Please see the attached pdf for comments.

Please see the supplement.

The manuscript addresses a significant knowledge gap regarding the role of highly oxygenated organic molecules (HOMs) in new particle formation (NPF) during the preindustrial era, which is critical for establishing accurate baseline conditions for radiative forcing calculations. The implementation of a semi-explicit HOMs chemistry scheme (in CAM6-Chem) represents a significant improvement compared to the simplified fixed-yield approaches. A very interesting finding is that the condensational growth (before Aitken mode particles are formed) rather than nucleation itself is the primary driver of CCN enhancement in preindustrial conditions. The manuscript is well written, with great supporting materials that help the readers to better understand the results. On the other hand, I think the manuscript could be further improved in the following aspects:

1) The manuscript identifies enhanced growth rates of small particles in the PI atmosphere as the primary driver for increased CCN concentrations and subsequent reduction in ERFaci. Since the impact of new treatment on sub-20nm particle growth under preindustrial (PI) conditions is one of the key findings of this study, it would be beneficial to include more analysis and discussion on this topic in the main text. For example, it would be useful to present figure S13 (panels c,d) and corresponding results for "PI_Inorg" and compare the growth rates between the two cases under PD&PI conditions. If there are model diagnostics of condensation rates by sulfuric acid gas and by organics, it would be valuable to compare them.

2) The present study discusses the impact of the new nucleation treatment on indirect aerosol effect. It would be more meaningful to also present total effective aerosol forcing changes (either in figure or table), in addition to the decomposed values, since there are often compensating effects between different forcing components.

3) Since the authors claim (line 284 and 316) that the CCN burden change and the indirect aerosol effect are mainly caused by ORGANIC condensational growth on sub-20nm particles, it would be useful to isolate this impact by performing an additional simulation with the organic condensational growth switched off (if it is straightforward). Otherwise, I would suggest stating it as "likely" or removing the emphasis on organics condensation.

Specific comments:

Figure 3: Is CDNC either vertically-integrated or at the top of low clouds? Which is correct?

Figure 4: Why are the values over ocean negative in panels a) and b)? Also, the caption is somewhat confusing. I suggest rewriting it.

Figure 6: It would be more meaningful to also present total effective aerosol forcing changes (either in figure or table), in addition to the decomposed values. There are often compensating effects between different forcing components.

Line 176: Should be Table 2.

Line 198: "rise" → "rises"

Line 220: "comparing to" → "compared to"

Line 230-231: Is this really the case in this study? It appears that the accumulation mode aerosol number concentrations have significant changes after considering organic nucleation.

Line 280: "organics rate" → "organics"

Line 295: Delete "was neglected"

Line 318: "is" → "are"

Line 324: Should be Figure 6 (not 9).

Line 325: "higher increase" → "greater increase"

Line 337: "with a greater reduction than estimated in previous studies." This appears inconsistent with Gordon et al.'s higher percentage reduction (27%) than this study (16%).