the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Mar 2023
Modelling the impacts of emission changes on O3 sensitivity, atmospheric oxidation capacity and pollution transport over the Catalonia region
Veronica Vidal
Sergi Ventura
Roger Curcoll
Ricard Segura
Gara Villalba
Abstract. Tropospheric ozone (O3) is an important surface pollutant in urban areas, and it has complex formation mechanisms that depend on the atmospheric chemistry and meteorological factors. The severe reductions observed in anthropogenic emissions during the COVID-19 pandemic can further our understanding of the photochemical mechanisms leading to O3 formation and provide guidance for policies aimed at reducing air pollution. In this study, we use the air quality model WRF-Chem coupled with the urban canopy model BEP-BEM to investigate changes in the ozone chemistry over the Metropolitan Area of Barcelona (AMB) and its atmospheric plume moving northwards, which is responsible for the highest number of hourly O3 exceedances in Spain. The trajectories of the air masses from the AMB to the Pyrenees are studied with the Lagrangian particle dispersion model FLEXPART-WRF. The aim is to investigate the response of ozone chemistry to changes in the precursor emissions. The results show that with the reduction in emissions: 1) the ozone chemistry tends to enter the nitrogen oxide (NOx)-limited or transition regimes; however, highly polluted urban areas are still in the Volatile Organic Compounds (VOC)-limited regime, 2) the reduced O3 production is overwhelmed by reduced nitric oxide (NO) titration, resulting in a net increase in the O3 concentration (up to 20 %) in the evening, 3) the increase in the maximum O3 level (up to 6 %) during the lockdown could be attributable to an enhancement in the atmospheric oxidation capacity (AOC), 4) the daily maximum levels of ozone and odd oxygen species (Ox) generally decreased (4 %) in May with the reduced AOC, indicating an improvement in the air quality, and, 5) ozone precursor concentration changes in the AMB contribute to the pollution plume moving along the S–N valley to the Pyrenees. Our results indicate that O3 abatement strategies cannot rely only on NOx emission control but must include a significant reduction in anthropogenic sources of VOCs (e.g., for power plants and heavy industry). In addition, our results show that mitigation strategies intended to reduce O3 should be designed according to the local meteorology, air transport, particular ozone regimes and AOC of the urban area.
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Alba Badia et al.
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-160', Anonymous Referee #1, 28 Mar 2023
This is a very nice analysis that provides a lot of useful information and insight regarding the production of ozone associated with the reduction of anthropogenic emissions during the COVID-19 pandemic, as well as the changes in the chemical regime associated with it.
Specific comments
Line 22: Add more recent references as Fleming et al (2018), Sillman et al (2021)
Line 70: remove 70
Section 2: some of the discussion belongs to Introduction.
Lines 174-185: the discussion could be part of the supplementary material.
Line 193: Fig 2 is refereed first time after Figs. 3 and 4
Section 3.1: Mar et al (2016), Im et al (2016) showed that RADM2 underestimates the O3 concentration when compared to other chemical mechanisms. A discussion about the choice of chemical mechanism would be beneficial since it looks like the Authors obtained the right answers for the wrong reasons.
Section 3.3: Please check the numbers in the Tables, not always the MB=MM-OM
Lines 301-314: A lot of this information should go to the Figures caption (e.g. “The dots in the lower row represent the land use for each grid cell, which is the key to understanding how industrial, open urban, compact urban, water, agriculture, natural open and forestland uses influenced the O3 regimes”)
Line 315: please specify the land-use categories that belong to “green areas”.
Figures 3-4: Increase the size of the cross and explain what it represents.
Figure 5 Sectors A and G, B and H, as well as the pollutants CO and NOx and NH3 and PM10 have similar colors and it is difficult to distinguish between different lines.
Figures 6-8 As before, we can’t really distinguish the colors. I would suggest using a discrete color scale.
Figures 12-14 There is no reference to these Figures in the text.
