Measurement report: On the difference in aerosol hygroscopicity between high and low relative humidity conditions in the North China Plain

Shi, Jingnan; Hong, Juan; Ma, Nan; Luo, Qingwei; He, Yao; Xu, Hanbing; Tan, Haobo; Wang, Qiaoqiao; Tao, Jiangchuan; Zhou, Yaqing; Han, Shuang; Peng, Long; Xie, Linhong; Zhou, Guangsheng; Xu, Wanyun; Sun, Yele; Cheng, Yafang; Su, Hang

doi:https://doi.org/10.5194/acp-22-4599-2022

Articles | Volume 22, issue 7

https://doi.org/10.5194/acp-22-4599-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-22-4599-2022

© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 22, issue 7

Measurement report

|

08 Apr 2022

Measurement report |

| 08 Apr 2022

Measurement report: On the difference in aerosol hygroscopicity between high and low relative humidity conditions in the North China Plain

Jingnan Shi, Juan Hong, Nan Ma, Qingwei Luo, Yao He, Hanbing Xu, Haobo Tan, Qiaoqiao Wang, Jiangchuan Tao, Yaqing Zhou, Shuang Han, Long Peng, Linhong Xie, Guangsheng Zhou, Wanyun Xu, Yele Sun, Yafang Cheng, and Hang Su

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Final revised paper (published on 08 Apr 2022)
Supplement to the final revised paper
Preprint (discussion started on 10 Jan 2022)

Interactive discussion

Status: closed

RC1:
'Comment on acp-2021-1010', Anonymous Referee #1, 27 Jan 2022
The manuscript by Shi et al. reports measurements of aerosol hygroscopicity under high and low relative humidity scenarios in the North China Plain. The results show that the kappa values are higher which mean more hygroscopic during high humidity episodes (HRH) than during low humidity episodes (LRH). This distinct difference was attributed to the different chemical composition of the particles under the two scenarios, particularly the O:C ratio, an indicative of the oxidation level. Hygroscopicity is an important aerosol property and hence understanding the influencing factors and the controlling processes is essential to mechanistic understanding the aerosol formation and the climate effects. The paper is well-prepared and can be publishable after the following issues are fully resolved.

In section 4.2, the comparison of CCOA and OOA between the HRH and the LRH is qualitatively fine; however, it might be more accurate to consider the significant difference of the organic fraction between the two scenarios, for example, for CCOA, they become 59%*29% (0.17) vs 46%*6% (0.028) and for OOA, the values become closer, i.e., 59%*18% (0.11) vs 46%*41% (0.19).

The description (lines 290-300 on p.11) of reaction mechanism for the two periods might need to be noted since there are no more evidences to dig out the formation mechanisms during the two periods. It seems they are just speculated in this case. Also, the average RH values for both periods should be given and compared to Sun et al. and Yu et al.’s studies. Similar notices should be given when describing Fig. 6e for the mechanisms (lines 327-329) in section 4.3.

The title of section 4.4 needs to be modified to reflect its content. This section describes the correlation between the O/C ratio and the kappa value under the two scenarios. The current title is similar to that of section 4.2. In addition, is there a better way to describe the oxidation state (level) except for the O/C ratio?

The following comments are rather minor:

Line 35 on p.2, “particles” should be deleted;

Line 68, “which” here is referred to chemical composition or ambient aerosols, it seems ambiguous;

Lines 78-79, “There also remain … more hygroscopic”, this is an ill sentence;

Lines 89, “since decades”? You probably cannot say “since tens of years”, right?

Line 90, “leaded to a fast…”?

Line 94, it is “showed” not “shown”;

Line 97, “extensive efforts to investigated the…”?

