The pH values of aerosols are very important and attract lots of controversies, and are the hotspot in the investigation of aerosols properties. This article introduced a non-ideality correction factor and investigated its governing factors. Besides, a parameterization method was proposed to estimate c_ni at given RH, temperature and NO₃^- fraction, and was validated against long-term observations and global simulations. The results are very interest, and provides a way for pH retrieval when chemical measurements are unavailable for the ammonia-buffered regions and periods. The manuscript is suitable to be published on Atmos. Chem. Phys. after considering the following comments.

Comments:

1. In the line 174-176, it is hard to understand the result that there was relatively small difference in pH predictions by E-AIM and ISORROPIA, but higher difference in estimated c_ni. Can the authors provide some more detail information to explain this result?
2. As the authors are mentioned, the cations of Na⁺, Ca²⁺, K⁺, and Mg²⁺ play a minor roles as their influence is more indirect. However, NH₃/NH₄⁺ plays important roles in multiphase buffer theory. What is the role of the NH₃/NH₄⁺ in the non-ideality coefficient?

This paper is significant work to understand the total contribution of NH3 on the acid-base equilibrium of condensed phase of atmospheric particles. Especially for the case of concentrated aqueous phase at low RH, non-ideality correction factors are explored. This paper should be published with considering the two comments: (1) when it gives the definition of pK_a,NH3^*i, physical significant of pK_a,NH3^*i should be more clear if the authors provide more description, i.e., both condensed chemical compositions and NH₃ content in gas phase determined the pH when chemical reactions in the particles change the pH of condensed phase, or other more better description easy understanding for readers. (2). line 80 in the equation, [NH₃(g)] is equivalent molarity of gaseous NH₃ in solution, its unit is molar.Kg^-1. In this case K_a,NH3^*,I= K_a,NH3(1+1/(H_NH3RTAWC), water density should not appear in the equation. The same is in 8a and 8b.