the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Characterization of tandem aerosol classifiers for selecting particles: implication for eliminating multiple charging effect
- 1College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, 310058, China
- 2Hangzhou Global Scientific and Technological Innovation Center, Zhejiang University, Hangzhou, 311200, China
- 3Zhejiang Provincial Key Laboratory of Organic Pollution Process and Control, Hangzhou 310058, China
- 4Key Laboratory of Environment Remediation and Ecological Health, Ministry of Education, Zhejiang University, 310058 Hangzhou, China
- 1College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, 310058, China
- 2Hangzhou Global Scientific and Technological Innovation Center, Zhejiang University, Hangzhou, 311200, China
- 3Zhejiang Provincial Key Laboratory of Organic Pollution Process and Control, Hangzhou 310058, China
- 4Key Laboratory of Environment Remediation and Ecological Health, Ministry of Education, Zhejiang University, 310058 Hangzhou, China
Abstract. Accurate particle classification plays a vital role in aerosol studies. Differential mobility analyzer (DMA), centrifugal particle mass analyzer (CPMA) and aerodynamic aerosol classifier (AAC) are commonly used to select particles with a specific size or mass. However, multiple charging effect cannot be entirely avoided either using individual technique or using tandem system such as DMA-CPMA, especially when selecting soot particles with fractal structures. In this study, we demonstrate the transfer functions of DMA-CPMA and DMA-AAC systems, as well as the potential multiple charging effect. Our results show that the ability to remove multiply charged particles mainly depends on particles morphology and instruments setups of DMA-CPMA system. Using measurements from soot experiments and literature data, a general trend in the appearance of multiple charging effect with decreasing size when selecting aspherical particles was observed. Otherwise, our results indicated that the ability of DMA-AAC to resolve particles with multiple charges is mainly related to the resolutions of classifiers. In most cases, DMA-AAC can eliminate multiple charging effect regardless of the particle morphology, while particles with multiple charges can be selected when decreasing resolutions of DMA and AAC. We propose that the multiple charging effect should be reconsidered when using DMA-CPMA or DMA-AAC system in estimating size and mass resolved optical properties in the field and lab experiments.
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Yao Song et al.
Status: final response (author comments only)
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RC1: 'Comment on amt-2021-436', James Radney, 09 Feb 2022
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AC1: 'Reply on RC1', Zhibin Wang, 17 Apr 2022
Dear professor Radney, thank you for your constructive suggestions and comments. Those comments are valuable and very helpful for improving our paper, as well as the important guiding significance to our studies. In the supplement, we provide a point-by-point response to individual comment.
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AC1: 'Reply on RC1', Zhibin Wang, 17 Apr 2022
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RC2: 'Comment on amt-2021-436', Anonymous Referee #2, 16 Feb 2022
Comments on “Characterization of tandem aerosol classifiers for selecting particles: implication for eliminating multiple charging effect”
This study looks at the potential effects of multiply-charged particles in tandem aerosol instruments such as DMA-CPMA and DMA-AAC systems. The results show that the ability of DMA-CPMA system to resolve multiply-charged particles mainly depends on mass-mobility exponent of fractal aggregates as well as the operational conditions of the instruments. Resolving multiply-charged particles with DMA-AAC system mainly depends on the resolution of instruments. The paper showed that the DMA-CPMA setup is more sensitive to multiple charging effect when particles are smaller or have a lower mass-mobility exponent.
General comments:
Overall, the paper is written well and the methodology used is sound. It is also a timely addition to the literature as various classifiers, such as DMA, AAC, and CPMA, are used in tandem to characterize aerosol particles. The text needs some improvement in terms of English language, grammar, and readability and I recommend that the entire text be checked for these issues. I have some minor comments (see below) that must be addressed adequately before the paper can be accepted for publication.
Specific comments:
- Line 88, Eq. (3): The equation for the transfer function of the DMA in non-diffusing case is not given in the general form. Eq. (3) is only correct when aerosol inlet and aerosol sampling flow rates are equal (i.e. the DMA is operated in balanced flow mode), leading to δ = 0 in the general form of DMA transfer function [Eq. (7) in Stolzenburg and McMurry (2008)]. This information should be noted in the paper.
