Please see comments in attached pdf file. 

“Quiet New Particle Formation is a significant aerosol source in the Amazon boundary layer” by Meller et al. describes a phenomenon that the authors associate with “Quiet New Particle Formation (NPF).” Quiet NPF was first described by Kulmala and colleagues and refers to NPF and growth events that are almost undetected due to their low number concentrations but are nonetheless important as they are believed to occur on days that were previously assigned as non-NPF event days. This is an interesting study from an important field site. While I appreciate the brevity of this manuscript, I feel that the authors have left out some key details. Please see the following comments (specific questions are preceded by line number).

One major question I had upon reading this manuscript was whether the authors are assuming that quiet NPF is occurring every day that would normally be assigned as a non-event day. Figure 1 shows average size distributions, and in several places the analysis suggest that non-event days are significant and relevant to quiet NPF, but there is never anything said directly about this. Relating to this are comments 1-5:

1. 64: This seems like a critical point to bring up the assumption that quiet NPF is NOT observed by viewing individual days, and that for the remainder of the manuscript the assumption is that this phenomenon is happening every day that a classical event is not observed. If this is not a correct assumption, then I am missing an important point of this paper and that, too, should be addressed.
2. 88: If my point for line 64 is made clear, then it will be understandable why this potential temperature analysis is being performed on all non-event days. As it is currently written, it seems to suggest that all non-event days are relevant to quiet NPF. I would argue that this point needs to be clearer here.
3. 102: It would be helpful to the reader to remind them that this growth rate analysis is being performed on the average normalized size distribution.
4. 121: This line is the clearest indication thus far that the average properties of quiet NPF are being uniformly applied to all non-event days. But is it true that ALL non-event days have quiet NPF? What if this were not the case? It seems, to me, that average properties can be used for analysis of such things as growth rates, but individual days can be analyzed for whether or no quiet NPF could have occurred.
5. 148: This statement requires the assumption that quiet NPF occurs on all days that are classified as non-events. This assumption again needs to be stated clearly and either be a caveat or justification needs to be provided.

Other questions are as follows:

6.    126: I am confused about what the dN/dt term is. The only description is that it “reflects the temporal distribution of the particle number,”    however it appears to be plotted together with coagulation and growth. This needs to be clarified in the manuscript.

7.    130: Is the coagulation term really just one pixel in amplitude in Figure 3? Why is it so consistent across the entire day?