This study attempted to investigate the role of cloud on the formation of brown carbon. A comprehensive and valuable dataset was collected, including the light-absorption properties of the cloud droplet residual, the cloud interstitial and cloud-free particles, the light-absorption and fluorescence properties of water-soluble organic carbon in the collected cloud water and PM2.5 samples, and the concentration of water-soluble ions. The presented data further indicate the formation of secondary BrC during cloud processing and a considerable contribution of water-insoluble BrC to total BrC light-absorption. Such results improve our understanding on the optical properties and secondary formation of BrC in cloud, and thus merit publication in ACP. Here are some minor issues that need to be addressed.

(1) Experiment section: why was PM2.5 inlet applied to rule out the cloud interstitial particles? Discussions should be provided on the possible uncertainty that may be introduced.

(2) "The contribution of water-insoluble BrC to the light-absorption is estimated to be ~75% for the cloud INT particles and ~48% for the cloud RES particles on average, based on these differences (Fig. 3)." It is interesting to know that water-insoluble BrC contributes to such a high fraction of BrC in the cloud INT particles and the cloud RES particles. I wonder if some of this insoluble fraction is secondary origin.

(3) Lines 197: The authors presented correlation analysis between the Abs365 of cloud water and PM2.5 aqueous extract with SNA (sulfate, nitrate, and ammonium) (r > 0.77, p < 0.01), and NOx (r > 0.58, p < 0.01), and the result supports the secondary formation of BrC. Why was PM2.5 aqueous extract included in the analysis? Does this result also indicate the significance of secondary production of BrC in PM2.5?

minor:

(1) Line 53：what does "These light-absorption species" refer to?

(2) Line 134："(SUVA, m2·g-1,)" error typo.

(3) Line 156："As expected, there is a positive correlation between Abs365 and WSOC concentration in cloud water and PM2.5 aqueous extracts (r > 0.61, p < 0.01)." Does it mean that WSOC in cloud water is mostly from PM2.5?

(4) Line 160："much lower than those in urban areas (as summarized in Table S1)". I suggest to include the observed values.

(5) Line 197：what does "wet particles" refer to?

(6) Line 208：revise "Consistently, the source and contribution apportionment of BrC" to "the source apportionment of BrC".

This study presents the results of brown carbon measurements in cloud, including cloud droplet residuals, cloud interstitial particles, and cloud water. The authors attempted to demonstrate the role of cloud processing in the formation of brown carbon. The dataset covers both the collected cloud water and cloud residuals, and thus may offer new insight into cloud processing of brown carbon, which has been rarely investigated. The topic is appropriate for Atmospheric Chemistry and Physics, but there are some issues that need to be addressed before publication.

1. Introduction: Generally, what are the major fractions contributing to the light-absorption of cloud water? The authors indicate that nitrophenols and aromatic carbonyls were the major fraction contributing to the light-absorption (~50%) of cloud water at Mt. Tai, but what about in other regions? Also, those related results for aerosol particles should be summarized herein.
2. Section 3.1 Line 172：The discussions related to the influence of aromaticity and molecular weight of WSOC in the light-absorption capacity should be improved. What is the real meaning for a medium negative correlation (r > 0.43, p < 0.05) with E250/E365? Is such evidence consistent with those obtained by the EEMs measurements in section 3.2?
3. Section 3.2: The authors came to the conclusion that NOx may enhance the formation of nitrogen-containing organics, based on the correlation analysis. I suggest including a discussion on the detailed mechanisms related to such a conclusion. Also, is there any evidence to exclude other pathways as indicated in the introduction?
4. Section 3.2: PMF model indicates a possible influence of biomass burning on the formation of secondary brown carbon. It would be much better to include and compare with those found for aerosol particles. The paper needs to provide more discussion on this issue.