Abstract
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.
Highlights
The nitrate radical (NO3) and dinitrogen pentoxide (N2O5) are the most important reactive nitrogen species in nighttime chemistry (Wayne et al, 1991)
The NO3 is dominantly formed by the reaction of NO2 with O3 (Reaction R1), which contributes to the night-time oxidation of volatile organic compounds (VOCs; Reaction R2) and the production of the organic nitrate (Fry et al, 2009; Riemer et al, 2003)
In the North China Plain areas, the high-NOx air masses often overlap with high aerosol loadings from both secondary aerosol particle formation as well as nearby natural sources and serve as ideal locations for the study of NO3 and N2O5 chemistry. To probe such potentially interesting chemistry in China, we developed a new light-emitting diode (LED)based incoherent broadband cavityenhanced absorption spectrometer (IBBCEAS) instrument for the detection of NO3 and N2O5
Summary
The nitrate radical (NO3) and dinitrogen pentoxide (N2O5) are the most important reactive nitrogen species in nighttime chemistry (Wayne et al, 1991). Kercher et al (2009) introduced an ion-molecule region (IMR) module wherein the ion reaction, I−+ N2O5 → I(N2O5)−, is enhanced so that N2O5 can be detected at 235 amu With this method, a direct measurement of N2O5 is achieved, showing a good comparison with the well-established CRDS system in Hong Kong (Wang et al, 2016). In the North China Plain areas, the high-NOx air masses often overlap with high aerosol loadings from both secondary aerosol particle formation as well as nearby natural sources (e.g. dust from the Gobi Desert in the spring) and serve as ideal locations for the study of NO3 and N2O5 chemistry To probe such potentially interesting chemistry in China, we developed a new light-emitting diode (LED)based IBBCEAS (incoherent broadband cavity-enhanced absorption spectrometer) instrument for the detection of NO3 and N2O5. The detailed setup of our instrument, lab characterizations, and its first field applications in Beijing are presented
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