An Ozone Episode in the Urban Agglomerations along the Yangtze River in Jiangsu Province: Pollution Characteristics and Source Apportionment

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript presents a WRF-CMAQ-ISAM modeling air quality study over cities along the Yangtze River of Jiangsu Province for an high-ozone event on Sep 6-8, 2022. The modeling method is straightforward, but its analysis and conclusion have some issues. For the most period, the local and regional anthropogenic emissions seem to the major contributors to this ozone events. However, this study does not have the corresponding analysis for these precursors, such as NOx and anthropogenic VOC. Instead, it focuses on long-range transport analysis using HYSPLIT trajectory, and study the impact of biogenic VOC analysis. The common unit of ozone should be ppb instead of μg m-3. The model-observation comparison is insufficient, mainly just Figure 2 for ozone. Here are specified comments.

 

Section 3.1. This section is the only one including model-observation comparison. Unfortunately, it is too short. It is better to include more comparison, meteorological variables, NOx, CO, VOC et al. It is needed to include discussion for this comparison, instead of just showing the results.

Section 3.2. It is better to include meteorological comparison in this section.

Section 3.3. This section is full of description for 500hPa geopotential height. It is not unclear how it is related to the high ozone events. Unless you add more clarification, it is better to remove this section.

Section 3.4. This section only shows HYSPLIT trajectory results without enough analysis. Why did not show the Sep. 7 event, in which the extra-regional contribution is higher?

Section 3.5. This section is mainly written in description language without further discussion. It is still unclear which emission or transport pattern causes the high ozone events.

Section 3.6. Does the Figure 8 show observed isoprene or modeled isoprene? It is better to have model-observation comparison. Also, the isoprene concentrations were lower than 0.4 ppbv everywhere and their impact on ozone were lower than atherogenic sources. Why did not assess the anthropogenic emission’s impact in this manuscript? 

Comments on the Quality of English Language

This manuscript's English can be improved

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript by Cai et al. analyzed a severe ozone episode occurred in cities along the Yangtze River of Jiangsu Province from September 6 to 8, 2022, with daily maximum 8-h average ozone concentrations in the range of 141–255 μg m^-3, peaking in Nanjing on September 7. Please find below some comments to improve the quality of the submitted manuscript.

- In my opinion, a high number of acronyms have been reported in this manuscript. I suggest to simplify them because the current version of the paper does not present a fluent reading.

- Another weak point of this paper is that it is referred only to a limited period of time. Please consider this aspect when you introduce new comments in your manuscript.

- The captions of figures and tables should more detailed otherwise it is not possible to fully understand their meaning.

- Is there a specific reason to select 96-h HYSPLIT back-trajectories?

- The Authors should better investigate the differences in the results obtained for each selected monitoring site. In my opinion, there are a lot of significant differences among the studied sites that have not been fully addressed in this manuscript.

Comments on the Quality of English Language

Moderate editing of English language required

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript entitled "An Ozone Episode in the Urban Agglomerations along the Yangtze River in Jiangsu Province: Pollution Characteristics and Source Apportionment” by Zhe Cai and coworkers presents an experimental and theoretical presentation of the ozone pollution in the western region of China along the Yangtze River. The manuscript presents an interesting discussion of ozone pollution from September 5 to September 8, 2022. The authors show detailed data collected within the days. The overall grade of the manuscript is good, however, some small problems need to be clarified:

1. What data are presented in Table 2? It is not clear whether are they average values, or measured at a specific time…

2. Why the simulated data are so different from the observed ones? Is it concerning that in some cases the difference between the measured and calculated values is almost 50%?

3. Why do we observe such a huge difference between the values presented in Table 2 and Figure 2? Presented in the table values are smaller than the ones presented in the figure. What is the explanation?

4. Figure 7 presents interesting results, but not so easy to understand. Why values are lower than 100%? Are they scaled? 

5. Why during the first night the percentage of contribution lower to almost zero whereas during the next night, such a process is not observed (figure 7)?

6. How should we understand the contributions of ozone sources? Why on ZJ's first day, do we observe only contributions from YZ? 

7. Very disturbing is a comparison of data presented in Figure 7 and Figure 6 when we focus on a city abbreviated as NJ. Why we do not see the influence of TZ on the presentation of data visible in Figure 7, clearly visible in Figure 6?

8. Why do we observe such disturbing differences between the data presented in Figure 4 and Figure 9a? It looks like the model used to simulate data does not work correctly.

In summary, although the manuscript presents interesting results it requires major improvements. The manuscript in its present form looks more like a report of the observed data, with a small explanation of the processes responsible for ozone pollution.

 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

After the revision, the manuscript looks better and can be accepted

Reviewer 2 Report

Comments and Suggestions for Authors

I believe that the Authors did a good job in the revision of their work that now is ready for publication in Atmosphere MDPI journal in my opinion.

Reviewer 3 Report

Comments and Suggestions for Authors

The Authors have provided the required changes and expanded the manuscript.

The publication of the article in its present form is justifiable.