Over a 10-year record of aerosol optical properties at SMEAR II

Luoma, Krista; Virkkula, Aki; Aalto, Pasi; Petäjä, Tuukka; Kulmala, Markku

doi:https://doi.org/10.5194/acp-19-11363-2019

Articles | Volume 19, issue 17

https://doi.org/10.5194/acp-19-11363-2019

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

https://doi.org/10.5194/acp-19-11363-2019

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

Articles | Volume 19, issue 17

Research article

|

09 Sep 2019

Research article |

| 09 Sep 2019

Over a 10-year record of aerosol optical properties at SMEAR II

Krista Luoma, Aki Virkkula, Pasi Aalto, Tuukka Petäjä, and Markku Kulmala

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Final revised paper (published on 09 Sep 2019)
Supplement to the final revised paper
Preprint (discussion started on 12 Nov 2018)
Supplement to the preprint

Interactive discussion

Status: closed

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

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RC1: 'Review comments on “Over a ten-year record of aerosol optical properties at SMEAR II”', Anonymous Referee #1, 04 Dec 2018
RC2: 'Review of Luoma et al. manuscript', Anonymous Referee #2, 17 Dec 2018
AC1: 'Authors' replies to both reviewers', Krista Luoma, 31 Mar 2019
- AC2: 'Revised manuscript with tracked changes', Krista Luoma, 01 Apr 2019
  - AC3: 'Revised supplementary', Krista Luoma, 01 Apr 2019

Peer-review completion

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

AR by Krista Luoma on behalf of the Authors (17 Apr 2019) Author's response

ED: Referee Nomination & Report Request started (26 Apr 2019) by Andreas Petzold

RR by Anonymous Referee #1 (02 May 2019)

Suggestions for revision or reasons for rejection

GENERAL COMMENT
The authors considered most of the technical suggestions provided by both reviewers in the first round. Thus, the quality of the observational data is very high. However, there are several major issues in the structure and content of the paper. The motivations and scientific questions at the base of the work are unclear, and I did not find a common redline developing throughout the manuscript. The authors should rethink the overall structure of the manuscript: identify the scientific questions/motivations and arrange the data interpretation and presentation. The manuscript needs additional literature research.

The long-term measurements of AOPs represent the backbone of the manuscript and I consider the trend analysis to be the major outcome of the paper. I would suggest to focus on this topic and to reduce or remove the analyis of size distribution and optical modeling. Both reviewers already rose some doubts about these topics.

Although I recommend rejection, I encourage the authors to consider my specific comments and resubmit the manuscript in the future.
SPECIFIC COMMENTS (arranged by section)

1 INTRODUCTION
The section is incomplete and not well structured.
The importance of AOPs for the estimation of the RF is not mentioned, Thus, the climatic motivations at the base of this study are unclear. The aerosol-cloud interaction is, presently, not of primary need. The description of the measurements and site (P2L16-30) is not of necessary, since it can be extensively described in the method section. Generally, I also find a serious lack of references. An introduction on aerosol trends, such as previous works , environmental policies, dimming, and brightening might underline the importance of your work.
2 MEASUREMENTS AND METHODS
All measurements and data analysis are fully described. However, I would suggest to restructure and reorganize the different sections, starting from the titles. Try to be a more specific and attract the interest of the reader avoiding general titles such as “The field site”, which could be changed into a more appealing “The SMEAR II boreal research station” (by the way here you have to insert the description given at P2L16-21). EFR needs a separate section. Sections 2.3.4 and 2.5 can be merged.

3.1 OVERVIEW OF THE DATA
Work on the titles and try to be a bit more original: “Characterisation of the boreal aerosol", or "Scandinavian background aerosol optical properties", etc... . It is important to define a target-topic for each section, I hardly see what you want to show here. The seasonal analysis can be used to describe the impact of different sources or the role of atmospheric processes on the AOPs.

3.2 TRENDS
A bit of rework on the redline and additional thinking on the climatic/environmental implications are needed.

3.3 AEROSOL OPTICAL PROPERTIES AND SIZE DISTRIBUTION
As already indicated by me and the second reviewer, I do not understand the goal of this section. I would definitely give more priority to the interpretation of trends rather than to the size distribution. Moreover, too many variables are discussed making the section quite chaotic. Potentially, a reduced/simplified discussion on the aerosol size distribution can be introduced in 3.1 as part of the aerosol characterization.

