This work reported the pollution characteristics and molecular composition of atmospheric chromophores in a certain city. Especially, based on previous studies, some conclusions were obtained in the study of organic aerosols by using EEMs and MS method. Generally speaking, it is interesting and and can be considered for publication after dealing with the following problems.

1. Abstract: The content describes the results too much and summarizes the conclusions or significance too little.

2.L85: Chen's series of studies have promoted the application of EEM methods in the field of atmosphere, and his recent studies have also combined typical sources and molecular substances with EEM (2021). The author should objectively confirm the use of these work in this study. In addition, EEM method is a comprehensive characterization method, and its advantage lies in its systematicness and integrity. Mass spectrometry and EEM methods can be complementary.

3.L06: unscientific expression of "~".

4.L26: I noticed that the observation time was almost a month, but the high resolution mass spectrometry results did not see so much data.

5.L138: The height of the sampling point is a little low, so it is easy to be affected by the ground or a small range.

6.L162: What is the collection efficiency of CIMS? How to calibrate?

7.L197: Why Ex. From 240?

8.L270: Title too simple.

9.L327: The author did not identify the origin of OA and chromophobe, because LV-OOA and SV-OOA cannot be considered as the source.

10.L365: Why did the author not analyze PAHs and OH-PAHs?

11.L405: Correlation analysis with molecular composition determines that the molecular composition of EEM is one-sided and must be explained in absolute quantities, otherwise the type of chromophores can only be said to be similar substances or sources.

12. Fig.2: Why MAE and AAE diagrams are made? Aren't they mathematically correct? What is the reason for the higher uncertainty of the red line in the AB diagram?

13. Fig.3: There are weak signals around Em.=290 in C3, why?

14. Fig.5: Comparison of recommendations with previous studies.

15. Fig.7: I can't understand what the author wants to express in this figure.

Jiang et al., present a study on exploring the optical and chemical composition of brown carbon. Comparing with previous studies, this study combines the optical measurements and chemical measurements (AMS and Fi) and can obtain more information on the sources and chemical processes of chromophores. They found LO-HULIS chromophore was primary with nitrogen-containing molecular and originated from biomass burning at the urban kerbside during winter. However, HO-HULIS chromophores were secondary and could be related with photochemistry during summer. Overall, the results and presentation are reasonable and clear. However, there are many minor issues in the manuscript which should be addressed before publication.

Major issues

Since the major focus of this manuscript is on BrC and filter measurement, the 2.2 and 3.1 sections could be concise and merged into other section or cited from other parallel publication. In method section, it is also important to describe the data matching between online and offline data.

The samples described in the method section are unclear. How many filter samples was collected during winter and season, how many samples were collected for one day, morning time or nighttime? What material filter was used? What is the instrument? What is the filter sampling strategy for CIMS analysis? This information should be clearly presented in method section.

Minor issues

1. Line 23-24: present the full name of AMS and more information on the measurement and restults (online or offline? How many factors were obtained). In the above, the PARAFAC analysis has present and directly use PARAFAC results.
2. Line 197-210: The results of PARAFAC on winter and summer season are significant different. Is this seasonal process conducted at a combined dataset or separated? It is better to input the combine dataset into the model.
3. Line 260-263: it is worth to mention the wavelength range of AAE in different studies which can significant influent AAE result.
4. Line 272-274: this information is already in method section.
5. lines 287-288, Change to “shorter excitation wavelength (< 250 nm) and shorter emission wavelength (< 350 nm)”.
6. line 289, Change “left” to “right”.
7. Line 308-309: the abbreviation of aerosol mass spectrometer should be consistent in the main text.
8. In section 3.3, the authors discussed the fluorophores only in MSOC, but the papers cited by the authors when determining the fluorescence components mostly about fluorophores in WSOC. See the previous papers where there are clear differences in the water-soluble and methanol-soluble fractions. https://doi.org/10.5194/acp-20-2513-2020
9. lines 321-322, “two different types of LV-OOA were observed LV-OOA1 and LV-OOA2”, what is the difference between LV-OOA1 and LV-OOA2? The sources of C2 and C3, which are respectively associated with LOOA1 and LOOA2 are both simply classified as a less volatile oxygenated organic aerosol in this study.
10. Section 3.4: It is common to definite SV-OOA and LV-OOA to LO-OOA and HO-OOA, respectively. For the elemental ratio calculation, it is better to mention the method for this calculation.
11. Line 340-341: The explanation on PLS is not convinced. This factor could be primary or secondary. Phenolic compounds have similar EEM feature with this factor. In addition, is there blank filter during sampling? If it is, it can be used comparison?
12. line 356, how to calculate “NFV”? NFV data shown in Figure 5c differs from other literature by several orders of magnitude; please confirm whether the normalization was done using the fluorescence volume integral value (RU-nm2).
13. Line 344-355: It is better to compare the seasonal variation on chemical and chromophore composition using the consistent filter samples. Since some filter samples were collected only during a few hours, these filter should be removed during seasonal comparation. The chemical processing on particulate and gas phase is complicated and cannot be got the conclusion for LO-HULIS and O3 only based on the correlation analysis.
14. Line 413-415: It is not suitable to cite the result from river chemistry.
15. In Figure 7, although the molecular weight are significant different in each figure, but the O/C and H/C are similar, does this right?

