General comments

The idea of this manuscript is clear. In this study, the composition of particulate matter and meteorological factors were deeply explored, which provided a good guidance for the collaborative treatment of ozone and particulate matter. The manuscript not only analyzed the relationship between PM2.5 and O3 and the boundary layer, but also focuses on the relationship between the components of PM2.5 and the boundary layer, which is a very valuable part of this paper. However, it has much room for improvement. The analysis of this paper is rough, many things are unclear, and key parameters are still lacking verification. The author needs to supplement relevant information. Other suggestions for improvement are listed below. To sum up, It is strongly recommended to make significant revisions to the article, otherwise it cannot be accepted.

Specific comments

1)    Lack of data profile description. For example, how many observatories are there, and what observation elements do each station have? The author should at least add a table that fully illustrates the data.

2)    Figure 2 is confusing. My understanding is that the proportion of different values occurring at a certain time should sum to 100%. But the sum expressed in the figure must be more than 100%.

3)    L111 How much deviation are the two instruments for measuring the composition of particulate matter? Were two different instruments used at different times? Please explain clearly.

4)    In view of the importance of MLH, the authors have not confirmed the calculation results. The authors use a very simple method to calculate the height of the mixed layer. It is suggested that the author make use of the meteorological profile or ERA5 reanalysis data to verify the reliability of the results. 

5)    Almost all the graphs in Figure 3 show the scatter distribution, why does Figure c not has a scatter plot?

6)    Generally, when the boundary layer rises, the wind speed will increase, especially when the boundary layer exceeds 1500 m, but this phenomenon is not shown in this study. In addition, in general, when precipitation occurs, strong convection occurs, and the height of the mixing layer will suddenly rise, which is different from the author’s study. Therefore, it is highly recommended that the authors validate the results of mixing layer height. 

7)    It is more appropriate to reflect the atmospheric oxidation capacity with the change of Ox.

8)    Figure 9 can be represented as a time-by-time coloring plot, as the mean may mask the characteristics of high-altitude transport. And ozone profile results are extremely abnormal, with very little ozone decline with altitude. Ozone lidar has great shortcomings in the summer when there are clouds and high humidity. Due to the extremely fast attenuation of shortwave radiation, radar echo signal will decay rapidly under the influence of water vapor, thus affecting the observation results. It is strongly suggested that delete this content.

9)    The authors need to find a case to fully present the relationship between the mixing layer and pollutants, and use the hourly concentration to illustrate the response of PM, its components and ozone to the mixing layer. 

10)    As discussed in Figure 10, it is suggested that the concentration classification of MDA8 ozone can be further refined to make the change of pollutants more obvious.

11)    In Figure 11, it is suggested to use red for positive correlation and blue for negative correlation, with the same color scale for ozone and particulate matter. Looking at the figure, the slope of particulate matter and MLH is very low, indicating that MLH has little effect on particulate matter. Please discuss the linear p-value and R2, if there is no significant correlation, it is meaningless to discuss the rate of change alone.

Technical comments

1)    L221 fund? found?

2)    Figure 5a and 5b It is recommended that the color of the value be uniform from small to large.

The article contains highly relevant results for the understanding of ozone and secondary PM episodes. This is especially important in areas where the WHO guidelines are widely exceeded. The relationship between the MLH and the measured concentrations can help diagnose more precisely the underlying causes of these high pollution episodes during the summer. Consequently, it is relevant for proper air quality control strategies.

While the results are important and support the authors' conclusions, there seems to be a lack of depth in their analysis. Additionally, there is a noticeable absence of indication regarding potential limitations and uncertainties in this study. The analyzed results are limited to only two summer months, which may not be easily extrapolated to other summers. It is essential to address why the three mentioned episodes are relevant and whether the selected two months are representative of typical patterns observed throughout the years. Were there any meteorological anomalies during this period? These aspects should clear throughout the entire manuscript to provide a more comprehensive understanding of the study's scope and implications.

Concentrations of daily averages are also analyzed, but in this kind of episodes, the relevance of hourly concentrations can be crucial. This should also be made clear somewhere, although the analysis of the episodes is only carried out to highlight certain results.

