As the authors mention, this is a unique and high-quality dataset describing VOCs in Marseille. The study features a well-executed source apportionment analysis using PMF modeling and provides valuable estimates of the impacts of these VOCs on ozone and secondary organic aerosol (SOA) formation. However, the manuscript would benefit from greater clarity regarding especially the new findings and a broader perspective. Additionally, some restructuring is recommended.

The results are currently discussed from a very localized perspective. It would strengthen the manuscript to explore the broader applicability of the methods and findings to other regions. For instance, the authors could discuss what implications the findings have for VOCs, OFP and SOAP in Europe more generally. The study could also highlight how a long-term dataset enables the investigation of seasonal variations in VOC sources, which are shown to be significant in this study, and compare these seasonal trends with emission inventories for Europe. How do the source contributions in this study relate to findings from other European locations or globally? What aspects of the emissions are unique to the Marseille site? Are there other areas in the world with similar unique emissions?  Additionally, how does the source apportionment differ from studies conducted in Chinese megacities or the United States?

While source apportionment studies on VOCs in Europe have been conducted for over two decades, it would be helpful to explicitly outline what new insights this study provides and to place greater emphasis on these novel findings  when presenting results and in the discussion.

The manuscript currently includes an extensive set of figures and tables. Please consider which are most critical and whether some could be presented more compactly or moved to the supplementary material. Figures should highlight new and significant results, while data supporting expected outcomes could be relocated to the supplement. Additionally, some figures could be presented in a clearer format.

Specific comments:

1. Section 2.2: What type of inlet system was used?
2. Section 2.2: Nafion dryers are known to introduce high and variable backgrounds for certain light alkenes, such as trans- and cis-butene. Was the blank measurement performed through the Nafion dryer?
3. Figure 3: Consider moving this figure to the supplementary material.
4. Section 3.3: It would be helpful to include the concentration levels of all studied compounds, perhaps in a table in the supplementary material.
5. Lines 222–223: Could the lower VOC concentrations in Athens (and possibly Beirut) compared to Marseille be due to poorer ventilation in those cities?
6. Table 8: The term "Rheating/BCwb" is not explained here and may already be presented in Table 7. Please clarify.
7. Lines 365–367 & related lines on terpenes: The results on terpenes are likely not quantitative due to losses and isomerization caused by the Nafion dryer. Please include a comment in the manuscript addressing this limitation or reconsider detailed discussions of these compounds.
8. Lines 367–368: Note that cleaning and personal care products are also significant sources of limonene.
9. Lines 483–485: Higher alkanes could serve as tracers for indoor air (e.g., Mai et al., 2024; https://doi.org/10.1016/j.heha.2023.100087). Please consider referencing this study.
10. Figure 14: Consider moving this figure to the supplementary material.
11. Line 517: Photochemistry remains critical for the most reactive VOCs. Please clarify this point.
12. Lines 521–522 & 613–615: These sentences are difficult to follow. Please rephrase for better clarity.
13. Lockdown effects: While the authors conclude that factor contributions decreased significantly during the lockdown, it would be valuable to quantify the impact on air quality. How strongly did the lockdown affect the OFP and SOAP of the studied VOCs?

General Comments:

The manuscript presents long-term VOC measurements at an urban site in Marseille using TD-GC-FID. The results are further analyzed with PMF for source apportionment across different seasons. Long-term measurements of speciated VOCs are rare and valuable globally, making this manuscript a significant contribution to understanding urban VOC sources.

However, the manuscript contains 15 figures and 12 tables, which might overwhelm readers. It would be helpful to streamline these details - consider consolidating some figures or moving others to the supplementary information. For instance, Figures 5, 8, 9, and 11 display multi-panel factor profiles across multiple seasons, which may be too detailed for a broad ACP audience. Simplifying these figures (perhaps like Figure 13, which is clear and informative) to show seasonal changes in profiles could reduce cognitive load for readers and enhance the presentation. Additionally, displaying a few key factor profiles in the main text, while relegating others to the SI, could balance detail with readability. Grouping the wind roses of different factors together in one place for easier comparison would also improve clarity.

Overall, the manuscript is compelling, offering novel insights into regional VOC sources in the Mediterranean urban region of Marseille. Streamlining the presentation would improve coherence and accessibility.

Specific Comments:

1. Comparisons with Other Studies: Table 4 does a great job comparing VOC mixing ratios in Marseille with other Mediterranean cities. It would be helpful to emphasize what makes the Marseille region unique, as well as the similarities and differences with other cities. A brief discussion addressing the "So what?" factor - why these comparisons matter - would enhance the impact of the findings.

2. Inconsistent Decimal Usage: I noticed inconsistent use of decimal points. In some tables, dots are used, while commas are used in most figures. This inconsistency could confuse readers, particularly American audiences, who might misinterpret a comma as a thousands separator. For example, Figure 3 could be misread as showing very high concentrations in ppm when the authors likely intended for the comma to indicate decimal points. I recommend standardizing the decimal notation (either dots or commas) throughout the manuscript. Also, consider reducing the number of significant figures in some cases - 10,000 ppb of toluene could be expressed as 10.0 or 10.00 ppb for clarity.

3. Mistral Impact: Section 3.3.7 discusses the impact of Mistral events. Is the hypothesis that these events dilute the sources or that they alter air circulation patterns in a way that affects VOC concentrations? Clarifying this point would strengthen the argument.

4. VOC-NOx Correlations: The relatively low Pearson coefficients in Table 9 for VOC-NOx correlations are intriguing. Have the authors considered constraining the analysis to daytime hours or using different subsets of VOCs to explore potential stronger dependencies? Also, I noticed that ozone was not included in the correlational analysis - was there a particular reason for this omission?

5. Biogenic Sources: Figure 13 is excellent, showing traffic peaks and seasonal contributions from different sources. However, I was surprised that the biogenic factor appeared only in summer. Given the vegetative nature of the region, I would expect biogenic contributions during spring and fall as well. Could it be that the biogenic contributions were merged with another factor? It would be interesting to know which factor monoterpenes and isoprene were assigned to.

6. Unconventional VOC Sources: The manuscript provides a valuable regional discussion of VOC impacts on SOAPs and OFPs, highlighting traffic as a major contributor. However, other less conventional sources - such as cooking (restaurants, fast food), asphalt, and human emissions (e.g., consumer care products) - weren’t discussed. These could be significant contributors, and I think it would strengthen the manuscript to briefly mention or speculate on these potential sources.

7. Biogenic VOCs (BVOCs): While the source apportionment work seems solid overall, the discussion of biogenic VOCs (BVOCs) seems somewhat underplayed. Given that BVOCs are important in Mediterranean coastal regions, it might be useful to include a brief mention of sea breeze effects or biogenics from seawater, as reported in other studies (e.g., Dayan et al., 2020).

Overall, this paper is informative and provides valuable insights into VOC sources in an urban Mediterranean setting. I recommend reorganizing the manuscript to create a more cohesive story with fewer figures in the main text (moving the rest to SI). This would help make the paper more accessible to a wider audience.

References:

Dayan, C., Fredj, E., Misztal, P. K., Gabay, M., Guenther, A. B., and Tas, E.: Emission of biogenic volatile organic compounds from warm and oligotrophic seawater in the Eastern Mediterranean, Atmos. Chem. Phys., 20, 12741–12759, https://doi.org/10.5194/acp-20-12741-2020, 2020.