Chemical composition of isoprene SOA under acidic and non-acidic conditions: effect of relative humidity

Nestorowicz, Klara; Jaoui, Mohammed; Rudzinski, Krzysztof Jan; Lewandowski, Michael; Kleindienst, Tadeusz E.; Spólnik, Grzegorz; Danikiewicz, Witold; Szmigielski, Rafal

doi:https://doi.org/10.5194/acp-18-18101-2018

Articles | Volume 18, issue 24

https://doi.org/10.5194/acp-18-18101-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-18-18101-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 24

Research article

|

20 Dec 2018

Research article |

| 20 Dec 2018

Chemical composition of isoprene SOA under acidic and non-acidic conditions: effect of relative humidity

Klara Nestorowicz, Mohammed Jaoui, Krzysztof Jan Rudzinski, Michael Lewandowski, Tadeusz E. Kleindienst, Grzegorz Spólnik, Witold Danikiewicz, and Rafal Szmigielski

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Final revised paper (published on 20 Dec 2018)
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Preprint (discussion started on 19 Mar 2018)
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Interactive discussion

Status: closed

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

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RC1: 'Chemical composition of isoprene SOA under acidic and non-acidic conditions: Effect of relative humidity', Anonymous Referee #1, 02 May 2018
- AC1: 'Authors response to reviewer 1 comments', Mohammed Jaoui, 14 Jul 2018
- AC2: 'Authors response to reviewer 1 comment as pdf', Mohammed Jaoui, 14 Jul 2018
- AC5: 'Final revised (R1) manuscript for all 3 reviewers', Mohammed Jaoui, 14 Jul 2018
- AC6: 'Final revised supplementary information for all 3 reviewers', Mohammed Jaoui, 14 Jul 2018
- AC3: 'Authors response to reviewer 2 comments as pdf file', Mohammed Jaoui, 14 Jul 2018
RC2: 'Review', Anonymous Referee #2, 17 May 2018
- AC3: 'Authors response to reviewer 2 comments as pdf file', Mohammed Jaoui, 14 Jul 2018
RC3: 'Major Revisions Needed', Anonymous Referee #3, 02 Jun 2018
- AC4: 'Authors response to reviewer 3 as pdf file', Mohammed Jaoui, 14 Jul 2018

Peer-review completion

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

AR by Mohammed Jaoui on behalf of the Authors (15 Aug 2018)

ED: Referee Nomination & Report Request started (27 Aug 2018) by Sergey A. Nizkorodov

RR by Anonymous Referee #3 (27 Oct 2018)

Suggestions for revision or reasons for rejection

Further comments:

I thank the authors for revising their manuscript and considering some of my initial comments. Unfortunately, there appears to be some major deficiencies remaining that must be addressed before full publication in ACP can be considered. My largest concern relates to the fact that extreme care must be given when applying GC/Ei-MS (or other thermal analytical methods) to the chemical characterization of isoprene SOA (and likely to other types of SOA in general):

1.) I would argue we (as a research community) need to get away from using GC/EI-MS with prior derivatiization for chemically characterizing isoprene SOA, and possibly for other SOA systems. Importantly, a new HILIC/ESI-HR-QTFOMS recently published by Cui et al. (2018, ESPI) from the Surratt group can measure both 2-methyletrols and organosulfates with the SAME non-thermal analytical method without the need of prior derivatization. Further, this is all done in negative ESI mode. Yes, the 2-methyltetrols can be measured by HILIC/ESI-HR-QTOFMS in the negative ion mode and can be resolved from the organosulfates! This is exciting. Furthermore, they showed that 2-methyltetrols measured by GC/MS with prior derivatization was so much higher than HILIC/ESI-HR_QTOFMS, and further showed with authentic standards that the IEPOX-derived organosulfates (i.e., 2-methyltetrol sulfates and 3-methyltetrol sulfates) decomposed into 2-methyltetrols and C5-alkene triols!!! This has to be considered here in this study! Thus, artifacts of GC/EI-MS must be acknowledged and this could affect the interpretation of the current results.

2.) Table 2: The C5H10O3 compounds in Table 2 are NOT IEPOX isomers. They are in fact 3-MeTHF-3,4-diols, which are now known to be thermal degradation products from organosuflates (as shown recently in Cui et al., 2018, ESPI). Further, Lin et al. (2012, ES&T) and Zhang et al. (2012, ACP) from the Surratt group showed that GC/MS measures these ions at m/z 262 and 118 as 3-MeTHF-3,4-diols. This was proven with the use of authentic standards. These are not the correct assignments shown here. Furthermore, these compounds are decomposition products of low-volatility products, such as the IEPOX-derived organosulfates (Cui et al., 2018, ESPI).

