This study assessed the effectiveness of reducing NH3, NOx, and SO2 emissions on PM2.5 in December 2018 by using the CMAQ model. In general, the method is well recognized, and the study is logically designed. A few modifications and clarifications are needed.

1. The title can be modified as ‘mitigating winter PM2.5 in Taiwan’ to be more accurate.
2. Equation 3: I don’t understand how the log calculation appeared here.
3. Model performance: For evaluation model performance on meteorology and air quality, there are certain criteria and statistical matrix to evaluate. The model performance can be accepted when compared to these criteria. A reference can be: Chem. Phys., 16, 10333–10350, 2016.
4. Some more detailed discussion on performance on the components should be provided, such as time series plots of obs vs. pre sulfate, nitrate and ammonium, as these are the core of the study.
5. The results in Fig. S7 and S9 are averages from 1-14 December. Why?
6. It will be more interesting to see whether the ‘effectiveness’ differs during the ‘high pollution’ period (such as beginning of December and middle December) and during relatively clean period.

This study is of value in that it provides PM_2.5 species measurements in Taiwan and assessed the emission control effects. However, the paper is not presented in a professional way. Many places are using non-scientific expressions in the field of atmospheric chemistry. Therefore, the whole paper needs to be substantially improved before it can be published on ACP. The problematic wording includes but not limited to –

1. Abstract line 1: “when particulate matter (PM2.5) levels …” should be “when fine particulate matter (PM2.5) levels …”
2. Line 13 please revise “In contrast, local NOx …”.
3. Line 35, it is misleading to say “such as sulfate, nitrate, and ammonium” after “gas-phase precursors”.
4. 3.1 section title: “sulfate sources” sounds better than “sulfate contribution”.
5. 3.2 section title "sulfate formation pathways".