The authors conducted a study to investigate the variations in tropospheric ozone (O₃) and peroxyacetyl nitrate (PAN) and their precursors at a high-altitude site in the southern Tibetan Plateau. They found that variations in O₃ and PAN were controlled by distinct processes, with O₃ being mostly determined by stratosphere-troposphere exchange (STE), while PAN being mostly influenced by tropospheric chemistry and transport. While local surface O₃ and PAN both revealed net photochemical production during daytime, the variability of PAN was more controlled by photochemical formation processes than O₃. Overall, the manuscript is well organized and fluent in language. The analysis methods and results are scientifically sound. To my knowledge, this is the first study in Tibet presenting simultaneous high time resolution measurements of O₃, PAN as well as its precursors, which are highly valuable data worth publishing. Additionally, this is the first evaluation of PAN formation in Tibet, which also fills in a gap of knowledge. Some minor issues need to be addressed before the manuscript can be accepted for publication.

Minor comments:

1. Lines 136-156: A slight concern on the PSCF analysis is that this is typically more suitable for the source analysis of atmospheric components with longer lifetimes, while PAN can have a long-lifetime in the free troposphere, O₃ seems to be more short-lived.
2. Lines 198-205: The authors only provided Propy-Equivalent VOCs concentrations, however, to put observations into context with those in other studies, it might also be necessary to provide direct VOCs concentrations in ppb or ppbC. How do VOCs levels compare with previous observations in Tibet or similar high-altitude sites around the world? Since the authors discuss O₃ and PAN photochemistry afterwards, this might be important for understanding the difference or similarities in their results with those in literature.
3. Lines 212-215: Again, how do NO₂ concentrations compare with previous observations in Tibet (if there are any)? The authors mention that there are natural and anthropogenic emissions in NO_x, can you name the detailed sources influencing NO_x variations at Nam CO? How do these sources impact the diurnal variation of NO_x?
4. Lines 252-260: Here the authors conclude that O₃ and PAN decreases after sunset are caused by dry deposition as well as the cutoff of free-tropospheric input, indicating that local formations O₃ and PAN are weak. However, in the later sections, PAN formation at least was revealed to be strong. Is there a contradiction?
5. Lines 258-264: PAN often revealed high concentrations at moderate PBLH, which the authors explained as “Whereas PAN in the free troposphere might have had higher variability, which resulted in largely different enhancements of PAN upon down mixing.”. Might it be that local PAN formation was controlling the large variability of PAN?

Technical comments:

1. Line 18 and later in text: “physiochemical” should be replaced with be “physicochemical”.
2. Line 28: “could by” should be “could be explained by”
3. Line 45: Change “nearly proportional to its OVOCs precursors” to “nearly proportionally to its OVOC precursors”.
4. Line 440: “reflects” should be “reflect”
5. Line 446: The “of” should be “or” in “from the west of from the south”

This paper reports spring and summer season O₃ and PAN levels and their variations in Tibet and presents an analysis of what has been controlling the changes of those two most important photochemical air pollutants at such a high-altitude site under very clean conditions. Different impacts of transport and photochemistry on O₃ and PAN have been detected, revealing distinct transport pathways and different sensitivity to photochemical formation processes. Overall, the topic of the paper fits well into the scope of Atmospheric Chemistry and Physics, the observation and analysis methods used are scientifically sound and the results revealed sufficient novelty. The manuscript can be accepted for publishing after the following questions have been well addressed.

1. Although the authors reported the contributions of transport or STE and local chemistry to the observed O₃ and PAN concentrations, most of the results are descriptive, particularly before section 3.3. It’s better to discuss the results more quantitatively and compare them with relevant studies.
2. The writing style needs to be improved. It is difficult to understand some conclusions because some key information in the figures is omitted.
3. Almost all the modeled PAN concentrations are higher than the observed values, while it is completely opposite for O₃. My question is whether it is suitable to evaluate the importance of local chemistry for O₃ and PAN chemistry using a box model under an extreme environment such as Tibet, where is greatly affected by transport or STE？
4. Did you warm up the model before simulating? How did you evaluate your model performance?
5. Figure 2b, it is difficult to differentiate the different components of VOCs. Figure 3b, what are the dotted lines
6. Please define the w wind, u wind, v wind.
7. Line 28: “However, only 0.1% of the springtime day-to-day O₃ variability could by STE processes, …”. Something is missing in this sentence.
8. Line 32: Make sure you really mean “diurnal” here and not “day-to-day”.
9. Line 115: There should be a comma before “which”
10. Line 288-291: South Asian countries obviously strong pollution sources close to Tibet, revealing PAN transport, especially in summer, however, O₃ transport seemed weaker in comparison (Fig. 8). Is that because of enhanced dry deposition in southerly low altitude airmasses?
11. Line 339: make sure of the consistency between “air mass” and “airmass”.
12. Lines 411-412: Since local photochemistry highly overestimates observed concentrations, does that mean that free tropospheric input and PBL growth results in diluted PAN concentrations?
13. Lines 420-421: OVOCs contributed overall largely to the total VOCs concentrations and the authors suggest that PAN revealed certain sensitivity towards OVOCs. Which OVOCs contributed most to the formation of PAN?
14. Line 445-446: “…, airmasses rich in O₃ were mainly associated with high altitude westerly airmasses that either entered the TP from the west of from the south, …” Replace “of” with “or”?