the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Sep 2024
Source contribution to ozone pollution during June 2021 in Arizona: Insights from WRF-Chem tagged O3 and CO
Abstract. This study reports the contribution of fire emissions on ozone (O₃) pollution in Arizona compared to local and regional anthropogenic emissions. Using the WRF-Chem modeling system with different O₃ and CO tags, we quantified the contributions of these emissions to O₃ levels during June 2021, a period when the region was experiencing both drought conditions and extreme heat. Our findings indicate that background O₃ levels accounted for about 50 % of the total O₃, with local anthropogenic emissions contributing between 24 % and 40 %. During the peak smoky time period, fire-contributed O₃ was significant across the Phoenix metropolitan area, ranging from 5 to 23 ppb or 5 % to 21 % of total O₃ levels, with an average of 15 ppb or 15 %. We verify these O₃ fire tags by conducting a model sensitivity test that excluded fire emissions, which showed strong agreement on the spatiotemporal pattern of O₃ due to fire emissions, although the magnitude of the contribution is underestimated by a factor of 1.4. This further demonstrates that wildfires exacerbate O₃ exceedances over urban areas. Our analysis also showed that the O₃ levels in Yuma are significantly influenced by transboundary pollution from California and Mexico, whereas Phoenix's O₃ levels are mainly driven by local anthropogenic emissions, with much smaller contributions from external sources during the study period. Consistent with previous reports, our findings highlight the role of wildfires and regional emissions in confounding the assessment of local O₃ pollution in urban environments, especially during dry and extremely hot summer in semi-arid/arid regions.
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CC1: 'Comment on egusphere-2024-2617', Mariano Mertens, 24 Sep 2024
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Dear Authors,
in your introduction you clearly define the difference between the sensitivity method and a source attribution technique like tagging. Despite the clear definition of the two methods we wonder about the statement “We verify these O₃ fire tags by conducting a model sensitivity test that excluded fire emissions”
The difference between tagging and perturbation has been discussed in many publications. The two methods answer different scientific questions. The perturbation approach calculates the response of a pollutant on an emission change (i.e. the perturbation). The tagging approach calculates the share of an emission sector (and/or region) to a pollutant for one specific state of the atmosphere (i.e. the contribution). The tagging approach provides no information on the sensitivity of an atmospheric chemical constituent on an emission change, and the perturbation approach gives no information about the share of a pollutant for one specific state of the atmosphere (Wang et al., 2009, Clappier et al., 2017, Mertens et al., 2018, Butler et al., 2018, Mertens et al., 2020). Only in a linear system both methods would yield equal results (Grewe et al., 2010, Grewe, 2013), for non-linear systems the results of the different methods are by definition not comparable and might even differ by the sign.
Given the different questions these methods answer, the results of the perturbation approach cannot be used (in a non-linear system) to verify the tagging approach (or vice versa). Both methods give complementary results, but the combination of results from the two methods can be very powerful to fully understand the response of atmospheric chemistry on an emission change (e.g. Mertens et al., 2021, Maruhashi et al., 2024).
This comment is not meant to hinder scientific publication of your results. This comment is also not meant to be regarded as a full scientific review. Our comment is meant to highlight the importance of clearly communicating the difference of the two methods.
