The authors present a new setup for measuring the vapor pressures of low-volatility organic compounds. They use an isothermal evaporation method observing the size loss of single-compound nanoparticles under dry conditions at room temperature. In addition, they performed COSMOtherm calculations to predict vapor pressures. They choose a number of compounds to compare to data available in the literature. This comparison is in general quite satisfactory taking the spread of vapor pressures reported previously into account.

The paper is well written, the techniques and data evaluation are well described and the conclusions supported by the data. The topic is relevant for the readers of ACP and I recommend publishing the paper.

I have only one questions/recommendations to the authors.  They state on line 167: “… and α is the accommodation coefficient that was set to unity in this study.” While I agree that this is a fair assumption because there are no data available, and no evidence for the evaporation coefficient being very small, its value could be easily a factor of 5 smaller, or not? How strong does this uncertainty effect the derived vapor pressure? In addition, the analysis of the data need the surface tension as a parameter. The authors show in their SI the values they took from the literature, but for example for xylitol they simply assume it to be equal to what has been reported for erythritol. All these data carry an uncertainty, which will critically effect the derived vapor pressure. As the authors discuss their retrieval of vapor pressures quite detailed in Section 2.2. I recommend adding a discussion on the propagation of these uncertainties.

Technical comment: 

For the dicaboxylic acids, Bilde et al. (2015) came up with a recommended value and uncertainty range based on all literature available at this time. Maybe add these numbers to your Fig. 2?

References sometimes list all authors, sometimes only a few, e.g. Bilde et al., Chemical Reviews 2015.

This work discusses a technique to determine saturation vapor pressures using a residence time chamber and monitoring the size change of particles during evaporation. This technique allows for the determination of saturation vapor pressures at atmospherically relevant temperatures and shows promise in determining p_sat for low volatility species. In this work single species, dry particles are investigated. This paper was very detailed and provided a lot of great discussion into the challenges of measuring saturation vapor pressures. The writing was clear and the limitations of the study were clearly discussed. The results of this work are reasonable, put into context, and fit well within the scope of ACP. Therefore I would recommend publication after a few minor comments are addressed.

1. I think more discussion on how this could be extend to multicomponent systems would help provide broader implications for this work. It seems like this technique was used in this way in previous work so why was that not discussed at all here?
2. The introduction discussing the various techniques for measuring p_sat was excellent in putting this work into the context of previous work. Including a brief discussion of Cain et al (2020) seems useful though. Some of the novelty here is in being able to do these measurements at atmospherically relevant temperatures and capturing low volatility species, both of which were goals in Cain et al’s work. Therefore comparing and contrasting to the technique used in that work could help strengthen the context already provided. (Kerrigan P. Cain, Eleni Karnezi & Spyros N. Pandis (2020) Challenges in determining atmospheric organic aerosol volatility distributions using thermal evaporation techniques, Aerosol Science and Technology, 54:8, 941-957, DOI: 1080/02786826.2020.1748172)
3. Equation 2: P is not defined.
4. Line 167: Is there a basis in the literature for setting the accommodation coefficient to 1?
5. Line 190: How was an appropriate number of iterations, J, determined?
6. Figure 3: A minor point, but the caption “no solvent” seems misleading as solvent was used in these experiments. Perhaps “no solvent effects.”