General Comments

This study addresses the important challenge of calibrating the FIGAERO-CIMS instrument for measuring the volatility of organic aerosol (OA) constituents, particularly for extremely low-volatility compounds (ELVOCs). Current calibrations typically rely on polyethylene glycols (PEGs) up to PEG-9, which limits the lower end of the volatility range. The authors extend this range by including PEGs up to PEG-15, thereby significantly improving calibration coverage.

The experiments are thoroughly conducted, with desorption temperatures (Tmax) carefully measured and reported. The authors also compare a comprehensive range of methods for estimating the vapor pressure (C*) of PEGs. The experimental results, vapor pressure estimates, as well as the discussion, provide valuable insights—not only for FIGAERO-CIMS users but also for the broader community using thermal desorption-based volatility measurements.

I strongly recommend the manuscript for publication, but I have a few comments and suggestions for clarification and improvement:

Specific Comments

(1) The conclusion regarding the linearity between C* and PEG number is somewhat misleading. A linear relationship should not be expected, and in fact, non-linear behavior is well documented in various parameterizations (e.g., L2016, S2018, M2019 in this study). In addition, different conformers of the same PEG molecule can exhibit varying intermolecular interactions, leading to different saturation concentrations. This is actually illustrated in Figure 1: the best-performing estimation methods (desorption model, COSMO-RS, MGM) show that C* values for larger PEGs tend to be non-linear and above the dashed line, contrasting with other parameterization methods.

Instead, the relationship between C* and the measured Tmax is more direct. In Figure 2, when considering the uncertainties in C* (as shown in Figure 1), the linear fit is not significantly worse than other fits. Furthermore, it is somewhat confusing that the Tmax values in Figures 1 and 2 are taken from two measurements (presumably A and B?), but C* from the desorption model is the averaged value from A, B, and C. Would it not be better to use the average T_max from all three measurements (A, B, and C) for consistency? Also, I am curious about the uncertainty of Tmax, which is not clearly mentioned.

(2) Please clarify whether the reported mass loading refers to individual compounds or the total mass, and maybe more important which one is more essential or more related to Tmax. It is unclear whether low mass loading (< 105 ng) could influence Tmax. If this is a potential factor, it should be discussed.

Technical Comments

Line 21: It’s unclear where the "150 °C" value comes from. This is described more clearly in Lines 75–76. Please ensure consistency across the manuscript.

Line 35: Instead of "now-known," consider using "best-estimated" for clarity and specificity.

Line 77: The sentence suggests methods were used to improve measurement accuracy. It would be more accurate to say that different methods were used to improve the prediction of vapor pressures.

Line 159: Remove "experimental".

Figure S1: It is unclear how the uncertainties for the magenta crosses were derived. The legend notes that the yellow crosses represent the model fits of C* (rather than ΔH) to experiments.

The study discusses calibration of the saturation vapor pressures of the FIGAERO-CIMS using the PEGs. The size range of the PEGs employed for the study was maximally up to PEG-15. Employment of the wide range of sizes of PEGs is the key novelty of the study. Since the experimental data for saturation vapor pressure of the PEGs with large sizes are unavailable, the authors employed various types of numerical approaches for estimating it. The desorption temperature of the PEGs was related with saturation vapor pressures using an empirical equation. The experiment was conducted sufficiently carefully. The manuscript is well-organized, and easy to follow. I suggest publication of this manuscript after the authors address the following comments.

Temperature and saturation vapor pressure

The FIGAERO-CIMS retrieves volatility by heating the sample. I believe that standard temperature for saturation vapor pressure for the study would be around 20–25 °C, while desorption temperature is much higher. For relating desorption temperature with saturation temperature, enthalpy for evaporation (Delta_H) of the calibrants and actual samples would play important roles. It would be great if the authors could explain why desorption temperature of the PEGs could be related with volatility of atmospheric (relevant) organic matter in more detail.

Typos and grammatical issues

There are some typos and grammatical issues with the manuscript. It may be a good idea to use a software or an online tool for checking the manuscript.