Modeling the global radiative effect of brown carbon: a potentially larger heating source in the tropical free troposphere than black carbon

Zhang, Aoxing; Wang, Yuhang; Zhang, Yuzhong; Weber, Rodney J.; Song, Yongjia; Ke, Ziming; Zou, Yufei

doi:https://doi.org/10.5194/acp-20-1901-2020

Articles | Volume 20, issue 4

https://doi.org/10.5194/acp-20-1901-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-20-1901-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 4

Research article

|

20 Feb 2020

Research article |

| 20 Feb 2020

Modeling the global radiative effect of brown carbon: a potentially larger heating source in the tropical free troposphere than black carbon

Aoxing Zhang, Yuhang Wang, Yuzhong Zhang, Rodney J. Weber, Yongjia Song, Ziming Ke, and Yufei Zou

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Final revised paper (published on 20 Feb 2020)
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Preprint (discussion started on 02 Jul 2019)
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Interactive discussion

Status: closed

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

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SC1: 'A couple of general comments', Jonathan Taylor, 18 Jul 2019
- AC1: 'Reply to 'A couple of general comments' from Jonathan Taylor', Aoxing Zhang, 30 Jul 2019
RC1: 'Review of Zhang et al.', Anonymous Referee #1, 04 Aug 2019
- AC2: 'A Point-by-point response to referee#1', Aoxing Zhang, 20 Sep 2019
- AC4: 'Revised manuscript version with marked-up based on the referee comments', Aoxing Zhang, 20 Sep 2019
RC2: 'Review of “Modeling global radiative effect of brown carbon…”', Anonymous Referee #2, 09 Aug 2019
- AC3: 'A Point-by-point response to referee#2', Aoxing Zhang, 20 Sep 2019
- AC5: 'Revised manuscript version with marked-up based on the referee comments', Aoxing Zhang, 20 Sep 2019
- AC6: 'Revised manuscript supplement with marked-up based on the referee comments', Aoxing Zhang, 20 Sep 2019

Peer-review completion

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

AR by Aoxing Zhang on behalf of the Authors (20 Sep 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (23 Sep 2019) by Qiang Zhang

RR by Anonymous Referee #1 (28 Sep 2019)

Suggestions for revision or reasons for rejection

This paper continues to have major flaws of presentation and interpretation. The wording and presentation of results are somewhat careless; there are also grammatical errors throughout. The manuscript is not publishable in current form.

1. Section 4.1 and Figure 5: There is no quantitative evaluation of BC mass concentrations presented here. Given that the conclusion on relative heating rates rely on an accurate simulation of BC (as well as BrC), the authors should provide an exact comparison (e.g. mean vertical profiles of BC for each HIPPO campaign comparing model and observations as in Figure 7)

2. Section 4.1: Why do the authors choose to compare to AOD (which as they rightly point out is dominated by aerosol scattering) rather than AAOD estimates from AERONET or OMI UV AI? There does not appear to be much value to the comparisons presented here.

3. Section 5.1: This section and discussion lack logical flow and the wording is often inconsistent with the figures. From Figure 7, the baseline simulation (NCNB) appears to perform equally well to the “best” simulation (ICB) which includes photobleaching and reduced scavenging. The authors therefore need to present a more compelling justification for their “best” simulation. This should begin with what (if any) flaws are apparent from the baseline simulation and then carefully explore, individually, the effects of photobleaching and reduced scavenging. And then finally make a case for their “best” simulation.

a. The comparison of Figure S2 should be moved into the main text, along with a comparison of OA mass concentrations. The authors need to show that their model simulation simultaneously meets the constraints of mass and optics for both BC and OA/BrC, and to make their case that the ICB simulation is superior to the NCNB simulation in this regard.

b. Lines 306-307: This statement is incorrect, the NCNB and ICB simulations are very similar.

c. Lines 308: The BrC/BC ratio is similarly underestimated in the ICB simulation > 8km

d. Line 310: This sentence is incorrect. The ICNB and NCNB simulations do not show very different profiles (i.e. lower trop to upper trop ratios) in Figure 7. The second pairing “ICB&NCB” is the wrong pair of simulations to compare – the NCB simulation should be compared to the ICBB simulation

e. Lines 315-316: If photobleaching were implemented as in previous studies (with a 25% floor) would the BrC/BC ratios in the NCB match the observations?

f. Lines 319-320: These statements are false. Figure S2 shows that only the ICNB simulation clearly overestimates BrC in the UT for both campaigns. Figure 7 shows that only two simulations (ICBB and NCB) clearly underestimate FT-UT BrC/BC

g. Lines 326-327: This statement is not supported; the authors have not shown the reader that the ICB simulation is superior to the baseline.

4. Figure 9c: requires a better choice of color bar so that the value of 1 can be distinguished. For current figure it is not clear where BC heating rates exceed BrC and vice versa.

5. Lines 401-408: The authors should be quantitative here to clarify the relative heating rates. From Figure 13 for > 600 hPA the BrC/BC mean heating rate ratio ranges from 0.9-1.2.

Minor

1. Line 29-30, suggest temper the language given uncertainties “This suggests that the contribution of BrC heating to the Hadley circulation and latitudinal expansion of the tropics may be comparable to BC heating.”

2. Lines 98-100: indicate explicitly whether the CAM5 meteorology was nudged to the same meteorological year as the observations (i.e. 2009-2011 for HIPPO, 2013 for SEAC4RS and DC3).

3. Lines 133-135: how do these optical properties compare with those used in previous modeling studies? And the literature more generally?

4. Lines 283-285: the correlation coefficient (R) is obtained for a population of points, how is it used here as a point-by-point filter?

5. Section 5.1: missing information and references for measurements from SEAC4RS and DC3 used in this study.

6. Lines 299-300: can the authors use a biomass burning tracer such as acetonitrile or HCN to confirm that this BC is from non-fire sources?

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RR by Anonymous Referee #2 (08 Oct 2019)

ED: Reconsider after major revisions (10 Oct 2019) by Qiang Zhang

AR by Aoxing Zhang on behalf of the Authors (14 Nov 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (27 Nov 2019) by Qiang Zhang

RR by Anonymous Referee #2 (14 Dec 2019)

ED: Publish subject to minor revisions (review by editor) (14 Dec 2019) by Qiang Zhang

AR by Aoxing Zhang on behalf of the Authors (21 Dec 2019) Author's response Manuscript

ED: Publish as is (23 Jan 2020) by Qiang Zhang

AR by Aoxing Zhang on behalf of the Authors (27 Jan 2020) Manuscript

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Short summary

Black carbon (BC) and brown carbon (BrC) are light-absorbing carbonaceous aerosols. We developed a module to simulate the emissions, atmospheric processing and direct radiative effect of BrC in the Community Earth System Model (CESM). We found that globally BrC is a significant absorber and is more centered in the tropical free troposphere compared to BC. The contribution of BrC heating to the Hadley circulation and latitudinal expansion of the tropics is comparable to BC heating.