Dual-Section DFB-QCLs for Multi-Species Trace Gas Analysis

Süess, Martin; Hundt, P. Morten; Tuzson, Béla; Riedi, Sabine; Wolf, Johanna; Peretti, Romain; Beck, Matthias; Looser, Herbert; Emmenegger, Lukas; Faist, Jérôme

doi:10.3390/photonics3020024

Cited by 26 publications

(27 citation statements)

References 29 publications

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“…Finally, the development of dual-wavelength QCL devices (Jagerska et al, 2014;Süess et al, 2016) opens the path towards mobile laser instruments that could measure NO and NO 2 simultaneously within the same compact footprint. Such measurements would give valuable insights into urban NO x chemistry.…”

Section: Discussionmentioning

confidence: 99%

Mid-IR spectrometer for mobile, real-time urban NO2 measurements

et al. 2018

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Abstract. Detailed knowledge about the urban NO2 concentration field is a key element for obtaining accurate pollution maps and individual exposure estimates. These are required for improving the understanding of the impact of ambient NO2 on human health and for related air quality measures. However, city-scale NO2 concentration maps with high spatio-temporal resolution are still lacking, mainly due to the difficulty of accurate measurement of NO2 at the required sub-ppb level precision. We contribute to close this gap through the development of a compact instrument based on mid-infrared laser absorption spectroscopy. Leveraging recent advances in infrared laser and detection technology and a novel circular absorption cell, we demonstrate the feasibility and robustness of this technique for demanding mobile applications. A fully autonomous quantum cascade laser absorption spectrometer (QCLAS) has been successfully deployed on a tram, performing long-term and real-time concentration measurements of NO2 in the city of Zurich (Switzerland). For ambient NO2 concentrations, the instrument demonstrated a precision of 0.23 ppb at one second time resolution and of 0.03 ppb after 200 s averaging. Whilst the combined uncertainty estimated for the retrieved spectroscopic values was less than 5 %, laboratory intercomparison measurements with standard CLD instruments revealed a systematic NO2 wall loss of about 10 % within the laser spectrometer. For the field campaign, the QCLAS has been referenced to a CLD using urban atmospheric air, despite the potential cross sensitivity of CLD to other nitrogen containing compounds. However, this approach allowed a direct comparison and continuous validation of the spectroscopic data to measurements at regulatory air quality monitoring (AQM) stations along the tram-line. The analysis of the recorded high-resolution time series allowed us to gain more detailed insights into the spatio-temporal concentration distribution of NO2 in an urban environment. Furthermore, our results demonstrate that for reliable city-scale concentration maps a larger data set and better spatial coverage is needed, e.g., by deploying more mobile and stationary instruments to account for mainly two shortcomings of the current approach: (i) limited residence time close to sources with large short-term NO2 variations, and (ii) insufficient representativeness of the tram tracks for the complex urban environment.

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Section: Discussionmentioning

confidence: 99%

Mid-IR spectrometer for mobile, real-time urban NO2 measurements

et al. 2018

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“…With the latest dual-wavelength QCL technology (Jagerska et al, 2014;Süess et al, 2016), the next generation of the QCLAS instrument could measure NO and NO 2 simultaneously within the same footprint. These measurements would give valuable insights into urban NO x chemistry.…”

Section: Discussion and Outlookmentioning

confidence: 99%

“…NO 2 concentrations can be predicted for any location in the city based on the spatial features of these locations and the regression tree. We used the R package "rpart" (Therneau et al, 2015) for the computations. 20 3 Results und discussion…”

Section: Statistical Modelling 15mentioning

confidence: 99%

Spectroscopic real-time monitoring of NO2 for city scale modelling

Hundt

Müller

Mangold

et al. 2017

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Abstract. Detailed knowledge about the urban NO 2 concentration field is a key element for obtaining accurate, individual exposure estimates. These are required for improving the understanding of the impact of ambient NO 2 on human health and for related air quality measures. We developed a compact and robust quantum cascade laser absorption spectrometer 10 (QCLAS) and deployed it on a tram in the city of Zurich (Switzerland) to perform mobile real-time concentration measurements of NO 2 . Thorough analysis of the obtained NO 2 data, for instance by comparison with data from fixed air quality monitoring (AQM) sites, revealed the instrument to be highly accurate and valuable for collection of data that can be used in statistical models for the calculation of spatio-temporally resolved NO 2 concentration maps. The combination of fast mobile measurements with AQM data proved to be very suitable, but the statistical data analysis also showed that a single 15 mobile instrument is not sufficient in the studied urban area, for mainly two reasons: (i) short residence close to sources with large short-term NO 2 variations and (ii) limited representativeness of the tram tracks for the entire urban environment.

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“…Dual-wavelength QCLs emitting in two distinct spectral ranges have been demonstrated for spectroscopy applications [5,6]. However, the two wavelengths were emitted in two distinct gain sections in this case, so that the emitted modes were completely independent.…”

Section: Introductionmentioning

confidence: 99%

Frequency stability of a dual wavelength quantum cascade laser

et al. 2017

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Abstract:We characterized the dual wavelength operation of a distributed Bragg reflector (DBR) quantum cascade laser (QCL) operating at 4.5 μm using two independent optical frequency discriminators. The QCL emits up to 150 mW fairly evenly distributed between two adjacent Fabry-Perot modes separated by ≈11.6 GHz. We show a strong correlation between the instantaneous optical frequencies of the two lasing modes, characterized by a Pearson correlation coefficient of 0.96. As a result, we stabilized one laser mode of the QCL to a N 2 O transition using a side-of-fringe locking technique, reducing its linewidth by a factor 6.2, from 406 kHz in free-running operation down to 65 kHz (at 1-ms observation time), and observed a simultaneous reduction of the frequency fluctuations of the second mode by a similar amount, resulting in a linewidth narrowing by a factor 5.4, from 380 kHz to 70 kHz. This proof-ofprinciple demonstration was performed with a standard DBR QCL that was not deliberately designed for dual-mode operation. These promising results open the door to the fabrication of more flexible dual-mode QCLs with the use of specifically designed gratings in the future.

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Dual-Section DFB-QCLs for Multi-Species Trace Gas Analysis

Cited by 26 publications

References 29 publications

Mid-IR spectrometer for mobile, real-time urban NO<sub>2</sub> measurements

Mid-IR spectrometer for mobile, real-time urban NO<sub>2</sub> measurements

Spectroscopic real-time monitoring of NO<sub>2</sub> for city scale modelling

Frequency stability of a dual wavelength quantum cascade laser

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Dual-Section DFB-QCLs for Multi-Species Trace Gas Analysis

Cited by 26 publications

References 29 publications

Mid-IR spectrometer for mobile, real-time urban NO&lt;sub&gt;2&lt;/sub&gt; measurements

Mid-IR spectrometer for mobile, real-time urban NO&lt;sub&gt;2&lt;/sub&gt; measurements

Spectroscopic real-time monitoring of NO&lt;sub&gt;2&lt;/sub&gt; for city scale modelling

Frequency stability of a dual wavelength quantum cascade laser

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Product

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Mid-IR spectrometer for mobile, real-time urban NO<sub>2</sub> measurements

Mid-IR spectrometer for mobile, real-time urban NO<sub>2</sub> measurements

Spectroscopic real-time monitoring of NO<sub>2</sub> for city scale modelling