|The authors have satisfactorily addressed most of my comments. I only have a few minor additional remarks that could be addressed in a revised manuscript. Line numbers refer to the new manuscript without annotations. |
l. 30: “Such a SOA formation could have a significant influence on tropospheric HOx chemistry and NO2 photolysis, which in turn affect O3.”
Comment: The meaning of this sentence is not clear. Are you suggesting that due to the increased SOA burden, photolysis rates in the atmosphere are influenced? As mentioned in my previous report, the total OH (and HO2) budgets are likely not largely influenced by the reactions in the aqueous phase. Just the presence of clouds suppresses the formation of OH in the gas phase.
l. 116: “The dehydration of many gem-diols is slower than the typical lifetime of cloud droplets “
Comment: The typical lifetime of cloud droplets is on the order of several minutes. However, in the cited literature (Doussin and Monod, 2013), dehydration constants on the order of k(dehydr) = 0.0015 – 0.025 s^-1 are listed which yields a half life of gem diols of ~30 - 460 s (= ln 2 / k(dehydr)). Thus, I do not think that it can be generalized that gem diols do not dehydrate in cloud droplets.
l. 160: “The formation of oligomers within cloud droplets is known to be a source of in-cloud SOA formation”
Comment: I think that the authors misunderstand the difference between oligomers and cloud SOA. I agree that SOA formation in clouds may be an efficient SOA source. However, this SOA is mostly not composed of oligomers.
Tan et al., 2009 and others discussed that SOA formation in clouds does not lead to oligomers but can be largely explained by the oxidation of small organics (e.g. glyoxal) by OH leading to oxalic acid and other carboxylic acids.
While in the study by Lin et al., (2012) the same reactive uptake coefficients for aerosol and clouds were used (in accordance with an earlier global model study), these authors also state “Furthermore, the same uptake coefficient for both cloud droplets and aqueous aerosols cannot account for the differences in the chemistry of carbonyl compounds between cloud water and aerosol water (Lim et al., 2010; Ervens and
Thus, they are aware that different chemical pathways exist in cloud and aerosol but could not account for it back then due to the lack of appropriate reaction parameters.
Therefore, I suggest to either remove the introductory sentence of this section or to reword it to
“The formation of oligomers within the atmospheric aqueous phase is known to be a source of SOA.”
l. 202: “In general, the photolysis of organic compounds competes with the other oxidation pathways (see Sect. 2.5) and is a major source of OH. In Rosanka et al. (2020a), the photolysis of OVOCs is estimated to be more than four time higher than the photolysis of H2O2.”
Comment: 1) This reads as if all organics can act as OH source. Please specify that only organic peroxides are photolysed.
Comment: 2) Please add a reference to an experimental study that demonstrates the much higher photolysis rate of organics as compared to H2O2.
Comment: 3) Typo: it should be ‘times’ not ‘time’ in the last sentence.