Dear Silvia,

Apologies for the processing of your manuscript. It is now in good shape for publication, after the following outstanding comments have been addressed:

Impactor artefact. You respond to Referee 1’s query regarding impactor artefacts in your response letter, but do not reflect their concern in the revised manuscript. Could you please add a sentence to say that 15% lower sulphate values may indicate some loss to bounce and also state that positive artefacts due to adsorption of gaseous organic species onto impaction substrates, backed up with a suitable reference.

P8L13. Ammonia was measured at BO and the data are presented in Sullivan et al. (2015); nitric acid was not measured at BO.

Reviewer 1 suggested you add detail on the boundary layer heights during the stagnant periods. You have done so in the response to the reviewer, but not in the revised manuscript.

You need to discuss uncertainties in the ALWC calculation. There is ample evidence that mixed aerosol particles containing nitrates and sulphates often do not effloresce under ambient conditions. For example, the ISORROPIA-2 algorithm, an alternative to E-AIM, would derive very different ALWC, depending on whether you allow the aerosol to exist in a metastable state.

Section 2.5. Why would the temperature variations during a 12-hour period have affected the ALWC calculation if a constant temperature of 298.15 was used throughout? How was sodium derived with the HR-TOF-AMS? This is far from trivial.

P16L31. I do not think that you can conclude with any certainty that SIA formation is mediated by the presence of aerosol liquid water, because ALWC is calculated from the SIA concentration and the argument is therefore, unlike for SOA, circular.

In the response to Reviewer 1’s comment to the original P11L25 you argue that at a loss of correlation between WSOC and sulphate is expected in the absence of photochemical production. In response to Reviewer 2’s comment to the original section you state that multi-day air mass history is important in controlling the concentrations of both components. These two responses appear to contradict each other. If the shared air mass history over days controls the concentrations of both compounds, they should remain correlated during night. Therefore, isn’t it more likely that at BO there is a local source of either WSOC or sulphate destroying the correlation at night?



The English of the new text is somewhat lacking compared with the original parts of the manuscript. Please correct the following mistakes:

P2L20: The double parentheses are not very elegant. In fact you don’t need to introduce the acronym WINC at all here as it is not used again in the abstract.

P3L3: “generally suffer from poor sensitivity …”

P3L4: “… analysis of coarse particle (>2.5 µm) chemical composition.”

P3L27 “… of the sum of regional background, urban contribution given by the sources inside the agglomeration, and road traffic for roadside sites.”

P4L12 “… SPC can be located downwind of BO”

P4L30 “An aliquot of each sample was analysed … was acidified … which was decomposed. … was obtained.”

P6L24 “… easterly breezes dominated during the late afternoon”

P6L24 “… persisting all day”

P13L36: Uses “raises” or “improves” rather than “rises”.

P6L32: “and in the morning hours”

P7L17 “fraction to the total”

P14L19 “contribution to the total variance”

P16L26. This sentence does not read right in its present form. Do you mean “well mixed, indicates that”? However, in this case I would question that photochemical SIA and SOA can indicate something. Do you mean the “Large concentrations of photochemical SIA and SOA …”? Or do you mean “The photochemical SIA and SOA occur at … SPC, which is particularly … well mixed. This indicates that a …”

P16L35. I am unsure what you meant by “tilted horizontally across the Valley”. With respect to the limitations of the Lenschow model it may be worth re-iterating here also that NH3 emissions (and concentrations) are larger in agricultural than in urban regions.

The titles of some of the references are written in capitals; please correct.

Fig. 3. Please label the vertical axis according to the entity it displays, not just its unit, as you have done elsewhere.

Table 1. Please harmonise the number of decimal places and/or significant figures with which you present the data. E.g. chloride is given as 0.043 and 0.05.

Table 2. Similarly here some trailing zeros appear to be missing to harmonize to two decimal places.

With best wishes,

Eiko Nemitz.