Aerosol composition and the contribution of SOA formation over Mediterranean forests

Freney, Evelyn; Sellegri, Karine; Chrit, Mounir; Adachi, Kouji; Brito, Joel; Waked, Antoine; Borbon, Agnès; Colomb, Aurélie; Dupuy, Régis; Pichon, Jean-Marc; Bouvier, Laetitia; Delon, Claire; Jambert, Corinne; Durand, Pierre; Bourianne, Thierry; Gaimoz, Cécile; Triquet, Sylvain; Féron, Anaïs; Beekmann, Matthias; Dulac, François; Sartelet, Karine

doi:https://doi.org/10.5194/acp-18-7041-2018

Articles | Volume 18, issue 10

https://doi.org/10.5194/acp-18-7041-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue:

CHemistry and AeRosols Mediterranean EXperiments (ChArMEx)...

https://doi.org/10.5194/acp-18-7041-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 18, issue 10

Research article

|

23 May 2018

Research article |

| 23 May 2018

Aerosol composition and the contribution of SOA formation over Mediterranean forests

Evelyn Freney, Karine Sellegri, Mounir Chrit, Kouji Adachi, Joel Brito, Antoine Waked, Agnès Borbon, Aurélie Colomb, Régis Dupuy, Jean-Marc Pichon, Laetitia Bouvier, Claire Delon, Corinne Jambert, Pierre Durand, Thierry Bourianne, Cécile Gaimoz, Sylvain Triquet, Anaïs Féron, Matthias Beekmann, François Dulac, and Karine Sartelet

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

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RC1: 'Review Freney et al.', Anonymous Referee #3, 14 Sep 2017
- AC1: 'Response to reviewer 3', Evelyn Freney, 10 Jan 2018
RC2: 'Review of Freney et al.', Anonymous Referee #1, 16 Sep 2017
- AC2: 'Response to reviewer 1', Evelyn Freney, 10 Jan 2018
  - EC1: 'Editorial comments', Xavier Querol, 11 Jan 2018

Peer-review completion

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

AR by Evelyn Freney on behalf of the Authors (10 Jan 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (11 Jan 2018) by Xavier Querol

RR by Anonymous Referee #1 (19 Jan 2018)

RR by Anonymous Referee #3 (26 Jan 2018)

Suggestions for revision or reasons for rejection

The authors have satisfactorily responded to all my comments and questions and significantly modified the manuscript accordingly. However, I still have some major issues regarding the revised text.

1/ P7, lines 21-27. The toluene to benzene ratio cannot be used to “assess contribution of anthropogenic emissions”. This ratio only provides information regarding the photochemical age (or the integrated OH exposure) of the anthropogenic fraction of the whole VOC mixture. A T/B ratio of 1.54 do not indicate a significant anthropogenic contribution but an integrated OH exposure of the anthropogenic inputs of about 16.106 molecules.cm3.h (ie. a photochemical age of about 11h, considering an initial (T/B) of 2, which is a little bit low from my opinion, and an OH concentration of 1.5 106 molecules cm-3) and this whatever is the contribution of anthropogenic VOCs to the whole VOC/SVOC mixture. In this study and considering the data shown in fig S6, benzene and toluene signals are very noisy (because very close to the dl of the instrument) which probably imply an important variability of the T/B ratio not directly related to the photochemical age of the potential anthropogenic inputs. Also, with such low toluene concentrations and although monoterpenes concentrations are low, the interference from the monoterpenes fragmentation’s in the drift tube (m/z93 representing classically about 5-10% of m/z137, depending on the E/N) could potentially be significant for the T/B ratio. While it’s always interesting to have a look to this ratio, I’d put much less emphasis on it and, above all, I’d used it wisely.

2/ P7, lines 27-30. An enhancement ratio (ER) of a parameter X is classically defined as follows: ER=X(t)/X(t0). In the case of the ratio HCHO/CH3CHO what is the reference (t0)? Authors must also specify how HCHO has been measured in the experimental section. If measured by PTRMS, are the HCHO concentrations corrected by the RH? Although a throughout analysis of the VOCs is expected in a future paper, this section must be clarified to make it understandable and meaningful.

