Intermittent turbulence contributes to vertical dispersion of PM<sub>2.5</sub> in the North China Plain: cases from Tianjin

Wei, Wei; Zhang, Hongsheng; Wu, Bingui; Huang, Yongxiang; Cai, Xuhui; Song, Yu; Li, Jianduo

doi:https://doi.org/10.5194/acp-18-12953-2018

Articles | Volume 18, issue 17

https://doi.org/10.5194/acp-18-12953-2018

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

https://doi.org/10.5194/acp-18-12953-2018

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

Articles | Volume 18, issue 17

Research article

|

10 Sep 2018

Research article |

| 10 Sep 2018

Intermittent turbulence contributes to vertical dispersion of PM_2.5 in the North China Plain: cases from Tianjin

Wei Wei, Hongsheng Zhang, Bingui Wu, Yongxiang Huang, Xuhui Cai, Yu Song, and Jianduo Li

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Final revised paper (published on 10 Sep 2018)
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Preprint (discussion started on 06 Apr 2018)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Interactive comment', Anonymous Referee #1, 22 Apr 2018
- AC1: 'Response to Referee #1', Wei Wei, 04 Jul 2018
RC2: 'Review ACP-2018-121', Anonymous Referee #3, 23 Apr 2018
- AC2: 'Response to Referee #3', Wei Wei, 04 Jul 2018
RC3: 'Referee comment', Anonymous Referee #2, 27 Apr 2018
- AC3: 'Response to Referee #2', Wei Wei, 04 Jul 2018

Peer-review completion

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

AR by Wei Wei on behalf of the Authors (04 Jul 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (06 Jul 2018) by Veli-Matti Kerminen

RR by Anonymous Referee #3 (13 Jul 2018)

Suggestions for revision or reasons for rejection

The authors responded my comments carefully. In the authors’ response, they further demonstrated non-stationarity of turbulence from their turbulent period (TS). Now I am totally confused.

The authors repeated the conventional understanding that intermittent turbulence is associated with stable conditions (P. 6, L18), but their intermittent turbulence index IF suggests large intermittent turbulence is during the weak stable period (TS) where turbulence is strong. That is, their definition of turbulence intermittency is opposite from those in the literature even though they claimed their intermittency index is consistent with others. It seems to me that what the authors captured is the magnitude of w fluctuations, which should be large when turbulence is strong, but that is not what turbulence intermittency supposes to mean. Turbulence intermittency means the magnitude of turbulent fluxes varies significantly not individual wind components. Wind components can fluctuate significantly but turbulent fluxes do not so that turbulent intermittency is zero. Basically what the authors show is turbulent mixing contributes to vertical dispersion of PM2.5, strong turbulence should be associated with large u*, and weak PM2.5. This is what we understand already. No wonder the authors claimed intermittent turbulence contributes to vertical dispersion of PM2.5. The authors’ concept of turbulent intermittency is completely wrong.

Another claim by the authors is heating at the top of the surface pollution layer by pollutants. As we know, the high pollutant concentration is highly correlated with the stable boundary layer. In other words, because of the development of the stable boundary layer, pollutants can be trapped near the surface where turbulent mixing is weak. One of the characteristics of the stable boundary layer is air temperature increases with height. Yes, pollutants as aerosols play a role in radiative heating/cooling the atmosphere, but the authors cannot use this character of the stable boundary layer to proof the role of pollutants on radiative heating. Air temperature always increases with height in any stable boundary layer even without pollutants.

Another claim from the authors is the role of LLJs in turbulence generation. The turbulence data used for calculating their turbulence intermittency index are at 200 m and below. The lowest wind speed measurement level from the wind profiler radar is at 200 m. All the LLJs in Fig. 9 are way above 200 m. There is no way that the authors can claim turbulence is generated way above. More likely turbulence at 200 m and below is generated by wind shear between 200 m and the surface, which is supported by the increase of wind speed at about 200 m at the beginning of the TS periods in Fig. 8.

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ED: Reconsider after major revisions (16 Jul 2018) by Veli-Matti Kerminen

AR by Wei Wei on behalf of the Authors (24 Aug 2018) Author's response Manuscript

ED: Publish as is (28 Aug 2018) by Veli-Matti Kerminen

AR by Wei Wei on behalf of the Authors (29 Aug 2018) Author's response Manuscript

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Short summary

Heavy particulate pollution events have frequently occurred in the North China Plain. Using the intermittency factor, we found that the turbulence during the transport stage is intermittent and not locally generated. Turbulence results from the wind shear of low-level jets and then transports downward, causing intermittent turbulence at lower levels. The intermittent turbulence contributes positively to the vertical dispersion of particulate matter and improves the air quality near the surface.

Intermittent turbulence contributes to vertical dispersion of PM2.5 in the North China Plain: cases from Tianjin

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Intermittent turbulence contributes to vertical dispersion of PM_2.5 in the North China Plain: cases from Tianjin