Spatiotemporal Differences and Dynamic Evolution of PM_2.5 Pollution in China

Round 1

Reviewer 1 Report

General comments:

1. This paper provides an evaluation of spatiotemporal variations in PM2.5 concentrations crossing 18 years in China. By using annual average PM2.5 concentrations, spatiotemporal variations are evaluated. The trend of the PM2.5 concentrations in different region were also evaluated using a decomposition method.

I think this paper should be accepted after addressing my comments shown below.

Major comments:

2. Figure 1, as authors have mentioned that the trend of the PM2.5 concentration can be divided into three stages. I suggest that the authors highlight these three stages in the figure. I also recommend the authors to add ambient air quality standard (either WHO or Chinese standard) in the figure for readers to quantitively find out if the PM2.5 concentrations are high or low.
3. In the paper, the authors mentioned that meteorological conditions are important factors affecting PM2.5 concentrations (Line#5 4). However, I did not see any discussion regarding how the meteorological condition affects the spatiotemporal variation in PM2.5 concentrations. It is ok to ignore the meteorological effects when studying a short time span (2-3 years). However, in this paper, the time span covers more than 10 years. I think author should consider the impact of meteorological condition when discuss their results.

Minor comments:

4. Line# 13-15 I think the sentence “The environmental protection and governance should be carried out under the guidance of green development. The air pollution, especially the urban haze, needs to be treated in a comprehensive way in order to solve prominent environmental issues that impact sustainable development.” Sounds like a conclusion instead of abstract. Please delete or rephrase the sentence.
5. Line# 108-109. “based on to obtain PM2.5 concentration data” is not a correct sentence.
6. Line# 173. A typo is shown. “1.95μ/m³”.
7. Line# 270. I think there should be a space between “target II” and “by WHO”.
8. Line# 271. It is fairly important to show how you divide the cities into three types since it could be a standard for readers to categorize their data. The definition of the different levels (light, moderate, severe) pollution should be provided in SI.
9. Line# 361. “(3) The sources and contributions of overall difference”. Is this a caption for a figure?

Author Response

Please refer to the attachment for details.

Author Response File: Author Response.doc

Reviewer 2 Report

I enjoyed the paper and think it creates a valuable exploration of the data and the problems of pm2.5 in China. 

I have 3 minor quibbles:

1. It was a significant slog to get through the writing.  The paragraphs were quite long and often contained several points that could have stood alone on their own merits.
2. There were also arguments made in the paper where statistical comparisons should have been made.   The distribution graphs in Figure 6 were well described in the text as being different and meaningful.  A Kruskal-Wallis or other test of distributional differences is in order.
3. Given that the authors collected none of their own data, I would have appreciated some pseudo controls such as running the temporal dynamics of the CIESIN 2.5 data over known pristine areas in each region or validating it against locations with longer ground-based monitoring.  Satellites suffer degradation and processing changes

Author Response

Please refer to the attachment for details.

Author Response File: Author Response.doc