A Portable Quantum Cascade Laser Spectrometer for Atmospheric Measurements of Carbon Monoxide
2. Materials and Methods
2.1. Selection of the Technique and of the CO Absorption Line
2.4. Acquisition and Data Processing
3.1. Laboratory Tests and Performances
3.2. In-Field Performances
- The selection of a calibration-free technique, as dTDLS, and the choice of optical and electronics components which work properly also without pressurization systems, allowed the realization of a portable device, entirely contained in one box only, that can be easily mounted on different platforms. The low weight, small size and low power consumption, with the only need of an access to sample the external air, make this instrument particularly suitable for installation on aircraft or balloons as piggyback in different missions.
- The robustness of COLD2 is guaranteed by a mechanical structure designed to damp vibrations and to decouple the movements of the box from the optical breadboard. Its robustness was demonstrated by its deployment onboard the M55 stratospheric aircraft, where it operated, without need of realignment and without any kind of damages, during 8 tropical flights in harsh environment, with pressure down to 50 mbar and external temperature variable between C or higher (when the sensor was forced to stay for long periods inside the aircraft on the apron before take-off) and C (in the stratosphere).
- For all the period of the tropical campaign in Nepal, the sensor worked completely unattended without failure and without need of external maintenance, as calibration procedures. Although the sensor experienced high humidity during each aircraft descent, the signal-to-noise ratio did not suffer significant degradation and a procedure of mirror cleaning was not necessary.
- The COLD2 acquisition time for each 1000 points spectrum is 1 ms. The device time resolution depends on the number of averages and can be easily set to fulfill the requirements of different applications. An Allan-Werle analysis demonstrated that an integration time of 1 s allows a sensitivity of 2 ppbV at atmospheric pressure and that this sensitivity increases at lower pressure. COLD2 is able to work at 10 Hz with a sensitivity between 5 and 8 ppbV and can reach a sensitivity lower than 1 ppb for integration time of 6 s. For ballonborne operation, when the time resolution can be smaller with respect to an aircraft, COLD2 can reach sub-ppbV performance.
- The dTDLS technique in conjunction with a 16 bit acquisition system guarantees enough vertical resolution to register and analyze the CO absorption spectrum in a large range of pressure, temperature and concentration values. The COLD2 large dynamic range is demonstrated by the measurement of the CO vertical profiles during the campaign on board the M55 stratospheric aircraft (as shown in Figure 12) .
- The COLD2 sensitivity is not significantly reduced by in-flight operation and it was demonstrated to be around 2 ppbV @ 1 s of integration time.
Conflicts of Interest
|QCL||Quantum Cascade Laser|
|CRDS||Cavity Ring Down Spectroscopy|
|CEAS||Cavity-Enhanced Absorption Spectroscopy|
|ICOS||Integrated Cavity Output Spectroscopy|
|WMS||Wavelength Modulation Spectroscopy|
|dTDLS||Direct Tunable Diode Laser Spectroscopy|
|FWHM||Full Width at Half Maximum|
|FSR||Free Spectral Range|
|FPGA||Field Programmable Gate Array|
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Sample Availability: Experimental data used in this paper are saved in the STRATOCLIM Project Wiki, available to Project partners only, according to the STRATOCLIM Data Protocol. They can be obtained upon request from the National Institute of Optics (CNR-INO).
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Viciani, S.; Montori, A.; Chiarugi, A.; D’Amato, F. A Portable Quantum Cascade Laser Spectrometer for Atmospheric Measurements of Carbon Monoxide. Sensors 2018, 18, 2380. https://doi.org/10.3390/s18072380
Viciani S, Montori A, Chiarugi A, D’Amato F. A Portable Quantum Cascade Laser Spectrometer for Atmospheric Measurements of Carbon Monoxide. Sensors. 2018; 18(7):2380. https://doi.org/10.3390/s18072380Chicago/Turabian Style
Viciani, Silvia, Alessio Montori, Antonio Chiarugi, and Francesco D’Amato. 2018. "A Portable Quantum Cascade Laser Spectrometer for Atmospheric Measurements of Carbon Monoxide" Sensors 18, no. 7: 2380. https://doi.org/10.3390/s18072380