Dear Authors,

This time the co-editor has evaluated the revised manuscript, on behalf of the two reviewers. I find the revised manuscript has been improved, based on the reviewers' comments. However, the following minor points still need to be clarified and justified. I would appreciate it if the authors could take them into account.

(line numbers are those for acp-2020-1251-ATC1.pdf, with track changes)

1. Have the authors compared the simulated VOC concentration levels (Fig. 5c and d) with the observations to confirm the adequacy? For biogenic VOC levels over 16 ppb (line 275), any support observations are present? The concentration range would be too high for isoprene/monoterpenes - is it mostly contributed from less reactive species such as methanol? Some discussion should be added, as this point is also critical in the determination of the regimes.

2. Line 257, Figure 5 and Table 3. How did the authors define the "daytime"? Any specific time period with the local time?

3. Section 6. How much were the total VOC CONCENTRATIONS (or reactivity) reduced with the 20% emission change? I am wondering if biogenic VOCs might have been dominant and thus there is no virtual change in the total concentrations of VOCs and their role, even if the emissions of "anthropogenic" VOCs are varied over a wide range (in Chongqing for example).

4. Line 351. Satellite observations of NO2 and HCHO have large uncertainties (of several tens of percents, e.g., Pinardi et al., 2020 for OMI NO2) and therefore the determination of regimes from the ratio would not be very certain.

Pinardi, G., Van Roozendael, M., Hendrick, F., Theys, N., Abuhassan, N., Bais, A., Boersma, F., Cede, A., Chong, J., Donner, S., Drosoglou, T., Dzhola, A., Eskes, H., Fries, U., Granville, J., Herman, J. R., Holla, R., Hovila, J., Irie, H., Kanaya, Y., Karagkiozidis, D., Kouremeti, N., Lambert, J.-C., Ma, J., Peters, E., Piters, A., Postylyakov, O., Richter, A., Remmers, J., Takashima, H., Tiefengraber, M., Valks, P., Vlemmix, T., Wagner, T., and Wittrock, F.: Validation of tropospheric NO2 column measurements of GOME-2A and OMI using MAX-DOAS and direct sun network observations, Atmos. Meas. Tech., 13, 6141?6174, https://doi.org/10.5194/amt-13-6141-2020, 2020.

5. Figure 8f, lines 397-400. To my eye, the point with 40% NOx increase and 0% VOC change would be within the VOC limited side. In Figure 9a also, at the point of NOx emission change of 40%, surface O3 change is almost saturated. Please double check.

6. Line 433. Although the authors simply state that all selected regions across the globe outside of China are NOx limited, I would suggest that the chosen resolution would affect and the real situation is not that simple. For example in the central Tokyo, when studied at a resolution of ca. 10 km, summertime ozone formation is clearly VOC limited (Inoue et al., 2019). The effectiveness of legislated VOC emissions reduction is seriously studied. I hope the authors could acknowledge this point. Maybe in line 433, after "NOx limited," it would be better to add "with the studied horizontal resolution".

Inoue, K., Tonokura, K. & Yamada, H. Modeling study on the spatial variation of the sensitivity of photochemical ozone concentrations and population exposure to VOC emission reductions in Japan. Air Qual Atmos Health 12, 1035?1047 (2019). https://doi.org/10.1007/s11869-019-00720-w

Yugo Kanaya, Co-Editor or ACP

Dear Authors,

I find the Editor comments were carefully taken into account and the manuscript was improved accordingly. I now recommend publication as is. Thank you very much for your submission to ACP.

Best regards,
Yugo Kanaya, ACP Co-Editor