Minor issues:
Line 258 – ‘those’ should read ‘thus’
Line 418 – in these data modern carbon is not ‘more significant’ than fossil carbon, it is 35% at most according to the preceding text.
Table 1 and 2 – OOA-REG is included as a factor, but never mentioned in the text. Not clear what that is.
Figure 1 – make site schematic readable – too small. Regarding the discussion of this in the context of gradients, I would say the BC and NOx wind roses suggest that you are not so much seeing the direct emission/roadway signature as a regional signature, or that the on-average higher windspeeds when the wind is from the roadway is counterbalanced by more stagnant conditions when wind is from other directions.
Figures 2 and 7 – bar charts of high-traffic and all data should be labeled (panel ID)
Mislabeled/swapped figures 8/9 – Modern/fossil figure is called Fig. 8 in text but labeled as Fig. 9; vice versa for HOA/BC figure.
Figure S12 is repeated as S14 in the SI.