We thank the referee for the very positive and thoughtful assessment of our work. We especially appreciate the recognition of the value of combining EMB experiments with MD simulations, and the insightful discussion regarding non-equilibrium processes in SOA growth. We address the specific comments below.

Comment 1: Representativeness of the molecular beam energy distribution

The referee notes that the narrow, directed energy distribution in a molecular beam differs from thermal atmospheric conditions and asks whether this leads to different surface dynamics.

Response: We agree that the incident energy distribution in a molecular beam differs from the thermal distributions in the atmosphere. We have clarified this point in the revised manuscript.

Importantly, the processes investigated here (energy accommodation, trapping, cluster dissociation, and desorption) are governed by surface-controlled energy redistribution following impact, rather than by the exact form of the incident velocity distribution. As shown in our results, the scattered flux is dominated by thermal desorption (TD) with negligible inelastic scattering contributions, indicating that the incident kinetic energy is efficiently dissipated into surface and internal degrees of freedom prior to desorption. This implies that the system rapidly loses memory of the initial beam conditions, and the observed kinetics reflect intrinsic surface properties (e.g., binding, morphology, and energy dissipation pathways). These quantities are directly transferable to atmospheric conditions and are the same parameters used in kinetic aerosol models.

To clarify this, we have added a paragraph in the revised manuscript (Section 2.1): “While the molecular beam has a narrow and directed energy distribution, the observed dynamics are governed by rapid energy accommodation at the surface. The dominance of thermal desorption indicates efficient redistribution of the incident energy, such that the system largely loses memory of the initial velocity distribution. The extracted kinetic parameters therefore reflect intrinsic surface-controlled processes and are transferable to atmospheric conditions.”

Comment 2: Temperature range and absence of water vapor

The referee asks how higher atmospheric temperatures and the presence of water vapor may affect the results and their interpretation.

Response: We thank the referee for raising this important point regarding atmospheric relevance.

(a) Temperature effects: We note that our experimental range (180 - 300 K) already overlaps with atmospherically relevant conditions, particularly for the upper troposphere and cold boundary layers. More importantly, the key outcome of the study is the identification of a competition between incorporation and thermally activated desorption, which is explicitly captured through Arrhenius kinetics and the effective uptake coefficient framework.

As temperature increases, desorption rates increase accordingly, shifting the system toward a more desorption-limited regime, as shown in our kinetic analysis (Section 3.2). This behavior is fully consistent with expectations for warmer atmospheric conditions. We have clarified in the revised manuscript that while higher temperatures increase surface mobility and desorption rates, they do not alter the fundamental distinction between thin-film (kinetic retention) and thick-film (desorption-limited) regimes, which is controlled by morphology.

(b) Role of water vapor: We agree that water vapor is a key factor in atmospheric heterogeneous chemistry. While its inclusion is experimentally challenging in EMB, we have expanded the discussion in the revised manuscript to address its potential effects. Specifically, water may compete for adsorption sites and modify hydrogen-bonding networks, plasticize organic coatings, increasing molecular mobility, and alter energy dissipation and cluster stabilization. Based on our mechanistic findings, we expect that thin, disordered coatings may become even more accommodating in the presence of water due to enhanced energy dissipation and hydrogen bonding, whereas thick, ordered coatings may become more liquid-like, potentially reducing delayed desorption.

We have added a paragraph in Section 4 (Atmospheric Implications) discussing how humidity may modulate, but does not invalidate, the morphology-dependent kinetic regimes identified in this study: “Under atmospheric conditions, higher temperatures and the presence of water vapor may influence surface mobility and intermolecular interactions. Increasing temperature enhances desorption rates, shifting the system toward a more desorption-limited regime, consistent with our kinetic framework. Water vapor may further modify surface properties through adsorption and hydrogen bonding, affecting energy dissipation and molecular accommodation. While these factors may alter quantitative behavior, the morphology-dependent kinetic regimes identified here are expected to remain robust.”

We thank the referee for the positive evaluation of the manuscript and for recognizing the importance of the results for understanding soot aging and SOA formation. We also appreciate the helpful suggestions for improving clarity.

Comment 1: Clarity of Arrhenius analysis in Figure 4

The referee notes an inconsistency between the figure caption and the main text regarding which datasets are included.

Response: We thank the referee for identifying this ambiguity. In the revised manuscript, we have: clarified in both the main text and the figure caption that the Arrhenius analysis includes both HOPG and the nopinone thick layer, and explicitly stated that the thin coating is excluded because the slow TD channel is absent for this case.

We have also revised the caption: "Figure 4. Arrhenius plot of butanol desorption rate constants for the slow TD channel from HOPG and the nopinone thick layer. Both datasets are included in the analysis and exhibit comparable activation energies and pre-exponential factors. No data are shown for the thin nopinone coating because the slow TD channel is completely suppressed on this surface."

Main text: "The analysis includes the two surfaces exhibiting slow TD behavior, HOPG and the nopinone thick layer, whereas the thin coating is excluded due to the absence of the slow TD channel."

Comment 2: Connection between MD simulations and experimental thickness regimes

The referee suggests clarifying how MD slab thicknesses relate to experimental thin and thick coatings.

Response: We thank the referee for this important suggestion.

In the revised manuscript, we have clarified the connection between the MD slab thicknesses and the experimental coating regimes. Experimentally, the “thin” coating corresponds to a very low-coverage regime, likely approaching a monolayer, although its exact thickness is below the detection limit. The MD slabs with 4–6 layers (~2.8–3.5 nm) therefore represent a comparable regime in which substrate effects and surface disorder remain significant.

In contrast, the experimentally defined “thick” layer (~1 μm) represents a limit where substrate influence is no longer accessible and surface properties are governed entirely by the organic phase. This is consistent with the MD 15-layer (~9 nm) slab, which is sufficiently thick to screen substrate effects and exhibits a more ordered, bulk-like surface structure.

We now explicitly state that the MD simulations are designed to capture the transition from substrate-influenced, disordered surfaces to bulk-like organic layers, focusing on morphology, disorder, and defect density rather than absolute thickness.

To clarify this, we have added the following text in the revised manuscript (Section 2.2): “In the present simulations, the slab thicknesses are chosen to capture the transition from substrate-influenced, thin coatings to bulk-like organic layers, rather than to reproduce the full atmospheric thickness range. The thinner slabs represent a low-coverage regime where substrate effects remain important, whereas the thicker slab corresponds to a regime in which the organic layer effectively screens the substrate.”