the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Oct 2025
A low-maintenance optoacoustic sensor for black carbon monitoring
Abstract. Regulation of black carbon (BC) emissions is necessary due to their negative impact to climate and human health. We present a low-cost optoacoustic sensor for Black Carbon (BC) emissions, which can provide continuous measurements that are suitable for long-term BC monitoring in highly contaminative environments with low need for frequent maintenance. Insensitivity to contamination is based on a sensor design that integrates protective flows of clean air around the sample measured, which minimizes BC deposition on the detector and optical windows of the sensor. A quantitative analysis shows that the negative effect of BC contamination on sensor performance is reduced by a factor of greater than 300 000 in comparison to an unprotected control sensor. We discuss how the reduced maintenance requirements make the design presented a promising candidate for continuous and long-term BC monitoring of high emitters, enabling disseminated monitoring necessary for regulatory and mitigation measures of BC emissions in the future.
Competing interests: Vasilis Ntziachristos is a founder and equity owner of Maurus OY, sThesis GmbH, Biosense Innovations P.C., Spear UG, and I3 Inc. Leonidas Ntziachristos, Nikolaos Kousias and Ioannis Raptis are founders and equity owners of Maurus OY. Leonidas Ntziachristos, Vasilis Ntziachristos, Uli Stahl, Linda Haedrich, Nikolaos Kousias and Ioannis Raptis are inventors on a pending patent application (Application No. GR2025000576) related to the sensor described in this work.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.-
Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(824 KB)
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Supplement
(220 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(824 KB) - Metadata XML
-
Supplement
(220 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-4532', Anonymous Referee #1, 25 Nov 2025
- AC1: 'Reply on RC1', Vasilis Ntziachristos, 25 Feb 2026
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RC2: 'Comment on egusphere-2025-4532', Anonymous Referee #2, 02 Jan 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-4532/egusphere-2025-4532-RC2-supplement.pdf
- AC2: 'Reply on RC2', Vasilis Ntziachristos, 25 Feb 2026
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2025-4532', Anonymous Referee #1, 25 Nov 2025
This manuscript presents an optimization of a previously published low-cost optoacoustic black carbon (BC) sensor designed for long-term BC measurements in highly polluted environments. The sensor is based on an ellipsoidal chamber that separates the quartz tuning fork transducer from the aerosol flow path. The optimization consists of a protective clean-air sheath flow that prevents BC from depositing on sensitive components while minimizing acoustic noise from the sheath flow. This results in a reduction in contamination by orders of magnitude, as demonstrated by an experimental study and statistical evaluation. The authors claim a significant reduction in maintenance requirements, enabling the deployment, monitoring, and regulation of BC emissions in harsh environments.
In my opinion, the paper is well organized, fits the scope of the journal, and should be published, subject to minor revisions as detailed below:
Methodology:
- At which temperature(s) were the sensors operated?
- The tests were mainly conducted with „dry“ soot - Would humidity and/or volatiles affect contamination?
Results section:
It would be interesting to see a performance comparison of the sensor with and without sheath flow regarding:
- *noise
- *LoD
- *rise time
- *linearity
- *Allan deviation
How is the baseline correction performed in more detail? Is a lock-in technique used? If yes, is the phase of the signal considered for the background subtraction?
Fig 3: the colors of the data points are hard to distinguish
Fig. 3a: What does the rising line represent?
Fig. 3b: Where are the spikes in the control and IDSS coming from?
Discussion:
- How was the sensor calibrated (MAC vs. BC mass concentration), and what would a calibration scenario for field deployment look like?
- Would there be a possibility to track possible contamination (e.g. resonance frequency of the tuning fork) during field deployments?
Citation: https://doi.org/10.5194/egusphere-2025-4532-RC1 - AC1: 'Reply on RC1', Vasilis Ntziachristos, 25 Feb 2026
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RC2: 'Comment on egusphere-2025-4532', Anonymous Referee #2, 02 Jan 2026
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-4532/egusphere-2025-4532-RC2-supplement.pdf
- AC2: 'Reply on RC2', Vasilis Ntziachristos, 25 Feb 2026
Peer review completion
Journal article(s) based on this preprint
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A low-maintenance optoacoustic sensor for black carbon monitoring Linda Haedrich and Nikolaos Kousias https://zenodo.org/records/17190856
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- 1
Linda Haedrich
Nikolaos Kousias
Ioannis Raptis
Uli Stahl
Leonidas Ntziachristos
Vasilis Ntziachristos
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(824 KB) - Metadata XML
-
Supplement
(220 KB) - BibTeX
- EndNote
- Final revised paper
This manuscript presents an optimization of a previously published low-cost optoacoustic black carbon (BC) sensor designed for long-term BC measurements in highly polluted environments. The sensor is based on an ellipsoidal chamber that separates the quartz tuning fork transducer from the aerosol flow path. The optimization consists of a protective clean-air sheath flow that prevents BC from depositing on sensitive components while minimizing acoustic noise from the sheath flow. This results in a reduction in contamination by orders of magnitude, as demonstrated by an experimental study and statistical evaluation. The authors claim a significant reduction in maintenance requirements, enabling the deployment, monitoring, and regulation of BC emissions in harsh environments.
In my opinion, the paper is well organized, fits the scope of the journal, and should be published, subject to minor revisions as detailed below:
Methodology:
Results section:
It would be interesting to see a performance comparison of the sensor with and without sheath flow regarding:
How is the baseline correction performed in more detail? Is a lock-in technique used? If yes, is the phase of the signal considered for the background subtraction?
Fig 3: the colors of the data points are hard to distinguish
Fig. 3a: What does the rising line represent?
Fig. 3b: Where are the spikes in the control and IDSS coming from?
Discussion: