General comments

Could the authors explain why the measurement was only conducted in winter season. The higher ozone concentrations and stronger light intensity could alternate the formation of particles. In addition, the wind direction and seasonal sources could be also contributed to the formation of the BC fractions.

Even the manuscript is satisfactory most presentation of the points, the language should be further polished by professional. Few non-scientific terms are being used.

More specific comments:

Line 243: Suggest change the presentation in format speech.

Line 267: Specify the timeline for rush hours

Line 275-284: The numbers and percentages should be given with the SD. Also check them out in the entire manuscript.

Line 428: It is not appropriate to us a non-scientific term. Please specify how is “big” defined.

Line 441: Do you mean the food ingredients? Replace “itself”

Line 447: Please specify “some” here. If that is the case, how could this inference the accuracy of the results of this study.

Line 488: Would SOR be changed while the RH is further lower? There is no comparison among a wider range of RHs.

Why was no OH radical correlation determined when the secondary formation is discussed?  

Line 619: Pleas use 24-h time scale.

Line 703: November 3^rd to 5^th

Line 718: SD?

Line 764: Replace “of course”

Line 766: how do you define the contributions were low? Please specify.

Line 767: the lowest

This manuscript by Cui et al. investigate the submicron refractory black-carbon containing (rBCc) particle sin Shanghai, via a combination of laser-only Aerodyne SP-AMS and a HR-AMS. The former allowed the determination of rBC-containing particles exclusively and the latter was for total submicron particles. Chemical properties, sources as well as derived size-resolved hygroscopicity of the rBCc were characterized in great details. The paper is overall very comprehensive, with in-depth analyses and discussions of the rBCc properties. This reviewer finds the major findings of this work are also of importance to advance our current understanding on rBCc properties as well as its environmental impacts, in particular, the primary sources and secondary ageing processes, hygroscopicity of the coating materials. I recommend a minor revision before its acceptance, my specific comments are listed below:

• PMF analysis resolved 6 factors that is well supported by relevant interpretation. I suggest to provide the mass spectra of 5 factors and 7 factors for reference (probably in the supplement) and support the best choice of 6 factors.
• ALWC calculation in Figure 3 and Figure S4 is less clear. I suggest briefly describe the E-AIM model and its procedures to obtain ALWC.
• The fact that the BBOA was resolved for rBCc but not in NR-PM1 OA, requires a bit more explanation in 346-358.
• It is interesting to find that only a small portion of sulfate was coated on rBC cores while the fraction of coated nitrate on rBC was relatively large. Any educated explanation? Since sulfate had lower volatility than nitrate, this is a bit surprising.
• Is it possible to provide the uncertainties of the regressed parameters for the expression of krBCc and kCT?