Mixing state of carbonaceous aerosol in an urban environment: single particle characterization using the soot particle aerosol  mass spectrometer (SP-AMS)

Lee, A. K. Y.; Willis, M. D.; Healy, R. M.; Onasch, T. B.; Abbatt, J. P. D.

doi:https://doi.org/10.5194/acp-15-1823-2015

Articles | Volume 15, issue 4

https://doi.org/10.5194/acp-15-1823-2015

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

https://doi.org/10.5194/acp-15-1823-2015

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

Articles | Volume 15, issue 4

Research article

|

20 Feb 2015

Research article |

| 20 Feb 2015

Mixing state of carbonaceous aerosol in an urban environment: single particle characterization using the soot particle aerosol mass spectrometer (SP-AMS)

A. K. Y. Lee, M. D. Willis, R. M. Healy, T. B. Onasch, and J. P. D. Abbatt

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Final revised paper (published on 20 Feb 2015)
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Preprint (discussion started on 12 Jun 2014)
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Interactive discussion

Status: closed

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

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RC C4698: 'Review of paper by Lee et al.', Anonymous Referee #1, 11 Jul 2014
- AC C8665: 'Response to Referee#1', Alex Lee, 30 Oct 2014
RC C4819: 'RC - Single particle characterization using the soot particle aerosol mass spectrometer (SP-AMS)” by A. K. Y. Lee et al.', Anonymous Referee #2, 14 Jul 2014
- AC C8666: 'Response to Referee#2', Alex Lee, 30 Oct 2014
RC C5282: 'Referee comment on Lee et al., 2014', Anonymous Referee #3, 24 Jul 2014
- AC C8667: 'Response to Referee#3', Alex Lee, 30 Oct 2014
RC C5484: 'Review of Lee et al.', Anonymous Referee #4, 31 Jul 2014
- AC C8668: 'Response to Referee#4', Alex Lee, 30 Oct 2014

Peer-review completion

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

AR by Alex Lee on behalf of the Authors (30 Oct 2014) Author's response Manuscript

ED: Referee Nomination & Report Request started (24 Nov 2014) by Peter DeCarlo

RR by Anonymous Referee #4 (08 Dec 2014)

RR by Anonymous Referee #3 (13 Dec 2014)

Suggestions for revision or reasons for rejection

The authors have made efforts to implement some of the corrections and changes suggested by the reviewers. Unfortunately, there are still a few points that should be clarified or corrected before final publication of the manuscript.
It seems like the authors did not properly understand all of my comments. I complained about the phrase “A clustering Analysis Panel was developed …”. This was rephrased by the authors, but my main concern, which was the term “panel” being rather slang and not clear for a reader unfamiliar with the software IGOR Pro was mostly ignored. What I wanted to be expressed by the authors was that they wrote a piece of software for the clustering based on IGOR Pro and the implemented k-means algorithm which includes a graphical user interface (GUI, in the IGOR environment also called panel), and additional functionality. I would sincerely ask the authors to correct their article regarding this term, and make it more comprehensible for a general audience unfamiliar with the software IGOR Pro.

Another point that should be considered is the ion threshold used by the authors. They state explicitly that they used a criterion of six ions for the detection of an rBC particle. However, this is simply wrong – the Aerodyne AMS uses a data acquisition based on an ADC (Analog-to-Digital converter). Unlike a TDC (time-to digital converter), this technology cannot detect individual ions. Therefore, the AMS community tries to calculate the area of a single ion. This calculation incorporates several corrections, for example for duty cycle, ionization efficiency, et cetera. However, it is not a measurement of individual ions. This is actually shown by the authors in Figure S3 (b) and (d) – if the instrument would measure individual ions, then there would not be any data points below one. Therefore I suggest clarifying this fact somewhere in the manuscript and changing the y-axis in this plot – measurements of ions < 1 are physically impossible.

In general, it might be good practice to somewhere list the detection limits of the instrument in standard AMS mode (i.e., vaporizer only operation) as well as in SP-mode.

Last, I would like to explain why I think that the k-means algorithm is rather inappropriate for atmospheric measurements. I agree that in many cases k-means will produce similar results like for example ART-2a. However, it has the general problem that it assumes a similar number of members in each class. The same is actually true for the c-means algorithm. Furthermore, when using k-means a particle can only be member of one class – which might be realistic for laboratory measurements but is rather unlikely for atmospheric conditions. Its successor, the c-means algorithm features a so called affiliation matrix which for each particle shows the affiliation with all classes. This information can be used to understand atmospheric processing and mixing, and together with time information for source apportionment. However, this might be well outside of the scope of this publication.

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ED: Publish as is (26 Jan 2015) by Peter DeCarlo

AR by Alex Lee on behalf of the Authors (27 Jan 2015)

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Short summary

Understanding the impact of black carbon (BC) particles on human health and radiative forcing requires knowledge of the BC mixing state. This work investigates the mixing state of BC and other aerosol species in a typical urban area using a single particle mass spectrometry technique. Our results provide quantitative insight into the physical and chemical nature of BC-containing particles near emission and can be used as a basis for our developing understanding of BC evolution in the atmosphere.