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.
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