the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 Dec 2024
VOC sources and impacts at an urban Mediterranean area (Marseille – France)
Abstract. Long-term measurements of VOC concentrations are crucial to improve our knowledge about their role in atmospheric chemistry, especially in region with high photochemistry such as the Mediterranean Basin. A field measurement campaign of 18 months has been conducted in Marseille from March 2019 to August 2020 with online measurement of C2 to C16 NMHC using two TD-GC-FID instruments. The positive Matrix Factorization model has been applied to this dataset for each season. Six factors were identified yearlong (traffic exhaust, fuel evaporation, industrial source, shipping, regional and local urban background and IVOC) and two were identified as seasonal factors (biogenic in summer and residential heating during cold period).
The traffic (exhaust and evaporation) is the first contributor to NMHC concentration measured with a relative contribution of about 40 % with the exception of spring 2020 where the relative contribution was only 25 %. The potential contribution of each factor to secondary pollutants formation has been evaluated. Results reveal that the shipping source is potentially one of the most important contributors to the Secondary Organic Aerosol formation potential despite the low contribution of this factor to NMHC concentration.
The impact of the lockdown due to Covid-19 is clearly visible on all sources and especially on the traffic source. The contribution of this source has decreased by a half during spring 2020 in comparison with other seasons.
A comparison of these results with emission inventories should be useful to evaluate their accuracy for a better understanding of the atmospheric pollution occurring at Marseille.
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Status: open (until 21 Jan 2025)
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RC1: 'Comment on egusphere-2024-3576', Anonymous Referee #2, 30 Dec 2024
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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:
- Section 2.2: What type of inlet system was used?
- 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?
- Figure 3: Consider moving this figure to the supplementary material.
- Section 3.3: It would be helpful to include the concentration levels of all studied compounds, perhaps in a table in the supplementary material.
- Lines 222–223: Could the lower VOC concentrations in Athens (and possibly Beirut) compared to Marseille be due to poorer ventilation in those cities?
- Table 8: The term "Rheating/BCwb" is not explained here and may already be presented in Table 7. Please clarify.
- 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.
- Lines 367–368: Note that cleaning and personal care products are also significant sources of limonene.
- 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.
- Figure 14: Consider moving this figure to the supplementary material.
- Line 517: Photochemistry remains critical for the most reactive VOCs. Please clarify this point.
- Lines 521–522 & 613–615: These sentences are difficult to follow. Please rephrase for better clarity.
- 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?
Citation: https://doi.org/10.5194/egusphere-2024-3576-RC1
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