The role of aerosol in altering North Atlantic atmospheric circulation in winter and its impact on air quality

Pausata, F. S. R.; Gaetani, M.; Messori, G.; Kloster, S.; Dentener, F. J.

doi:https://doi.org/10.5194/acp-15-1725-2015

Articles | Volume 15, issue 4

https://doi.org/10.5194/acp-15-1725-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-15-1725-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 15, issue 4

Research article

|

19 Feb 2015

Research article |

| 19 Feb 2015

The role of aerosol in altering North Atlantic atmospheric circulation in winter and its impact on air quality

F. S. R. Pausata, M. Gaetani, G. Messori, S. Kloster, and F. J. Dentener

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Final revised paper (published on 19 Feb 2015)
Preprint (discussion started on 02 Sep 2014)

Interactive discussion

Status: closed

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

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RC C7484: 'Review: Interesting, but not convincing', Anonymous Referee #1, 29 Sep 2014
- AC C7882: 'Preliminary answer to Reviewer #1', Francesco S.R. Pausata, 10 Oct 2014
RC C8486: 'comments on the manuscript by Pausata et al', Anonymous Referee #2, 26 Oct 2014
- AC C9461: 'Answers to reviewers' comments', Francesco S.R. Pausata, 24 Nov 2014

Peer-review completion

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

AR by Francesco S.R. Pausata on behalf of the Authors (24 Nov 2014) Author's response Manuscript

ED: Referee Nomination & Report Request started (03 Dec 2014) by Maria Kanakidou

RR by Anonymous Referee #1 (22 Dec 2014)

Suggestions for revision or reasons for rejection

Review #2 of “The role of aerosol in altering North Atlantic atmospheric circulation in winter and impact on air-quality”.

I feel this version of the manuscript is very much improved over the previous version. I appreciate that this took a lot of work, but in my opinion it has improved and strengthened the manuscript appreciably.

I would recommend publication after revisiting a number of rather minor comments and one more important clarification.

My most serious remaining concern is the reader is left with the impression that aerosol emission reductions will lead to an increase in extreme pollution events over the Western Atlantic (e.g., p 13, line 423) as meteorological conditions become more conducive to extreme events. However, if I understand Figure 5 the severity increases with respect to the winter climatology of that simulation and not with respect to the control climatology circa 2000. In other words while the authors are showing how the relative shape of the distribution changes, the mode of the aerosol distribution also likely changes. In fact I would expect large decreases in the mode as the aerosol emissions decrease under the basic MFR scenario. The authors should make clear who wins: does the actual magnitude of severe pollution events increase? Or is the increase only relative to the mode whereas the skew may increase but the decrease in the mode more than makes up for this. In the latter case the pollution events actually decrease in severity.

Minor Comments:
1. Line 287: “Nevertheless, the GHG increase seems to provide a stronger contribution to the NAO shift ….” I would delete this sentence. The end result is they are not statistically significant and it seems somewhat nonsensical to say one is more statistically significant than the other.

2. Line 311-312: “By regressing the NAOI and the SCOAI time-series onto the …”. This is somewhat misleading because the appendix actually discusses the regression onto rainy days. The authors should clarify that they use the technique here as applied to the rainy day regression in the appendix.

3. Table 3: “Percentiles of PM anomaly distributions”. You are actually not showing percentiles of the anomaly distributions. I would rephrase to state “PM anomaly distributions at different percentiles”. Please also make clear what the 1st and 3rd row in this table refer to.

4. Lines 458-460: “This result also supports the hypothesis of Pausata et al. (2013) that climate change will lead to more extreme pollution events over the western Mediterranean, forcing southern European countries to implement more stringent abatement measures to counteract adverse changes in PM variability.” Do you mean the GHG experiment? Otherwise the climate change is connected with aerosol reductions which, while they may lead to increased skew in some distributions, are also likely to shift the overall mean downwards (See comment above).

5. Line 461: “partially counterbalanced by a lower”. The authors should explicitly state the extent of this counterbalance.

6. Rainy days are defined in appendix C, but discussed in appendix B. Please make sure to define rainy day when first used.

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ED: Reconsider after minor revisions (Editor review) (22 Dec 2014) by Maria Kanakidou

AR by Francesco S.R. Pausata on behalf of the Authors (31 Dec 2014) Manuscript

ED: Publish as is (18 Jan 2015) by Maria Kanakidou

AR by Francesco S.R. Pausata on behalf of the Authors (18 Jan 2015)

Short summary

our study suggests that future aerosol abatement may be the primary driver of increased blocking events over the western Mediterranean. This modification of the atmospheric circulation over the Euro-Atlantic sector leads to more stagnant weather conditions that favour air pollutant accumulation especially in the western Mediterranean sector. Changes in atmospheric circulation should therefore be included in future air pollution mitigation assessments.