This study used the results of three black carbon instruments, AE33, PAX, and OCEC, combined with offline component analysis, to analyze the optical properties of black carbon and brown carbon. Some of the results are very interesting and important (i.e., Lines 252-265), and it is recommended to publish them after minor revisions:

1. Conclusion and Abstract: Both mention Eabs, but there is no introduction of Eabs in the main text, only MAC. It is suggested to add it, e.g., near Fig. 11.
2. Lines 45-47, 52-62: The effectiveness of China's air pollution policy is evident to all. However, it seems that the background content in this study is too lengthy. However, the 'various detection approaches' are difficult for readers. Suggest adding introductions comparing devices such as PAX, AE33, and OCEC.
3. Lines 116-117: First of all, I completely agree with your point of view: the default correction of AE33 seems too rough, but such important content, which is also the core of this article, should not be included in the attachment. Or at least it needs to be clarified in the text that PAX is a standard measurement used to compare with AE33.
4. 1: Considering the stage comparison in the following text, it is recommended to clarify the time periods corresponding to different stages in this section. Maybe use different color.
5. Table 1: Have you considered conducting machine learning simulations on C * in your future work
6. Lines 195-196: Quartz film is a half day sample, so how to compare AE33 with offline needs to be introduced
7. Lines 203-210: t is not clear for readers to understand why to discuss filter tapes?

The manuscript by Cheng et al. investigated the optical properties of carbonaceous aerosols under changeable conditions of haze pollution in Northeast China. For this purpose, the authors combined on-line data (from a PAX, an AE33 and analyzers for several gaseous pollutants) and off-line results (from a high-volume PM2.5 sampler) measured during April, 2023, when different types of haze episodes were encountered. They first explained the discrepancies between the light absorption results from different methods, and then discussed the influences of agricultural fire emissions and secondary aerosol formation on the optical properties of carbonaceous aerosols. In general, the results and discussions were scientifically sound. Given that the studied region is distinct (especially regarding the agricultural fires) but largely overlooked by previous studies, the manuscript is suitable for a measurement-report paper in ACP. My overall assessment is that it could be considered for publication after the following concerns were properly addressed.

Major points.

1. Lines 22-25. The two sentences were not well connected. It is completely unclear why the dust episodes need to be excluded.
2. Lines 56-62. The new standard has been released. The statements need to be revised correspondingly.
3. Table 1. Fractions in total data points should also be given for the SSA bins.

Minor points

1. Lines 12-13. Suggest replacing “Northeast China” by a more specific term, e.g., the site type (urban, suburban, rural, etc.) would be more useful.
2. Lines 37-41. The sentence is difficult to follow. Revise it.
3. Line 70. I guess the average temperature was for winter. Clarify it.
4. Line 75. It is better to use “emission system”.
5. Line 84. It should be “secondary”.
6. Line 119. Suggest using “over” instead of “in”.
7. Line 169. It should be “obtained”.
8. Line 217. Suggest using “different types of filters”.
9. Line 219. Move “heavily loaded” to the next sentence, as the detailed carbon loadings had been given here.
10. Lines 220-221. I think PM2.5 concentrations were not highly relevant to the statement here, i.e., in addition to PM2.5 concentration, filter loading also depends on the sampling volume or, more precisely, face velocity.
11. Lines 444-445. It is better to explain (babs)@370 first, which is the basis for the calculation of (babs)BrC@370.
12. Line 453. Change “used” to “considered as”.
13. Line 462. It is unnecessary to define the ratio again.
14. Lines 545-546. “Eabs” should be introduced, as it was mentioned in the abstract. Accordingly, it is unnecessary to define it again in Line 596.
15. Line 561. To my understanding, the C* factor was used to correct for the overall effect of the multiple scattering by the filter media and the scattering by the collected particles. Clarify it.
16. Line 600. Remove the comma before “and effectively”.