the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
08 Jan 2021
08 Jan 2021
Comparative characterization of bio-aerosol nebulizers in connection to atmospheric simulation chambers
- 1Dipartimento di Fisica - Università di Genova, via Dodecaneso 33, 5 16146, Genova (IT)
- 2INFN – Sezione di Genova, via Dodecaneso 33, 16146, Genova (IT)
- 1Dipartimento di Fisica - Università di Genova, via Dodecaneso 33, 5 16146, Genova (IT)
- 2INFN – Sezione di Genova, via Dodecaneso 33, 16146, Genova (IT)
Abstract. The interplay of bio-aerosol dispersion and impact, meteorology, air quality is gaining increasing interest in the wide spectrum of atmospheric science. Experiments conducted inside confined artificial environments, such as the Atmospheric Simulations Chambers (ASCs), where atmospheric conditions and composition are controlled, can provide valuable information on bio-aerosol viability, dispersion, and impact. We focus here on the reproducible aerosolization and injection of viable microorganisms into an ASC, the first and crucial step of any experimental protocol to expose bio-aerosol at different atmospheric conditions. We compare the performance of three nebulizers specifically designed for bioaerosol applications: the Collison nebulizer, the Blaustein Atomizing Modules (BLAM) and the Sparging Liquid Aerosol Generator (SLAG), all manufactured and commercialized by CH TECHNOLOGIES. The comparison refers to operating conditions and the concentration of viable bacteria at the nebulizer outlet, with the final goal to measure the reproducibility of the nebulization procedure and assess the application in experiments at ASCs. A typical bacterial test model, Escherichia coli (ATCC® 25922™), was selected for such characterization. Bacteria suspensions, with a concentration around 108 CFU ml−1, were first aerosolized at different air pressures and collected by a Liquid Impinger, to obtain a correlation curve between airflow and nebulized bacteria, for each generator. Afterwards, bacteria were aerosolized inside the atmospheric simulation chamber ChAMBRe (Chamber for Aerosol Modelling and Bio-aerosol Research) to measure the reproducibility of the whole procedure. An overall reproducibility of 11 % was obtained with each nebulizer through a set of baseline experiments.
Silvia G. Danelli et al.
Status: open (until 30 Apr 2021)
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RC1: 'Comment on amt-2020-490', Anonymous Referee #1, 13 Feb 2021
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General comment
The paper focuses on an analysis of performances of nebulizers to produce airborne bacteria in laboratory experiments. The topic is interesting and it has useful application in bio-aerosol laboratory studies. The paper is well readable and suitable for the Journal. However, there are some aspects not very convincing or at least not very clear (see my specific comments). Therefore, I would suggest to consider the paper for publication after a major revision step.
Specific comments
One aspect that is not very clear to me is that the paper is focused on the analysis of performance of nebulizers evaluated in terms of viable bacteria. I can understand the setup with the impinge that seems the one used to really evaluate the efficiencies. However, it should be explained what is the role of chamber experiments in the context of efficiencies of nebulizers. Have these experiments be used somewhat to calculate efficiencies? A discussion on this aspect is needed.
Figure 3 shows efficiencies larger than one, even if by definition should be limited to one. It does not seem to be a problem of uncertainty in the counting because several points are larger than one even including the error bars. What is the explanation? An interpretation of this values should be provided in the manuscript.
Figures 6, 7, and 8 show that when more viable bacteria are injected in the chamber, more viable bacteria are collected after deposition on petri dishes in similar conditions. This seems quite straightforward; I believe that a discussion explaining how the slopes are related to the efficiencies of nebulizers should be included. The differences in the slopes are due to the efficiencies of nebulizers or the injected bacteria in the x-axis have been corrected for the different efficiencies? Are they compatible with the efficiency found with the impinge setup?
The title should probably include the word performances, like bio-aerosol nebulizers performances” or something similar.
Line 9. Better atmospheric sciences.
Lines 65-66. This sentence is not clear. It should be added that counting errors are assumed to be equal to the square root of counting in agreement with a Poisson statistics. Or something similar.
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CC1: 'Reply on RC1', Silvia Giulia Danelli, 16 Feb 2021
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The authors want to thank the Anonymous Referee #1 for the very useful comments, which will be addressed in the revised version of the manuscript.