- Line 139: The primary reference for the miniature inverted soot generator is as follows, which should be cited in the text: Kazemimanesh, M., Moallemi, A., Thomson, K., Smallwood, G., Lobo, P. and Olfert, J.S., 2019. A novel miniature inverted-flame burner for the generation of soot nanoparticles. Aerosol Science and Technology, 53(2), pp.184-195.
- Line 138-140: To reproduce the experiments in this study, it is necessary to give details of propane and air flow rates used in the soot generator.
- Lines 145-155: For one or two mobility-selected particles, please add representative plots for the measured spectral density of mass (dN/dlog mp) and aerodynamic diameter (dN/dlog dae), either in the paper or in the supplementary material.
- Lines 198-199: It states that the ability of DMA-CPMA to eliminate multiply charged particles depends on the resolutions of both DMA and CPMA; however, dependence on the resolution of CPMA is not obvious from Eq. (25). Can the authors clarify this?
- Line 201: The sentence states that a larger β is necessary to reduce the potential of multiply-charged particles, but it seems that Eq. (25) shows the opposite. Can the authors double-check this?
- Line 303: In Fig. 5c and all related figures, the unit used incorrectly for absorption cross section is Mm-1, which is the unit for absorption coefficient (length-1). The correct unit for absorption cross section should be m2 particle-1 (derived from absorption coefficient/particle number concentration).
- Lines 306-310: It is not very clear to me why multiple charging effects due to the use of DMA-CPMA would affect the MAC or DRF of soot particles. As far as I understand, global climate models consider a specific (mostly constant) MAC value for black carbon particles to estimate their DRF, without regard for multiple charging. Unless the authors are claiming that the MAC values used in current climate models are grossly incorrect.
- Introduction and discussion section: There are a few recent studies that have looked at tandem measurements of mobility diameter, mass, and aerodynamic diameter to study the effective density and shape factor of spherical and non-spherical particles. These studies have used a combination of DMA, AAC, and APM or CPMA and, in my view, are relevant to this paper and should be mentioned in the introduction and their results discussed where necessary:
- Yao, Q., Asa-Awuku, A., Zangmeister, C.D. and Radney, J.G., 2020. Comparison of three essential sub-micrometer aerosol measurements: Mass, size and shape. Aerosol Science and Technology, 54(10), pp.1197-1209.
- Kazemimanesh, M., Rahman, M.M., Duca, D., Johnson, T.J., Addad, A., Giannopoulos, G., Focsa, C. and Boies, A.M., 2022. A comparative study on effective density, shape factor, and volatile mixing of non-spherical particles using tandem aerodynamic diameter, mobility diameter, and mass measurements. Journal of Aerosol Science, 161, p.105930.
Editorial and technical corrections (sentences that need to be corrected grammatically):
- Line 41-44.
- Line 49.
- Line 88, Eq. (3): Use the tilde over letter “Z” only, not over “Zp”. Correct this in all subsequent occurences.
- Line 103-104.
- Line 105.
- Line 107: radical à radial
- Line 272: I cannot find Eq. (30) in the paper.
- Lines 279-280: Fig. S2(a) and S2 (b) refer to 100-nm particles. The data for 150-nm particles are shown in Fig. S2(d) and S2(e).
- Line 300: Change to “The method to calculate PNSDve is described in section S1 of the Supplementary Material.”
- Line 301: Change the sentence to “Subsequently, absorption cross section, σabs, was derived using the absorption coefficient and total number concentration of particles with different charging states.”
- Lines 308-310: This sentence is written very poorly (huge amount? huge error?). Please rephrase this sentence and avoid ambiguous adjectives.
- Line 312: Reference to Table 3 should be given in the earlier paragraph (perhaps in line 302).
- Line 318: Severe à noticeable, significant. Leaded to à lead to
- Line 324: … but the method can suffer from multiple charging when decreasing the …
- Caption of Fig. 2: Subscripts and superscripts in this caption are not typed correctly.
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AC2: 'Reply on RC2', Zhibin Wang, 17 Apr 2022
Dear reviewer, thank you for the constructive suggestions and comments. Those comments are valuable and very helpful for improving our paper, as well as the important guiding significance to our studies. In the supplement, we provide a point-by-point response to individual comment.
Yao Song et al.
Yao Song et al.
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