The T-bird is a great idea and the ability to make measurements down low where an aircraft cannot operate opens up great possibilities. I am not an aerosol person, but I have a couple of comments about the aerosol portion of the paper.

• I would think a more apple-to-apple comparison would have been nice. Since the instruments in the T-bird are not large, having those in the aircraft in addition to what they call the standard instruments would have made for a more apt comparison, in my opinion. 
• I think a good use for the T-bird could be to porpoise the platform up and down to generate a profile of the conditions below the aircraft

I think I would adjust the title of the paper. There is very little in here about the wind and turbulence part of the platform instrument suite. I am not sure referencing it need to be in the title. If it does, then it shouldn't be listed before aerosol properties which is what the paper is about. I will be interested in seeing the follow on to this paper about the winds and turbulence data. For the little that it talks about it, I do have some questions.

• What Aventech 5-hole probe model are you using. They list nothing on their website that has a response at 100 Hz. Are you using their pressure transducers? Is this an AIMMS instrument. Definitely need more info here and description. At best their stuff updates at 40 Hz and even then their frequency response tails off when you get to 10 hz or so from my experience.
• I haven't seen any other listing of a Rosemount 102 deiced TAT sensor that updates at 100 hz, can you provide some more info. Even if you want to sample that fast, it generally only responds at most at a couple of hertz and much slower than the non-deiced version. 

All in all I think this is a good introduction to the T-bird but some more details would be nice to see. I am also not an aerosol person so they may have way more to say than I since this turned out to be an aerosol paper. I don't see any showstoppers here but some more fleshed out info would be nice. 

The paper is in excellent shape, and I have only minor comments and suggestions in rather random order:

1) “nest” was not described, please add a sentence

2) please provide temperature control range/ stability in T-BIRD when used, and range as tested/flown.

3) I suggest that you cut data/discussion of POPS/SMPS comparison when POPS was not within operational parameters; this does not relfect a properly operating instrument, and so is not relevant. 

4)Was the  SMPS geometric diameter for Protector comparison only calculated from 10-300 nm diameter range? Please specify

5) please address apparent inconsistency between POPS/SMPS concentrations > 300 nm in figure 6b

6) Lin e103 - it looks like a calculation error on the total flow into the isokinetic inlet (0.37 cm diameter at 60 m/s->~40 lpm)

7) I suggest combining figure 7 and 8 so that they can be seen together.

8) Line 405 - the BC mass concentrations provide no information about the BC’s microphysical mixing state (as suggested by the use of the term “internally mixed”). Perhaps you mean to suggest that the FT airmass is apparently homogeneous?

9) For context: is the instrument payload of TBIRD imagined to be adjustable for different missions, or is it fixed effectively permanently?

10) The section describing the results shown in figure 10 was a bit confusing, and would benefit from careful editing. For the figure, panel C, I wonder why the 100m TBIRD point is not associated with sampling error bars, and why the associated POLAR-6 point at ~150m appears to show enhanced flux (based on simply looking at Ramanelli and Zardi, AMT 2004 figure 2 to establish expectations…). Is this a cause for concern?

11) some information about the relative scale of TBIRD motion (other than directly forward) to wind/turbulence measurement would be usefule for context/uncertainty evaluation. 

12) Can you use data from TBIRD in the climb/descent portions of the flights? If data collection is limited to level legs (even if just for aerosol concentrations/size), that is an important limitation to mention.