Best regards,
Mariano Mertens, Patrick Jöckel, Volker Grewe
References:
Butler, T., Lupascu, A., Coates, J., and Zhu, S.: TOAST 1.0: Tropospheric Ozone Attribution of Sources with Tagging for CESM 1.2.2, Geosci. Model Dev., 11, 2825–2840, https://doi.org/10.5194/gmd-11-2825-2018, 2018
Clappier, A., Belis, C. A., Pernigotti, D., and Thunis, P.: Source apportionment and sensitivity analysis: two methodologies with two different purposes, Geosci. Model Dev., 10, 4245–4256, https://doi.org/10.5194/gmd-10-4245-2017, 2017
Grewe, V., Tsati, E., Hoor, P., On the attribution of contributions of atmospheric trace gases to emissions in atmospheric model applications, Geosci. Model Dev., 3, 487-499, 2010
Grewe, V.: A generalized tagging method, Geosci. Model Dev., 6, 247–253, https://doi.org/10.5194/gmd-6-247-2013, 2013
Maruhashi, J., Mertens, M., Grewe, V. and Dedoussi, I. C.: A multi-method assessment of the regional sensitivities between flight altitude and short-term O3 climate warming from aircraft NOx emissions, Environ. Res. Lett. 19 054007, https://doi.org/10.1088/1748-9326/ad376a, 2024
Mertens, M., Grewe, V., Rieger, V. S., & Jöckel, P.: Revisiting the contribution of land transport and shipping emissions to tropospheric ozone, Atmospheric Chemistry and Physics, 18, 5567–5588, https://doi.org/10.5194/acp-18-5567-2018, 2018
Mertens, M., Kerkweg, A., Grewe, V., Jöckel, P., & Sausen, R.: Attributing ozone and its precursors to land transport emissions in Europe and Germany, Atmospheric Chemistry and Physics, 20, 7843–7873, https://doi.org/10.5194/acp-20-7843-2020, 2020
Mertens, M., Jöckel, P., Matthes, S., Nützel, M., Grewe, V., & Sausen, R.: COVID-19 induced lower-tropospheric ozone changes, Environmental Research Letters, https://doi.org/10.1088/1748-9326/abf191, 2021
Wang, Z. S., C.-J. Chien, and G. S. Tonnesen, Development of a tagged species source apportionment algorithm to characterize three-dimensional transport and transformation of precursors and secondary pollutants, J. Geophys. Res., 114, D21206, doi:10.1029/2008JD010846, 2009
Citation: https://doi.org/10.5194/egusphere-2024-2617-CC1 -
CC3: 'Reply on CC1', Yafang Guo, 26 Sep 2024
reply
Dear Reviewers,
Thank you very much for your thoughtful comments and for highlighting the key distinctions between the sensitivity and tagging methods. We appreciate your insight and the references provided, which contribute to a more robust discussion of these two approaches.
We would like to clarify that we are not attempting to verify the tagging method using the sensitivity test. Our intention was to compare the results of the two methods, acknowledging that they answer different scientific questions. We agree that these methods are not interchangeable. Indeed, we have found that their results differ significantly in magnitude and even in sign.
In light of your feedback, we will rephrase our statement to more accurately reflect the purpose of the sensitivity test in our study. In the abstract and discussion section we have mentioned “verify”. Rather than suggesting any form of verification, we will emphasize that we use the sensitivity test for comparative purposes only, recognizing the distinct contributions of both approaches to understanding the impact of fire emissions. We will also revise Figures 11 and 12 accordingly to better show the negative values from perturbation method which will illustrate the non-linearity better. We will include discussion on these comparisons.
Additionally, we fully agree that combining these two methods can be powerful. In this study, the comparison between them offers a more comprehensive understanding of the effects of fire emissions.
Thank you again for your valuable feedback. We will make the necessary revisions to ensure that the differences between these two methods are communicated clearly.
Sincerely,
Yafang Guo
On behalf of all authors
Citation: https://doi.org/10.5194/egusphere-2024-2617-CC3 -
CC4: 'Reply on CC1', Yafang Guo, 26 Sep 2024
reply
Dear Reviewers,
Thank you very much for your thoughtful comments and for highlighting the key distinctions between the sensitivity and tagging methods. We appreciate your insight and the references provided, which contribute to a more robust discussion of these two approaches.
We would like to clarify that we are not attempting to verify the tagging method using the sensitivity test. Our intention was to compare the results of the two methods, acknowledging that they answer different scientific questions. We agree that these methods are not interchangeable. Indeed, we have found that their results differ significantly in magnitude and even in sign.
