Li et al. present observations of chloroacetic acid at a rural site in Hong Kong and showed that its formation cannot be fully explained by existing mechanisms. They propose two potential pathways for its production: (1) isoprene and its oxidation products, and (2) multiphase reactions. The draft is well-structured, and the results are clearly presented. However, I suggest the authors address the following comments before the manuscript is accepted for publication in ACP:

1. The estimation of the reactive uptake coefficient relies on linear relationship models based on several OVOCs. I recommend evaluating the accuracy of this linear model and discussing the uncertainties associated with these uptake coefficients.
2. The updated gas-phase chlorine chemistry and VOC-Cl model predict Cl-OVOCs concentrations up to 1 ppb, which significantly exceeds the observed values. The authors should provide an explanation for this large discrepancy.
3. The inclusion of both updated gas-phase chemistry and heterogeneous reactions increases the simulated levels of chloroacetic acid by 32–56%. I suggest adding a discussion on the potential role of other missing mechanisms to account for the remaining gap.
4. Line 193: Considering the slow rate of hydrolysis reactions, how do QC calculations support the plausibility of chloroacetic acid formation via multiphase processes? This result appears contradictory.
5. Lines 131–134 and Figure S1: The correlation coefficient between Sa and C2H3O2Cl is not strong enough to indicate a robust correlation. Please address this limitation.
6. Figure 1: Why are the observed C2H3O2Cl levels higher in 2020 compared to 2021? Can this discrepancy be explained by the proposed mechanisms?
7. Figure 4: The model-simulated diurnal cycle of Cl-OVOCs does not match the observed diurnal pattern of C2H3O2Cl shown in Figure 1. Please explain this inconsistency.
8. Figure 4: The gray shading representing C2H3O2Cl is not visible in the plot. Please clarify or correct this issue.

The manuscript “Mechanistic insights into chloroacetic acid production from atmospheric multiphase VOC-chlorine chemistry” by Li et al. describes the potential heterogeneous processes of chloroacetic acid production in observations at Hong Kong by performing quantum chemical calculations and chemical box model simulations. The formation mechanism of chloroacetic acid in the atmosphere is poorly understood, as such, I feel this study, which provides a comprehensive assessment of this chemistry, is of interest to the community and falls within the scope of ACP. The manuscript is also well written and organized. I recommend publication after addressing the following points.

1. Page 3, line 93-: I am not very sure whether a linear relationship analysis between hydrolysis of OVOCs and their reported γ values could be used to predict γ of Cl-VOCs. For N₂O₅ in liquid water maybe it is fine as its bulk hydrolysis rate is quite fast, and there are no other significant processes in pure liquid water. But here, the hydrolysis rates of Cl-VOCs are slow, oxidation in aqueous phase also plays a role, and the composition in aerosol water is really complicated. Please discuss whether these factors would have an impact.
2. It seems that the method for deriving γ also assumes that gas-phase diffusion limitations were negligible, is this true? Please clarify.
3. Page 3, line 70, please also report measurement accuracy.
4. Page 5, first paragraph: it seems that the correlations could be mostly attributed to diurnal variation, is this true? Considering the diurnal variation of oxidants, VOCs and other emissions, it is not surprised to have chloroacetic acid, aerosol mass, photolysis rate, etc. all peak in daytime. Similarly, correlation with RH could also be due to the diurnal variation of humidity.
5. Page 5, line 150-152: the energy barrier (~8 kcal mol^-1) between IM1 and IM2 is unclearly shown in the 3-D relaxed scan (Fig. 2). Texts on the axes need to be clearer.
6. According to Figure 1, 4, 6, and 8, it seems that the diurnal variation of Cl-OVOCs/chloroacetic acid can only be represented by adding a reactive uptake, and cannot be resolved by adding another gas formation pathway related to oxidants levels. Is this correct? If so, this could be evidence to support the importance of multiphase process. Also, does adding reactive uptake change the diurnal pattern of precursors?
7. Figure 8 has not been mentioned in the main text, please add it to the corresponding description.
8. Figure 8: Why does adding reactive uptake (scenario VI) decrease chloroacetic acid level at night (compare to scenario IV).
9. I might suggest adding description for simulated contribution from heterogeneous reactions of chloro-acetaldehyde to the observed chloroacetic acid in abstract and conclusion.
10. Abstract: “multiphase processes in VOC-Cl chemistry” in the last sentence may lead to confusion. It sounds like a multiphase process involve gas VOC with oxidation by Cl in aqueous phase. Please consider rephase.