|In the revised manuscript, the authors have extended some of their discussions. I suggest some minor revisions, after which I recommend publication.|
1# Table S2: Please report the particle size information for the bulk OA as well, since the particle size is an important parameter for the evaporation kinetic model. In Table S2, the SOA size diameter peak in 2018 data set is 600 mm and 380 mm in 2017 data set. Any explanation for such big difference in SOA size distribution between two years?
#2. Please clarify the plug flow residence time at what temperature? I guess it is at room temperature.
#3. Page5, L-6: Please provide the C* bin range and rationale for choosing that range.
#4. Page 6-7: There are some discussions on volatility comparison between this study and other cities based on TD evaporation data, which are not well supported. I would discourage such comparison. For example, Page-6 “28% of particulate organics evaporated at 50°C, a fraction larger than that observed 5 in Shenzhen (~10%) (Cao et al., 2018), Centreville and Raleigh (Kostenidou et al., 2018;Saha et al., 2017) and Athens (Louvaris et al., 2017), yet similar to the observations in Paris (Paciga et al., 2016), suggesting that OA contained relatively high volatility compounds in Beijing compare to most other sites.”
Since we all know the observed evaporations in TD depend on many experiment specific parameters and thus not a robust measure of volatility, I would suggest to move such discussions in the Sec. 3.3 (Volatility distribution of OA factors) and make comparisons based on the derived volatility distributions.
#5. PMF of TD data: I understand the authors performed the PMF for the MS (ambient) and MS (ambient +TD). I assume here MS (ambient +TD) includes all TD data at all the operating TD temperatures. It would be helpful if they can extend the discussion about how they obtained the PMF factors at different TD temperatures.
#6. Figure 7: In my sense, this is a key figure (summary plot) of this paper. I would recommend extending this figure into three panels showing total OA, SOA, and POA from experimental and WRF-simulated results. In addition to OA mass fraction, I would suggest including absolute OA concentrations at different volatility bins, e.g., the left y-axis can show absolute OA concentration (COA), and the right y-axis can show the OA mass fraction.
#7. The volatility of “BC containing POA (C* 0.69 ug/m3)” and “ambient POA (C* = 0.37 ug/m3)” are substantially different. How does the volatility of BC containing POA compare with the volatility of ambient HOA? I think some related discussion would be helpful for the readers.
#8. The term “ambient OA” and “BC-containing OA” sounds confusing sometimes. All the measured OA are ambient. I think an appropriate term would be “BC-containing ambient OA”. I would suggest to clarify it.