** General comments **

The authors use CAM6-Chem to explore regional trends in organic aerosol concentrations over China. In addition to quantifying the trends, they discuss reasons for the trends.

Following minor revisions, the paper could be a useful contribution to the scientific literature.

** Specific comments **

1. In the data availability statement, I have been unable to identify where the authors' CAM6-Chem model data can be accessed. Should the relevant model data not be published to comply with ACP's data policy and support reproducibility? Would it also be possible to publish the analysis code used to produce the figures?

2. The clarity of some of the figures could be improved. Ideally, each figure should be understandable without referring to the caption. To improve readability, I offer the following suggestions:

(i) give each subfigure panel a short title (as has been done in e.g. Fig. 2, but not Figs. 1 & 7);

(ii) label colorbars with units;

(iii) explain the difference between the solid and dashed lines in the Fig. 1e legend (not just the caption);

(iv) share colorbars across subfigure panels where possible (as has been done in e.g. Fig. 3a–c, but not Fig. 2a–c);

(v) use the same y-axis limits in Fig. 9a and 9b.

3. The precision of the numbers in the Fig. 1c colorbar (-1.80 to 1.80) differs from that in Fig. 1f (-1.8 to 1.8). Should they not be consistent?

4. In Fig. 4, why are normal distributions fitted? The normal distribution does not provide a good approximation to the underlying empirical distributions. The exponential distribution may be more appropriate.

5. The number of acronymns may be overwhelming to many readers. Is it possible to use fewer acronyms? For example, could "PRD" be replaced by "Pearl River Delta" throughout the paper?