Development of a portable cavity-enhanced absorption spectrometer for the measurement of ambient NO<sub>3</sub> and N<sub>2</sub>O<sub>5</sub>: experimental setup, lab characterizations, and field applications in a polluted urban environment
A small and portable incoherent broadband cavity-enhanced absorption spectrometer (IBBCEAS) for NO<sub>3</sub> and N<sub>2</sub>O<sub>5</sub> measurement has been developed. The instrument features a mechanically aligned non-adjustable optical mounting system, and...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-04-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | http://www.atmos-meas-tech.net/10/1465/2017/amt-10-1465-2017.pdf |
| Summary: | A small and portable incoherent broadband cavity-enhanced absorption
spectrometer (IBBCEAS) for NO<sub>3</sub> and N<sub>2</sub>O<sub>5</sub> 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
N<sub>2</sub>O<sub>5</sub> and NO<sub>3</sub>, respectively, for our experimental setup. The
limit of detection (LOD) was estimated to be 2.4 pptv (1<i>σ</i>) and
2.7 pptv (1<i>σ</i>) at 1 s intervals for NO<sub>3</sub> and N<sub>2</sub>O<sub>5</sub>,
respectively. The associated uncertainty of the field measurement was
estimated to be 19 % for NO<sub>3</sub> and 22–36 % for N<sub>2</sub>O<sub>5</sub>
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
NO<sub>3</sub>+N<sub>2</sub>O<sub>5</sub> was observed with the presence of high aerosol
loadings, which indicates an active night-time chemistry in Beijing. |
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| ISSN: | 1867-1381 1867-8548 |