Responses to Reviewer 4 Comments

The authors conducted thermodynamic modeling analysis on the acidity and inorganic aerosol gasparticle partitioning in the South Korea during an aircraft field campaign. The authors also determine the “chemical regime” of PM sensitivity to ammonia and nitrate availability and found that the aerosol formation is always sensitive to HNO3 levels, especially in highly polluted regions, while it is only exclusively sensitive to NH3 in some rural/remote regions. This manuscript is well written and organized, and the topic of PM control strategy is relevant to this journal. However, I am concerned about the validity of the new approach.