To summarize, the whole section 3.1 needs to be significantly improved and developed before publication.

3/P8, line 11-21. This is now much clearer. I’d change the title of fig 4a accordingly: “homogeneously mixed amorphous organic aerosol particle”

4/P10 lines 6-9. I agree with this conclusion, but the caveats developed above must be considered here.

5/ P10 lines 25-30.
“plotting the two species as a function of..”. Be more accurate. In fig S10, Delta MOOA and Delta LOOA are reported without defining what the delta stands for.
“we observe a significant increase of the LOOA species with air mass age until a maximum is reached at ratios of 0.65.” Here the question is what happen for higher m/z71 to m/z 69 ratio?
“MOOA remains relatively stable, indicating an independent source.” That’s a little bit short. As MOOA is associated to SO4, one can suspect that MOOA is related to long range transport episodes or regional pollution impacted by anthropogenic emissions. Does it make sense? Considering the modelling results (fig 9) it seems that anthropogenic SOA cannot be neglected (17-28% of OA, fig 9).

6/ P11, line15 : “we do not believe that isoprene derived SOA contributed significant amounts to the OA measured during these flights”. Replace by : “we assume that….. do not…” but 15-35% (fig9) is not totally insignificant.

7/ P12, lines 25-28: “Although isoprene emissions are much higher than those of monoterpenes and sesquiterpenes over that region” Please be more quantitative
“Isoprene derived SOA represent only about 15 to 35%” 15-35% is a high contribution, from my perspective, considering isoprene-SOA.
“4% to 7% are from semi-volatile organic compounds (pinic acid, norpinic acid and pinonaldehyde)” Please be homogenous with the legend of fig 9 :”Monoterpene products”
“17% to 23% from organic nitrate” Considering this potential very high contribution of organic nitrates, they should be evidenced by the ratio NO+/NO2+

8/P13, line 19 : again, 15-35% of isoprene SOA is significant.

9/ P17 line 29. Lee et al (2016) was added in the reference list, but never cited in the text. As well, f91 is not discussed. Such discussions could bring valuable insights on the Biogenic SOA importance and origin.

Non-exhaustive list of technical corrections (figures/legends, mostly)

P2, line 4. The acronym of methacrolein is defined as MACR, but MCR is used all throughout the manuscript and in the figures (except in table 1).
Figure 1 : add the flight numbers in the legend.
Figure 4 a) change the legend (see comment 3)
Figure 5 : Y axis label. What is the lower cut off diameter of the SMPS 15 or 17 nm?
Figure 6 : Y axis label : add units ; figure legend : 17 or 15 nm?
Figure 7 : explicit the Delta
Figure 9 : Put side by side all the monoterpenes derived SOA components.
Figure S3 : X axis : wrong units ! , MCR+Isoprene? / Legend : ISOPOOH is missing
Figure S6 : No identified Y axis for benzene, X axis : I suppose it’s Toluene/Benzene and not Benzene/Toluene
Figure S7 : Develop and modify the legend (you didn’t calculate airmass age, just used proxies). Define Delta, flight numbers
Figure S11 : Wrong legend

(Please be more rigorous when submitting a paper, especially a revised manuscript)

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ED: Reconsider after major revisions (28 Jan 2018) by Xavier Querol

AR by Evelyn Freney on behalf of the Authors (27 Mar 2018) Author's response Manuscript

ED: Publish as is (04 Apr 2018) by Xavier Querol

AR by Evelyn Freney on behalf of the Authors (16 Apr 2018) Manuscript

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Short summary

The focus of these experiments, within the ChArMEx project, were to better understand the chemical properties of ambient aerosols over the Mediterranean region. A series of airborne measurements were performed aboard the French research aircraft, the ATR42, during the summer period. Aerosol and gas-phase chemical mass spectrometry allowed us to understand the sources and formation of organic aerosols. Numerical models were incorporated into this study to help interpret our observations.