Table 1 define F0, F1, F2, F3
Fleming, Z., Doherty, R., Von Schneidemesser, E., Malley, C., Cooper, O., Pinto, J., Colette, A., Xu, X., Simpson, D., Schultz, M., Lefohn, A., Hamad, S., Moolla, R., Solberg, S., and Feng, Z.: Tropospheric Ozone Assessment Report: Present-day ozone distribution and trends relevant to human health, Elementa, 6, 12, https://doi.org/10.1525/elementa.273, 2018
Sillmann, J., Aunan, K., Emberson, L., Büker, P., Van Oort, B., O'Neill, C., Otero, N., Pandey, D., and Brisebois, A.: Combined impacts of climate and air pollution on human health and agricultural productivity, Environ. Res. Lett., 16, 093004, https://doi.org/10.1088/1748-9326/ac1df8, 2021.
Mar, K. A., Ojha, N., Pozzer, A., and Butler, T. M.: Ozone air quality simulations with WRF-Chem (v3.5.1) over Europe: model evaluation and chemical mechanism comparison, Geosci. Model Dev., 9, 3699–3728, https://doi.org/10.5194/gmd-9-3699-2016, 2016.
Im, U., Bianconi, R., Solazzo, E., Kioutsioukis, I., Badia, A., Balzarini, A., Baro, R., Bellasio, R., Brunner, D., Chemel, C., Curci, G., Flemming, J., Forkel, R., Giordano, L., Jimenez-Guerrero, P., Hirtl, M., Hodzic, A., Honzak, L., Jorba, O., Knote, C., Kuenen, J.J.P., Makar, P.A., Manders-Groot, A., Neal, L., Perez, J.L., Pirovano, G., Pouliot, G., San Jose, R., Savage, N., Schroder, W., Sokhi, R.S., Syrakov, D., Torian, A., Tuccella, P., Werhahn, K., Wolke, R., Yahya, K., Zabkar, R., Zhang, Y., Zhang, J., Hogrefe, C., Galmarini, S., 2015. Evaluation of operational online-coupled regional air quality models over Europe and North America in the context of AQMEII phase 2. Part I: Ozone. Atmos. Environ. 115, 404e420.
Citation: https://doi.org/10.5194/egusphere-2023-160-RC1 -
RC2: 'Comment on egusphere-2023-160', Anonymous Referee #2, 07 May 2023
This is an interesting paper looking at the impact of emissions reductions on atmospheric chemistry. It takes the area in and around the Barcelona metropolitan area as a natural laboratory, and studies two periods in 2020 as exemplar systems to understand the effect of emissions reductions on ozone and NO2.
The paper describes a model study using WRF-Chem coupled to an urban canopy model to look at atmospheric processes over the AMB region, and FLEXPART-WRF to do some trajectory analysis to study the chemistry occurring as air flows inland.
This is an ambitious study which aims to use the connection between the natural experiment of emissions reductions in the months of April/May 2020, and through analysis of idealised counterfactual experiments perform attribution of the effect of
emissions reductions.The experimental design and analysis appear sound and this manuscript fits well within the scope of ACP. I feel the structure of the manuscript could be improved, and the discussion should be improved in places before publication.
The title is the first area to address - I felt it was perhaps a bit too general, as the main focus is the impact of lockdown. The abstract can also be a bit more explicit eg L8/9 'response of ozone chemistry to changes' could make more explicit what reduction is under discussion. AOC needs to be defined in the abstract, and for the sake of clarity that it excludes O3 oxidant.
Abstract Conclusion # 3 is not clear - what is the mechanism? Conclusion #4 could the authors explain why May is important? Conclusion 5 - not sure what is meant by a change contributing to a plume. Perhaps re-word?
S2 describes the region selected for study, geography, Barcelona's air quality with respect to guidelines, the Vic Plain and the ozone situation in 20202. Two periods are identified for closer study, and also days of even closer study. I feel the manuscript would be more readable if it would it be possible to decide on a single consistent nomenclature for the two periods, eg P1 and P2 and so avoid changing between Mar-Apr/lockdown/first period and May/relaxation through the text
L174-185 Some of this section could be grouped with the discussion of the trajectory experiments, as it mixes model description with some analysis that probably belongs with the discussion in S5.3. It would be interesting to better justify why these days were chosen for further study - what aspects do these days/analysis bring out?
