CO Editor

Suggestions for revision or reasons for rejection

Sichuan Basin is one of the regions in China with severe aerosol pollution, while the chemical component analysis is still rare. This study fills the gap in this area. Under this condition, the short-term (four selected months) and low time resolution sampling is still acceptable. Thus, I suggest it published after major revision.

In general, the manuscript is not well organized. Authors should put related results together to support one conclusion. The results now are presented with several short paragraphs which are not carefully ordered, e.g., section 3.1.2. From line 197 to line 234, it shows the results of SNA, SNA, carbonaceous aerosols, and SNA again. The readers can hardly find the sufficient information to know and understand the results.

Presentation should be modified by native speaker before publication.

There are many qualitative speculations in the article. Without robust evidence, to do such speculations is unreliable and may even mislead readers. Many conclusions are not based on strict logic.
Line 203: “The majority of PM2.5 components showed a summer minimum, which was caused by high planetary boundary layer height favoring pollutants dispersion and abundant precipitation favoring wet scavenging. ” I think it will be more appropriate to show precipitation to support this statement.
Line 208 and 217. The statement could not only be supported by other references. Other mechanisms can also lead to similar or opposite results. More observed results are needed.
Line 237: “ Although none of the two sites alone can represent the whole region of the Sichuan basin, the similarities in the characteristics of the major pollutants between the two sites should represent the regional-scale characteristics of urban-environment pollution while the differences between the two sites should reflect the sub-regional characteristics of urban pollution.” As the authors response to previous suggestions, “The two monitoring sites selected in this study should represent the typical urban environment in their respective cities”. Thus, many similarities reflect the characteristics of urban region instead of the whole region.
Line 403, the interaction between aerosol and ozone are quite complicated. Aerosols can provide an interface for the heterogeneous reaction of ozone products. Previous study shows that this mechanism usually contributes more than the impact through photochemical process. Fig S5 also could not support that “the formation of SO42- during the polluted periods was dominated by heterogeneous aqueous processes rather than photochemical reactions”.
Line 365, “Similar diurnal variations were also found between clean and polluted periods for CO (Fig. S4), suggesting no significant extra CO emission during polluted periods.” Is that possible to give a quantitative value to support that the variations are similar? Also, I don’t consider this can support no extra CO emission directly.
Some speculations are even self-contradictory. Line 208: “It is also noted that the seasonal variations of NO3 were much larger than those of SO4 and NH4. This can be explained by the enhanced formation of NO3 under high RH in winter, and volatility of NH4NO3 in summer under high temperature condition.” And Line 348: “In contrast, RH remained high during clean or polluted periods in the present study, suggesting that high RH might not be the driving force for the pollution episodes in Sichuan Basin.” Also, it is not convinced to claim RH might not be the driving force supported by this. Many factors including meteorological conditions and emission are combined together to form polluted episodes.

The conclusions part are all qualitative even without a number.

Besides, I have some specific comments on the manuscript as follows:
1. Line 238, “regional” instead of “reginal”.
2. Line 453, It is better for understanding if “Neijiang, Zigong, Yibin and Luzhou” could be marked in Fig 1.
3. The period should be stated in caption of Fig 6 and Fig 7.
4. Line 415, the ref should not be in brackets.

Interactive discussion

Peer-review completion