3.) Page 2, Line 6: Again, this statement "although the SOA yield of isoprene tends to be low," is misleading. This is true if you look back at the prior literature from Kroll et al. (2005, GRL), Kroll et al. (2006, ES&T), Edney et al. (2005, AE), but if you consider the multiphase chemistry of its oxidation products (especially IEPOX), then using the SOA yield approach in determining amount of SOA possilbe from isoprene is not a good way to model it. Specifically, the EPA CMAQ model no longer uses the Odum 2-product model approach to constrain the products from isoprene oxidation. Specifically, it models SOA from isorpene as a multiphase chemical processes by modeling the reactive uptake of IEPOX and other important products.

4.) Page 2, Line 11: change "products include" to "products, including...."

5.) Page 2, Line 11: change "reported including" to "previously reported include"

6.) Page 2, Lines 14-15: Previous analytical work suggests as you heat isoprene SOA you see the off gassing of 2-MTs and C5-alkene triols, especially in thermodunders and FIGAERO-CIMS (Lopez-Hilfiker et al., 2016, ES&T). As shown in the FIGAERO-CIMS, the 2-methyltetrols and C5-alkene triol peaks didn't make sense due to their location in the low-volatility section of the thermograms. Thus, as this study showed, 2-methyltetrols and C5-alkene triols were likely thermal degradation products of lower volatility compounds in isoprene SOA. Importantly, the Cui et al. (2018, ESPI) from the Surratt Group recently demonstrated with authentic standrads that the 2-methyletrol sulfates (2MT-OS) and 3-MT-OS degrade in GC/MS with prior derivatization into C5-alkene triols and 2-methyltetrols! This is a huge deal, as it appears that most of the isorpene SOA is in the organosulfate forms of IEPOX (including sulfated oligomers). This has important consequences for the results presented here. Previous statements about artifacts from GC/MS can NO LONGER be neglected and these authors must recognize this now in their analyses.

7.) Page 3, Lines 31-33: The authors should note that "Subsquent studies..." is not correct for the fact they cite Zhang et al. 2011 (ACP). Zhang et al. (2011, ACP) was published before Nguyen et al. (2011), right? They were published very close together though.

8.) Page 5, Lines 28-30: What was the average RH? Especially during the day ?

9.) Page 5, Line 32: As shown by the many previous studies (e.g., Gaston et al., 2014, ES&T; Riedel et al., 2015, ES&TL; etc.) sulfate aerosol is the most important field parameter to report over SO2 concentrations. Its the sulfate particles that provide the surface for the multiphase chemical reactions to occur on.

10.) Page 6, Line 29: What were exactly the appropriate surrogate standards used to determine the recoveries for LC/MS?

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RR by Anonymous Referee #1 (29 Oct 2018)

Suggestions for revision or reasons for rejection

The authors greatly improved the quality of the paper. I still have a few comments that should be addressed before this study can be accepted:

If the authors want to use acronym they should be consistent (e.g. OS vs OSs) and use them. For instance, in many places, the authors used organosulfates rather than OS or OSs. So please go through the article and make it consistent.

Line 14, page 2. It needs to be rephrased. As it is written it can be understood that the gas phase oxidation of isoprene can lead to the formation of 2-MT. The authors used Kleindienst et al, to support such a statement. However, in this previous the authors discussed the following part: "Here was some evidence that methyl tetrols might also be present at low levels in the denuder sample represented by Fig. 2. The finding could be attributed to the presence of the methyl tetrols in the gas phase based on estimated saturation vapor pressures for tetrols reported by Angove et al. (2006)."
So the authors need to be careful and do not suggest that the presence of 2-MT is due to a gas phase oxidation process. Instead, they should clearly mention that it is probably due to the re-evaporation of the 2-MT as recently suggested. (Isaacman-VanWertz et al., 2016 ES&T).

The aerosol acidity aspect is still a bit confusing. In the review, the authors claimed that they cannot estimate the aerosol acidity because they didn't have any particle phase measurement providing the concentrations of inorganic species. However, they know the concentrations of the initial solutions and they know the mass injected inside the chamber. Therefore they should at least be able to estimate the initial pH and LWC of the seed aerosols. In addition, at different places, they mentioned that the seed injections and aerosol concentrations were similar to Lewandowski et al., 2015. In this previous study the same authors estimated the aerosol acidity, so why don't they use their previous study to determine the aerosol acidity if the parameter (besides the RH) were identical?

Finally, the experiments performed using AS as seed aerosols are a bit strange. At RH < 40% the seed aerosols should be effloresced and be metastatic (i.e., a crystal). However, the results presented in this study clearly show that the RH matter, which is a bit surprising (e.g., Fig. MS at 9% vs 19%). How do the authors explain such results? It should be mentioned and further discussed in the paper. One explanation might be the larger wall losses due to humid walls but that would imply that 2mGAd are not formed in particle phase.

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RR by Anonymous Referee #2 (29 Oct 2018)

ED: Reconsider after major revisions (29 Oct 2018) by Sergey A. Nizkorodov

AR by Mohammed Jaoui on behalf of the Authors (27 Nov 2018)

ED: Publish as is (29 Nov 2018) by Sergey A. Nizkorodov

AR by Mohammed Jaoui on behalf of the Authors (30 Nov 2018) Author's response Manuscript

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