S3 describes the WRF-Chem experiments performs some model evaluation against observations. The model is shown to be more skillful in meteorology than chemistry, with ozone biases around 20-30% shown. The authors do not discuss if the bias in the model means that the model correctly simulates the difference in ozone/NO2 from a change in emissions. Given the chemistry is non-linear, would the response be greater/smaller in a less biased model? Would it make sense to compare ozone changes in the model with differences in climatology/COVID period at the observation stations of interest to assess if the model gets delta_O3 correct?
S4 describes the results of the experiments. This section in the MS has the most potential for improvement, I feel. Firstly, the changes in O3, NO2 and Ox are given in the supplementary. Is it worth moving figures S3 and S4 into the main text? I appreciate the changes are given in absolute (LH) and relative (RH) terms for both period 1 adn period 2. Could the labelling of these figures be improved to indicate what data are plotted in each of the four rows are? There are no labels on each of the second and fourth rows. The text in S4.1 could do with a further polish, e.g.
L27 is 1% significant?
L285 the 'two simulations' of what?
L287 constant between what?SS5.1 is interesting. I presume the graphs shown are for model results, and it would help to have this stated. Did the authors consider performing a similar analysis for observational data for this period? Is it difficult due to a lack of VOC data? The captions of Figure 6-8 needs to state explicitly that these are 'Changes...' between BAU and COVID
Colouring data by ozone change and land use/land cover is interesting, and the broken lines make the analysis goal clear. I would like to see the analysis better justified, though. I assume it is correct to use the lines which are derived from an analysis of transition regimes based on NOx and VOC emissions in Sillman (rather than changes in NOx/VOC levels used here) but I'd like the paper to discuss somewhere how these regimes apply when discussing a _change_ in O3 and a change in NOx or VOC levels, particularly in identifying regions of the diagrams here with NOx- or VOC-limited regimes, which seems key. I've not seen an analysis like this before, so would like to see this expanded upon.
L315 and on, could the authors explain how the figures can be used to support this statement? L326, L330 the discussion reverts to ozone levels, not differences between scenarios. Could this discussion be made more consistent?
L319 grid points not grid.
SS5.2 discusses the oxidising capacity in terms of OH and NO3. Is there any impact on ozone budgets seen from changing HO (and presumably OH:HO2 ratio), particularly in HO2 + NO vs OH + NO2 vs OH + O3?
SS5.3 is very nice, and might be improved in consistency with a discussion of Ox (and maybe formation of Ox/NOx reservoirs and sinks) as in previous sections.
S6 summarises nicely. The sentence in L438 'this was consistent...' needs to be expanded.
L454 'data used in this study...' add 'are'
Overall
Citation: https://doi.org/10.5194/egusphere-2023-160-RC2 -
AC2: 'Reply on RC2', Alba Badia Moragas, 09 Jun 2023
We thank the reviewers for the constructive comments and suggestions which have helped us improve the manuscript. Below we give full detailed answers to each issue raised by each reviewer. Our response is in blue, to differentiate from the comment which is in black. Furthermore, we include any new text added in the manuscript in red, to facilitate this second revision.
To summarize the main changes to the manuscript, we would like to point out:
-
We have expanded the discussion section to include 1) a more detailed description of the two different photochemical regimes that describe the sensitivity of O3 to its precursors, 2) a new figure entitled “O3 concentration as a function of VOC/NOx concentration.”, 3) more description of the trajectory experiments using the FLEXPART-WRF model and 4) further justification of the chemical scheme chosen for the simulations.
-
We have rewritten the main text to clarified that changes in the oxidation capacity are related to O3 concentrations given that VOC and CO oxidation by OH are the initial reactions for ozone formation and we have expanded the discussion of the oxidation capacity.
-
We have added more references to support the main text when introducing the tropospheric ozone and O3 photochemical regimes.
