Dear authors,

thank you for your detailed replies to the reviewer comments and also for submission of this manuscript to ACP. Especially the direct observation of the enol form of methylglyoxal is an important finding.

Below please find some minor typographical comments as well as some comments about your interpretation of the Yu et al. (cited in your manuscript) results that should be quick to address.

If you have any questions please do not hesitate to contact me.

Thanks again for submitting this interesting manuscript to ACP!

Best Regards,

Frank Keutsch




p.1 line 10 I think it should be “indicating that XAS in the” rather than “indicating that the XAS in the”

p.2 line 35, for ammonia please also cite Galloway et al. 2009

P.2 line 41 I think this should be “has a lower value” and not “has lower value”

p. 3. Line 61-62 Can a statement be made on the purity of the glyoxal and methylglyoxal solutions?

P.3 line 76 Perhaps better “pumped through the liquid cell with a flow rate …”

p. 4 Table 1. Could the authors please double check the solubility of NaCl. It seems a little high, as I thought it was around 36g of NaCl per 100g of water with little temperature dependence.

p. 5 line 96. Perhaps better “The C K-edge spectra of pure water were subtracted from the C K-edge spectra of the samples to …”

p.9 figure 3. What are the energies for the oligomeric C-O-C acetal. This could have a high enough concentration for glyoxal to be observed see figure S9 in Yu et al. 2011 especially as those were only 1M solutions?

P.10 line 182-183. Regarding the absorption edge energy increase with decreasing concentration of glyoxal (2M to 1M) and with addition of salt. Could this be explained by a decrease of the oligomer to monomer ratio with decreasing glyoxal concentration and increasing salt concentration as hypothesized by Yu et al. 2011? I think this is consistent with the results presented here?

P. 15 line 270 -271 p. 16 line 299-300. Yu et al. did not conclude that glyoxal exists entirely in its fully hydrated form, as they were able to observe aldehyde 1H NMR signals. The NMR intensities of the aldehydic hydrogen was very low but the authors were able to show that upon addition of salts the dihydrate to monohydrate signal increased, see Table 1 in their paper.

p. 16 line 288, please add “to the sensitivity of our measurements”

Supplement p1. Line 28. Should this be aldehydic rather than ketonic for glyoxal, as it has only aldehyde groups and no keto groups? What is the purity of the solution. Glyoxal has a very high Henry’s law constant, could contaminations of higher vapor pressure glyoxylic or glycolic acid cause the feature at 288.7eV?