This paper investigated the changes in the optical properties, fluorophores, and molecular composition of WSOM derived from the combustion of biomass (RS) and coal (YL) during aqueous photolysis and hydroxyl radical (·OH) photooxidation. Results show distinct photochemical aging effects for RS and YL WSOM, characterized by photobleaching in RS WSOM and photoenhancement in YL WSOM. Additionally, ·OH photooxidation induces more substantial alterations than photolysis, degrading 61.6% of RS and 65.0% of YL WSOM molecules, compared to 14.9% and 23.1% during photolysis, respectively. The oxidation products were characterized by larger molecular weights and higher oxidation levels, including tannin-like substances and a type of black carbon-like compounds, whereas photolysis causes minor changes. These findings are helpful for us to understand the photochemical evolution of combustion-derived WSOM and its environmental and climate impacts. However, I have some questions should be addressed:

1. Line 127-128: How about the difference between the light intensity under laboratory conditions (290-400 nm, 12.5 mW/cm²) and the actual solar exposure? How about the actinic flux of the Xe lamp used in present study
2. For the photolysis and ·OH photooxidation, how many experiments were repeated in the present study?
3. Authors are strongly suggested to use the more detailed index: nominal oxidationstate of carbon (NOSC) (Geochimica et Cosmochimica Acta Volume 75, Issue 8, 15 April 2011, Pages 2030-2042), rather than the simplified index: state of carbon oxidation.
4. Line 202: present -> presented
5. Line 305: The logical subject of the 'with' structure is unclear, it is recommended to replace it with 'while'.
6. Line 330: Confirm the spelling of professional terms (such as "condensed" vs. "condensated")
7. Line 407: What are the similarities between the newly produced condensated aromatic compounds which assigned as BC-like substances and the traditional DBC?
8. The ·OH oxidationof WSOM in atmosphere can happen in light and dark conditions. Could your add a discussion between the ·OH photooxidation and dark ·OH oxidation in the paper?
9. Fig 3: the name of vertical axisshould revised to “Relative intensity”.

The research component of this manuscript examines the changes in optical properties, fluorophores, and molecular composition of WSOM from biomass and coal combustion during aqueous photolysis and hydroxyl radical (·OH) photo-oxidation. The results show that the ·OH photo-oxidation process leads to the degradation of more WSOM molecules, producing products with higher molecular weights and higher levels of oxidation, including tannins and newly formed black carbon analogs. While the photolysis products show relatively little change. These findings provide new insights into the photochemical evolution of WSOM from combustion and help predict its impact on the environment and climate change. In conclusion, this manuscript is highly recommended to be accepted for publication with a few modifications:

1. Line 102-103: Please provide basic information about the two fuels.
2. Line 116-119: Please present the WSOC measurement protocol in the manuscript or SI: instrumentation, general experimental methods.
3. Line 129-132: What is the approximate OH concentration during the corresponding oxidation time? How much H₂O₂ is consumed in this process? Is there any estimate?
4. Line 184-185: What physical properties of WSOC can be characterized by α254 and α365?
5. Line 350-354: The results in this section show that the content of condensed aromatic compounds increases after photolysis, but the results of α254 and α365 of rice straw calculated in the absorption section show that the aromaticity decreases. Is there any connection or difference between the results in these two sections? Please explain
6. Figure 4: It is recommended that the sub-graphs in Figure 4 be numbered to make it easier to distinguish the results for coal and biomass.