-
-
AC2: 'Reply on RC2', Alba Badia Moragas, 09 Jun 2023
-
AC1: 'Comment on egusphere-2023-160', Alba Badia Moragas, 09 Jun 2023
We thank the reviewers for the constructive comments and suggestions which have helped us improve the manuscript. Below we give full detailed answers to each issue raised by each reviewer. Our response is in blue, to differentiate from the comment which is in black. Furthermore, we include any new text added in the manuscript in red, to facilitate this second revision.
To summarize the main changes to the manuscript, we would like to point out:
-
We have expanded the discussion section to include 1) a more detailed description of the two different photochemical regimes that describe the sensitivity of O3 to its precursors, 2) a new figure entitled “O3 concentration as a function of VOC/NOx concentration.”, 3) more description of the trajectory experiments using the FLEXPART-WRF model and 4) further justification of the chemical scheme chosen for the simulations.
-
We have rewritten the main text to clarified that changes in the oxidation capacity are related to O3 concentrations given that VOC and CO oxidation by OH are the initial reactions for ozone formation and we have expanded the discussion of the oxidation capacity.
-
We have added more references to support the main text when introducing the tropospheric ozone and O3 photochemical regimes.
-
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-160', Anonymous Referee #1, 28 Mar 2023
This is a very nice analysis that provides a lot of useful information and insight regarding the production of ozone associated with the reduction of anthropogenic emissions during the COVID-19 pandemic, as well as the changes in the chemical regime associated with it.
Specific comments
Line 22: Add more recent references as Fleming et al (2018), Sillman et al (2021)
Line 70: remove 70
Section 2: some of the discussion belongs to Introduction.
Lines 174-185: the discussion could be part of the supplementary material.
Line 193: Fig 2 is refereed first time after Figs. 3 and 4
Section 3.1: Mar et al (2016), Im et al (2016) showed that RADM2 underestimates the O3 concentration when compared to other chemical mechanisms. A discussion about the choice of chemical mechanism would be beneficial since it looks like the Authors obtained the right answers for the wrong reasons.
Section 3.3: Please check the numbers in the Tables, not always the MB=MM-OM
Lines 301-314: A lot of this information should go to the Figures caption (e.g. “The dots in the lower row represent the land use for each grid cell, which is the key to understanding how industrial, open urban, compact urban, water, agriculture, natural open and forestland uses influenced the O3 regimes”)
Line 315: please specify the land-use categories that belong to “green areas”.
Figures 3-4: Increase the size of the cross and explain what it represents.
Figure 5 Sectors A and G, B and H, as well as the pollutants CO and NOx and NH3 and PM10 have similar colors and it is difficult to distinguish between different lines.
Figures 6-8 As before, we can’t really distinguish the colors. I would suggest using a discrete color scale.
Figures 12-14 There is no reference to these Figures in the text.
Table 1 define F0, F1, F2, F3
Fleming, Z., Doherty, R., Von Schneidemesser, E., Malley, C., Cooper, O., Pinto, J., Colette, A., Xu, X., Simpson, D., Schultz, M., Lefohn, A., Hamad, S., Moolla, R., Solberg, S., and Feng, Z.: Tropospheric Ozone Assessment Report: Present-day ozone distribution and trends relevant to human health, Elementa, 6, 12, https://doi.org/10.1525/elementa.273, 2018
Sillmann, J., Aunan, K., Emberson, L., Büker, P., Van Oort, B., O'Neill, C., Otero, N., Pandey, D., and Brisebois, A.: Combined impacts of climate and air pollution on human health and agricultural productivity, Environ. Res. Lett., 16, 093004, https://doi.org/10.1088/1748-9326/ac1df8, 2021.
Mar, K. A., Ojha, N., Pozzer, A., and Butler, T. M.: Ozone air quality simulations with WRF-Chem (v3.5.1) over Europe: model evaluation and chemical mechanism comparison, Geosci. Model Dev., 9, 3699–3728, https://doi.org/10.5194/gmd-9-3699-2016, 2016.
