We thank the comment of Ye Kuang highlighting the uncertainties introduced by the selection of AAE_BC. Indeed, both experimental methods and modeling approach are prone to uncertainties when the AAE_BC is determined. For example, in the papers cited in the comment, the spectral dependence of AAE_BC is considered but under the strong assumption that BrC particles do not absorb at 520 nm. It has been shown that the BrC contribution at 520 nm can reach up to more than 30% (e.g. Cuesta-Mosquera et al., 2024). In order to take into account this, other studies have calculated the AAE_BC using absorption measurements between 880 and 950 nm where the assumption of negligible BrC contribution is very reasonable. However, the AAE_880-950 can have a high uncertainty at some sites, and especially at more remote environments, where the aethalometer signal at 950 can be very low. 

We also agree with Dr. Kuang that the smallest AAE_BC could not always correspond to situations when influence of BrC is negligible. This might happen at sites where BrC particles dominate the absorption throughout the year which is not commonly observed at the surface. Moreover, the fact that the values of the 1th percentile presented here lie between 0.9 and 1.1 further confirm a reasonable removal of BrC signal in the determination of AAE_BC.

Due to the general uncertainty associated with the determination of AAE_BC, here we preferred to follow the approach from Tobler et al. (2021). Following this approach, the calculation of 1st percentiles were performed after filtering the AAE values when the fit had R2>0.99. This should somehow also solve the possible spectral dependence of AAE_BC. Moreover, recently, Zhang et al. (2020) have reported an uncertainty of approximately 11% in the estimation of the BrC contribution to total absorption at 370 nm when using different AAE_BC values ranging from 0.9 and 1.1.

This is a reasonable uncertainty considering the overall uncertainty of the AAE method. Moreover, also the modeling part presented in this work is prone to uncertainties and any change of AAE_BC can add uncertainties that however lie well within the overall uncertainty of the approach presented in this manuscript.

Based on the above consideration, we prefer to keep here the use of the 1th percentile to determine the AAE_BC based on aethalometer data only. 

In order to consider Dr. Kuang comments, the following sentence (line 152 of the submitted manuscript):

 “……where AAE_BC is the Absorption Angstrom Exponent (AAE) of BC, which allows for the calculation of babs,BC(λ) (in units of Mm−1) from the measurements of babs,BC(λ) at 880 nm assuming that BrC does not absorb at 880 nm (e.g., Qin et al., 2018). The main source of uncertainty in equations 1 and 2 is the AAE assumed for BC. In many studies a value of 1 was used (Liakakou et al., 2020; Tian et al., 2023; Cuesta-Mosquera et al., 2023, e.g.,). However, theoretical simulations have shown that the AAE_BC can reasonably vary between 0.9 and 1.1 depending on the size and internal mixing of BC particles (Bond et al., 2013; Lu et al., 2015, e.g.,). Here we estimated the site dependent AAE_BC as the first percentile of the AAE frequency distribution. The AAE can be calculated from multi-wavelengths (370, 470, 520, 590, 660, 880, and 950 nm) total absorption measurements as the linear fit in a log-log of the total absorption versus the measuring wavelengths. The effect of BrC absorption is to increase the AAE and, consequently, the first percentile of AAE represents conditions where the absorption is dominated by BC. In order to reduce the noise, the 1st percentile at each site was calculated from AAE values obtained from fit with R2 > 0.99 (Tobler et al., 2021). For sites included here, the 1st percentile method provide AAE_BC values ranging from 0.928 to 1.088 confirming that this experimental method can provide reasonable estimations of the AAE_BC.”

Will be modified as follow during the review process:

 “……where AAEBC is the Absorption Angstrom Exponent (AAE) of BC, which allows for the calculation of babs,BC(λ) (in units of Mm−1) from the measurements of babs,BC(λ) at 880 nm assuming that BrC does not absorb at 880 nm (e.g., Qin et al., 2018). The main source of uncertainty in equations 1 and 2 is the AAE assumed for BC. In many studies a value of 1 was used (Liakakou et al., 2020; Tian et al., 2023; Cuesta-Mosquera et al., 2023, e.g.,). However, theoretical simulations have shown that the AAEBC can reasonably vary between 0.9 and 1.1 depending on the size and internal mixing of BC particles (Bond et al., 2013; Lu et al., 2015, e.g.,). Here we estimated the site dependent AAEBC as the first percentile of the AAE frequency distribution. The AAE can be calculated from multi-wavelengths (370, 470, 520, 590, 660, 880, and 950 nm) total absorption measurements as the linear fit in a log-log of the total absorption versus the measuring wavelengths. The effect of BrC absorption is to increase the AAE and, consequently, the first percentile of AAE represents conditions where the absorption is dominated by BC. In order to reduce the noise, the 1st percentile at each site was calculated from AAE values obtained from fits with R2 > 0.99 (Tobler et al., 2021). The applied R2 filtering also helped reducing the uncertainties associated to the fact that AAEBC can vary as a function of wavelength. For example, Wang et al. (2018) and Li et al. (2019) used a combination of Mie theory and experimental data to explore the wavelength dependence of AAEBC and proposed an estimation of babs,BrC(λ) based on the ratio between the AAE calculated from 370 to 520 nm and from 520 to 880 nm. However, this methodology assumed that BrC particles do not absorb at 520 nm whereas it has been shown that the contribution of BrC to absorption at this wavelength can be high (e.g. Cuesta-Mosquera et al., 2024). As a consequence, other studies (e.g. Zhang et al., 2018; Luo et al., 2022) used the AAE calculated from 880 to 950 nm to calculate the AAE_BC assuming that BrC particles do not absorb in the near_IR. Nevertheless, the latter methodology may suffer from additional uncertainties related to the possible low aethalometer signal at 950 nm, frequently observed especially at more remote sites. Thus, it should be considered that the methodologies proposed to estimate AAE_BC, including the use of the 1st percentile applied here, are prone to uncertainties. On the other hand, Zhang et al. (2020) have reported an uncertainty of approximately 11% in the estimation of the bAbs,BrC370 contribution to bAbs370 when using different AAE values ranging from 0.9 and 1.1. For the sites included here, the 1st percentile method provides AAE_BC values ranging from 0.928 to 1.088 confirming that this experimental method can provide reasonable estimations of the AAE_BC.” 

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