the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
A Highly Sensitive and Selective Laser-Based BTEX Sensor for Occupational and Environmental Monitoring
Mhanna Mhanna
Mohamed Sy
Ayman Arfaj
Jose Llamas
Aamir Farooq
Abstract. A mid-infrared laser-based sensor is designed and demonstrated for trace detection of benzene, toluene, ethylbenzene, and xylene isomers at ambient conditions. The sensor is based on a distributed feedback inter-band cascade laser emitting near 3.29 μm and an off-axis cavity-enhanced absorption spectroscopy configuration with an optical gain of ~2800. Wavelength tuning and a deep neural networks (DNN) model were employed to enable simultaneous and selective BTEX measurements. The sensor performance was demonstrated by measuring BTEX mole fractions in various mixtures. At an integration time of 10 seconds, minimum detection limits of 11.4, 9.7, 9.1, 10, 15.6, and 12.9 ppb were achieved for benzene, toluene, ethylbenzene, m-xylene, o-xylene, and p-xylene, respectively. The sensor can be used to detect tiny BTEX leaks in petrochemical facilities and to monitor air quality in residential and industrial areas for workplace pollution.
Mhanna Mhanna et al.
Status: open (until 11 Jul 2023)
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CC1: 'Comment on egusphere-2023-514', Dean Venables, 25 Apr 2023
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This is a valuable spectroscopic contribution to realtime detection of aromatics. The authors should cite and compare their system to the recent, directly-relevant paper by Wang et al.:
Meng Wang, Ravi Varma, Dean S Venables, Wu Zhou, Jun Chen. A Demonstration of Broadband Cavity-Enhanced Absorption Spectroscopy at Deep-Ultraviolet Wavelengths: Application to Sensitive Real-Time Detection of the Aromatic Pollutants Benzene, Toluene, and Xylene, Anal. Chem., 94(10):4286-4293, 2022.
doi: 10.1021/acs.analchem.1c04940.
Citation: https://doi.org/10.5194/egusphere-2023-514-CC1 -
AC1: 'Reply on CC1', Mhanna Mhanna, 08 May 2023
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Thank you for suggesting this relevant paper, we will add a comparison in our manuscript.
Citation: https://doi.org/10.5194/egusphere-2023-514-AC1
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AC1: 'Reply on CC1', Mhanna Mhanna, 08 May 2023
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RC1: 'Comment on egusphere-2023-514', Anonymous Referee #1, 15 May 2023
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Although the authors have an interesting subject for a scientific study, the manuscript is not convincing and lacks scientifically too many flaws to be accepted for publication.
- The discussion on the cavity enhanced absorption (line 87 to 99) is confusing and not according the generally agreed formula’s. I suggest to follow the formulas in the article: Cavity-enhanced absorption spectroscopy of molecular oxygen by the Gianfrani et al., Journal of the Optical Society of America B Vol. 16, Issue 12, pp. 2247-2254 (1999) https://tf.nist.gov/general/pdf/1324.pdf There is also shown that the increase in path length (or absorption) is equal to π.sqrt(R)/(1-R)
- Figure 1 is not convincing concerning an interference free and selective sensing. I do not see the advantage compared to the UV. Where are the fingerprint spectra of the gases next to their absorption strengths? How orthogonal are the gases to each other?
- The discussion on the proper selection of the spectral wavelength is not convincing. Show the broadband spectra (between 3000 and 3100 cm-1), next to the spectra of water vapor and CO2. The latter two are important because their concentrations are orders of magnitude higher.
- Since BTEX consist of 6 molecules, give all 6 bands.
- Line 124: The focusing lens is not described. How is the beam divergence of the ICL? What was the type and performance of the oscilloscope?
- Line 127-128 give a reference
- Line 140: A BTEX mixture was used containing 6 gasses. What was the uncertainty in the concentration of each of the gases in the mixture? It seems here that al the gases are in one mixture, although line 153 states something else…?
- A 99.97% reflectivity of the mirrors means an enhancement of 10470 in path length (see reference). With a cavity length of 5 cm, the total path length should be 520 meter. In the manuscript the Gain is 2800; can these two be compared? How is the overall NEAS (Noise Equivalent Absorption Sensitivity) of the system?
- What was the averaged transmitted power through the cavity? How is this compared to the detector sensitivity and where is the performance of the latter in the Allan curve (Fig.3)?
- The spectra leading to Fig.4 are not shown, while these are essential to convince the interested reader. Furthermore, I do not see any error bars in the figure.
- Equation 11: Why is k limited from 1-4 and not extended to 6 (of higher, due to interfering species)?
- While the uncertainty of alpha(CEAS) was determined to be 2% (line 160), the mixtures were calculated to be 3-digit accuracy (line 210-). There is no convincing performance of the DNN model to be justified.
- Fig 7 cannot be properly judges due to all the raised questions above
- Fig 8 is not convincing.
Citation: https://doi.org/10.5194/egusphere-2023-514-RC1
Mhanna Mhanna et al.
Mhanna Mhanna et al.
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