Im, U., Bianconi, R., Solazzo, E., Kioutsioukis, I., Badia, A., Balzarini, A., Baro, R., Bellasio, R., Brunner, D., Chemel, C., Curci, G., Flemming, J., Forkel, R., Giordano, L., Jimenez-Guerrero, P., Hirtl, M., Hodzic, A., Honzak, L., Jorba, O., Knote, C., Kuenen, J.J.P., Makar, P.A., Manders-Groot, A., Neal, L., Perez, J.L., Pirovano, G., Pouliot, G., San Jose, R., Savage, N., Schroder, W., Sokhi, R.S., Syrakov, D., Torian, A., Tuccella, P., Werhahn, K., Wolke, R., Yahya, K., Zabkar, R., Zhang, Y., Zhang, J., Hogrefe, C., Galmarini, S., 2015. Evaluation of operational online-coupled regional air quality models over Europe and North America in the context of AQMEII phase 2. Part I: Ozone. Atmos. Environ. 115, 404e420.
Citation: https://doi.org/10.5194/egusphere-2023-160-RC1 -
RC2: 'Comment on egusphere-2023-160', Anonymous Referee #2, 07 May 2023
This is an interesting paper looking at the impact of emissions reductions on atmospheric chemistry. It takes the area in and around the Barcelona metropolitan area as a natural laboratory, and studies two periods in 2020 as exemplar systems to understand the effect of emissions reductions on ozone and NO2.
The paper describes a model study using WRF-Chem coupled to an urban canopy model to look at atmospheric processes over the AMB region, and FLEXPART-WRF to do some trajectory analysis to study the chemistry occurring as air flows inland.
This is an ambitious study which aims to use the connection between the natural experiment of emissions reductions in the months of April/May 2020, and through analysis of idealised counterfactual experiments perform attribution of the effect of
emissions reductions.The experimental design and analysis appear sound and this manuscript fits well within the scope of ACP. I feel the structure of the manuscript could be improved, and the discussion should be improved in places before publication.
The title is the first area to address - I felt it was perhaps a bit too general, as the main focus is the impact of lockdown. The abstract can also be a bit more explicit eg L8/9 'response of ozone chemistry to changes' could make more explicit what reduction is under discussion. AOC needs to be defined in the abstract, and for the sake of clarity that it excludes O3 oxidant.
Abstract Conclusion # 3 is not clear - what is the mechanism? Conclusion #4 could the authors explain why May is important? Conclusion 5 - not sure what is meant by a change contributing to a plume. Perhaps re-word?
S2 describes the region selected for study, geography, Barcelona's air quality with respect to guidelines, the Vic Plain and the ozone situation in 20202. Two periods are identified for closer study, and also days of even closer study. I feel the manuscript would be more readable if it would it be possible to decide on a single consistent nomenclature for the two periods, eg P1 and P2 and so avoid changing between Mar-Apr/lockdown/first period and May/relaxation through the text
L174-185 Some of this section could be grouped with the discussion of the trajectory experiments, as it mixes model description with some analysis that probably belongs with the discussion in S5.3. It would be interesting to better justify why these days were chosen for further study - what aspects do these days/analysis bring out?
S3 describes the WRF-Chem experiments performs some model evaluation against observations. The model is shown to be more skillful in meteorology than chemistry, with ozone biases around 20-30% shown. The authors do not discuss if the bias in the model means that the model correctly simulates the difference in ozone/NO2 from a change in emissions. Given the chemistry is non-linear, would the response be greater/smaller in a less biased model? Would it make sense to compare ozone changes in the model with differences in climatology/COVID period at the observation stations of interest to assess if the model gets delta_O3 correct?
S4 describes the results of the experiments. This section in the MS has the most potential for improvement, I feel. Firstly, the changes in O3, NO2 and Ox are given in the supplementary. Is it worth moving figures S3 and S4 into the main text? I appreciate the changes are given in absolute (LH) and relative (RH) terms for both period 1 adn period 2. Could the labelling of these figures be improved to indicate what data are plotted in each of the four rows are? There are no labels on each of the second and fourth rows. The text in S4.1 could do with a further polish, e.g.
L27 is 1% significant?
L285 the 'two simulations' of what?
