Quantifying black carbon light absorption enhancement with a novel statistical approach

Wu, Cheng; Wu, Dui; Yu, Jian Zhen

doi:https://doi.org/10.5194/acp-18-289-2018

Articles | Volume 18, issue 1

https://doi.org/10.5194/acp-18-289-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-18-289-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 1

Research article

|

11 Jan 2018

Research article |

| 11 Jan 2018

Quantifying black carbon light absorption enhancement with a novel statistical approach

Cheng Wu, Dui Wu, and Jian Zhen Yu

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Final revised paper (published on 11 Jan 2018)
Supplement to the final revised paper
Preprint (discussion started on 20 Jul 2017)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'review of Wu, Wu and Yu', Anonymous Referee #2, 17 Aug 2017
- AC1: 'Response to review #2', Cheng Wu, 15 Oct 2017
RC2: 'Referee comment', Anonymous Referee #1, 01 Sep 2017
- AC2: 'Response to review #1', Cheng Wu, 15 Oct 2017

Peer-review completion

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

AR by Cheng Wu on behalf of the Authors (15 Oct 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (16 Oct 2017) by Manabu Shiraiwa

RR by Anonymous Referee #2 (23 Oct 2017)

Suggestions for revision or reasons for rejection

Response to revised manuscript

The authors have made a number of improvements to the manuscript and adequately addressed my original comments with two important exceptions, detailed below. If these can be addressed to the satisfaction of the editor I recommend publication in ACP.

The response to comments regarding the influence of RH on the Aethalometer measurements is not adequate. The response states that a previously observed strong correlation between a non-dried Aethalometer and a dried photoacoustic instrument remained high even under elevated RH conditions. First, a strong correlation does not mean one of the instruments is not biased. For example, an instrument biased by a constant factor of two will still be strongly correlated with a reference measurement. A bigger point is that the data shown in the response show no increase in absorption measured by the Aethalometer relative to a dried reference measurement for RH values approaching 100%. This means that f(RH) is flat (1.0) for the Guangzhou data and there is no LWC influence on absorption. There could be real reasons for a difference in f(RH) during the two studies, but if this is the case, the Guangzhou data cannot be used to validate the response of the Aethalometer, since the conditions are different. Until the response of the Aethalometer has been validated against a reference instrument at high relative humidity conditions and at a location where there is an RH impact on absorption, Aethalometer data alone has too many uncertainties to draw the types of conclusions made in Section 4.5.

The addition of the tests to investigate impact of bias on the results is helpful, however my original comments were meant to question effects of time-varying biases on the data that depended on the amount of “coating” present or other physical processes not related to the real enhancement of light absorption. I apologize for not being more clear. The authors should generate a test data set with varying EC and prescribed “coating” contributions to measured absorption and EC, then introduce a bias to both data sets that depends on the amount and/or contribution of coating. Also useful would be tests or demonstrations of how other phenomena could affect the MSR method (e.g., a period of dust impact that affects absorption but not EC, or affects EC through mineral catalysis of EC, evaporation and/or adsorption of semi-volatile material from and/or onto filters in both the Aethalometer or OC/EC method). I believe this is merited given the novelty of the approach and analysis.

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RR by Anonymous Referee #1 (23 Oct 2017)

ED: Reconsider after major revisions (23 Oct 2017) by Manabu Shiraiwa

AR by Cheng Wu on behalf of the Authors (27 Nov 2017) Author's response Manuscript

ED: Publish as is (28 Nov 2017) by Manabu Shiraiwa

AR by Cheng Wu on behalf of the Authors (29 Nov 2017)

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Short summary

This work presents a new approach, minimum R squared (MRS) method, to quantify black carbon aerosols light absorption enhancement factor, E_abs, from ambient measurements using an Aethalometer and field carbon analyzer. Application of MRS on 1 year of measurement is demonstrated. This study provides a potential alternative to explore the E_abs information using inexpensive instrumentation with wider temporal coverage.