Line 100, I think it is better not to use article before “different sources” here;

Line 224, don’t need “the experimental”;

Line 237, “this phenomenon” not “this phenomena”;

Line 269, “usually considered as mainly from…”, as here is a pronoun so it needs an object;

Line 288, “by” should be deleted;

Line 343, “contribute” needs a “to” here;

Line 379, it is better to change “has to be” to “was” here;

Line 392, “marginally increase” should be “marginal increase” as increase is a noun here.
Citation: https://doi.org/10.5194/acp-2021-1010-RC1
- AC1: 'Reply on RC1', Juan Hong, 03 Mar 2022
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-1010/acp-2021-1010-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2021-1010-AC1
RC2:
'Comment on acp-2021-1010', Anonymous Referee #2, 07 Feb 2022
The manuscript gives a report of aerosol hygroscopicity (HT-DMA) and composition (ACSM) measurements in the North China Plain. The authors examine data from two periods they identified based on ambient RH. They conclude that the observed difference in aerosol hygroscopicity between these two episodes was due to different chemical composition (specifically O:C ratio) of ambient aerosol particles.

The manuscript is generally written well and is fit for publication after the following issues are addressed.

Specific questions and comments

HRH and LRH episodes and Figure 1. While the figure does give a (small and blurry) overview of the conditions during the measurement period, the actual numbers (and statistics) of the RH/T values for these periods should also be presented. Especially if these numbers are used to classify the measurement period into distinct episodes.

Figure 1.

Please make the plot larger and use higher resolution. If this is a limitation of the preprint stage of publication, then that's understandable, but for the final publication it should be more readable.

Black line in κ plots – it's mentioned in the text what it is, but please add a label/description also to the figure itself or the caption.

Page 8, line 220: "... mode were almost always observed for all sized particles ...". Please quantify "almost always". Also, Fig. 1 seems to argue against that statement as the LH and MH modes are not continuous in time and have frequent gaps. As an example, LH mode for 100 nm particles during the HRH episode seems to be present (judging by the small plot) about 60% of the time.

Figure 6: why was NF_MH omitted from the plots?

Please include a description of and results from particle size distribution measurements mentioned in the manuscript (p. 13, after Eq. 5) and used to justify the use of 200 nm HT-DMA data.

Figure 8:

What are the red points with error bars – averages over some range? Please describe.

The figure caption says the red line is a fit to data. Should it be "black line" instead?

How much did the ambient RH vary between individual data points on each plot? Looking at Figure 1, the RH had a fairly large diurnal variation. Also, one could almost group the individual data points and see several trends. If the data points were, for example, colored by the ambient RH, would distinct groups emerge?

Page 14, line 385: "... RH ... was also quite high ...". Please quantify "quite high". Same comment for "... low RH conditions ..." on line 394 on the same page.

Minor comments

Please check the use of underscore vs. dash throughout the manuscript. Examples include "HT-DMA_measured" and "ACSM_derived" on page 2.

Page 3, line 68: what varies – aerosol or composition?

Page 3, line 83: "... quite hygroscopicity ...". Please review language.

Page 6, line 162: missing "r" in "analyzer".

Page 9, line 229: sentence starting with "Compared with ...". Please review language and grammar. Currently it reads as if aerosols were somehow obtained and stored.

Page 10, line 282: first sentence – please review language and grammar.

Figure 5: suggest adding the meanings of the acronyms to the figure caption for easier reference.

Page 11, line 291: Kuang et al. (2020) isn't on the references list.

Beginning of section 4.3: Figure 6 is discussed, but not referenced.

Eq. (5) on page 13: some of the text seems very small – were nested subscripts used by accident (from ε_BC onward)?

Page 14, line 383: "... moderately hygroscopic". Please fix.

Page 14, line 392: please review language and grammar.
Citation: https://doi.org/10.5194/acp-2021-1010-RC2
- AC2: 'Reply on RC2', Juan Hong, 03 Mar 2022
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-1010/acp-2021-1010-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2021-1010-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Juan Hong on behalf of the Authors (03 Mar 2022) Author's response Author's tracked changes Manuscript

ED: Publish as is (04 Mar 2022) by Markus Petters

AR by Juan Hong on behalf of the Authors (07 Mar 2022) Manuscript

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Short summary

In this study, we investigated the hygroscopicity of submicron aerosols at a rural site in the North China Plain during the winter of 2018, using a HTDMA and a CV-ToF-ACSM. We observed differences in aerosol hygroscopicity during two distinct episodes with different primary emissions and secondary aerosol formation processes. These results provide an improved understanding of the complex influence of sources and aerosol evolution processes on their hygroscopicity.