Review Reports - Characterization of Chemical Components and Optical Properties of Toluene Secondary Organic Aerosol in Presence of Ferric Chloride Fine Particles

Round 1

Reviewer 1 Report

This paper titled, "Characterization of chemical components and optical properties of toluene secondary organic aerosol in presence of ferric chloride fine particles" by Wang et al simulated photoxidation of Toluene in the presence of ferric chloride particles and investigated the chemical constituents and optical properties of SOA formed in Smog Chamber experiments. This study is in accordance with the aims and objectives of the journal "Atmosphere". It will aid the scientific community related to ambient particulates and specifically SOA to further explore avenues such as investigating the role of metals in enhanced secondary particle formation under varying concentration of gasses and seed particles. Therefore, I recommend this publication. However, there are certain major comments which are very important to address which can further add value to the manuscript. These comments are as below:

Major Comments:

1- Line 106: How toluene was added to chamber, please briefly provide details?

2- At what temperature and RH, experiments were performed? How temperature and RH were controlled, please explain briefly.

3- How proper mixing of the reactants were ensured?

4- Ferric chloride seed particles were injected, what was the particle number concentration right after injection? There has to be a certain particle number concentration after injection which is in fact not evident in the relevant figure such as figure 2 in the manuscript.

5- Was SOA corrected for wall loss? From Figure 2, it seems that it’s corrected but how? Please provide details?

6- Kindly provide a representative figure for any experiment to demonstrate the RH, temp, gaseous and particle profiles during the course of experiments.

7- Lines 119-120: What was the rational of conducting experiments at O3 and toluene concentrations of 10 ppm and 1 ppm, respectively?

8- Add a paragraph at any suitable place in manuscript to describe the atmospheric implications and futuristic studies in the context of this study.

9- In the introduction section, it’s important to briefly explain the importance of Smog Chambers considering atmospheric chemical processes and refer to following references:

a. Shao, Y., Wang, Y., Du, M., Voliotis, A., Alfarra, M. R., O'Meara, S. P., ... & McFiggans, G. (2022). Characterization of the Manchester Aerosol Chamber facility. Atmospheric Measurement Techniques, 15(2), 539-559.

b. Chu, B., Chen, T., Liu, Y., Ma, Q., Mu, Y., Wang, Y., ... & He, H. (2022). Application of smog chambers in atmospheric process studies. National Science Review, 9(2), nwab103.

c. Babar, Z. B., Park, J. H., Kang, J., & Lim, H. J. (2016). Characterization of a smog chamber for studying formation and physicochemical properties of secondary organic aerosol. Aerosol and Air Quality Research, 16(12), 3102-3113.

Minor Comments:

10- Line 113: Omit “and components”.

11- Kindly specify the flowrates of all sampling instruments in the methodology section.

12- Lines 123-124: These lines are really confusing, please rephrase them for clarity.

13- Line 127: Add “of” after 5 mL and (v/v) after 2%.

14- Line 40: Add following references in addition to already mentioned reference # 6 and 7:

a. Qi, X., Zhu, S., Zhu, C., Hu, J., Lou, S., Xu, L., ... & Cheng, P. (2020). Smog chamber study of the effects of NOx and NH3 on the formation of secondary organic aerosols and optical properties from photo-oxidation of toluene. Science of the Total Environment, 727, 138632.

b. Babar, Z. B., Park, J. H., & Lim, H. J. (2017). Influence of NH3 on secondary organic aerosols from the ozonolysis and photooxidation of α-pinene in a flow reactor. Atmospheric environment, 164, 71-84.

c. Liu, S., Huang, D., Wang, Y., Zhang, S., Liu, X., Wu, C., ... & Wang, G. (2021). Synergetic effects of NH 3 and NO x on the production and optical absorption of secondary organic aerosol formation from toluene photooxidation. Atmospheric Chemistry and Physics, 21(23), 17759-17773.

Author Response

Dear reviewer,

Our revised manuscript entitled “Characterization of chemical components and optical properties of toluene secondary organic aerosol in presence of ferric chloride fine particles” by Weichao Wang et al. is submitted to Atmosphere for the consideration of publication.

Thank you very much for the suggestions about the further improvement of it. We have carefully considered the comments and revised the manuscript accordingly. The detailed replies to the comments we have made are listed in the document of "Responses to Reviewer 1".

Best Wishes!

Sincerely Yours

Weichao Wang, Mingqiang Huang

Author Response File: Author Response.doc

Reviewer 2 Report

Review for atmosphere-2378998 “Characterization of chemical components and optical properties of toluene secondary organic aerosol in presence of ferric chloride fine particles”

This study conducted a chamber study to characterize the formation of SOA from toluene ferric chloride. The manuscript can be published after addressing the following concerns.

Major comments:

1) A brief description of ALTOFMS should be provided, since the version of ALTOFMS used in the current study is different from that used in the authors’ previous studies. For example, a 248 nm KrF excimer laser was used in Huang et al. (2014) for ionization, while in this study, a 266 nm Nd: YAG laser was used for ionization.