In light of your feedback, we will rephrase our statement to more accurately reflect the purpose of the sensitivity test in our study. In the abstract and discussion section we have mentioned “verify”. Rather than suggesting any form of verification, we will emphasize that we use the sensitivity test for comparative purposes only, recognizing the distinct contributions of both approaches to understanding the impact of fire emissions. We will also revise Figures 11 and 12 accordingly to better show the negative values from perturbation method which will illustrate the non-linearity better. We will include discussion on these comparisons.
Additionally, we fully agree that combining these two methods can be powerful. In this study, the comparison between them offers a more comprehensive understanding of the effects of fire emissions.
Thank you again for your valuable feedback. We will make the necessary revisions to ensure that the differences between these two methods are communicated clearly.
Sincerely,
Yafang Guo
On behalf of all authors
Citation: https://doi.org/10.5194/egusphere-2024-2617-CC4 -
CC5: 'Reply on CC1', Yafang Guo, 26 Sep 2024
reply
Dear Reviewers,
Thank you very much for your thoughtful comments and for highlighting the key distinctions between the sensitivity and tagging methods. We appreciate your insight and the references provided, which contribute to a more robust discussion of these two approaches.
We would like to clarify that we are not attempting to verify the tagging method using the sensitivity test. Our intention was to compare the results of the two methods, acknowledging that they answer different scientific questions. We agree that these methods are not interchangeable. Indeed, we have found that their results differ significantly in magnitude and even in sign.
In light of your feedback, we will rephrase our statement to more accurately reflect the purpose of the sensitivity test in our study. In the abstract and discussion section we have mentioned “verify”. Rather than suggesting any form of verification, we will emphasize that we use the sensitivity test for comparative purposes only, recognizing the distinct contributions of both approaches to understanding the impact of fire emissions. We will also revise Figures 11 and 12 accordingly to better show the negative values from perturbation method which will illustrate the non-linearity better. We will include discussion on these comparisons.
Additionally, we fully agree that combining these two methods can be powerful. In this study, the comparison between them offers a more comprehensive understanding of the effects of fire emissions.
Thank you again for your valuable feedback. We will make the necessary revisions to ensure that the differences between these two methods are communicated clearly.
Sincerely,
Yafang Guo
On behalf of all authors
Citation: https://doi.org/10.5194/egusphere-2024-2617-CC5 -
AC1: 'Reply on CC1', Avelino F. Arellano, 26 Sep 2024
reply
Dear Reviewers,
Thank you very much for your thoughtful comments and for highlighting the key distinctions between the sensitivity and tagging methods. We appreciate your insight and the references provided, which contribute to a more robust discussion of these two approaches.
We would like to clarify that we are not attempting to verify the tagging method using the sensitivity test. Our intention was to compare the results of the two methods, acknowledging that they answer different scientific questions. We agree that these methods are not interchangeable. Indeed, we have found that their results differ significantly in magnitude and even in sign.
In light of your feedback, we will rephrase our statement to more accurately reflect the purpose of the sensitivity test in our study. In the abstract and discussion section we have mentioned “verify”. Rather than suggesting any form of verification, we will emphasize that we use the sensitivity test for comparative purposes only, recognizing the distinct contributions of both approaches to understanding the impact of fire emissions. We will also revise Figures 11 and 12 accordingly to better show the negative values from perturbation method which will illustrate the non-linearity better. We will include discussion on these comparisons.
Additionally, we fully agree that combining these two methods can be powerful. In this study, the comparison between them offers a more comprehensive understanding of the effects of fire emissions.
Thank you again for your valuable feedback. We will make the necessary revisions to ensure that the differences between these two methods are communicated clearly.
Sincerely,
Yafang Guo
Citation: https://doi.org/10.5194/egusphere-2024-2617-AC1
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CC3: 'Reply on CC1', Yafang Guo, 26 Sep 2024
reply
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CC2: 'Comment on egusphere-2024-2617', Mariano Mertens, 24 Sep 2024
reply
Publisher’s note: this comment is a copy of CC1 and its content was therefore removed on 26 September 2024.
Citation: https://doi.org/10.5194/egusphere-2024-2617-CC2
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