This manuscript describes chamber experiment results on the gas-phase reaction of ent-kaurene with ozone. Ent-kaurene represents one of the typical diterpenes that emit from biogenic sources. The authors have measured and quantified ent-kaurene using a PTR-CIMS and reported its fragmentation pattern. They have further characterized less oxygenated and highly oxygenated reaction products using a PTR-CIMS and a nitrate-CIMS, respectively. The results show that the total HOM yield from ent-kaurene ozonolysis is around 2 %, with the oxygen atom number for most of the monomers and dimers below 10. Further, the steady-state concentration of highly oxygenated products decreases as the mass loading of seed particles increases, while less oxygenated products are insensitive to the mass loading changes. The research topic of this paper is novel and the measurement techniques used for product characterization are state-of-the-art. Overall this is a very relevant study fitting perfectly into the scope of ACP.

However, the way the results are presented and discussed needs certain revisions in order to enhance the usefulness to the CIMS community and also be comprehensible for non-specialist readers. And the results would be more robust if the experiment quality could be improved, but I guess it is a bit unrealistic here. Nevertheless, here are my major remarks:

1. The authors have discussed some formation mechanisms when identifying the oxidation products. But I strongly encourage the authors to draw a reaction scheme for clarity. Otherwise, every reader would need to draw their own ones to make sense of the chemistry.
2. Figure 3 is useful, but it is too busy to comprehend, and readers are actually not able to zoom in to figure out the details. It would make sense to just show a few time intervals instead of the entire period, and put this one in SI.
3. For Figure 4, the authors should probably either label the peaks with the reagent ion (e.g. M.NO3-) or subtract the mass of the reagent ion. The authors have written a disclaimer in the text, but it can still be a bit misleading.
4. The calibration factor of 1*10^10 cm^-3 for HOM quantification may not be that accurate, because the m/z of diterpene oxidation products are possibly 100-200 Th larger than those of monoterpene products. This is where the mass-dependent transmission does matter. The authors should at least show the transmission curve; and if the m/z of major products are sitting on the edge of the curve, a transmission coefficient needs to be included in the calculation of HOM concentration.
5. Ent-kaurene concentrations in this paper are at the ppb level, while in real atmosphere ppt or ppq levels. The reactant concentration obviously has an effect on RO2 chemistry. Then is the HOM yield determined in this paper applicable to the real atmosphere? The authors would need to discuss this.
6. The authors would need to clarify how the uncertainty for HOM yield is obtained, i.e. show the calculation of error propagation.
7. As to product volatility, I am not sure if varying the condensation sink is the right way to probe it. First of all, increasing the CS would reduce the lifetime of some first-gen products, and in turn alter the second-gen chemistry, which may influence the fraction remaining. Moreover, I think it is the accommodation coefficient and not the volatility that faction remaining associates to. This is probably why LVOC and ELVOC have pretty much the same faction remaining (their accommodation coefficients are probably all near unity), while their volatilities differ by several orders of magnitude. The authors would need to re-think and rephrase the related discussion.

Minor comments:

1. Line 27: “with 4–5 O-atoms needed for the main monomeric species to condense”. It might make sense to modify the conclusion by adding constraints like “to condense onto xx nm particle”. (In theory, any compound can condense at sufficient high supersaturation.)
2. Line 40: remove “new”.
3. Line 126: change “after a collision” to “after collisions”.
4. Line 280: move the experiment conditions to the “Methods” section.
5. Line 334: “It is also possible that the nitrate CI-APi-TOF might be more sensitive towards less oxygenated dimers if there are 40 C-atoms rather than 20 in their skeleton, if a larger molecule increases the likelihood of forming a stable cluster with NO3-”. Is it possible? Please explain more.
6. Line 468: should the “with carbon skeleton” be removed?
7. The authors state in line 365: “HOM yield ranged between 0.1%-3%”, while in Table 1 “0.5-10”, which one is correct?