|The authors seem to have responded to both sets of comments and questions posed by the two reviewers. I have specific concerns on a few of the responses (see below) but should note that most of my concerns are centered around the description of the methods (and not the results). I am generally okay with the response and changes made to the manuscript and recommend publication of this paper in GMD after the authors have had a chance to review my additional concerns below. |
1 Reviewer 1, point 1:
a. Thanks for providing additional details on the PTR data but I still think the paper would benefit from a brief description of the PTR measurements, speciation information, and how those species were aggregated for use in the model, including the rationale (e.g., reduced-form?) and limitations (e.g., highly lumped?) of this approach. This detail is limiting comprehension of the modeling sections in 2.2 and 2.3 and could be done in the SI if there are issues with space.
b. Can you show how the measurements were used to calculate the OH reaction rate constant? Is there a citation for this calculation?
2. Reviewer 1, point 2: I still maintain that determining SVOC and IVOC emissions from POA emissions (that are susceptible to vagaries of partitioning) is a poor choice. It should be fine for this work but needs to be discussed in light of arguments made in earlier work, e.g., Lu et al. (2018; https://doi.org/10.5194/acp-18-17637-2018).
3. Why is the sum of the molar yields in Table 1 for IVOCs larger than 1?
4. Reviewer 1, point 2: If I understand this correctly, the model assumes that there is only a single IVOC-like precursor that reacts with OH to form biomass burning SOA and that all other precursors (e.g., single-ring aromatics) are ignored. When the IVOC emissions are determined and adjusted to remove other more traditional SOA precursors in CAMx, a few assumptions are being made but none are explained. It assumes that benzene, toluene, and xylenes are the only other traditional SOA precursors. What about larger aromatics, isoprene, monoterpenes, and the likes? It assumes that the yields of the now-removed traditional SOA precursors are identical to the IVOC-like SOA precursor that is being added. On a related note, why weren’t the traditional precursors explicitly accounted for in the box model so parameters specific to the IVOC-like SOA precursor could be directly determined and applied in CAMx?
5. Reviewer 1, point 8: Sinha et al. (2018) heated the aerosol and heating itself could change the mass accommodation coefficient through changes in the viscosity/bulk diffusion coefficient. So, I don’t see that study as directly refuting the findings from Cappa and Akherati that used isothermal dilution to probe changes in POA.
6. Reviewer 1, point 9: The different k_w seem to scale inversely with chamber size. This fact could be mentioned.
7. Reviewer 1, point 11: See Figure 4 and Figure S10 in Krechmer et al. (2016).