The authors have done a fine job responding to the first round of review. Most items are adequately addressed. I recommend the manuscript be published in ACP after additional consideration of a few items listed below. Further review is not needed.
Cross-sections for product quantification: To extend the impact the these observations, it would be useful to include the absolute IR cross-sections used to quantify the 2-MB and the oxidation products in this work. This could be done in a number of ways. For example, the Y-axes of Figure S6 could be shown in cross-section units, or a Table of integrated band cross-sections could be included, or single point cross-sections could be given for strong lines (with instrumental optical parameters).
Butane: Still surprised that the small yield of butane can be determined so well (to ~3% uncertainty) using the FTIR in the face of the overlapping bands from other species. Could you provide more insight into this. Perhaps add butane to Figure S9, and show an example spectral fit?
Autoxidation: The products identified (and proposed) by the authors are generally high volatility in nature, and unlikely to be able to account for particle nucleation and/or growth from very small clusters. It has recently been shown that certain autoxidation mechanisms can be quite fast and rapidly lead to low volatility materials which potentially could help explain the rapid onset of particle formation and growth. This question was posed to query the potential role for autoxidation in the formation of the observed SOA. Do the authors have additional ideas for which pathways lead to the SOA?
ROOH: These species are challenging to measure. They can rapidly decompose on various surfaces to other species. The initial questions regarding ROOH were trying to probe whether these species are stable in the employed apparatus and could be quantified by the instrumentation used. Even different instruments of the same type (e.g. PTRMS) can have significantly different efficiencies for decomposing ROOH (see e.g., https://doi.org/10.1002/2014GL061919). In addition, is it possible the lifetime of the ROOH over the glass surface is fairly short?
LN30-32: Suggest replacing ‘diurnal’ with ‘daytime’ here. While technically correct, some readers may interpret ‘diurnal’ to mean ‘over 24 hrs’ not simply ‘when the sun is out’. Also, it may be simpler not to mention O3 chemistry?
LN65-67: I understand this is historically how these observations have been reported. But, why not present 1-nm integrated cross-sections? Are these not be more useful? For many molecules (including this one) there probably is very little difference between single-point UV absorption cross-sections, and 1-nm integrated cross-sections, but for some species, those with highly structured cross-sections, this may not be the case. In addition, to understand what is meant by ‘single point absorption cross-sections’, one needs additional information regarding spectrometer optical resolution and data collection resolution—parameters which should be added to the manuscript.
Table S4: This addition is great. Can you specify what is represented by the uncertainties written here (+- numbers). Is this total uncertainty, or just regression uncertainty? One or two sigma?