Review of “An updated microphysical model for particle activation in contrails: the role of volatile plume particles” by Joel Ponsonby et al.

This study proposes an updated scheme for particle activation in contrails and evaluates its performance in two parcel models. The topic is both timely and highly relevant, and the work brings a valuable and novel contribution to the existing literature. The manuscript is well written and scientifically robust, and I therefore support its publication. I have only a few comments and suggestions that could help further strengthen the paper before publication.

Main comment:

Evaluation against observations: It would be good to assess the extent to which the inclusion of vPM activation (using the framework proposed here) affects simulated AEI_ice for some case studies where observational data are available, e.g. PAZI-2, ECLIF II, CONCERT – see Table 1 in Bier and Burkhardt (2022).

Minor comments:

1. Section 5.1 needs to articulate more clearly the extent to which current global contrail simulations are impacted by the limitations addressed by this proposed new scheme. The current text implies that all existing global contrail models rely on nvPM properties to parameterise AEI_ice, leading to the conclusion that “current global contrail simulations may underestimate global contrail forcing” (line 643). This is not necessarily true, as there are significant differences in how existing contrail schemes in climate models initialize contrails.
2. Lines 9-11: While the study suggests that including vPM activation in models is likely to increase contrail cirrus RF estimates, the use of “however” in the second sentence of the abstract could be interpreted to imply the opposite. I recommend rephrasing this to avoid potential confusions.
3. The phrase “both models” on line 16 of the abstract is unclear, as the two models are not introduced beforehand. Consider revising the opening sentences to explicitly mention the models being compared, which will help orient the reader.

Technical corrections:

1. Line 230: at least on my screen what is referred to as green lines appear in fact as grey.
2. Line 550: Fig. 7 caption should mention 211-223K rather than 211-213K.

This paper update two different microphysical model and perform sensitivity analysis to input parameters with only one of this model, the one that seems the most realistic. Their update consist in adding a distribution to account for volatile particles in order to be able to compute contrail formation in low soot regime. Overall the model modification are well explained as well as most of the underlying hypothesis; however several informations are missing such as what is the density of the volatiles particles, the surface tension... The main limitation of this study in my opinion, that they fix the number of volatile particles but little is done to look at the dependency of the results to this parameter.