A broadband cavity-enhanced spectrometer for atmospheric trace gas measurements and Rayleigh scattering cross sections in the cyan region (470–540 nm)
Date
2019-02-27
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Publisher
Copernicus
Abstract
An incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instrument for quantification of atmospheric trace gases that absorb in the cyan region of the electromagnetic spectrum (470 to 540 nm), including NO2and I2, is described. The instrument uses a light-emitting diode coupled to a 1 m optical cavity consisting of a pair of mirrors in stable resonator configuration. Transmitted light is monitored using a grating spectrometer and charge-coupled device array detector. The average mirror reflectivity was determined from the N2/He and Ar/He ratios of scattering coefficients and was∼99.98 % at its maximum, yielding an effective optical path length of 6.3 km. Cross sections of N2, O2, air, Ar, CO2, and CH4 scattering and of O4 absorption were measured and agree with literature values within the measurement uncertainty. Trace gas mixing ratios were retrieved using the spectral fitting software DOA-SIS (DOAS intelligent system) from 480 to 535 nm. Under laboratory conditions, the 60 s, 1σ measurement precisions were ±124 and ±44 pptv for NO2and I2, respectively. The IBBCEAS instrument sampled ambient air in Ucluelet, BC,Canada, in July 2015. IBBCEAS retrievals agreed with in-dependent measurements of NO2by blue diode laser cavity ring-down spectroscopy (r2=0.975), but ambient I2concentrations were below the detection limit.
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Citation
Jordan, N., Ye, C. Z., Ghosh, S., Washenfelder, R. A., Brown, S. S. & Osthoff, H. D. (2019). A broadband cavity-enhanced spectrometer for atmospheric trace gas measurements and Rayleigh scattering cross sections in the cyan region (470–540 nm). "Atmospheric Measurement Techniques", 12, 1277-1293. http://dx.doi.org/10.5194/amt-12-1277-2019.