the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 Nov 2023
Technical note: Characterization of a single-beam gradient force aerosol optical tweezer for droplet trapping, phase transitions monitoring, and morphology studies
Abstract. Single particle analysis is essential for a better understanding of the particle transformation process and predicting its environmental impact. In this study, we developed an aerosol optical tweezer (AOT)-Raman spectroscopy system to investigate the phase state and morphology of suspended aerosol droplets in real time. The system comprises four modules: optical trapping, reaction, illumination and imaging, as well as detection. The optical trapping module utilizes a 532 nm laser and a 100x oil immersion objective to stably trap aerosol droplets within 30 seconds. The reaction module allows us to adjust relative humidity (RH) and introduce reaction gases into the droplet levitation chamber, facilitating experiments to study liquid-liquid phase transitions. The illumination and imaging module employs a high-speed camera to monitor the trapped droplets, while the detector module records Raman scattering light. We trapped sodium chloride (NaCl) and 3-methyl glutaric acid (3-MGA) mixed droplets to examine RH-dependent morphology changes. Liquid-liquid phase separation (LLPS) occurred when RH was decreased. Additionally, we introduced ozone and limonene/α-pinene to generate secondary organic aerosol (SOA) particles in situ, which collided with the trapped droplet and dissolve in it. To determine the trapped droplet’s characteristics, we utilized an open-source program which based on Mie theory to retrieve diameter and refractive index from the observed whispering gallery modes (WGMs) in Raman spectra. It is found that mixed droplets formed core-shell morphology when RH was decreased, and the RH dependence of the droplets phase transitions generated by different SOA precursors varied. Our AOT system serves as an essential experimental platform for in-situ assessment of morphology and phase state during dynamic atmospheric processes.
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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
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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
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-2238', Anonymous Referee #1, 17 Nov 2023
To give an insight into the physicochemical properties of atmospheric aerosols, it is essential to establish effective measurement methods and techniques. However, many techniques currently applied for aerosol measurement cannot acquire information from a single aerosol droplet, such as flow tube and smog chamber, and data acquired from these means are average results of aerosol population, which may omit specific properties of single droplet. In this technical note, the authors presented details of an aerosol optical tweezer-Raman spectroscopy system, and verified its effectiveness in determining characteristics of single aerosol droplet, Generally, I recommend this paper for publication after considering the following comments:
- Line 108-109: Humidity in the levitation chamber was maintained by mixing humidified and dry airflow, and the RH results were measured by two sensors at both the inlet and outlet of the chamber. So, I wonder how the authors determined the actual chamber RH, were the final results an average of the two sensors? Since there was a significant difference between the results from the two sensors as shown in Fig.3.
- Line 131-132: During reactivity experiments, the author declared that the replaceable intermediate part was altered from a flat type to a circular barrier type, can the authors give schematic diagrams of these parts?
- Line 183: The program was developed by who? The reference was missing.
- Line 220: The position shift of WGMs from ~30 min to ~200 min in Fig.3(c) was not continuous but discrete, can the authors give some explanations?
- Line 232-233: How much time was needed for the chamber to reach the set RH?
Citation: https://doi.org/10.5194/egusphere-2023-2238-RC1 -
AC1: 'Reply on RC1', Zhibin Wang, 02 Feb 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2238/egusphere-2023-2238-AC1-supplement.pdf
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RC2: 'Comment on egusphere-2023-2238', Anonymous Referee #2, 01 Dec 2023
The authors systematically introduced their aerosol optical tweezers coupled with Raman spectroscopy system in a detailed way. They developed a new environmental chamber which has a double-floor and a replaceable intermediate plate, which facilitates stable trapping while introducing different species such as VOC and SOA to the system. In addition to studying the liquid-liquid phase separation (LLPS) of premixed NaCl and 3-methyl glutaric acid (3-MGA) droplets, they were able to in-situ generate and deposit SOA on a NaCl microdroplet and investigate LLPS afterward. Their findings indicate that the AOT system is a powerful tool to in-situ monitor changes in physical and chemical properties of droplets during their evolution under different conditions. I would recommend the paper for publication after addressing the following questions.
Major comment:
The RH is a key parameter in the LLPS measurements, and the authors compared their experimental measurements with theoretical calculations for the relationship between wet particle diameter and RH (Figure 4a). They only provided the data for a short RH range (around 77% to 86%), and it appears that that experiment deviated from theory at higher RH (83%-86% RH). What are the results for a higher RH range, say 86% to 99%?