Very quickly, the authors want to point out that, in Fig. 3, the nebulization efficiency is given as a percentage values (i.e. the maximum is around 1.2%). We will revise the figure caption to avoid misunderstandings.
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CC1: 'Reply on RC1', Silvia Giulia Danelli, 16 Feb 2021
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RC2: 'Comment on amt-2020-490', Michel Attoui, 12 Apr 2021
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Very interesting paper because the generation methods are always needed for the experimental works in aerosol science.
I have only few remarks to help the readers.
Line 63 NaCl 0,9 % is it by volume or by weight?
CFU ml-1 should give how many CFU in air in the best conditions?
Page 3 line 80 Collison nebulizer can be supplied in non-recirculation mode with a syringe pump. Line 90 inch is imperial unit. Why not cm?
Page 5 line 140 too many different units are used cfm; standard CFM; lpm; °C; K . I would suggest to keep lpm (1cfm = 28.4 lpm) and °C rather than Kelvin.
Page 6 line 175 blam slag produce how many particles /cc ?
Line 209 cambre should be chamber.
Page 4 line 113 remove the dot after 2.1
Page 4 line 126. The temperature accuracy unit is not given. Is it 0.2% or 0.2 °C?
Page 5 and others. The pressure is given in mbars. This unit is not legal unit. The pressure must be given in Pascal. The authors can add between parenthesis mbar if they want.
Page 5 line 149. ‘The pressure in the ChAMBRe arise from 10-5 mb to atmospheric pressure with air (I guess)’ . A precision should be given about this air? Is it atmospheric air (called lab air) or air from a cylinder? If lab air is used then the authors should precise the RH. Indeed it seems that they are not using any drying system.
Page 5 line 153. The pressure given is little bit incorrect 990 and 1020 bars are too high as pressure. I guess that the unit is mbars (again).
Page 7 line 203. What it means PM10? The size distribution is monitored with an optical particle counter. That will be very nice to give more details on the measured distributions since the OPC gives them. Are they reproducible? What is the sigma g of the distributions? What is the density value used to calculate this relatively high mass concentration (200 mg/m3) from the number concentrations given by the OPC? 200mg/m3 seems monumental form me.
The sampling experiments in the ChAMBRe are conducted by gravitational settling. The gravitational settling of a particle of 1 µm is 3.5 10-5 m/s in still air. I think that your method penalizes the generator. I would prefer a single stage bio impactor if I had to carry these experiments.
The short conclusion of the paper is not giving the results of each generator clearly. It will be better to give the concentration 5CFU/m3 for each generator to help the reader. It will be good to recall the concentrations at the outputs of each generator always to help the reader.
I would suggest to add one paper at least on bio aerosols and atmosphere (for example Joung 2017 : Bioaerosol generation by raindrops on soil: Nature communications 8 : 14668)
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RC3: 'Comment on amt-2020-490', Jing Wang, 12 Apr 2021
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It is a very interesting paper that compares the performance of three nebulizers for the work of bio-aerosols in atmospheric simulation chambers (ASC). The authors investigated the efficiencies of the nebulizers in association with the airflow and the subsequent viable fraction of the bacterial cells after nebulization into an ASC. The paper points out nicely the advantages and disadvantages regarding the performances of each nebulizer and allows the reader to follow easily by pointing out a clear conclusion in the end.
Just a few remarks from my side:
- Make sure to use the same font, size, ect. to fullfill the formart requirements
- It's difficult to understand what the 11% (line 22) refer to exactly. Make it more clear in both the abstract and results section
- Line 39: "non-trivial"
- Line 65: "of the cfu..."
- I think it is very nice how you described the different nebulizers in 2.2, however it would make more sense to move this section to the Introduction section
- Line 142: "sterilization system, too"
- In section 3.1 it would be nice to read a bit more about how it is possible to compare one nebulizer in ml, while the other one is in minutes
- Avoid statements that are vage such as in line 186: "output of viable bacteria turned out to be quite high" and rather write those results with clear statements (eg. by including numbers)
- Use the same units throughout the whole paper
Silvia G. Danelli et al.
Silvia G. Danelli et al.
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