Next, I will mention a series of specific comments in the order of the text. Some of them are recommendations to facilitate reader comprehension.

1) The acronyms OC and OM are mixed.

2) In the graphical abstract, it would be more convenient to increase the font size of the particle compounds. Regarding the arrow for ozone at the MLH between 900 and 1200, what does it mean? Is ozone not increasing, or is it at its maximum at that MLH? It would be clearer to have a separate arrow for O3 and PM2.5.

3) I feel that the statement on line 80 needs further elaboration. It goes from negative to positive, but why? Could it be due to them being more of a secondary type rather than primary, or have there been changes in emissions?

4) Line 95, are those months the most "problematic"?

5) In the map of Figure 1, it is advisable to specify the exact locations of the measurements. Are they conducted within cities? What environments have been selected, and what criteria were used for their selection? Is there any measurement that could be heavily influenced by local emissions? Additionally, another legend could indicate the locations of the soundings (vertical profiles) shown in Figure 9.

6) Line 106, the meteorological variables are measured at the same measurement site, right?

7) What is the temporal resolution of the meteorological measurements? Have they been averaged to obtain daily averages? It is not clear.

8) Line 117, "other pollutants" is too vague. What does it refer to?

9) Point 2.2. The methodology for calculating the MLH seems somewhat simplistic. While estimating MLH can be complex, it would be advisable to compare the results with sounding data (already shown) or reanalysis data to determine their coherence with the calculated values.

10) The % ratio of occurrence shown in Figure 2 should be mentioned in the methodology. How has it been calculated? The WS (Wind Speed) is barely mentioned, and I miss the Wind Direction. Although the authors discard advection, how can authors be certain that it is not always due to the same emission source or the same synoptic pattern?

11) It would be interesting to mark some of the issues mentioned in the text in Figure 2 to assist the reader.

12) In the sentence starting at line153, it lacks clarification on "how." Although it is mentioned later.

13) The sentence in 161 is not clear.

14) Line 186, when stating "low boundary layer height," adding a value in parentheses would be helpful.

15) In the sentence at 191, it presents a dichotomy between vertical transport and photochemical formation. Can't both factors happen simultaneously?

16) Line 202, authors could add wet deposition for ozone as another elimination pathway, not only as a slowdown of photochemistry.

17) The paragraph starting at line 211 and ending at 236 needs to be rephrased. These are not results.

18) In the statement on line 240, it is true that SO4 and OC values reach their maximum at 900-1200m, but they are not significantly lower until 300-600m. How significant is this maximum? The same applies to NO3 and NH4 mentioned in line 242.

19) Line 249: "Changes in NH4 were a consequence of the changes in SO4 and NO3." It would be helpful to add the reason why; this sentence does not seem to be properly linked to the rest.

20) In line with the previous discussion, line 261, "competing changes in NO3 and SO4," does it mean that what decreases in one goes to the other?

21) I believe Figure 7 is mentioned before Figure 6.

22) In line 265, the phrase "the partitioning of semi-volatile nitrate is temperature-dependent" is not clear in relation to the previous information.

23) The statement in line 270 "When MLH fell in the range..." should reference the figure. The same applies to what it is mentioned up to line 278.

24) In line 291, the WHO guideline is suddenly mentioned. Why is it brought up all of a sudden?

25) Lines 293 to 296: "Under low MLH..." Where is all this observed?

26) Line 302: "The upward trend..." is not clear.

27) The paragraph starting at line 306 does not reference the figures, making it hard to understand.

28) In section 3.4, why is only one episode analyzed? If analyzing a single episode, it would be convenient to include a map with the synoptic evolution of those days.

29) When presenting the soundings, the interpretation of the data and the significance of the extinction coefficient should be explained. Why were soundings taken in those cities?

30) In Figure 8, acronyms like OS and SO, do they mean the same thing?

Linguistic issues in English to review:

Expressions erroneously translated that result in: 'To the first order', 'as the MLH fixed', 'serious' (subjective), 'atmospheric dissipation (or dispersion?) potential', 'obvious (subjective)', 'the above analysis', 'MLH prefers'."