2) Regarding the MAC calculation, the light absorption in the solution is ~2 times higher than that in the air owing to artifacts (Liu et al., 2013; Shetty et al., 2019), which should be pointed out.

3) It would be better to report the MAC at 365 nm, which is more commonly used in the literature. In this way, the MAC obtained from this study can also be compared with literature values.

4) It is suggested to include differential mass spectra to illustrate the effect of with/without ferric chloride fine particles.

5) Because ferric chloride was used, the author should clarify how to differentiate the effect of chlorine-initiated oxidation of toluene (Dhulipala et al., 2019) from the effect of Fe3+.

6) The concentration of Fe3+ particles used in the chamber study was three orders of magnitude higher than the typical ambient concentration in the air. The authors should justify the link between this chamber study and ambient implications.

References

Dhulipala, S. V., Bhandari, S., and Hildebrandt Ruiz, L.: Formation of oxidized organic compounds from Cl-initiated oxidation of toluene, Atmos. Environ., 199, 265-273, doi: https://doi.org/https://doi.org/10.1016/j.atmosenv.2018.11.002, 2019.

Huang, M., Liu, X., Hu, C., Guo, X., Gu, X., Zhao, W., Wang, Z., fang, L., and Zhang, W.: Aerosol laser time-of-flight mass spectrometer for the on-line measurement of secondary organic aerosol in smog chamber, Measurement, 55, 394-401, doi: https://doi.org/https://doi.org/10.1016/j.measurement.2014.05.038, 2014.

Liu, J., Bergin, M., Guo, H., King, L., Kotra, N., Edgerton, E., and Weber, R. J.: Size-resolved measurements of brown carbon in water and methanol extracts and estimates of their contribution to ambient fine-particle light absorption, Atmos. Chem. Phys., 13, 12389-12404, doi: https://doi.org/10.5194/acp-13-12389-2013, 2013.

Shetty, N. J., Pandey, A., Baker, S., Hao, W. M., and Chakrabarty, R. K.: Measuring light absorption by freshly emitted organic aerosols: optical artifacts in traditional solvent-extraction-based methods, Atmos. Chem. Phys., 19, 8817-8830, doi: https://doi.org/10.5194/acp-19-8817-2019, 2019.

Minor editing of English language required

Author Response

Dear reviewer,

Best Wishes!

Sincerely Yours

Weichao Wang, Mingqiang Huang

Author Response File: Author Response.doc

Reviewer 3 Report

This manuscript describes and compares the main chemical characteristics and optical properties (i.e., UV-Vis spectra) of toluene secondary organic aerosol (SOA) in the absence and presence of ferric chloride seed fine particles. Overall, it is an interesting study that contributes for the current understanding of the chemical reactivity of air particles rich in transition metals, such as iron (e.g., dust aerosols). Nevertheless, this reviewer has a few comments and suggestions that should be addressed by the authors. These are as follows:

Line 16 and throughout the text: Please, avoid using this "heavy metal" term. At least, the authors should refer to iron as a "transition metal". Otherwise, simply use the term "metals" (but not "heavy metals").

Line 20: What do you mean by "condition without fine particles"? The abstract should be rewritten and better organized to improve its reading and a better understanding of the topic under discussion.

Line 24: "spectral information" instead of "spectrogram information".

Lines 74-75: The text "PM2.5 of urban atmospheric aerosol" should read simply as "urban PM2.5".

Lines 83-84: Please, rewrite this sentence to improve its meaning and reading within the paragraph as a whole.

Lines 122 and throughout the text: "irradiation" instead of "illumination".

Lines 132-133: If the sample was measured without a chromatographic column, what was the purpose of using a LC-MS? The authors were only interested in using the MS detector? This is confusing and additional explanations are required.

Lines 143-144: This is another sentence requiring a thorough revision to improve its reading.

Lines 144-146: What was the procedure employed to remove the methanol from the extracting solution of toluene SOA particles before assessing the organic carbon content of these solutions using the TOC analyser?

Lines 150-157: A schematic figure is required here to guide the potential reader through these mechanistic reactions.

Figure 3: In the axis title it should read "Concentration" instead of "Concentartion".

Additional comment: There is a very interesting critical review article published recently that addresses the current state of knowledge on iron chemistry that led to SOA formation. The authors should consider this review article when discussing the acquired data. This article is as follows: Hind A. Al-Abadleh (2021) Aging of atmospheric aerosols and the role of iron in catalyzing brown carbon formation, Environ. Sci.: Atmos., 1, 297-345. DOI: 10.1039/D1EA00038A.

Extensive editing of English language is required to improve the reading and a better understanding of the manuscript.

Author Response

Dear reviewer,

Best Wishes!

Sincerely Yours

Weichao Wang, Mingqiang Huang

Author Response File: Author Response.doc

Round 2

Reviewer 1 Report

Manuscript has been revised thoroughly. All the comments have been addressed properly which improved the quality of the paper.

Reviewer 2 Report

Accept.

Minor editing of English language required.

Reviewer 3 Report

As a whole, the revised manuscript has ameliorated with respect to its first version. This Reviewer has particularly appreciated the discussion of the concerns raised in the first review, as well as the way by which the authors have included the suggested amendments.