Dear Authors,

I have looked through your revised manuscript and your replies to the referees and I am recommending publication once the following minor comments have been addressed:

i) the description of the zero air cylinder (grade, subsequent scrubbing or not) should be included in the manuscript; suggest adding these details to section 3.1
ii) move '(Fig 1, no 2)' on line 122 to line 123 after 'detection cell'
iii) line 129: should be '(fig 1, no 4)'
iv) move line 486 to after the new text that was inserted
v) I don't think the second figure in figure 2 satisfies referee 3's second comment. I think they are requesting a schematic of the timings of the instrument - eg relative to a 't0' when does the laser fire..when is the PMT is switched on.. when is the fluorescence collected..
vi) For Fig. 8 caption suggest : 'the relative 1 minute precision of GANDALF is shown for PARADE-2011 as a function of NO2 mixing ratios. The relative precision is calculated from randomly selected PMT signals during a calibration period'