3.4 SEASONAL VARIATION
As said before, I would move and merge it with 3.1

3.5 VARIATION BETWEEN THE PM10 AND PM1 MEASUREMENTS
As already argued in the first review, this section is of scarce interest. In fact, a good part of the section is used to justify the differences
from previous works (P20L27-P21L7) and the high uncertainty (P21L21-27).

3.6 RADIATIVE FORCING EFFICIENCY
The section reads nice and might represent the final outcome of the manuscript. However, I have some suggestions:
a) The title can be improved: “Seasonality and trend of ”.
b) The text is very intricated, limiting the understanding.
c) Figure 7 tells that humidity is very important in summer (hence
hygroscopicity is a critical property of the aerosol in order to asses
RF) and that optical properties have a smaller impact of RF compared to
environmental factors. Considering these two messages and the high number of assumptions for the RFE calculation, Fig. 8 is quite approximative. A full investigation of the impact of AOPs on RF would need a full separated paper. Thus, I would suggest excluding, this time, Fig. 8 and the subsequent (very short) discussion.

4 SUMMARY AND CONCLUSIONS
As a consequence of all the above comments, the conclusion section needs rethinking and rewriting.

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ED: Reconsider after major revisions (28 May 2019) by Andreas Petzold

AR by Krista Luoma on behalf of the Authors (05 Jul 2019) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (17 Jul 2019) by Andreas Petzold

Dear Krista, dear Aki

Thank you for revising the manuscript another time very carefully. It is now accepted for publication in ACP once few technical corrections have been made. They are mainly linguistically:

GENERAL REMARKS

You often use the phrase “The X is …” when you refer to the value of the property X. I suggest rephrasing it in way like “The value of X …” or “The parameter X …”.

Please check also the use of singular and plural throughout the text.

You sometimes use the phrase “white” and “dark” aerosol. This is not very physical. Particularly the phrase “dark” should be replaced by “absorbing”.

When you introduce RFE on page 10, line 3 you must mention here that the values you use for the calculation of RFE are global average values which may be completely different from the regional situation. Calculating RFE by these global mean values does not mean anything for the regional effects but may only be used to compare the aerosol properties to values reported for other types of aerosol from other parts of the world. You say that in the next paragraph but a clear statement at the very beginning would be better.

SPECIFIC COMMENTS

Abstract, page 1, line 16: it should read “… aerosol number and volume concentrations …”. Please check the text since you used the singular word “concentration” a couple of times when the plural would be correct.

Same paragraph, line 18: I suggest writing: “… absorb less light than at the beginning of the measurements.” The same sentence is written in the main text later where I suggest also correcting the phrase.

Page 2, line 22: rephrase: “… particles formed by gas-to-particle conversion.” Same page, line32: Rephrase “… both scattering and absorption coefficients …”.

Page 4, line1: I suggest introducing the symbols for the Ångström exponents here, like you do in the next line for the extensive properties.

Page 5, It should read”… described by the empirical …”.

Page 8, line 11: It should read “…linked to the …”.

Page 9, line 11: Delete “are”.

Page 10, line 4: Please insert: “the values were chosen according to …”.

Page 16: There is no description or reference given for Fig. 2b.

Page 17: There are no descriptions or references given for Figs. 5b and 5c.

Page 21, 2nd paragraph: I assume you refer here to Fig. 6b instead of Fig. 7b.

As soon as you have inserted the technical corrections I want to have a final quick look and give a Go for the publication.

Best wishes,

Andreas

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AR by Krista Luoma on behalf of the Authors (27 Jul 2019) Author's response Manuscript

ED: Publish as is (29 Jul 2019) by Andreas Petzold

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Short summary

We present an over 10-year-long time series of aerosol optical properties (AOPs) measured at a rural boreal forest site. Knowledge of AOPs is needed in determining the direct effect of aerosol particles on climate. We observed decreasing trends in scattering and absorption and increasing trends in backscattering fraction and single-scattering albedo. Trends of single-scattering albedo and backscattering fraction increased the efficiency of aerosol particles to scatter radiation back into space.