NO3 radicals are one of the very important trace gases in the atmosphere. Accurate measurements of NO3 can provide data support for atmospheric chemistry research. Due to the extremely low content of NO3 radicals in the atmosphere, it is a challenge to accurately detect it. In this paper, an incoherent broadband cavity-enhanced absorption spectrometer (IBBCEAS) with high sensitivity is developed for measuring atmospheric NO3. The IBBCEAS absorption spectra of NO3 in the range of 648–674 nm are measured. The concentration of NO3 is retrieved by fitting the absorption cross-section of NO3 to the measured absorption coefficient using the least square method. The interference absorption of water vapor is effectively removed by an iterative calculation of its absorption cross-section. The detect limit of the spectrometer is analyzed using the Allan variance and the standard variance. The NO3 detection limit (1σ) of the spectrometer is 1.99 pptv for 1 s integration time, and improves to be 0.69 pptv and 0.21 pptv for 10 s and 162 s integration time, respectively. The developed spectrometer with pptv level sensitivity is applied to the measurements of the real atmospheric NO3 for verifying the effectiveness.

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