Mechanisms for a remote response to Asian anthropogenic aerosol in boreal winter

Wilcox, Laura J.; Dunstone, Nick; Lewinschal, Anna; Bollasina, Massimo; Ekman, Annica M. L.; Highwood, Eleanor J.

doi:https://doi.org/10.5194/acp-19-9081-2019

Articles | Volume 19, issue 14

https://doi.org/10.5194/acp-19-9081-2019

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

https://doi.org/10.5194/acp-19-9081-2019

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

Articles | Volume 19, issue 14

Research article

|

17 Jul 2019

Research article |

| 17 Jul 2019

Mechanisms for a remote response to Asian anthropogenic aerosol in boreal winter

Laura J. Wilcox, Nick Dunstone, Anna Lewinschal, Massimo Bollasina, Annica M. L. Ekman, and Eleanor J. Highwood

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Final revised paper (published on 17 Jul 2019)
Preprint (discussion started on 13 Nov 2018)

Interactive discussion

Status: closed

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

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RC1: 'Interesting results, but needs more details.', Anonymous Referee #3, 28 Dec 2018
RC2: 'Review of Wilcox et al.', Anonymous Referee #1, 03 Jan 2019
RC3: 'Review', Anonymous Referee #2, 04 Jan 2019
AC1: 'Author response to reviewers', Laura Wilcox, 18 Feb 2019

Peer-review completion

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

AR by Laura Wilcox on behalf of the Authors (18 Feb 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (05 Mar 2019) by Nikos Hatzianastassiou

RR by Anonymous Referee #2 (06 Mar 2019)

RR by Anonymous Referee #1 (16 Mar 2019)

RR by Anonymous Referee #3 (08 Apr 2019)

Suggestions for revision or reasons for rejection

The goal of this study is to understand the mechanisms by which changes in anthropogenic aerosol and precursor emissions from Asia drive far-field regional responses in temperature and precipitation during boreal winter. The study uses a combination of a fully coupled atmosphere-ocean general circulation model and a steady-state primitive equation model. The topic is of interest to readers of Atmospheric Chemistry and Physics. There are some interesting and informative results in the study. The authors have addressed my major comments, though a few questions arose in the revised manuscript. I recommend publication after the clarification of the following points.

It was suggested in the last around of review that the phrase “aerosol emissions” should be replaced with “aerosol and precursor emissions”; however, there are still a few places in the text where “Asian aerosol emissions” is used in an inappropriate way. Most of the aerosol mass does not come from direct emissions, but rather is formed by chemical processes involving gas-phase species, e.g., sulfate from oxidation of sulphur dioxide; nitrate from nitric acid, which is formed from chemical reactions involving NOx; etc. Thus, “aerosol emissions” account for a small portion of the total aerosol mass (and small portion of aerosol optical depth). Where using “Asian aerosol and precursor emissions” is cumbersome, using “Asian anthropogenic emissions” would be more appropriate than “Asian aerosol emissions”.

Page 3, line 31: What about increases in nitrogen oxides (NOx = NO + NO2) and ammonia emissions? NOx contributes to aerosol nitrate and ammonia contributes to aerosol ammonium.

Page 4, line 28: Does “biogenic aerosol” mean bioaerosol or is this an error? Other than bioaerosols, there is no biogenic aerosols that is emitted. Rather, biogenic aerosol typically refers to biogenic secondary organic aerosol (SOA) that are formed in the atmosphere from oxidization of biogenic volatile organic compounds (VOCs). Regardless, “biogenic” by definition is not anthropogenic, making the mention of “biogenic” in this sentence about anthropogenic emissions confusing. Collins et al. (2011) indicate that HadGEM2 uses climatology for biogenic aerosols, suggesting that year-specific biogenic emissions are not used for the purpose of biogenic aerosols in HadGEM. These contradictions need to be clarified.

Figure 1b: Similar to the above comment, having “Biogenic x5” here in a figure about anthropogenic contribution is confusing. Even more confusing is why the biogenic contribution has an increasing trend that closely follows the trend of anthropogenic contribution if climatology is used for biogenic aerosols, as indicated by Collin et al. (2011). Even though year-to-year trends in biogenic SOA follow year-to-year trends in fossil fuel organic carbon due to the characteristic of organic gas-aerosol partitioning, this interaction would not be accounted for if HadGEM uses climatology for biogenic aerosol. Again, clarification is needed.

Figure 1b legend: All the lines in the legend are black; they should be colored to match the plotted lines.

Minor Edits:

Page 5, line 6: “increase in Asian emissions” -> ”increase in Asian anthropogenic emissions”.

Page 6, line 3: “Asian anthropogenic aerosol emissions” ->“increases in Asian anthropogenic emissions”.

Page 6, line 13: “can” -> “could”

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ED: Publish subject to minor revisions (review by editor) (18 Apr 2019) by Nikos Hatzianastassiou

AR by Laura Wilcox on behalf of the Authors (09 May 2019) Author's response Manuscript

ED: Publish subject to minor revisions (review by editor) (25 May 2019) by Nikos Hatzianastassiou

AR by Laura Wilcox on behalf of the Authors (29 May 2019) Author's response Manuscript

ED: Publish as is (19 Jun 2019) by Nikos Hatzianastassiou

Short summary

Asian anthropogenic aerosol emissions have increased rapidly since 1980. In winter, this has resulted in warming over China and cooling over India. Using models of different levels of complexity, we show that Asian-aerosol-induced heating anomalies in the western and northern North Pacific establish a circulation pattern that causes cooling in North America and Europe. This connection makes these regions potentially sensitive to any reductions of Asian aerosol emissions in the near future.