The work ”AIDA Arctic transport experiment (part 1): simulation of northward transport and aging effect on fundamental black carbon properties ” is well presented.  The temporal evolution of BC and the influence of aging processes on the morphological transformations of BC throughout their atmospheric transport to the Arctic regions are systematically investigated through controlled experimental simulations employing realistic atmospheric parameters in the AIDA simulation chamber. The results demonstrate that aging processes coupled with Arctic-bound atmospheric transport induce transformative modifications to the physicochemical properties of BC and the methodology presented demonstrates the pressing need to bridge the gap between laboratory-based measurements and real-world scenarios. The compositional variability of organic and nitrate coating on BC particles during transport under summer and winter conditions is presented for the first time.

Specific comments

The discrepancy between AIDA measurements and ERA-5 data (Fig. 3) should be discussed. Could it be due to differences in methodologies used, or varying in ambient conditions.

Technical comments

-In the abstract norward should be replaced with northward

-replace twentyfour with 24 in line 200

-rewrite the sentence after Eq. 7 line 375

The manuscript "AIDA Arctic transport experiment (part 1): simulation of northward transport and aging effect on fundamental black carbon properties" is a nicely written report on the ARTEX experiment. The authors used the AIDA simulation chamber to mimic the atmospheric processes that age black carbon particles during transport from the mid-latitudes to the Arctic region. In Part 1, they report changes in the physical properties of the aerosol (e.g. diameter, fractal dimension, coating) and relate them to atmospheric conditions. The manuscript is clear and well written, but some sections need more explanation. These parts are summarised below, with some other technical suggestions.

44: "primarily" >> BC is exclusively emitted from combustion sources.

109: "Siberian open fires"  >>  In fact, many of the BC particles transported to the Arctic come from forest fires. On the other hand, burning biomass releases not only BC but also huge amounts of organic aerosol (OA), which is mostly mixed internally with BC. The OA emissions from the burner used in the experiment are negligible compared to the combustion of biomass. OA ageing and secondary OA contribute to changes in the physical and optical properties of the aerosol mixture. I miss the inclusion of organic components in the experiment. You should mention the importance and role of OA and explain why you focused mainly on nitrate-based coatings.

111: The NO2/BC ratio was fixed according to the CAMS data set. However, the OA/BC ratio was specific to the burner. This means that your experiment represents evolution of the inorganic coating only. This is not a problem, but you should state this fact explicitly. Otherwise, based on the introduction, the reader is expecting a comprehensive simulation of the Arctic transport of BC particles emitted by wildfires.

183-184: In the results you did not separate BC into hydrophilic and hydrophobic parts. In this respect, this sentence is misleading.

274: A plot of the rBC mass distribution and the fit would be useful.

302-303: "Since the concentrations of sulfate, ammonium, and chloride consistently remained below the detection limit" >> yes, because you did not inject.

304: Source of organic components? The burner only? Why is it representative of forest fires in Siberia? Or for other sources of Arctic BC?

228-229: Eq2 gives d_f as the slope of the regression if you plot log(m) against log(k D^d_f) . In a log-log representation the slope has different meaning. This way the sentence and Fig S1c are ambiguous.

353: Equation 4 gives the average material density of a particle with two components. The average material density is the same as the density of the particle if a solid core-shell structure is considered. Here this model cannot be applied since the core is a spongy structure (fractal-like particle), so the "coating" not only covers the surface but also fills the holes and cavities of the core particle. Thus, the coating increases the density through the compactness of the particle even if it has the same material density as the core particle. It would therefore be better to use the term "average material density".

380: Eq8 is only valid for spherical solid core-shell structures (for the reason mentioned above). The actual coating thickness can be obtained from the SP2 measurement. It would be interesting to compare the measured and calculated coating thicknesses, which may give an indication of the core particle compactness.

Figure 3: The discrepancy between CASM and AIDA RH and NO2/BC values should be discussed. Especially for WL and WH scenarios. How do those differences affect the representativeness of the simulation?

468: Any explanation why the size distributions of the low and high scenarios do differ? And SL and WL? Could the chamber temperature/pressure affect the particle properties after injection?

Figure 4 caption: what do you mean "Concentrations adjusted to the ambient conditions inside the AIDA chamber."

514: Figure 6 is not dicussed in the text.

521: Where is the FM_org result presented? A relevant figure should be added.

548: Same for FM_NO3.

553: same

571-572: Do you have any explanation for this? Temperature effect? Slower chemistry?

Figure 5: Note which are the direct measurement results, and which are calculated ones (e.g. particle density)?

Figure 5: What are the gaps between the points?

625-626: This finding should be more elaborated. What is the exact relationship you found between coagulation growth and coating?

661: More explanation and/or reference is needed for Hill equation.

Supplement:

Figure S1: Mention the instrument/technique used to obtain the results. For example plot a) is an SMPS result I guess? Plot c) APM vs. SMPS and so on.

Figure S1a: Any explanation why the size distributions of the low and high scenarios do differ? And SL and WL? Could the chamber temperature/pressure affect the emission after injection?

Figure S3: only 3 curves are visible in panel a). WH is missing I guess.

The manuscript titled "AIDA Arctic transport experiment (part 1): simulation of northward transport and aging effect on fundamental black carbon properties" presents a well-structured and insightful experimental investigation into black carbon (BC) aging under conditions representative of Arctic transport.  To accurately quantify and understand the impact of atmospheric aging on BC properties and radiative forcing, the ARCTEx project simulated BC aging under quasi-realistic Arctic conditions in the AIDA. Informed by reanalysis data, four distinct scenarios were developed to capture seasonal and altitudinal variability during Arctic transport.  The use of the AIDA chamber to emulate these variations is methodologically sound and lends credibility to the experimental design.  The results on coating composition, morphological evolution, and aging timescales provide valuable empirical constraints for improving the representation of BC aging in atmospheric models.

Specific comments

1. While the dominance of nitrate and organic coatings is clearly demonstrated, the absence of sulfate or ammonium in coatings (Section 2.4.3) should be discussed. Clarifying this would help readers assess the generalizability of the findings.
2. Section 3.5: Briefly justify the use of the Hill equation for modeling aging timescales.
3. The manuscript could be further strengthened by discussing implications for global or regional climate models, particularly in light of recent developments in BC aging parameterizations (e.g., https://doi.org/10.5194/acp-25-2613-2025 and DOI:10.1029/2024JD041135).
4. Figure 3: Adding error bars or uncertainty shading would help visualize variability.
5. Line 599 and 619: The unit “kg m³” should be corrected to “kg m^-3”.
6. Figure 8: The variable label “Rm_Coat” should be revised to “Rm_coat” to ensure consistency.
7. Table A1: Please verify that the list of abbreviations is complete. For example, “Rm_coat” appears in the manuscript but is missing from the table.
8. Ensure consistent use of notation，like kg m^-3 in the manuscript and “Kg m^-3” in the Table A1.