the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Jan 2024
Evaluation of modelled versus observed NMVOC compounds at EMEP sites in Europe
Abstract. Atmospheric volatile organic compounds (VOC) constitute a wide range of species, acting as precursors to ozone and aerosol formation. Atmospheric chemistry and transport models (CTMs) are crucial to understanding the emissions, distribution, and impacts of VOCs. Given the uncertainties in VOC emissions, lack of evaluation studies, and recent changes in emissions, this work adapts the European Monitoring and Evaluation Programme Meteorological Synthesizing Centre – West (EMEP MSC-W) CTM to evaluate emission inventories in Europe. Here we undertake the first intensive model-measurement comparison of VOCs in two decades. The modelled surface concentrations are evaluated both spatially and temporally, using measurements from the regular EMEP monitoring network in 2018 and 2019, and a 2022 campaign. To achieve this, we utilised the UK National Atmospheric Emission Inventory to derive explicit emission profiles for individual species and employed a `tracer' method to produce pure concentrations that are directly comparable to observations. Model simulations for 2018 compare the use of two European inventories, CAMS and CEIP, and of two chemical mechanisms, CRIv2R5Em and EmChem19rc; those for 2019 and 2022 use CAMS and CRIv2R5Em only.
The degree to which the modelled and measured VOCs agree varies depending on the specific species. The model successfully captures the overall spatial and temporal variations of major alkanes (e.g., ethane, n-butane) and unsaturated species (e.g., ethene, benzene), but less though for propane, i-butane, and ethyne. This discrepancy underscores potential issues in the boundary conditions for these latter species and in their primary emissions from in particular the solvent and road transport sectors. Specifically, potential missing propane emissions and issues with its boundary conditions are highlighted by large model underestimations and smaller propane to ethane ratios compared to the measurement. Meanwhile, both the model and measurement show strong linear correlations among butane isomers and among pentane isomers, indicating common sources for these pairs of isomers. However, modelled ratios of i- to n-butane and i- to n-pentane are approximately one-third of the measured ratios, which is largely driven by significant emissions of n-butane and n-pentane from the solvent sector. This suggests issues with the speciation profile of the solvent sector, or underrepresented contributions from transport and fuel evaporation sectors in current inventories, or both. Furthermore, the modelled ethene-to-ethyne and benzene-to-ethyne ratios differ significantly from measured ratios. The different model performance strongly points to shortcomings in the spatial and temporal patterns and magnitudes of ethyne emissions, especially during winter. For OVOCs, modelled and measured methanal and methylglyoxal display a good agreement, which demonstrates that the model captures the overall photo-oxidation processes reasonably well. However, the insufficiency of suitable measurements limits the evaluation of other OVOCs. Finally, the model exhibits very similar performance across simulations using different inventories, which suggests that the emission profiles are likely to exert a more significant impact on the agreement between modelled and measured data than the total emissions reported for each sector. Therefore, the future focus may need to shift towards refining these speciation profiles through for example new emission measurement campaigns to improve the model accuracy.
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RC1: 'Comment on egusphere-2023-3102', Anonymous Referee #1, 28 Feb 2024
Yao Ge et al. utilise the EMEP chemical transport model and measurements to assess VOCs in Europe. They evaluated CEIP and CAMS emission inventories and different chemical mechanisms, conducting extensive analyses of VOC species and modelled versus observed ratios. By doing so, the authors were able to identify several uncertainties, particularly in emissions, that should be further investigated by the scientific community. I appreciate the authors highlighting the need for updated speciation profiles and improvements in the VOC measuring networks. Therefore, this paper gives an important step towards reducing the knowledge gap on VOCs. While, I think it deserves publication in EGUsphere, there are some questions/issues that need to be addressed, which can be found bellow:
- Clarify the rationale for evaluating both 2018 and 2019, as the focus seems primarily on 2018 without clearly presenting key conclusions on the differences/similarities between years. Also, it should be important to clarify the selection of these years.
- (Fig. 2) What could be behind the big differences between both inventories of the total VOC emissions of “C-Other combustion” and “D-Fugitive”? Looking at the speciation used, it seems that these sectors are important for some of the species evaluated in this study.
- Table 4 and Fig. 3 present the same information. I would remove/move to appendix one of them.
- The information provided in Section 4 feels out of place and should be introduced before. Table 5 should be moved to section 3.5 when presenting the model experiments. From L.293 to L.304, the information presented is related to the measurements and therefore should be moved to section 3.4.
- (L.293-304) It is relevant to mention the measurements’ time resolution. However, I would expect that not all the stations use the same measurement techniques. This should also lead to a certain degree of uncertainty when comparing the different stations. So, it would be interesting to also mention it.
