Wu et al. presented the field aircraft campaign results in investigating a half-day evolution of flaming burning dominated smoke aerosols over the Senegal region. The chemical and optical properties of the smoke aerosols during transport were monitored and analyzed to depict the rapid transformation of the absorbing particles, and they found increasing contribution from secondary BrC in bulk aerosol absorption during the initial aging procedure. There is enormous amount of publications in studying the emission and evolution of biomass burning related light absorbing carbonaceous particle. This study is surely a good addition. I suggest publication after addressing the following minor comments.

Minor comments:

1. More background information is suggested to provide in the manuscript, including aging environment, exact time profile for the smoke transport and flights (morning or afternoon). Figure S2 should be better moved to manuscript.
2. In discussing organic characters as measured by AMS systems, it should be described how to check the possible influence of so-called Pieber effects/artefacts (i.e., Pieber et al., ES&T, 2016; Freney et al., AST, 2019), especially for inorganic salts contributing to a considerable portion of the bulk aerosol.
3. Did the authors consider the influence of dynamic inorganic mixing in absorption characterization of smoke aerosol?

Specific comments:

1. Page 2 Line 60: change to “though both estimates are associated with considerable uncertainties.”
2. Page 2 Lin 61: delete “than this”
3. Page 3 Line 75: add “coated” or “internal mixed” before “BrC”
4. Page 5 Line 161: where was the impactor installed? Ahead of the PAS?
5. Page 6 Line 164: check equation 1, AAE is positive value
6. Page 7 Line 198: “Further details in the processing ……”
7. Page 8 Line 248: MCE of 0.9 is a simple threshold to classify burning phase, MCE of 0.9 and beyond roughly indicates flaming burning dominated in a fire event.
8. Page 10 Line 307: chemical formulas for these specific ions should be added
9. Page 18 Line 560-561: Work by Li et al. (2020) was nighttime NO₃ radical reaction that enhanced light absorption by BB-BrC, the reaction pathway should be different from the photochemical aging in the manuscript. Saleh et al. (2003) reported secondary BrC formation in photochemical aging of BBOA, but these secondary BrC had less absorption than primary BrC at wavelength beyond 400 nm. Commonly, OH radical photochemical oxidation diminishes light absorption by primary BrC, unless NOx involving to prohibit the bleaching via new chromophore formation (Li et al., 2019. DOI:10.5194/accp-18-1-2018).
10. Page 20 Line 634-635: confused. Do you mean that 20% of the observed aerosol is background one after half-day transport?
11. Page 21 Line 661: levoglucosan is not chromophore, the positive correlation between absorption and marker fragment ratio indicated primary BrC emission from biomass burning, and the aging played a major bleaching role.
12. Page 21 Line 665: confused. “Chemical reaction loss” means absorption decrease due to reaction or levoglucosan decomposition indicated by f60 decrement in aging?
13. Page 21 Line 670: do you mean smoldering burning is more efficient in primary BrC emission?

This manuscript by Wu et al. presents aircraft measurements of ageing smoke plumes of agricultural and savannah flaming fires in the Senegal region. The measurements characterized the evolution of size distributions, chemical composition, and light-absorption properties of the aerosol emissions for plume ages up to 12 hours. The major findings include (1) observed significant chemical transformation of the organic aerosol (OA) but without increase in OA loading, which is attributed to a combination of primary OA oxidation, secondary OA formation, and primary OA evaporation due to dilution; and (2) increase in brown carbon absorption with atmospheric age. The paper is well-written and is a valuable contribution to the atmospheric chemistry literature. I have just one major comment on the optical calculations, detailed below.

Major comment:

The use of different models to calculate MAC values and derive BrC contribution to absorption does not seem to add useful insight to the analysis and conclusions regarding the evolution of BrC absorption in the plumes. With absence of detailed information on particle morphology and actual MAC_BC, there is a lot of uncertainty that goes into these MAC calculations. (1) The calculations are based on the assumption that MAC_BC = 7.5 m2/g at 550 nm applies to the measurements in this study. This alone can lead to substantial uncertainty. Any over/underestimation in BC mass concentration measurements and/or over/underestimation in light-absorption measurements would lead to misattribution of absorption enhancement to lensing and/or BrC absorption. (2) It is not clear that the experimental conditions on which the empirical models (Liu, Wu, Chak) were based apply to the aerosol in this study.

The message on the evolution of BrC absorption with plume age, which I believe is an interesting one, can be delivered more cleanly by just relying on MAC_measured_BC and AAE. Instead of Figure 6 (which is a bit hard to follow), I would add another panel to Figure 5 that shows box plots of MAC_measured_BC at different ages.

As for BrC contribution, I believe that the simple AAE attribution method (with absence of detailed information to allow more involved modeling) is the best that could be done. In fact, the AAE method seems to yield more reasonable results (in terms of wavelength-dependence of fractional BrC absorption) than the modeling methods which show very weak wavelength-dependence of fractional BrC absorption.

Specific comments:

Line 169: the statement about inverting the SMPS data is not clear.

Line 224: It is not clear why modeled MAC instead of B_Abs was used to calculate AAE.

Line 233: replace “some” with a number (more quantitative).

Line 234: what is the assumption that the plumes are less than 0.5 hours old based on?

Line 321: add “aerosol” after “secondary organic”.

This paper describes aircraft measurements from three flights in west Africa that sampled biomass burning. The authors examine the aerosol optical properties as a function of transport age over 0 - 12 hours. The paper is well-written and well-organized.

Major comments:

- Section 2: It would be useful to provide a basic overview of the campaign and the fires sampled in a few sentences. Specifically: What were the dates of the study? How many total flights were made? What was the aircraft duration? What were the criteria for selecting these three flights for this study?

- Section 2.2: What is the minimum detectable fire size for MODIS? Were most of the fires in the region detected?

- Section 3.1: What was the fuel for the agricultural fires? What was the burn area? How long did the fires persist? How similar were the fuels and burn conditions for the different fires? These are important questions because the analysis of different smoke ages represent different fires sampled during different flights. If the fire conditions differed between the flights, that will affect the trends.

- Figure 1 shows that transects for each flight were all sampled at the same distance downwind. Why not make multiple downwind transects at increasing distance from the source?

- Section 3.3: What was the uncertainty of the SMPS scans? Due to the slow time response, it is more typical to use an optical particle counter for aircraft measurements. Was there a reason that the SMPS was used?

Minor comments:

- Line 35-37: The aerosol aren't evolving in the fires, they are evolving downwind. This sentence might be clearer as "Different treatments of absorbing aerosol properties from smoldering and flaming combustion and their downwind evolution should be considered..."

- Lines 56-57: Consider including earlier references.

- Line 64: "The initial relative contribution of OA and BC varies...." It is unclear if you mean the mass contribution or the absorption contribution.

- Line 75: Consider including older Lack and Langridge references?

- Line 97: Could the acronym "MR" be eliminated and replaced with MnonBC/MBC? By the time it appeared here, I had to search for the definition again.

- Lines 396-397: What RI is assumed for BC?

- Figure 1: Color the MODIS-detected fires according to the three flights (blue, green, pink).

- Figure 1 Caption: Change "1-day back trajectory of selected sampled smoke over the Atlantic Ocean during flight C006 (c) and C007 (d)" to "1-day back trajectory of sampled smoke from flight C006 (c) and C007 (d)" because it sounds like the back trajectory is over the Atlantic Ocean but its actually the flight that was over the Atlantic Ocean.

- Figure 2: Upper whiskers are hidden on the bar chart.

- Figure 4: It is unclear which traces are assigned to the left and right axes.