|Comments on previous referee reports:|
The authors seemed to have addressed most of the comments from the referees to a satisfactory extent. However, there are a number of places in which the text was changed and the remaining language seems vague as a result (for example, response to comment 6 in the response document). Also, the response to comment 11 includes some helpful ‘scoping’ calculations that it seems should be included in the actual paper text, as the importance of RO2+RO2 chemistry was highlighted by both referees.
In general I found the paper to be interesting and mostly clear description of these experiments and analysis. There were a number of instances where assumptions or approaches are not well justified and this reduces confidence in the quantitative results, though the general point (that TMB SOA contains low volatility material not captured in yield experiment-based product distributions) is well supported. One general comment is that there is quite a bit of literature on the potential influence of chamber walls on SVOC/IVOC measurement, and none of that is mentioned/discussed here, either in terms of influence on your measurements or interpretation of yield experiments. I think this and other lines of evidence have pointed to the fact that the ‘traditional’ yield-experiment-based VBS parameters are probably wrong and missing material. A bit more discussion of this would be helpful.
Specific points (Page/Line number):
P6, L10 – This should mention particle diameter for SOA experiments. Also, ‘other processes’ is very vague and could this be attributable for different loss in the chamber? Did you monitor loss with and without oxidant?
P8, L17 – there appears to be an extra or missing word: ‘are and dimers’
P8, L31 – assuming gas-particle equilibrium? (missing word).
P9, L10 – Not very clear what equation you’re mentioning here.
P9, L13 – There are many ways to average here, presumably this is weighted by total mass fraction? Should be specified
P10, L34 – I don’t believe this statement is justified. You have one ‘aged’ experiment and if error bars are similar to the one shown, they might well overlap. How is ‘significantly higher’ defined? Variation in particle loading, diameters and other properties can lead to changes in observed evaporation as well. Similarly, should not compare thermograms across studies (e.g. P11, L6).
P11, L21 – Is there evidence of thermal decomposition of dimers? Did you try LC/MS analysis on thermally treated aerosol?
P12, L2 – I think you are fitting this alpha value, but it seems like it is assumed. This section needs to be made more clear and the actual fit approach/uncertainty discussed.
P12, L24 – Why should volatility distribution and alpha be linked? One is thermodynamics and the other kinetics?
P13, L1-13 – I find this section unconvincing. Given the lack of very low concentration data, it’s unclear how well constrained bins down to 0.01 ug /m3 are constrained by this dilution data. Could the same fits be achieved using a narrower range of volatility? This seems like it might be over-fitting since you’re using 4 data points to fit 6 parameters (or maybe 5). Also, the effects of walls is not mentioned at all. Is the aerosol concentration measured at equilibrium used? This will reflect the loss to your secondary chamber wall, which may not be a good representation of the conditions dictating partitioning of the suspended particles (or else wouldn’t things keep evaporating away?)