The motivation behind this study is to update the nucleation and growth parameterizations in the WRF-Chem model, enabling it to simulate the particle formation and CCN formation processes in a coastal city in China. While some earlier studies have found a negative contribution of NPF to CCN, this study finds a positive contribution of NPF to CCN by adjusting the SI-SOA yield. The major updates include changes to key parameters, such as the H2SO4 accommodation rate, the HNO3 condensation rate, the direct emission of primary organic aerosol, and, most importantly, the SI-SOA yield. This type of work is encouraged and fits within the scope of ACP.

[disclaimer: I’m not an expert who can judge whether the authors’ model and setups represent the most advanced knowledge in their community.]

Major comments:

1. The authors should directly change the mass accommodation coefficient of H2SO4 from 0.1 to 1. There is enough experimental evidence showing this is the case. All other results should be revised with respect to this change. See 10.5194/acp-20-7359-2020
2. L263: I believe it's time for everyone to stop using the activation scheme, given that the studies supporting it are from 2006-2007 and even the authors themselves may have moved on. Moreover, the dependence of J on H2SO4 is evidently non-linear. Several studies in Chinese megacities have demonstrated the significance of H2SO4-DMA nucleation. While the situation might be different in a coastal city, it's unlikely that there is no NH3 present. Incorporating DMA and NH3 into WRF-chem may be challenging, as their sources may not be explicitly described. However, I encourage the authors to employ the H2SO4-NH3 nucleation mechanism and rates in their study. They could use an estimated NH3 concentration, as the nucleation rate from H2SO4-NH3 is less dependent on NH3 than on H2SO4. The authors should compare the results obtained using the activation scheme with those obtained using the H2SO4-NH3 mechanism. If the latter yields superior results, it should be used as the default for other sensitivity tests. Conversely, if the H2SO4-NH3 mechanism does not improve the results, this issue should be discussed. The problem may lie in other less certain modules instead of this experimentally confirmed mechanism.
3. I find Session 3.4 to be particularly fascinating, but it's currently buried amidst a lot of less significant information. This session should be considered one of the key findings of this study and given prominence in both the abstract and conclusion. The yield of SI-SOA remains highly uncertain, and I'm surprised to learn that such a small change in the reaction rate coefficient can have such a significant impact on the contribution of NPF to CCN. I hadn't expected this result at all. This finding underscores the need for further research into SI-SOA yield in polluted environments, particularly since urban environments are highly complex and model treatments are often oversimplified. Clearly, a better understanding of NPF's contribution to CCN hinges on a better grasp of this prerequisite knowledge.

Minor comments:

L39-41: a number of observations may be misleading. There are more than enough observations showing the positive correlation of NPF and CCN. Additionally, while some simulations do not show positive correlation of NPF and CCN in a global scale, many of the models do. If the authors’ statement is about e.g., polluted environments or more specific the Chinese city, the authors should clearly be stating so. Otherwise they should modify this sentence properly.

L74: high-efficiency nucleation  efficient nucleation

L110-121: it appears the authors are only talking about WRF-chem. They should carefully mention this clearly in the manuscript that it is the WRF-chem model, not a general “model” that is observing negative correlation between NPF and CCN.

L190: change C* to c* (italic, lower case) throughout the manuscript.

L199: Please write explicitly the used equation and all the parameters.

L333: try to reduce using MFB etc. Use the abbreviations only for models runs otherwise readers easily get confused.

L347: space between µg m−3play

L349: Does this mean that all the vapours only have two different volatilities?

L354: Gas phase POA forms close to the emission source. However, with…

L356: Therefore, POA may not contribute to particle growth away from the emission sources. Or something similar.

L364: Please label the Figure S1 panels. There are also clear signs of grey bars in the figure. Please remove those when putting the figures together.

L412: Avoid using too many abbreviations (PNC).

L416: Which nucleation mechanism is used in this study?

L506: Are there measurement data for figures d,e,f?

L538: This session is very interesting. I think this is worthy to be emphasised.