Measurement techniques for identifying and quantifying hydroxymethanesulfonate (HMS) in an aqueous matrix and particulate matter using aerosol mass spectrometry and ion chromatography

Dovrou, Eleni; Lim, Christopher Y.; Canagaratna, Manjula R.; Kroll, Jesse H.; Worsnop, Douglas R.; Keutsch, Frank N.

doi:https://doi.org/10.5194/amt-12-5303-2019

Articles | Volume 12, issue 10

Atmos. Meas. Tech., 12, 5303–5315, 2019

https://doi.org/10.5194/amt-12-5303-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Atmos. Meas. Tech., 12, 5303–5315, 2019

https://doi.org/10.5194/amt-12-5303-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 12, issue 10

Research article 07 Oct 2019

Research article | 07 Oct 2019

Measurement techniques for identifying and quantifying hydroxymethanesulfonate (HMS) in an aqueous matrix and particulate matter using aerosol mass spectrometry and ion chromatography

Eleni Dovrou et al.

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Final revised paper (published on 07 Oct 2019)
Preprint (discussion started on 07 May 2019)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of Dovrou et al', Anonymous Referee #2, 01 Jun 2019
- AC1: 'Response to the comments of referee #2 for the open discussion of the manuscript “amt-2019-127”', Eleni Dovrou, 29 Jul 2019
- AC4: 'Response to the comments of referee #2 for the open discussion of the manuscript “amt-2019-127”', Eleni Dovrou, 29 Jul 2019
RC2: 'Review of Dovrou et al, Measurement techniques...', Anonymous Referee #3, 10 Jun 2019
- AC2: 'Response to the comments of referee #3 for the open discussion of the manuscript “amt-2019-127”', Eleni Dovrou, 29 Jul 2019
RC3: 'Review comments', Anonymous Referee #1, 11 Jun 2019
- AC3: 'Response to the comments of referee #1 for the open discussion of the manuscript “amt-2019-127”', Eleni Dovrou, 29 Jul 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Eleni Dovrou on behalf of the Authors (29 Jul 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (30 Jul 2019) by Pierre Herckes

RR by Anonymous Referee #1 (12 Aug 2019)

RR by Anonymous Referee #2 (13 Aug 2019)

Suggestions for revision or reasons for rejection

This is a review of the revised version of amt-2019-127 by Dovrou et al. My comments below pertain primarily to my review of the author responses to prior reviewer comments. Based on the responses to the reviewer comments, I am concerned about the methodology used to evaluate and report the data here, particularly in terms of uncertainties and limits of detection, which brings into question the analytical rigor of the study.

Major Comments:
Title (all three reviewers): The title revision to mention HMS and PM is an improvement. However, it is misleading to mention cloud water, since this was not measured in this study. I also highly recommend specifically mentioning AMS and IC in the title so that the manuscript can be more easily identified by researchers searching on these methods. The other techniques discussed in the manuscript are simply in the background/intro material and do not constitute new knowledge added through this study.

Limit of Detection (LOD), Pages 7-8 (Response to Reviewer 1, Comment 2 & Reviewer 2, Comment 5): I am concerned by how the authors have defined and determined their detection limit by running multiple concentrations and defining the LOD as the lowest concentration for which a measurable peak was efficiently quantified. Under most circumstances, LOD is defined at the 3* standard deviation of the noise +/- uncertainty and is not determined in the way described by the authors. I believe the Thermo Chromeleon software provides a LOD based off the Hubaux and Vos method using an entire calibration curve. However, Ragland et al. (2014, Analytical Chem.) described the weaknesses of this method for chromatography, and even the Hubaux and Vos method was not used by the authors for an unknown reason. A recommended method often used to calculate the LOD from a calibration curve is to calculate 3*sensitivity/slope. Especially since this is a method paper, it is important that the LODs be reported accurately.

Uncertainty (Reviewer 2, Comments 6-7): Related to the last comment, how can there only be a 4% uncertainty when there is an underestimation of over 15% of HMS? Did this occur near the detection limit, such that this may be an issue of being below the limit of quantitation (typically defined at 3.3*LOD)? The points here about limit of detection are also related to the determination of uncertainty. Typically uncertainty is reported as 3*standard deviation of triplicate runs, rather than by just looking at the differences in the values and choosing one decimal point (response to Reviewer 2, Comment 7); however, again, the authors did not assess this rigorously, which again opens questions about the analytical methodology in this manuscript.

Reviewer 1, Comment 2; Page 9: The pH of the eluent is noted, but where is the actual IC eluent composition and concentration provided? Further, it is stated that the stability of the HMS has a strong pH dependence. What is the pKa of HMS? This would be useful to report.

Page 9, Lines 24-26: Please report the required concentration to distinguish sulfate and HMS in uM, rather than ug m-3, which is far less useful, since it depends on filter extraction protocol. It is stated that sulfate needs to be in lower concentration than HMS for the method to be viable, but is there a scenario in the atmosphere where this is expected to occur?

Reviewer 3, Comment 3: Based on comparison of the discussion of the method in the Conclusions section and throughout, it would appear that CE would be a superior technique in terms of efficient separation and sensitivity to detect HMS, based on Scheinhardt et al (2014), which has now been added to the manuscript. For example, the LOQ was determined to be ~20 ng m-3 in that study, compared to >2 ug m-3 in this study. If these direct comparisons are not fair, then this should be even further discussed, especially in the conclusions section when the reviewer is assessing the best methods going forward.

Minor Comments:
Page 4, Lines 19-21: Please fix this sentence as it has typos and is not understandable as written.

Page 3, Lines 14-16: Fix the phrasing “single-particle analysis by laser mass spectrometry (PALMS) (Lee et al., 2003) and single-particle mass spectrometry (rapid…” to “single-particle mass spectrometry (single-particle analysis by laser mass spectrometry: PALMS, Lee et al., 2003; rapid…” since PALMS is a single-particle mass spectrometry technique.

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ED: Publish subject to minor revisions (review by editor) (13 Aug 2019) by Pierre Herckes

AR by Eleni Dovrou on behalf of the Authors (03 Sep 2019) Author's response Manuscript

ED: Publish as is (05 Sep 2019) by Pierre Herckes

Short summary

Measurement techniques commonly used to analyze particulate matter composition can result in the possible misidentification of sulfur-containing species, especially for the case of sulfate and hydroxymethanesulfonate (HMS). The efficiency and limitations of these techniques, along with a method that enables further studies of the contribution of sulfur-containing species, S(IV) versus S(VI), to particulate matter under low-light atmospheric conditions, are described in this work.