Cleaning up the air: effectiveness of air quality policy for SO2 and NOx emissions in China

van der A, Ronald J.; Mijling, Bas; Ding, Jieying; Koukouli, Maria Elissavet; Liu, Fei; Li, Qing; Mao, Huiqin; Theys, Nicolas

doi:https://doi.org/10.5194/acp-17-1775-2017

Articles | Volume 17, issue 3

Atmos. Chem. Phys., 17, 1775–1789, 2017

https://doi.org/10.5194/acp-17-1775-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: East Asia emissions assessment (EA2)

Atmos. Chem. Phys., 17, 1775–1789, 2017

https://doi.org/10.5194/acp-17-1775-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 17, issue 3

Research article 06 Feb 2017

Research article | 06 Feb 2017

Cleaning up the air: effectiveness of air quality policy for SO₂ and NO_x emissions in China

Ronald J. van der A et al.

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Final revised paper (published on 06 Feb 2017)
Preprint (discussion started on 31 May 2016)

Interactive discussion

Status: closed

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

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RC1: 'Review of van der A et al.', Anonymous Referee #1, 04 Jun 2016
- AC1: 'Author response to referee #1', Ronald van der A, 18 Jun 2016
RC2: 'Review', Anonymous Referee #2, 03 Aug 2016
- AC2: 'Author response to referee #2', Ronald van der A, 15 Sep 2016

Peer-review completion

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

AR by Ronald van der A on behalf of the Authors (15 Sep 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (19 Sep 2016) by Gregory Frost

RR by Anonymous Referee #1 (24 Sep 2016)

RR by Anonymous Referee #2 (04 Oct 2016)

Suggestions for revision or reasons for rejection

The authors have modified the original manuscript, but several of the requested "major revisions" have not been resolved.
I cannot recommend publication before the following issues have been adressed adequately:

1. My main concern about the study is that the authors are quite bold with there statement that Chinese NO2 levels would be higher by 30% (now 25%) without regulations.
This is quite speculative and not supported by the shown data: on the one hand, the authors claim that regulations were increasingly taken over the last years, while on the other hand the 25% reduction is just estimated based on the value in 2015. So if the authors would have had written their study one year earlier, based on data for 2005-2014, they would have had to conclude that the many regulations taken so far are useless!
So unless the authors provide a good (and quantitative) explanation on why the NOx per fossil fuel ratio kept almost constant in 2010-2014, despite regulations, they cannot claim that the oberved reduction in 2015 allows for a direct interpretation as "this is the accurately quantified benefit of regulation efforts".
I already made this point in my first review. The reply given by the authors and their modifications in the text expand the discussion of (a) the changing role of transport and shipping, and (b) the effectiveness of SCR equipment.
However, (a) is provided qualitatively (which is fine for undestanding the general pattern, but far too vague to assess the robustness of the 25% reduction estimate),
while (b) refers to a submitted paper, not accessible yet, and now suddenly claims SCR equipment playing a key role (something not mentioned at all in the first version nor in the introduction of the second version).
In addition I would like to point out that if you have to consider changes of the relative role of traffic (without having a specific number for this), the concept of the simple NOx/fuel ratio is meaningless.
So the authors have to actually explain the years 2010-2014 as well as the year 2015 with data for (ship) traffic, SCR, etc. (including some error estimate of the NOx/fuel ratio, which is affected by uncertainties in both NOx emissions and fossil fuel inventory), or have to weaken their statements on NOx reduction.

2. The topic of the paper is regulation, but the reader learns almost nothing about it.
In my first review, I have asked to "discuss the different possibilities in general, and the taken measures in detail". While the authors have addressed the second point in a new table, the general possibilities/techniques for reducing NOx emissions for cars, PPs etc. are not discussed in the introduction. This has to be added (including SCR!) with appropriate references.

3. Finally, I have asked for analysis on province level, as well as the other reviewer. While the authors now provide provincial data, they do not actually provide provincial analysis. This, however, would provide a qood opportunity to shed light on the discussion of the effectiveness of regulations. So, how does the NOx per fuel ratio look like for different provinces? Is it different for coastal provinces (with significant ship emissions)? Can you relate the temporal patterns per province to SCR equipment? Are the temporal patterns for Shanghai Expo/Olympic games/APEC matching our expectations?
Such an in-detail analysis on provincal level would reveal how robust the presented ratio actually is.

Additional comments:

- Section 3.3: "Total NOx emissions in East China reached their peak levels in 2012, and have been decreasing since".
From Figure 5, I would rather claim that overall emissions have stayed constant for 2012-2014, and decreased in 2015.

- Table 2: Please include a column on the expected NOx reduction.

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ED: Reconsider after major revisions (18 Oct 2016) by Gregory Frost

AR by Ronald van der A on behalf of the Authors (02 Dec 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (05 Dec 2016) by Gregory Frost

RR by Anonymous Referee #1 (07 Dec 2016)

RR by Anonymous Referee #2 (23 Dec 2016)

ED: Reconsider after minor revisions (Editor review) (29 Dec 2016) by Gregory Frost

AR by Ronald van der A on behalf of the Authors (06 Jan 2017) Author's response Manuscript

ED: Publish as is (09 Jan 2017) by Gregory Frost

Short summary

The SO₂ concentrations and NO_x emissions over China derived from satellite observations are compared with the national fossil fuel consumption and air quality regulations. It is shown that not only NO₂ concentrations but also NO_x emissions in all Chinese provinces decreased in the last 2 years. We conclude that without the air quality regulations the SO₂ concentrations would be about 2.5 times higher and the NO₂ concentrations would be at least 25 % higher than they are today in China.