The manuscript by Zhang et al. presents a theoretical evaluation on the role of organic acids in MSA-MA NPF. Among all considered organic acids, they found that formic acid (ForA) has the highest potential to stabilize the MA-MSA cluster and can enhance MSA-MA nucleation at atmospheric conditions via catalyzing the formation of clusters in the initial stage of NPF. The structural factors that affect the enhancing potential of organic acids on MSA-MA NPF were also revealed. The selected topic should be interesting across a range of atmospheric chemistry community. The work is technically well performed and calculated data can well support the conclusion. The manuscript is well written and easy to follow. Therefore, I recommend publication of this manuscript after consideration of the following comments:

• The accuracy of DLPNO-CCSD(T)/aug-cc-pVTZ calculation depends on selected keywords for the convergence. Please clearly present the selected keywords for the DLPNO-CCSD(T)/aug-cc-pVTZ calculation in the Computational Details section.
• Lines 82-83, in my opinion, the range for the number of initial configurations (1000-10000) for each cluster is large and it would be better to explain the reason.
• It is better to test how the selection of coagulation sink affects the core conclusion.
• Line 98, please cite the references for the equation (1).
• Lines 174-175, in order to explain why SucA and AdiA are outliers, the authors should clearly present the even/odd pattern of dicarboxylic acids.
• Please provide the equation for calculating the binding free energy of (SA)₁(amine)₁(OAs)₁ in Table S3 and point out whether the calculated [(SA)₁(amine)₁(OAs)₁] is the mean values based on concentration of precursors.
• Please check the guidelines of Atmos. Chem. Phys. for references, and all the references should be cited in the same style.
• Some minor mistakes are shown in the manuscript, e.g., Line 79, “global minimum structures” instead of “global minima structures”; Line 135, “ones” should be “clusters”; Lines 223-224, it should be written as “ The evaporation rate of the (ForA)₂ cluster is found to be comparable to that of (MSA)₂”.

The manuscript by Zhang et al. is devoted to the role that organic acids (OA) may play in new particle formation from methanesulfonic acid (MAS) and methylamine (MA) molecules. It is based on high-level quantum chemical calculations of the formation free energies of selected MA-MSA-OA ternary clusters and on results obtained from ACDC (Atmospheric Cluster Dynamics Code) simulations. The main conclusion of the paper is that the formic acid (ForA) molecule is of particular interest because ForA might have an important role in MSA-driven new particle formation (NPF) in relevant atmospheric conditions. The various factors that affect the enhancing potential of the organic acids, especially ForA, on MSA-MA NPF were also thoroughly analysed.

The work is technically well performed and the results of the calculations well support the conclusions. The manuscript is almost clearly written and should be interesting for the community of atmospheric chemists.

I recommend publication of this manuscript after the following (minor) points have been taken into account :

• When comparing the various dicarboxylic acid molecules considered in the calculations, it is found that only maleic and glutaric acid can interact via their two carboxylic groups. It is however suprising that such configuration has not been found for Succinic acid. This has to be discussed.
• Although the ACDC code has been presented elsewhere, it is quite disappointing not having here a brief presentation of its main inputs and outputs. In particular, this would greatly improve understanding of section 3.4 and Figure 6.
• Finally, when comparing the DeltaG values, it should be clearly stated that the discussion in the paper is based on the absolute values, whereas relative values are given in Tables and Figures. Then, « higher values » in the text correspond in fact to « lower values » in the Tables/Figures.