Review of “Changes in surface ozone in South Korea on diurnal to decadal time scale for the period of 2001-2021” by Kim et al.

This manuscript addressed an issue of observed surface ozone increases in South Korea by analyzing a long-term dataset and 3-d air quality model simulations for divulging its attribution. The surface ozone increase in South Korea and China is a compelling issue for which previous literature extensively attempted to investigate its causes. Compared to them, I find it quite challenging that this work shows a new contribution to the scientific understanding of the issue or a new idea that needs to be investigated in the future. In addition, the manuscript should be reshaped to highlight its main findings by adding descriptions of how the authors reached conclusions, which were mostly based on immature analyses. I will elaborate on them below.

P2,L2 - “Increasing trends of tropospheric ozone in South Korea” is a bit misleading because ozone in surface air does not always reflect tropospheric ozone. Needs to be revised to surface ozone.

P4,L11 - Here and elsewhere, references at not in the reference section. Please check all the citations and include other previous studies on the same issue (e.g., Colombi et al., ACPD, 2022, and the references are therein).  

P4,L11 - “Ozone in South Korea …” this sentence requires a citation.

P8,L11 - Stratospheric ozone appears to have a significant effect on ozone in the troposphere and even in surface air in this study. However, I cannot find out how the effect of stratospheric ozone on tropospheric and surface ozone was quantified in the manuscript. I think that it should be elaborated on here.

Sections 2.4, 2.5. – This study used model simulations to understand the observed characteristics of surface ozone in South Korea. Therefore, an extensive model evaluation should be conducted and discussed somewhere in the manuscript by focusing on how good the model is to reproduce the observations and their variability.

P9,L4 – Years for the WRF-Chem simulations were missing. Did you conduct simulations for all years or for a particular year?

P9,L7 – It appears that the authors used different meteorology to drive CAM-Chem simulations and WRF-Chem simulations. Have you ever thought about using identical meteorology for both models?

P9,L14 – The time information of emissions inventory used in the model is missing. Did you also consider biomass burning emissions in the model?

P10,L9, - You analyzed the 4^th highest MDA8 O3. I wonder how this metric well represents ozone air quality because these could be rather extreme events, which rarely happen. In other words, how frequently people in South Korea were exposed to this metric?  

P10,L14 – The trend in Jeollanam-do differs from other provinces. This is explained by “MDA8O3 in Jeollanam-do is high before 2010”. I do not understand why this is the case. Here and elsewhere, please check out the proper usage of provinces and city names.

P10,L15-17 – This sentence includes several factors, contributing to ozone increases in South Korea. Proper citations are required.

P11,L2 – “Investigating seasonal differences in ozone in South Korea” has been examined by Lee and Park (2022). Any consistency or dissimilarity from the previous study is worth being mentioned.

P13,L1-13 – Stratospheric influences are quite large, which are still debatable. As I mentioned above, how did you obtain the stratospheric ozone influences on low tropospheric and surface ozone concentrations in South Korea? Does the model reproduce observations well? You have to elaborate a lot on this part.

P13,L14-20 – Colombi et al. (2022) already performed a nice analysis on the effect of precursor changes on observed surface ozone increases in South Korea. You have to compare your work with theirs.

P14,L6-20 – Previous studies published the observed increase in ozone in China and South Korea during the pandemic due to less titration of NOx. This result is contrary to previous studies and please compare the differences between this and previous work.

Section 4. You presented simulated vertical profiles in Seoul and Gangwondo during the KORUS-AQ. Could you include aircraft observations in Figure 11? I also wonder how the model simulates surface ozone concentrations.

Please see uploaded file