Dear authors. Congratulations on such a great manuscript. I spotted a few minor things in the text that you may want to correct before the final version appears in ACP.

Page 2, line 15: to be dependent -> to depend
Page 6, lines 3-4: delete [,because of its intermediately volatile nature] (the reason vanillin does not stay in the particle has to do with its lower tendency to polymerize compared to glyoxal, not with its volatility)
Page 6, line 16: before -> above
Page 9, line 12: even present -> even if they were present (and also sulfate -> sulfates)
Page 10, line 10: there is no reason to introduce abbreviation ODEs if it is only used once. I would check the text for occurrence of other abbreviations that are only used one time, and remove them.
Page 23, line 18: cloud -> cloud water
Page 26: if you recorded UVVIS spectra of the solutions after A and B experiments, would it be possible to include the absorption spectra in the supporting information? For example, a figure showing absorption spectrum of the initial solution of vanillin, spectrum of its H2O2+UV oxidation products, and spectrum of its UV photolysis products in the same graph? If you did not record such spectra feel free to ignore this suggestion (I do not suggest that you should do additional experiments).
Page 29, line 31: fix H2O2 (subscripts needed)
Page 29, line 34: fix NO3- (3 should be subscript, not superscript)
Figure captions: your captions on page 35 and under the figures do not always match. Please make sure they are the same.

Best regards,
Sergey Nizkorodov.