L287 constant between what?SS5.1 is interesting. I presume the graphs shown are for model results, and it would help to have this stated. Did the authors consider performing a similar analysis for observational data for this period? Is it difficult due to a lack of VOC data? The captions of Figure 6-8 needs to state explicitly that these are 'Changes...' between BAU and COVID
Colouring data by ozone change and land use/land cover is interesting, and the broken lines make the analysis goal clear. I would like to see the analysis better justified, though. I assume it is correct to use the lines which are derived from an analysis of transition regimes based on NOx and VOC emissions in Sillman (rather than changes in NOx/VOC levels used here) but I'd like the paper to discuss somewhere how these regimes apply when discussing a _change_ in O3 and a change in NOx or VOC levels, particularly in identifying regions of the diagrams here with NOx- or VOC-limited regimes, which seems key. I've not seen an analysis like this before, so would like to see this expanded upon.
L315 and on, could the authors explain how the figures can be used to support this statement? L326, L330 the discussion reverts to ozone levels, not differences between scenarios. Could this discussion be made more consistent?
L319 grid points not grid.
SS5.2 discusses the oxidising capacity in terms of OH and NO3. Is there any impact on ozone budgets seen from changing HO (and presumably OH:HO2 ratio), particularly in HO2 + NO vs OH + NO2 vs OH + O3?
SS5.3 is very nice, and might be improved in consistency with a discussion of Ox (and maybe formation of Ox/NOx reservoirs and sinks) as in previous sections.
S6 summarises nicely. The sentence in L438 'this was consistent...' needs to be expanded.
L454 'data used in this study...' add 'are'
Overall
Citation: https://doi.org/10.5194/egusphere-2023-160-RC2 -
AC2: 'Reply on RC2', Alba Badia Moragas, 09 Jun 2023
We thank the reviewers for the constructive comments and suggestions which have helped us improve the manuscript. Below we give full detailed answers to each issue raised by each reviewer. Our response is in blue, to differentiate from the comment which is in black. Furthermore, we include any new text added in the manuscript in red, to facilitate this second revision.
To summarize the main changes to the manuscript, we would like to point out:
-
We have expanded the discussion section to include 1) a more detailed description of the two different photochemical regimes that describe the sensitivity of O3 to its precursors, 2) a new figure entitled “O3 concentration as a function of VOC/NOx concentration.”, 3) more description of the trajectory experiments using the FLEXPART-WRF model and 4) further justification of the chemical scheme chosen for the simulations.
-
We have rewritten the main text to clarified that changes in the oxidation capacity are related to O3 concentrations given that VOC and CO oxidation by OH are the initial reactions for ozone formation and we have expanded the discussion of the oxidation capacity.
-
We have added more references to support the main text when introducing the tropospheric ozone and O3 photochemical regimes.
-
-
AC2: 'Reply on RC2', Alba Badia Moragas, 09 Jun 2023
-
AC1: 'Comment on egusphere-2023-160', Alba Badia Moragas, 09 Jun 2023
We thank the reviewers for the constructive comments and suggestions which have helped us improve the manuscript. Below we give full detailed answers to each issue raised by each reviewer. Our response is in blue, to differentiate from the comment which is in black. Furthermore, we include any new text added in the manuscript in red, to facilitate this second revision.
To summarize the main changes to the manuscript, we would like to point out:
-
We have expanded the discussion section to include 1) a more detailed description of the two different photochemical regimes that describe the sensitivity of O3 to its precursors, 2) a new figure entitled “O3 concentration as a function of VOC/NOx concentration.”, 3) more description of the trajectory experiments using the FLEXPART-WRF model and 4) further justification of the chemical scheme chosen for the simulations.
-
We have rewritten the main text to clarified that changes in the oxidation capacity are related to O3 concentrations given that VOC and CO oxidation by OH are the initial reactions for ozone formation and we have expanded the discussion of the oxidation capacity.
-
We have added more references to support the main text when introducing the tropospheric ozone and O3 photochemical regimes.
-
Peer review completion
Journal article(s) based on this preprint
Alba Badia et al.
Alba Badia et al.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(51101 KB) - Metadata XML
-
Supplement
(6867 KB) - BibTeX
- EndNote
- Final revised paper