Dear authors,

I'm happy to accept your manuscript for publication in Atmospherics Chemistry and Physics. There are a few minor technical errors and a couple comments you should consider before uploading the final files. - See list below.

Best regards
Barbara Ervens

-----------------------------
p. 2, l. 3: ‘organisms’ misspelled
p. 4, l. 30; and caption of Figure 2: use degree symbol (ASCII: ‘Alt’ 248), not superscript zero
p. 5, l. 2: ‘pressure’ misspelled
p. 5, l. 4: ‘on each of the size fractions’ --> ‘in each of the size fractions’
p. 5, l. 17: filters --> filter
p. 5, l. 26, and p. 11, l. 23: Sulphur --> sulfur (in order to be consistent with the rest of the manuscript)
p. 8, l. 19: Equation 2 shows total sulfate [SO42-] not total d34S. Obviously the two are related but that should be made clearer here.
p. 11, l. 13: section 45 --> Section 4.5
p. 12, l. 18: ‘…two periods that this is clearly…’ --> ‘…two periods where (or ‘in which’) this is clearly…’
Table 2, caption (l. 2): aerosols --> aerosol
Figure 2 (caption), l. 4: ‘temperatures’ and ‘not’ misspelled
Figure 3: The figure is very blurry and it is hard to read the numbers in the legend.
Figure 6, y axis: SO42-, not SO2-4
Figure 6, Caption, l. 3: ‘those’ misspelled