General comments

Brown carbon (BrC) compounds are important constituents of atmospheric aerosols. Although in the past decades, BrC aerosols have been a subject of extensive researches in the atmospheric scientific community, their formation pathways, optical properties, and climatic effects are not well investigated yet. This study provides a comprehensive report on the optical properties, chemical composition, and major BrC chromophores collected at a kerbside at different seasons in a typical urban environment in western Europe. This manuscript fits the scope of ACP and well written, but the authors may want to address the following issues before publication. Please see my comments in detail below.

1.    BrC defined in this manuscript is dissolved in methanol, however, only a part of BrC is methanol-soluble, and even some highly-absorbing BrC is not soluble in any solvent. I suggest to replace BrC to methanol-soluble BrC (MS-BrC) where needed throughout the manuscript.

2.    In Sec.3.3, the authors compared their methanol-soluble fluorophores with many water-based studies. I believe that even for a single chemical species, there might be some differences between its water-based and methanol-based EEMs, in other words, they may not be comparable. The authors may want to discuss this issue. 

Specific comments

1、    Please reduce words in the abstract and a single paragraph is recommended. 

2、    L85-87. Meaning of this sentence is not clear.

3、    L97. Earlier references need to be cited here. For instance, Lin et al., Molecular Characterization of Brown Carbon in Biomass Burning Aerosol Particles, DOI: 10.1021/acs.est.6b03024. 

4、    L167. Why was different duration time applied for FIGAERO-CIMS analysis?

5、    Eq.3. I suggest to use a power-law regression to calculate AAE, instead of use the information of only two single wavelengths. Eq. 3 here is usually used for techniques with limited wavelengths, like aethalometer.

6、    L199. Why did the authors use different emission wavelength increments for summer and winter samples? With different data size, how did the authors assemble data in the PARAFAC model? 

7、    L206. The authors used methanol-based solution rather than water-based, why did you use water Raman peak to normalize the fluorescence intensity? Please explain it or cite proper literatures.

8、    Figure 2a,b. There is a shoulder peak at ~300 nm for summer sample, it is not usually see for aerosol samples. Could the authors put some words on that?

9、    L281. The maximum EM wavelengths of C3 is ~400 nm, not significantly above. 

10、    L288. In Chen et al., 2016, C4-like chromophore was partially assigned to phenol- and naphthalene-like substances. Are they possible assignment for C4 chromophore in this manuscript?

11、    L328. What is used to do the correlation analysis between AMS and PARAFAC components? Relative contributions or absolute intensities?

12、    L344-355. In L340, the authors mentioned sampling artifacts for the samples with shorter sampling time. How did the diurnal variation of chromophores can be inferred from unreliable samples?

13、    L357. In my opinion, higher NFV of samples #5 and #6 may not only due to sampling contamination. Species in these samples with higher fluorescence efficiency may also lead to this phenomenon. For instance, in Fig. 5b, samples #5 and #6 have higher fraction of LV-OOA1.

14、    L380. I am confused here. The authors showed that major 5 NACs concentration in their samples was 1.6 ± 0.9 ng m-3 on average. It is one magnitude lower than 10-20 ng m-3.

15、    L394. How did the authors calculate the mass fraction of potential BrC?

16、    Figure 6a. Only 8 samples were analyzed by FIGAERO-CIMS? Which samples were selected?

17、    L396 (Table S8). Are those molecules commonly appeared in all 8 samples? Or all potential BrC molecules detected in every sample. if later one is the case, n values of correlative analysis should be noted as well.

18、    Table S8. The correlation coefficient is calculated between Abs365 and what parameter for potential BrC molecules?

19、    Sec. S3. L37-38. I do not understand here. Without standards, how can the authors derive the mass concentrations of 321 potential BrC molecules?

20、    Sec. S3. In earlier studies, relative fluorescence of PARAFAC components were correlated with relative intensities of each MS peak, not mass concentration fractions. The authors may want to take a look at this paper: Stubbins et al., What’s in an EEM? Molecular Signatures Associated with Dissolved Organic Fluorescence in Boreal Canada, 2014, dx.doi.org/10.1021/es502086e.

21、    Table S11. Molecular weight and O/C are intensity weighted or arithmetic mean, should be clarified. 

22、    Fig. 7. What are bubble sizes mean? Peak intensities? Needs to be clarified.

23、    Sec. 3.5.3. The discussion of molecular characteristics of molecules assigned to each fluorescence components may needs to be in more detail. Double bond equivalent, aromaticity index, carbon oxidation state and so on, all these metrics are also worth to show.