This manuscript “High-resolution analyses of concentrations and sizes of black carbon particles deposited on northwest Greenland over the past 350 years – Part 2: Seasonal and temporal trends in black carbon originated from fossil fuel combustion and biomass burning” submitted by Goto-Azuma et al., provided monthly resolved 350-year records of concentrations and size distributions of black carbon (BC) particles from an ice core that was drilled in the northwest Greenland Ice Sheet. The authors discussed sources of BC particles originated from biomass burning and fossil fuel combustion based on backward trajectory analyses, and estimated the potential albedo reductions. The main advantage of this work concerns with the extremely high resolution records from the updated CFA system that was consisted of single-particle soot photometer and a high-efficiency nebulizer. As a result, the annual layer of the SIGMA-D ice core can be reasonably divided into 12 months, which provides a chance to decipher the monthly variations of the ice core BC particles that have been impossible before. However, these monthly-averages depend on assumptions, such as evenly month distribution of precipitation, that can be hardly met. Therefore, uncertainties due to the assumptions should be examined carefully before a solid conclusion can be reached.

Other minor comments:

Lines 196-197: Please give pieces of evidence that contribution of dry deposition can be ignored.

Section 3.2. Is there possibility that corresponding of the seasonal Na and BC peaks (Fig. 10) can be disturbed by signal dispersion in the CFA system?

Figure 3: The extremely high peak around 1710 needs to be explained.

Line 257: “GriIS” →“GrIS”

Figure 6: Please indicate the meaning of the X axis.

Line 291: “Of the two size parameters, mBC is easier to calculate than MMD; hence, it can be used to investigate changes with high temporal resolution”. This is not a good reason to choose mBC.

Lines 300-301: An objective statistical method should be applied to reach the results.

Figure 10: The time range of Figure 10C is not 1915-2003.

The manuscript entitled

High-resolution analyses of concentrations and sizes of black carbon particles deposited on northwest Greenland over the past 350 years - Part 2: Seasonal and temporal trends in black carbon originated from fossil fuel combustion and biomass burning 

by Goto-Azuma et al., 

presents data of concentrations and size distributions of refractory black carbon (rBC) particles from an ice core in the Arctic based on a novel CFA system equipped with a more efficient nebulisation system used to fed a wide-range SP2 system, used for the rBC determination. Overall the system provide an unprecedented temporal resolution and extend the size range of rBC determination.

The manuscript (labelled Part2) discusses trends and sources of BC particles, presents a back trajectory analysis, the identification of potential sources  (biomass burning and fossil fuel combustion) and an estimation of potential albedo reductions.  The results presented in this manuscript rely strongly on the technical details presented in Part 1 paper. I recommend Part2 to be finalised after the acceptance of Part1. 

Major points

The assumptions used to obtain the monthly resolution looks artificial because has been obtained by assuming an equally spaced monthly time step. This imply the assumption of a constant monthly dry and wet deposition rate which is not the case in particular considering the 350 years time span investigated. Furthermore it is not clear how much the signal is blurred by the dispersion in the CFA system. Indeed, the data have a clear and well resolved seasonal signal, which is already a very nice results in my opinion. The sections of the manuscript where the monthly analysis is presented should be revised.

Back Trajectories analysis -  The 1958-2015 timeframe was used for BT calculations. This period is not necessarily representative of the entire 350 years covered by the ice core. Also, monthly precipitation data have been used to weight BT's  which is highly uncertain. Finally, dry deposition processes have been neglected in this analysis. Overall this part of the work is weak.

Minor points:

1-rBC (refractory BC) should be used in place of  BC everywhere in the paper.

2-line 18 - "roles" is vague. "processes" ?

3- line 40  - "Changes in". -->   "Increase of"

4- line 177 - 179 -  Na+ was used for annual layer counting a part cases when this was not possible because of the low signal. Therefore the authors recurred to the standard 18O isotope signal.  Using Na+  is interesting but why 18O was not used if the signal is more clear?  A brief explanation should be given.

5- Figure 6 - the meaning of the x axis is not clear. Also, what happen to the IC contribution at the D4 site for low x values?

6- Figure 8 the normalisation procedure should be briefly described

7- line 284 - why a Gaussian distribution is assumed? usually a log normal distribution is more appropriate.

8-lines 285 -301  how the use of a single MMD or single mBC parameter to describe the entire BC size distribution can be consistent with two very different BC sources ?

9- Figure 10 - What I see in these plots are yearly BC mass concentration trends. Not monthly BC concentration trends.

10-line 351-353.  the BT analysis was inconclusive and should not mentioned further

11- line 366 -  how long the high peaks have really lasted? It is possible to catch strong events shorter than 1 season if 

"the data for a few months after large BC concentration peaks could have been affected" (as affirmed by the authors

at  line 206-207).

This study presents a high-resolution (monthly resolved) black carbon (BC) record covering the past 350 years from an ice core drilled on northwest Greenland. There has been much focus on BC during the past decades because of its impact on the Earth’s radiation budget. However, BC in snow and ice can be analyzed with several different methods capturing different particle sizes, thus, there is a problem comparing the records and making conclusions about spatial and temporal variations.

The BC record presented in this paper is based on an improvement of a continuous flow analysis (CFA) system providing both BC particle size and mass/number concentrations. This new method is described in another submitted paper by the first author. The particle size analysis makes it possible to distinguish the impact from anthropogenic and biomass burning. As a results it has now been possible to more accurately pinpoint the timing of anthropogenic impact to this part of Greenland than any of the previous studies of BC in ice core from Greenland which have only based their results on mass concentrations. This is a new and important finding. In addition, the results show a shift in seasonality of the annual concentration peak of BC related to the type of impact. A backward trajectory analysis suggests North America as the main source, in agreement with similar ice core-based studies from Greenland.

The paper is generally well written, and the figures are illustrative. However, I consider the lack of incorporation of the accumulation record in the discussion of the temporal variability of the BC a problem. The accumulation variability will have a direct impact on the BC transport and deposition and I recommend that this is included in the paper.

Overall, this is an important study that clearly demonstrates how ice cores and the continuous work in development of different analytical methods can help in understanding the long-range transport of BC to the Arctic.

Specific comments

Line 182-187: I appreciate the careful explanation of the dating, but nature is complex. To have distinct seasonal variability there must be precipitation all year around and the lack of such information in the papers makes it difficult to fully assess the reliability of this statement. Is there any AWS nearby? Maybe this information is included in one of the previous papers, but I think that this must be included in this manuscript since one of the main conclusions is the change of seasonality in the BC input depending on biomass burning or anthropogenic sources.

Line 196: The study is assuming only wet deposition of BC. What is that based on?

Line 303. In this paragraph it becomes evident that the temporal variability of accumulation is not included in the discussion in this paper. As already mentioned, I think this is such a fundamental part of the interpretation of the BC record that it cannot be left out.

With the mean annual temperature of -23ºC I assume that there are not any melt layers that is disturbing the stratigraphy but there could still be ice lenses created by solar radiation during the summer. Is that the case here?