1. In this paper, the SOA was produced from the photooxidation of various alkanes in the absence of NOx. As authors described, alkanes are a major part of anthropogenic VOC emissions.  This means that the atmospheric oxidation of alkanes is more liked processed in the presence of NOx.  In particular, urban air environments are typically in the high NOx region.  Authors need to discuss about the potential impact of NOx on HOM productions and alkanes SOA yields.
2. Lines 75-80. Is there a specific reason why RH was set to 22%.
3. Line 89-92. Please describe the difference between the measured and modelled OH exposure more quantitatively. In a typical experiment, how big of a difference would this be in calculated precursor consumption values?
4. Line 113-115. Were wall losses to the PAM and/or tubing corrected for? If not, how can the measured SOA mass concentrations, and thus yields, be trusted if HOM condensation to the wall is a significant issue? Is it possible to lower the oxidant concentrations in the PAM and reduce the number of instruments used at a time in order to reduce HOM yield and sample flow to improve the HOM measurements? If HOMs would be significantly lost regardless of sample flow, how can any particle mass measurements be trusted?
5. Lines 148-155 on page 6 and page 7. Please explain why cycloalkanes had the highest SOA yields.
6. Line 151 on page 7. Authors mentioned that SOA mass concentration were at atmospherically relevant levels (< 20 µg/m3) for all precursors. All experiments were under controlled environments and not relevance to atmospheric conditions. The description about SOA mass concentrations is not appropriate.
7. Lines 174-179. Please clarify the seed types and their role on SOA yields. In the absence of inorganic seed, SOA formation can be retarded but its yield is not affected. The organic seed aerosol can increase SOA yields.  
8. Line 201-206. Authors need better explanation on why this study is not expected to be in the range of ambient SOA studies. Even if they include some biogenic SOA with lower H/C ratios, wouldn’t that only lower the bottom of the range without having an impact on the upper limit of the range? What were the oxidation conditions (i.e NOx and oxidant concentration) of the vehicle exhaust studies? Are they comparable with this study?
9. Figure 3. Again, environmental conditions of alkane SOA formation of this study is very different from ambient air. Authors need to explain why alkane SOA of this study is comparable with SOA in ambient air.
10. Figure 4. Overall, mechanistic explanations for different HOM yields are weak. For example, among oxygenated VOC, why did different VOCs yield different HOM productions?
11. Figure 5. The reviewer cannot understand the role of Figure 5 to explain the formation of HOMs. Naturally, higher concentrations of precursor with a given concentration of oxidants will produce less oxidized products and vice versa.
12. Line 227-231. HOMs are discussed in the introduction in relation to autoxidation (line 46). Typically, the RO radical that initiates the alkane autoxidation process is formed in the reaction with NO. Discuss the significance of the RO2 + RO2 reaction in no NOx conditions.
13. Line 231-235. It would be beneficial to the reader to provide a mechanism where oxidation is initiated and proceeds through the major reactions that are expected to occur under these conditions which ultimately lead to HOM (>6 Oxygen atoms) identified in Figs. A2-A8.
14. What is the impact of heterogeneous chemistry on SOA yields?
15. Appendix A. There is a dilution flow (10 LPM).  What is the impact of dilution of air stream on SOA production?  Some SOA products can be off-gassing from the aerosol.  Please clarify this issue.
16. Figures A2-A8. What is the signal to noise (S/N) ratio?  In general, the signal should be 3 times higher than the noise. Were elemental compositions marked on Figures statistically significant.

Please find my detailed review report in the attached pdf.