The manuscript reports the impacts of control measures on environmentally persistent free radicals (EPFRs) and reactive oxygen species (ROS) in Beijing during the 2015 China Victory Day Parade period. The findings reveal the changes in sources and formation processes of EPFRs and ROS in different control period. The paper is well organized and the topic is interesting for the control of hazardous species. However, some issues should be modified before publication, specific comments are as follow:

1. Abstract: You should provide the variation of the main sources before and after CP period as a comparison for those during the CP period.
2. Graphical abstract: The resolution of figure is too low.
3. Line 36: “correlations”, between what?
4. Line 67: this sentence should be rewritten more clearly.
5. Line 87: it is not clear here, the sampling information here are for PM?
6. Line 98: “elementary” should be “elemental”.
7. Line 104: it should be “Real-time SO₂, NO₂, and O₃ concentrations”.
8. Line 176: “spin” should be “spins”
9. Figure 6: The horizontal axis should be changed to continuous time.
10. Line 202-210: The authors should provide some discussions of the comparison of reduction effects in G-ROS and P-ROS during control periods.
11. Line 271-273: Why the percentage contribution from vehicle emissions increased?
12. Conclusions: In the conclusion section, the authors should include some recommendations for future research needs on ROS and EPFR.
13. Line 390: Please check the references and unified format.

This measurement report reports measurements of EPFRs and ROS in Beijing, highlighting the impact of emission control and reductions in 2015. There is good evidence for their conclusions with scientific data, however their results fail to give error bars or uncertainty values that would make their conclusions stronger. I have several major comments that need to be addressed as below.

Major comments:

1. I found that introduction misses some key information and references are missing. I suggest citing several pioneering works on EPFR by Dellinger and coworkers, by making it clear that EPFRs are mainly generated by incomplete combustion and traffic emissions. In addition, a recent study has shown that biomass burning is a significant source of EPFRs (Fang et al., DOI: 10.1039/d2ea00170e). I would also mention in introduction that heterogeneous chemistry could be a source of EPFRs (Borrowman et al., DOI: 10.1039/C5CP05606C).

2. Secondary organic aerosols (SOA) have been shown to be a significant source of ROS (Venkatachari et al., DOI: 10.1080/02786820601116004; Wang et al., DOI: 10.1080/02786826.2011.633582), including OH, superoxide, H2O2 and organic radicals (Tong et al., DOI: 10.1021/acs.est.8b03695, Wei et al., DOI: 10.1021/acs.est.0c07789). This should be mentioned/discussed especially because secondary processes are found to be source of ROS in this study.

3. As using Mg²⁺ and Ca²⁺ standards to calibrate EPFR for g-factor and absolute spin amount is uncommon, please elaborate on this procedure.

4. For measurements of ROS, are they mostly H2O2? Could your measurements also sensitive to other short-lived ROS such as OH and superoxide, or organic hydroperoxides? Please make it clear in the method section, as it is ambiguous throughout the manuscript.

5. Semi-quinone radicals are regarded as O-centered radicals (L116), but they have resonance structure and can have an unpaired electron on a carbon atom.

6. It was interesting to see a positive correlation of O3 with EPFRs, given that a previous study has observed a negative correlation (Hwang et al., DOI: 10.1021/acsearthspacechem.1c00135). Please discuss the difference.

7. I found Sect. 3.5 not robust or justified well. First, please discuss each factor more in detail and why each factor is assigned to have specific source. Such discussion is completely missing, so it is totally unclear why top factor is assigned to be secondary aerosols, 2^nd as vehicle, etc. What are key tracers and features in each factor? This needs to be elaborated. I also do not understand fully, how Fig. 9 is constructed from Fig.

8. How did you quantify contributions of each factor (or source) to EPFR or ROS, even though the strength or contribution of EPFR or ROS in each factor is different? Without these clarifications, the results of Fig. 9 is highly questionable and would suggest omitting this analysis if not clarified.

9. Error analysis and uncertainties are missing for some figures. Please include error bars in Fig. 1, 2, 4, 5, and possibly also 6.

Line 171: Please include the standard deviation for this reduction 18.3 ± ??.? %. Are three significant figures appropriate considering error calculations? It appears that the EPFRs are actually highest in the strict control period. Comment on this.

10. Line 270: Before it was mentioned that more complex formation of EPFRs happened during control periods, possibly from secondary reactions. However, based on the PMF SOA decreased, as well as precursor gasses of secondary aerosols, and vehicles were the largest source. Please comment on whether these two conclusions agree or disagree with each other. There is an apparent increase in “other sources” that could tie into this complex formation of EPFRs during the CP.

Other minor comments:

Line 34: And/Or used in this context is unclear, consider rephrasing.

Line 41: Grammatical correction- should be changed to “enables free radicals to be highly reactive”

Line 51: Consider including your source of dust formation of EPFRs to this sentence in addition to the following one.

Line 56: Not the correct source- shouldn’t it be Gehling 2014 (Environ. Sci. Technol. 2014, 48, 8, 4266–4272)?

Line 74: Detail the short-term emission measures put in place that may be relevant to this study.

Line 76: List other pollutants that have been measured and their importance to your study.

Line 96: What are the differences between “regularly control measures” and “stricter control measures”? Detail the control measures put in place. 

Line 96: May be clearer to say either “regulatory control measures” or “regular control measures.”

Line 120: Define GAC-ROS

Line 127: Specify what was used as standards. “Flesh standards” should be changed to “fresh standards.”

Line 143: Specify which elements are measured, is this from ICP-MS?

Line 148: What is MMW-PAHs?

Line 151: There are 3 percentages listed for decreases by NO₂ and SO₂, but there should only be 2. Remove the percentage not associated with NO₂ and SO₂ decrease. The first percentage may refer to O₃, in which O₃ should be added to the sentence.

Line 154: State the decrease in O₃ concentration.

Line 159: Elaborate on why there would be increased traffic at night. Is this common for this location?

Line 180: EPFRs are also formed during irradiation. Please elaborate on what EPFRs may be converting to during irradiation, or include a source for this theory.

Line 181: Similar to my comment above, please include a source for why it is thought that traffic increased at night, as it is unlikely in other areas.

Figure 2/Line 185: Include error bars in this graph if available.

Line 194: Cite how you know that emissions primary combustion sources are significantly reduced. Is this specifically included in control measures?

Line 194: Grammatical suggestion: consider replacing “restricted” with “reduced” or “decreased” as restricted seems like it is contained within the control measures.

Line 195: Possible misuse of “antioxidant properties.” Please clarify why a more oxidized EPFR would have antioxidant properties. Do you mean instead not as easily oxidized compared to NCP?

Line 196: Clarify what is meant by “higher level” of H_p-p. Looking at the graph it appears the difference between the line width in strict CP and NCP falls within the same range, and the apparent difference may be due to the lesser amount of data points. Please comment on whether or not you think this may be the case.

Line 203-205: Include standard deviation for these measurements. Is the difference between them significant?

Line 207: Clarify “much more,” is that a factor of 2?

Line 236: Please elaborate on this further. How does this compare to NO₃ nighttime oxidation?

Line 284: The percentages are not in the correct order. Other sources are very significant (~30%) in the pie chart but only are listed as ~3%.