Development of an incoherent broadband cavity-enhanced absorption spectrometer for measurements of ambient glyoxal and NO<sub>2</sub> in a polluted urban environment
<p>We report the development of an instrument for simultaneous fast measurements of glyoxal (CHOCHO) and <span class="inline-formula">NO<sub>2</sub></span> based on incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) in the 438–465&thins...
| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-04-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/12/2499/2019/amt-12-2499-2019.pdf |
| Summary: | <p>We report the development of an instrument for
simultaneous fast measurements of glyoxal (CHOCHO) and <span class="inline-formula">NO<sub>2</sub></span> based on
incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) in
the 438–465 nm wavelength region. The highly reflective cavity mirrors
were protected from contamination by <span class="inline-formula">N<sub>2</sub></span> purge gas. The reduction of the
effective cavity length was calibrated by measuring collision-induced oxygen
absorption at <span class="inline-formula">∼477</span> nm of pure oxygen gas input with and
without the <span class="inline-formula">N<sub>2</sub></span> mirror purge gas. The detection limits of the developed
system were evaluated to be 23 parts per trillion by volume (pptv, 2<span class="inline-formula"><i>σ</i></span>) for CHOCHO and 29 pptv (2<span class="inline-formula"><i>σ</i></span>) for <span class="inline-formula">NO<sub>2</sub></span> with a 30 s acquisition
time. A potential cross-interference of <span class="inline-formula">NO<sub>2</sub></span> absorption on
accurate CHOCHO measurements has been investigated in this study, as the
absorption of <span class="inline-formula">NO<sub>2</sub></span> in the atmosphere could often be several hundred-fold
higher than that of glyoxal, especially in contaminated areas. Due to
non-linear spectrometer dispersion, simulation spectra of <span class="inline-formula">NO<sub>2</sub></span> based on
traditional convolution simulation did not match the measurement spectra
well enough. In this work, we applied actual <span class="inline-formula">NO<sub>2</sub></span> spectral profile
measured by the same spectrometer as a reference spectral profile in
subsequent atmospheric spectral analysis and retrieval of <span class="inline-formula">NO<sub>2</sub></span> and
CHOCHO concentrations. This effectively reduced the spectral fitting
residuals. The instrument was successfully deployed for 24 d of
continuous measurements of CHOCHO and <span class="inline-formula">NO<sub>2</sub></span> in the atmosphere in a
comprehensive field campaign in Beijing in June 2017.</p> |
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| ISSN: | 1867-1381 1867-8548 |