Minor comments:
OT was introduced as the abbreviation of optical tweezer in Line 46, there is no need to introduce it once more in Line 51.
Line 55: Change “This results” to this “This result”.
Line140: “…to prevent droplet deposition” the surfactant cannot prevent droplet deposition. It helps the deposited droplets to spread on the surface of the coverslip.
Line 183: developed by, something is missing after “by”.
Citation: https://doi.org/10.5194/egusphere-2023-2238-RC2 -
AC2: 'Reply on RC2', Zhibin Wang, 02 Feb 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2238/egusphere-2023-2238-AC2-supplement.pdf
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AC2: 'Reply on RC2', Zhibin Wang, 02 Feb 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-2238', Anonymous Referee #1, 17 Nov 2023
To give an insight into the physicochemical properties of atmospheric aerosols, it is essential to establish effective measurement methods and techniques. However, many techniques currently applied for aerosol measurement cannot acquire information from a single aerosol droplet, such as flow tube and smog chamber, and data acquired from these means are average results of aerosol population, which may omit specific properties of single droplet. In this technical note, the authors presented details of an aerosol optical tweezer-Raman spectroscopy system, and verified its effectiveness in determining characteristics of single aerosol droplet, Generally, I recommend this paper for publication after considering the following comments:
- Line 108-109: Humidity in the levitation chamber was maintained by mixing humidified and dry airflow, and the RH results were measured by two sensors at both the inlet and outlet of the chamber. So, I wonder how the authors determined the actual chamber RH, were the final results an average of the two sensors? Since there was a significant difference between the results from the two sensors as shown in Fig.3.
- Line 131-132: During reactivity experiments, the author declared that the replaceable intermediate part was altered from a flat type to a circular barrier type, can the authors give schematic diagrams of these parts?
- Line 183: The program was developed by who? The reference was missing.
- Line 220: The position shift of WGMs from ~30 min to ~200 min in Fig.3(c) was not continuous but discrete, can the authors give some explanations?
- Line 232-233: How much time was needed for the chamber to reach the set RH?
Citation: https://doi.org/10.5194/egusphere-2023-2238-RC1 -
AC1: 'Reply on RC1', Zhibin Wang, 02 Feb 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2238/egusphere-2023-2238-AC1-supplement.pdf
-
RC2: 'Comment on egusphere-2023-2238', Anonymous Referee #2, 01 Dec 2023
The authors systematically introduced their aerosol optical tweezers coupled with Raman spectroscopy system in a detailed way. They developed a new environmental chamber which has a double-floor and a replaceable intermediate plate, which facilitates stable trapping while introducing different species such as VOC and SOA to the system. In addition to studying the liquid-liquid phase separation (LLPS) of premixed NaCl and 3-methyl glutaric acid (3-MGA) droplets, they were able to in-situ generate and deposit SOA on a NaCl microdroplet and investigate LLPS afterward. Their findings indicate that the AOT system is a powerful tool to in-situ monitor changes in physical and chemical properties of droplets during their evolution under different conditions. I would recommend the paper for publication after addressing the following questions.
Major comment:
The RH is a key parameter in the LLPS measurements, and the authors compared their experimental measurements with theoretical calculations for the relationship between wet particle diameter and RH (Figure 4a). They only provided the data for a short RH range (around 77% to 86%), and it appears that that experiment deviated from theory at higher RH (83%-86% RH). What are the results for a higher RH range, say 86% to 99%?
Minor comments:
OT was introduced as the abbreviation of optical tweezer in Line 46, there is no need to introduce it once more in Line 51.
Line 55: Change “This results” to this “This result”.
Line140: “…to prevent droplet deposition” the surfactant cannot prevent droplet deposition. It helps the deposited droplets to spread on the surface of the coverslip.
Line 183: developed by, something is missing after “by”.
Citation: https://doi.org/10.5194/egusphere-2023-2238-RC2 -
AC2: 'Reply on RC2', Zhibin Wang, 02 Feb 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2238/egusphere-2023-2238-AC2-supplement.pdf
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AC2: 'Reply on RC2', Zhibin Wang, 02 Feb 2024
Peer review completion
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Xiangyu Pei
Yikan Meng
Yueling Chen
Huichao Liu
Yao Song
Zhengning Xu
Fei Zhang
Thomas C. Preston
Zhibin Wang
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1374 KB) - Metadata XML