Articles | Volume 10, issue 4
https://doi.org/10.5194/amt-10-1465-2017
https://doi.org/10.5194/amt-10-1465-2017
Research article
 | 
19 Apr 2017
Research article |  | 19 Apr 2017

Development of a portable cavity-enhanced absorption spectrometer for the measurement of ambient NO3 and N2O5: experimental setup, lab characterizations, and field applications in a polluted urban environment

Haichao Wang, Jun Chen, and Keding Lu

Abstract. A small and portable incoherent broadband cavity-enhanced absorption spectrometer (IBBCEAS) for NO3 and N2O5 measurement has been developed. The instrument features a mechanically aligned non-adjustable optical mounting system, and the novel design of the optical mounting system enables a fast setup and stable operation in field applications. To remove the influence of the strong nonlinear absorption by water vapour, a dynamic reference spectrum through NO titration is used for the spectrum analysis. The wall loss effects of the sample system were extensively studied, and the total transmission efficiencies were determined to be 85 and 55 % for N2O5 and NO3, respectively, for our experimental setup. The limit of detection (LOD) was estimated to be 2.4 pptv (1σ) and 2.7 pptv (1σ) at 1 s intervals for NO3 and N2O5, respectively. The associated uncertainty of the field measurement was estimated to be 19 % for NO3 and 22–36 % for N2O5 measurements from the uncertainties of transmission efficiency, absorption cross section, effective cavity length, and mirror reflectivity. The instrument was successfully deployed in two comprehensive field campaigns conducted in the winter and summer of 2016 in Beijing. Up to 1.0 ppb NO3+N2O5 was observed with the presence of high aerosol loadings, which indicates an active night-time chemistry in Beijing.

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Short summary
A new incoherent broadband cavity-enhanced absorption spectrometer for ambient NO3 and N2O5 detection is developed. This new instrument is featured with a mechanically aligned non-adjustable optical mounting system. Fast setup and stable running of this N2O5 spectrometer were successfully achieved during recent field campaigns in China due to this new feature. In addition, a dynamic reference spectrum is used for the CEAS type of instrument by NO titration for the first time.