Potential impacts of cold frontal passage on air quality over the Yangtze River Delta, China

Kang, Hanqing; Zhu, Bin; Gao, Jinhui; He, Yao; Wang, Honglei; Su, Jifeng; Pan, Chen; Zhu, Tong; Yu, Bu

doi:https://doi.org/10.5194/acp-19-3673-2019

Articles | Volume 19, issue 6

https://doi.org/10.5194/acp-19-3673-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

Regional transport and transformation of air pollution in...

https://doi.org/10.5194/acp-19-3673-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 19, issue 6

Research article

|

21 Mar 2019

Research article |

| 21 Mar 2019

Potential impacts of cold frontal passage on air quality over the Yangtze River Delta, China

Hanqing Kang, Bin Zhu, Jinhui Gao, Yao He, Honglei Wang, Jifeng Su, Chen Pan, Tong Zhu, and Bu Yu

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Final revised paper (published on 21 Mar 2019)
Supplement to the final revised paper
Preprint (discussion started on 30 Oct 2018)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Comments on Kang et al.', Anonymous Referee #1, 08 Nov 2018
- AC1: 'Reply to RC1', H. Kang, 30 Dec 2018
RC2: 'review', Anonymous Referee #2, 09 Nov 2018
- AC2: 'Reply to RC2', H. Kang, 30 Dec 2018

Peer-review completion

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

AR by H. Kang on behalf of the Authors (30 Dec 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (19 Jan 2019) by Tong Zhu

RR by Anonymous Referee #1 (21 Jan 2019)

RR by Anonymous Referee #2 (22 Jan 2019)

Suggestions for revision or reasons for rejection

This version is much better than previous one.

But following sentences are still vague:
1) page 1, line 21: “However, in the Yangtze River Delta (YRD), cold fronts pose a potential threat to air quality”. Cold fronts threat air quality?
2) page 2, line 15: “Cold fronts are important ways of pollutant transport”. Cold fronts are …transport ways?
3) page 6, line 20: “That means cold front frequently exacerbates air pollution over YRD in wintertime, however, we did not notice it before.” Cold front exacerbates air pollution?
4) page 15, line 2-3: “Cold fronts are important ways of PM2.5 transport in wintertime, removing aerosol particles as soon as they reach the BTH”. “cold fronts remove local aerosol particles and can also introduce upstream pollutants”, Cold fronts are …transport ways again? And other roles?
5) page 15, line 23: “This result indicates that cold fronts are a potential threat on air quality over YRD”. Cold fronts are a potential threat on air quality again?

I do not satisfy the authors response about the role of cold front, which has complex structure. The explanation and conclusion in this paper about the cold front and its role playing to local air quality is over simplified. My opinion is, as a synoptic phenomenon, cold front itself cannot be a threat to air quality, if there is no emission of air pollutants. In all literatures the authors mentioned, the phase of "cold front activity" or "cold front passage" is used, rather than cold front itself. Actually, cold front play multiple roles in air quality, since it relates to strong wind, enhancement of turbulence, boundary layer deformation, air lifting and subsidence, etc. Therefore, strong wind and air lifting may be favorite to long-range transport of air pollutants; enhanced turbulence may increase dust emission from the surface (e.g., in case of sand storm); boundary layer depression may help accumulation of air pollutants, and so on. In the case of this paper, cold front passage and its related processes (transport), do have impacts on the air quality of YRD, as the results have shown.

So, I suggest the paper title changes to “Potential impacts of cold front passage on air quality of YRD, …”.

I also suggest to clearly indicate what part of the cold front plays respective roles. For example, the air mass behind the cold front? The airflow ahead of the front? Or just the surface frontal zone? And furthermore, how the frontal passage and frontal structure impact the local air quality?

The figure in the response is interesting, it may be attached to the paper as supplement data.

Other points should be considered:
Figure 3, red line and green bar, should indicate which is wind speed, which is PM2.5.
Figure 7, profiles of VDIF, ZADV, etc., should indicate over which site or area/zone.

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ED: Reconsider after major revisions (26 Jan 2019) by Tong Zhu

AR by H. Kang on behalf of the Authors (20 Feb 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (21 Feb 2019) by Tong Zhu

RR by Anonymous Referee #2 (26 Feb 2019)

ED: Publish as is (26 Feb 2019) by Tong Zhu

AR by H. Kang on behalf of the Authors (28 Feb 2019)

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Short summary

In this study, we found that a cold front can transport air pollutants from the polluted North China Plain to the Yangtze River Delta (YRD), thereby deteriorating air quality over the YRD. Before the cold frontal passage, a warm and polluted air mass over YRD climbed to the free troposphere (1.0–2.0 km) along the frontal surface. After the cold frontal passage, high pressure behind the frontal zone resulted in a synoptic subsidence that trapped PM_2.5 in the surface.