|The manuscript has been improved for almost all the items that were critically highlighted by reviewers.|
The heterogeneity of the modelling approaches used to reproduce PNC concentrations in the different cities remains a limit, but is now properly commented and discussed by the authors.
The paper can be published after minor revision and technical corrections.
Page 4, line 34:
The reference to TRANSPHORM web site “(ww.transphorm.eu)” needs a correction.
Page 7, Table 1:
Reference stile in Athens column “Petzold et al. (2010) and (Lee et al, 2010).” should be made uniform.
Page 8, lines 8-9:
It would be better to explicitly specify which models include emissions from stationary sources and residential heating, as it is specified in the previous text lines for other sources.
Page 8, lines 22-24:
The sentence “For obtaining an improvement…” causes the following question: the use of local data for Oslo, London and Rotterdam was not necessary because LOTOS-EUROS provided better results for those cities, or this choice only depended on the local modelers approach and choice?
Page 10, lines 2-4:
This sentences contain a repetition and can be simplified/shortened.
Page 10, lines 4-6:
Why emission factors for passenger cars are not specified and commented? Only heavy and light-duty vehicles emission factors are specified.
Page 10, lines 13-14:
The reference to the web site needs to be corrected, probably “indexe” should be “index”.
Page 11, lines 33-38 and Page 12, lines 15-18:
What about possible house heating contribution for Rotterdam and London? No comment is provided about this source at variance with Helsinki and Oslo subsections.
Page 13, lines 30-31:
The reason why model simulation for year 2005 had to be performed is not clear.
Page 21, line 16:
The references stile should be checked.
Page 15, Figure 5 caption:
Does “particles/a” mean particles/year ?
Page 26, line 7:
The number of mentioned sites should turn from three to eight.
Page 26, line 29:
The generic mention to “different settings of the measurements.” Is quite obscure.
Pag 37, lines 13-18:
I would reinforce the sentence on emission inventories explicitly saying that they should be completed for all the source sectors. Some sectors are still missing, not only characterized by low accuracy.
Figures editing should be checked.