- In section 4.2.2, when compared to other sections, I was expecting more discussion on the results. For example, some comments on the station CH0053R.
- (L.550) The authors mention that ethyne and benzene share a similar source, but when looking at the speciation profiles (Fig.2) used for the different sectors I fail to see it. For example, the sector “C-other combustion” shows a big share for benzene but none for ethyne.
- (L.554) “....but the emission inputs need to be scrutinized and potentially revised to better reflect real-world conditions.” How so?
- The authors mention that the default speciation in the EMEP model is EmChem19rc, so why are the results presented mainly using CRIv2R5Em (L.305)? For the sensibility analysis, could the two chemical mechanisms show a very different sensitivity on ozone to changes in VOCs?
- I understand that the sensibility analysis presented in section 4.6 and Appendix G is beyond the scope of the study. My main concern goes towards the selection of the speciation profile. Why did the authors use a gasoline vehicle speciation profile to represent solvent emissions?
Technical corrections:
- Could be just a question of the formatting but some figures seem to appear misplaced in other subsections, e.g. Fig. 3 should be in section 3.4, Fig. 16 in section 4.3.2.
- (L.608) “ose”?
- Standardise, e.g., i-butane/iso-butane, i-pentane/iso-pentane, throughout the text.
- I leave the decision to the authors, but consider moving time series plots (Fig. 13 and 15) to the appendix.
Citation: https://doi.org/10.5194/egusphere-2023-3102-RC1 -
AC1: 'Reply on RC1', Yao Ge , 11 Apr 2024
We thank the reviewer for their time spent reading our manuscript and for their recommendation for publication upon addressing their comments. In the attached file, we include all the reviewer’s comments and provide in blue text our point-by-point responses. Please note that all section numbers and line numbers mentioned in our responses refer to the clean revised manuscript (not the track-changed version).
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RC2: 'Comment on egusphere-2023-3102', Anonymous Referee #2, 01 Mar 2024
This work evaluated the modeled VOC emissions based on surface measurements using a “tracer” method. They found overall good agreement on spatial and temporal variations of major alkanes and unsaturated species, but less for propane, i-butane and ethyne. It’s suggested that the emission profiles are likely to have a more significant impact than the total emissions on the model performance. There are lots of information but less organized. The figure quality also needs to be improved.
My detailed comments are listed below.
- Line 10-12: I feel like the detailed configuration is not appropriate in the abstract.
- Line 15-16: boundary conditions have the same impact for all species, why do you emphasize the impact for the latter species? Doesn't make sense. Please elaborate more.
- Line 24-25: In winter, the lifetime is longer. How will the bias of meteorology and chemistry affect the model performance?
- Line 26: It's complicated. OVOC can also emitted from biofuel combustion, etc.
- Line 29-30: I don’t get the logic of this sentence. Since the performances are similar, how can you draw a conclusion on the significant impact of emission profiles?
- Line 104: what’s the difference between these two chemical mechanisms? Why do you choose these two?
- Table 1: Don't understand to choose o-xylene as a tracer. They're active in chemical reaction, and can be produced as a secondary product. Why don't use benzene? Also, the same question for choosing C2H5OH as a tracer.
- Figure 4: Please improve this figure and the following ones. The labels are overlapped and hard to tell.
Citation: https://doi.org/10.5194/egusphere-2023-3102-RC2 -
AC2: 'Reply on RC2', Yao Ge , 11 Apr 2024
We thank the reviewer for their time spent reading our manuscript. In the attached file, we include all the reviewer’s comments and provide in blue text our point-by-point responses. Please note that the line numbers mentioned in our responses refer to the clean revised manuscript (not the track-changed version).
Status: closed
-
RC1: 'Comment on egusphere-2023-3102', Anonymous Referee #1, 28 Feb 2024
Yao Ge et al. utilise the EMEP chemical transport model and measurements to assess VOCs in Europe. They evaluated CEIP and CAMS emission inventories and different chemical mechanisms, conducting extensive analyses of VOC species and modelled versus observed ratios. By doing so, the authors were able to identify several uncertainties, particularly in emissions, that should be further investigated by the scientific community. I appreciate the authors highlighting the need for updated speciation profiles and improvements in the VOC measuring networks. Therefore, this paper gives an important step towards reducing the knowledge gap on VOCs. While, I think it deserves publication in EGUsphere, there are some questions/issues that need to be addressed, which can be found bellow:
- Clarify the rationale for evaluating both 2018 and 2019, as the focus seems primarily on 2018 without clearly presenting key conclusions on the differences/similarities between years. Also, it should be important to clarify the selection of these years.
- (Fig. 2) What could be behind the big differences between both inventories of the total VOC emissions of “C-Other combustion” and “D-Fugitive”? Looking at the speciation used, it seems that these sectors are important for some of the species evaluated in this study.
