 Jul 2022
Status: this preprint is currently under review for the journal AMT.

A lightweight broadband cavity-enhanced spectrometer for NO2 measurement on uncrewed aerial vehicles

Caroline C. Womack1,2, Steven S. Brown2,3, Steven J. Ciciora2, Ru-Shan Gao2, Richard J. McLaughlin2, Michael A. Robinson1,2, Yinon Rudich4, and Rebecca A. Washenfelder2 Caroline C. Womack et al.
  • 1Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA
  • 2Chemical Sciences Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80305, USA
  • 3Department of Chemistry, University of Colorado, Boulder, CO 80309, USA
  • 4Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 7610001, Israel

Abstract. We describe the design and performance of a lightweight broadband cavity-enhanced spectrometer for measurement of NO2 on uncrewed aerial vehicles and light aircraft. The instrument uses an LED centered at 457 nm, high-finesse mirrors (reflectivity=0.999963 at 450 nm), and a grating spectrometer to determine optical extinction coefficients between 430–476 nm, which are fit with custom spectral fitting software and published absorption cross sections. The instrument weighs 3.05 kg and has power consumption less than 35 W at 25 °C. A ground calibration unit provides helium and zero air flows to periodically determine the reflectivity of the cavity mirrors using known Rayleigh scattering cross sections. The precision (1σ) for laboratory measurements is 43 ppt NO2 in 1 s and 7 ppt NO2 in 30 s. Measurement of air with known NO2 mixing ratios in the range of 0–70 ppb agreed with the known values within 0.3 % (slope=0.997±0.007; r2=0.99983). We demonstrate instrument performance using vertical profiles of NO2 mixing ratio acquired onboard an uncrewed aerial vehicle between 0–120 m above ground level in Boulder, Colorado.

Caroline C. Womack et al.

Status: open (until 25 Aug 2022)

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Caroline C. Womack et al.

Caroline C. Womack et al.


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Short summary
We present a new miniature instrument to measure nitrogen dioxide (NO2) using cavity-enhanced spectroscopy. NO2 contributes to the formation of pollutants such as ozone and particulate matter, and its concentration can vary widely near sources. We developed this lightweight (3.05 kg) low-power (<35 W) instrument to measure NO2 on unscrewed aircraft vehicles (UAVs) and demonstrate that it has the accuracy and precision needed for atmospheric field measurements.