|The authors have fairly thoroughly addressed the concerns raised in my previous review. I find the revised manuscript more compelling in terms of the conclusions it draws regarding regional vs. local transport. There are a few relatively minor issues noted below, which should be addressed prior to publication.|
There remain some typos and odd English, As far as I can tell, none of the authors are from an English-speaking institution, so that is understandable, but it might be useful to a service proofread for English. Examples of these issues include:
P1L31: "have been undertaking"
P3L1: "It is meaningful in learning"
P3L25: "street road"
P5L11: "half to several hundred meters away"
P6L29: "Terrestrial plantations"
P7L11-12: "concentrations of ... concentrations"
P7L28: "influenced by multi-factors"
P2L3: "IPCC", though a well-known abbreviation should probably still be defined. Similarly "the IPCC report" is fairly informal. Probably the report itself should just be cited, as opposed to a link to the IPCC website.
P3L24-25: The phrase "(between 3- and 4-ring)" would probably be very confusing to someone lacking knowledge of Beijing's layout. Maybe changed to "(between the 3rd and 4th Ring Road)" or something like that.
P5L26: The authors use WSOC and OC concentrations to determine that aerosol are well mixed, then go on to describe differences in composition at each height. Wouldn't differences in composition imply that the aerosols are indeed not completely well mixed?
P7L5: The increase in concentration is not uniform, it is driven by some of the species (particularly 2-MTs, I think). It is thus a bit odd to discuss it as a whole, since the reasons for it are potentially specific to those species. For instance, if it is 2-MTs (which are almost entirely particle phase) regional transport is likely more dominant, but if it is driven by pinic acid (which partitions based on vapor pressure) then the lower temperatures may be more important.
P7L9: My original suggestions for 2-MT_eryth were not literal, rather I was trying to convey that "eryth" would be a subscript (but indicating this is limited by the textbox into which I enter my report). Using "_eryth" is fairly non-standard, though could be used if the editor is okay with it.
P8L13: I don't know the work of Ding et al., but are the authors certain quantification was performed the same way? A difference in 2-MT or 2-MGA quantification (for which authentic standards are lacking) could bias the ratio. It wouldn't impact the conclusions drawn within this dataset, but it complicates comparisons to other work.
P8L16: I really don't see where in Wang et al. 2005 they suggest C5-ATs are convert to 2-MTs, could the authors please point me toward that claim in that work that they are referencing? Everything I see in there is that C5-ATs are formed from IEPOX (which can also be converted to 2-MTs)
P10L27-28: Given the relatively small fraction of OC accounted for my the SOC tracer apportionment, do the authors have any thoughts or speculation about what the remaining portion may be? Is it all POA, or is it just due to uncertainty in the tracer apportionment? Relatedly, sesquiterpene and monoterpene SOC are presented as roughly similar - that is fairly unusual in most places, with monoterpenes usually dominating. Do the authors think this is real, or just an artifact of the tracer apportionment? Are there any other papers that have observed this?