Contrasting size-resolved hygroscopicity of fine particles derived by HTDMA and HR-ToF-AMS measurements between summer and winter in Beijing: the impacts of aerosol aging and local emissions

Fan, Xinxin; Liu, Jieyao; Zhang, Fang; Chen, Lu; Collins, Don; Xu, Weiqi; Jin, Xiaoai; Ren, Jingye; Wang, Yuying; Wu, Hao; Li, Shangze; Sun, Yele; Li, Zhanqing

doi:https://doi.org/10.5194/acp-20-915-2020

Articles | Volume 20, issue 2

https://doi.org/10.5194/acp-20-915-2020

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

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In-depth study of air pollution sources and processes within...

https://doi.org/10.5194/acp-20-915-2020

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

Articles | Volume 20, issue 2

Research article

|

24 Jan 2020

Research article |

| 24 Jan 2020

Contrasting size-resolved hygroscopicity of fine particles derived by HTDMA and HR-ToF-AMS measurements between summer and winter in Beijing: the impacts of aerosol aging and local emissions

Xinxin Fan, Jieyao Liu, Fang Zhang, Lu Chen, Don Collins, Weiqi Xu, Xiaoai Jin, Jingye Ren, Yuying Wang, Hao Wu, Shangze Li, Yele Sun, and Zhanqing Li

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Interactive discussion

Status: closed

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

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RC1: 'Comment', Anonymous Referee #1, 11 Sep 2019
- AC1: 'response to reviewer1', Fang Zhang, 22 Nov 2019
RC2: 'Comments', Anonymous Referee #2, 27 Oct 2019
- AC2: 'response to reviewer2', Fang Zhang, 22 Nov 2019

Peer-review completion

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

AR by Fang Zhang on behalf of the Authors (22 Nov 2019) Manuscript

ED: Referee Nomination & Report Request started (02 Dec 2019) by James Allan

RR by Anonymous Referee #1 (02 Dec 2019)

Suggestions for revision or reasons for rejection

Zhang et al. present a study comparing water uptake and predicted water uptake of aerosols in Beijing and North China. The authors have addressed reviewer comments and present a revised manuscript that is considerably clearer to read. I recommend publication once the following comments are addressed:

(1) Novelty
The novelty of the study could be improved. Mei et al. (2013), Zhang et al. (2016) and Zhang et al. (2017) have compared kappa derived from composition measurements to kappa measured by co-located instruments. Mei et al. (2013) derive an empirical relationship between f44 and kappa_org based on their observations. This relationship may not apply to dissimilar field sites. The correlation between f44 or O:C ratio and kappa is not always linear. The correlation between oxidation and kappa is strong but nevertheless an empirical relationship resulting from underlying molecular composition. Zhang et al. (2016), Zhang et al. (2017), and the current study discuss over- and under-prediction of kappa for their measurements. I think it is generally acknowledged that different emission profiles result in different chemistry – I recommend discussing these differences, and perhaps de-emphasizing the poor representation of the measurement by published empirical models. This model/measurement disagreement has already been discussed (Zhang et al., 2016, Zhang et al., 2017).

(2) Coating effect
I think that the coating effect on hygroscopicity should be discussed with appropriate caveats. I find it unlikely that a coating of organic material on an inorganic core limits uptake of water as implied. Studies have shown that water diffusion into viscous organics is fast. These rates are published and will show that for nanoscale aerosol, it is unlikely that condensing SOA prevents water uptake by an inorganic core. Various other quantities go into kappa_chem, including e.g. density as the other reviewer has mentioned and also composition (and hygroscopicity) of the organic. These are good candidates for the underlying mechanisms causing poor agreement between model and measurement.

(3) Technical corrections
The manuscript would benefit from a careful reading to correct technical errors. Two examples are included here, but there are many more.
Lines 27-28: This sentence needs reworking. “the hypothesis” is mentioned before it is defined.
Line 29: on average

(4) References:

Mei, F., Setyan, A., Zhang, Q., and Wang, J.: CCN activity of organic aerosols observed downwind of urban emissions during CARES, Atmos. Chem. Phys., 13, 12155–12169, https://doi.org/10.5194/acp-13-12155-2013, 2013.

Zhang, F., Wang, Y., Peng, J., Ren, J., Collins, D., Zhang, R.,...Li, Z. (2017). Uncertainty in predicting CCN activity of aged and primary aerosols. Journal of Geophysical Research: Atmospheres, 122. https://doi.org/10.1002/2017JD027058

Zhang, F., Li, Z., Li, Y., Sun, Y., Wang, Z., Li, P., Sun, L., Wang, P., Cribb, M., Zhao, C., Fan, T., Yang, X., and Wang, Q.: Impacts of organic aerosols and its oxidation level on CCN activity from measurement at a suburban site in China, Atmos. Chem. Phys., 16, 5413–5425, https://doi.org/10.5194/acp-16-5413-2016, 2016.

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RR by Anonymous Referee #2 (09 Dec 2019)

ED: Publish subject to minor revisions (review by editor) (09 Dec 2019) by James Allan

AR by Fang Zhang on behalf of the Authors (11 Dec 2019) Manuscript

ED: Publish subject to technical corrections (18 Dec 2019) by James Allan

AR by Fang Zhang on behalf of the Authors (24 Dec 2019) Author's response Manuscript

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Short summary

Aerosol effects on visibility and climate are influenced by their hygroscopicity. By contrasting data from two techniques between summer and winter in Beijing, we investigate the effect of aerosol aging, mixing state, and local sources on its hygroscopicity. We revealed that inappropriate use of the density of BC and organics results in large uncertainty in calculating aerosols hygroscopicity. Our results are helpful for parameterization in models.