- Table 4 and Fig. 3 present the same information. I would remove/move to appendix one of them.
- The information provided in Section 4 feels out of place and should be introduced before. Table 5 should be moved to section 3.5 when presenting the model experiments. From L.293 to L.304, the information presented is related to the measurements and therefore should be moved to section 3.4.
- (L.293-304) It is relevant to mention the measurements’ time resolution. However, I would expect that not all the stations use the same measurement techniques. This should also lead to a certain degree of uncertainty when comparing the different stations. So, it would be interesting to also mention it.
- In section 4.2.2, when compared to other sections, I was expecting more discussion on the results. For example, some comments on the station CH0053R.
- (L.550) The authors mention that ethyne and benzene share a similar source, but when looking at the speciation profiles (Fig.2) used for the different sectors I fail to see it. For example, the sector “C-other combustion” shows a big share for benzene but none for ethyne.
- (L.554) “....but the emission inputs need to be scrutinized and potentially revised to better reflect real-world conditions.” How so?
- The authors mention that the default speciation in the EMEP model is EmChem19rc, so why are the results presented mainly using CRIv2R5Em (L.305)? For the sensibility analysis, could the two chemical mechanisms show a very different sensitivity on ozone to changes in VOCs?
- I understand that the sensibility analysis presented in section 4.6 and Appendix G is beyond the scope of the study. My main concern goes towards the selection of the speciation profile. Why did the authors use a gasoline vehicle speciation profile to represent solvent emissions?
Technical corrections:
- Could be just a question of the formatting but some figures seem to appear misplaced in other subsections, e.g. Fig. 3 should be in section 3.4, Fig. 16 in section 4.3.2.
- (L.608) “ose”?
- Standardise, e.g., i-butane/iso-butane, i-pentane/iso-pentane, throughout the text.
- I leave the decision to the authors, but consider moving time series plots (Fig. 13 and 15) to the appendix.
Citation: https://doi.org/10.5194/egusphere-2023-3102-RC1 -
AC1: 'Reply on RC1', Yao Ge , 11 Apr 2024
We thank the reviewer for their time spent reading our manuscript and for their recommendation for publication upon addressing their comments. In the attached file, we include all the reviewer’s comments and provide in blue text our point-by-point responses. Please note that all section numbers and line numbers mentioned in our responses refer to the clean revised manuscript (not the track-changed version).
-
RC2: 'Comment on egusphere-2023-3102', Anonymous Referee #2, 01 Mar 2024
This work evaluated the modeled VOC emissions based on surface measurements using a “tracer” method. They found overall good agreement on spatial and temporal variations of major alkanes and unsaturated species, but less for propane, i-butane and ethyne. It’s suggested that the emission profiles are likely to have a more significant impact than the total emissions on the model performance. There are lots of information but less organized. The figure quality also needs to be improved.
My detailed comments are listed below.
- Line 10-12: I feel like the detailed configuration is not appropriate in the abstract.
- Line 15-16: boundary conditions have the same impact for all species, why do you emphasize the impact for the latter species? Doesn't make sense. Please elaborate more.
- Line 24-25: In winter, the lifetime is longer. How will the bias of meteorology and chemistry affect the model performance?
- Line 26: It's complicated. OVOC can also emitted from biofuel combustion, etc.
- Line 29-30: I don’t get the logic of this sentence. Since the performances are similar, how can you draw a conclusion on the significant impact of emission profiles?
- Line 104: what’s the difference between these two chemical mechanisms? Why do you choose these two?
- Table 1: Don't understand to choose o-xylene as a tracer. They're active in chemical reaction, and can be produced as a secondary product. Why don't use benzene? Also, the same question for choosing C2H5OH as a tracer.
- Figure 4: Please improve this figure and the following ones. The labels are overlapped and hard to tell.
Citation: https://doi.org/10.5194/egusphere-2023-3102-RC2 -
AC2: 'Reply on RC2', Yao Ge , 11 Apr 2024
We thank the reviewer for their time spent reading our manuscript. In the attached file, we include all the reviewer’s comments and provide in blue text our point-by-point responses. Please note that the line numbers mentioned in our responses refer to the clean revised manuscript (not the track-changed version).
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Cited
2 citations as recorded by crossref.
- On the uncertainty of anthropogenic aromatic volatile organic compound emissions: model evaluation and sensitivity analysis K. Oliveira et al. 10.5194/acp-24-7137-2024
- Shipping and algae emissions have a major impact on ambient air mixing ratios of non-methane hydrocarbons (NMHCs) and methanethiol on Utö Island in the Baltic Sea H. Hellén et al. 10.5194/acp-24-4717-2024