Most of the surface ozone contributing to deaths in Europe is 'imported' pollution from elsewhere
Gergana Milkova
News Article:
https://drive.google.com/file/d/1RVWtc3J4JWR8dQFoPHMxpvSh8GZl_JJa/view?usp=drive_link
Journal Article:
Geographic sources of ozone air pollution and mortality burden in Europe | Nature Medicine
Background:
The discovery of the ozone hole over Antarctica resulted in the
international community creating the Montreal Protocol in 1987. This agreement
resulted in 198 countries committing to phasing out the production of
ozone-depletion substances. These substances were
found to have severely damaged the ozone layer exposing life on earth to harmful
ultraviolet light that can cause damage on the cellular level.
While stratospheric ozone acts as protective shield, ozone at the ground level is classified as a harmful air pollutant. (1) Ozone has been continuously linked to declining respiratory health and increase in pulmonary diseases. (2) Tropospheric ozone can be formed through precursor gases such as NOx and volatile organic compounds (VOCs) in the presence of sunlight.(3) Studies have shown that O3 formation can from VOC or NOx limited regimes (4) requiring in-situ observations to determine regional ozone formation and propagation.
Previous studies have shown that concentrations of ground level ozone (O3) in a given region may not only be influenced by local emissions but also by transboundary transport. (5,6) Current strategies implemented by environmental agencies aim to regulate emissions contributing to local ground-level ozone (O3) formation. (7) These efforts, however, may not produce the results necessary to achieve air quality standards because it disregards contributions of imported O3 which are sometimes the dominant contributor to tropospheric O3 concentrations. Identifying the geographical sources that contribute to the cumulative O3 concentration in particular region can help to design more effective mitigation strategies to lower pollutant concentrations.
Peer Reviewed Article:
The paper “Geographic sources of ozone air pollution and mortality burden in Europe” by Achebak et al. in Nature Medicine conducts a novel analysis on O₃-related mortality across Europe with a focus on the continental-wide geographic sources of O₃ pollution.(8) The study utilized air quality modeling systems to predict ozone concentrations across 813 connecting areas within 35 European countries during summertime (May-September 2015-2017).
CALIdad del aire Operacional Para España (CALIOPE), a high-resolution air quality modeling system, was utilized by the authors and has been been able to reproduce measured
O₃ concentrations within ±10 µg/m³. Several
models were integrated within CALIOPE. The Weather Research and Forecasting
(WRF) model provided meteorology data while HERMES and MEGAN characterized anthropogenic
and biogenic emissions for the 813 areas. All of these inputs were further fed
into Community Multiscale Air Quality model (CMAQ) which simulated ozone
formation by tracking its precursors, NOx and VOCs, to produce hourly surface
O₃ concentrations across designated domains. CMAQ’s tagging module allowed
for levels of O₃ to be categorized as either local, other countries, maritime
or hemispheric (outside study domain). CMAQ-derived O₃ concentrations were then
coupled with Eurostat mortality data to calculate O₃-linked deaths.
 |
Figure 1: Illustrates a simplified workflow of the Achebak et al. study, created for clarity in this blog post but not originally present in study. |
The study reported that average summertime daily maximum O₃ levels across Europe was 101.9 µg/m³. Values of O₃ ranged from 76.7 µg/m³ in Finland to 129.6 µg/m³ in Malta. Higher levels were reported in southeastern Europe which was expected because higher temperatures in the region enhance photochemical ozone formation. Southeastern European countries such as Bulgaria, Serbia, Greece, Hungary, and Romania showed the highest O₃-linked mortality rates correlating to higher O₃ levels found there.
Approximately 114,447 premature deaths during May-September 2015-2017 were attributed to O₃ exposure. The majority (88.3%) of these deaths were linked to imported ozone, with 56.7% originating from hemispheric sources outside Europe,
20.9% from other European countries, and 7.2% from maritime transport. Only 11.7% of deaths were due to national
sources.
 |
Figure 2. Source contributions to ozone levels and mortality, showing the dominance of imported over national sources across Europe (Achebak et al). |
Some limitations of the paper are that the authors did not provide an economic evaluation for the mortality
burden caused by O₃-linked deaths which could’ve informed future policy decisions.
The findings of the study also do not align well with the European Environment
Agency’s (EEA) estimates of ozone mortality deaths which is 32.6 deaths per
million versus 72 per million reported in the peer-reviewed paper. This could be attributed
to EEA using a uniform mortality level per country while the authors utilize actual
observed deaths per region made possible by the Eurostat mortality dataset.
Overall, Achebak et al provides compelling evidence that mitigation of O₃ levels should include both global and regional cooperation. While O₃ concentrations in Europe are predominantly hemispheric in origin, this should not in any way discourage regional mitigation efforts of O₃ reduction. Rather, both global and regional efforts are required.
News Article:
Lauren Chadwick’s piece, “Most of the surface ozone contributing
to deaths in Europe is 'imported' pollution from elsewhere” communicates the
results of Achebak et al in the multilingual news media outlet, EuroNews. The
article is broken down into two sections.
The first section does a great job of breaking down the methodology of the
study and reports all impactful statistics faithfully and within proper context.
The second section discusses how more heavily industrialized countries contribute
to O₃-attributable deaths in neighboring countries. Considering that the media
outlet is consumed primarily by a European audience, I appreciate Chadwick’s
commentary on how her target audience is actually impacted by the findings in this study.
She also weaves in quotes from authors of this paper and leading experts in the atmospheric monitoring field, which adds a personal touch and gives the researchers a platform to advocate for their science to the public. This makes the article feel more engaging and gives weight to the calls for action. One quote that really stood out was by Dr Laurence Rouil who serves as the Director of the Copernicus Atmosphere Monitoring Service (CAMS). Dr. Raoil emphasized that “no decreasing trends of background ozone levels are observed at regional or global scales despite stringent emission reduction policies” underscoring why Achebak et al. consistently advocate for the implementation of coordinated global actions to improve air quality.
The background science is explained clearly too. I especially liked how
she pointed out the difference between tropospheric and stratospheric ozone since
that distinction may sometimes be overlooked by a a general audience.
That said, the article missed an opportunity by not including figures from the paper itself. In Figure 2, Achebak et al managed to condense quite a bit of data into simple visual assessment that uses stacked bar plots to show robust trends in O3 source apportionment across Europe by country. Another downside is that the article didn’t hyperlink the original paper.
Still, the overall coverage was strong and accurate. The article managed to connect the research to bigger conversations about policy and global cooperation. I would give this article an 9/10 overall.
Citations:
(1) U.S. Environmental Protection Agency. Health Effects of Ozone Pollution. U.S. EPA, Mar 13, 2025. https://www.epa.gov/ground-level-ozone-pollution/health-effects-ozone-pollution?utm_source=chatgpt.com
(2)Zhang, J., Wei, Y. & Fang, Z. Ozone pollution: a major health hazard worldwide. Front. Immunol. 10, 2518 (2019).
(3) U.S. Environmental Protection Agency. Ground-level Ozone Basics. https://www.epa.gov/ground-level-ozone-pollution/ground-level-ozone-basics (accessed Sept 5 2025).
(4) Sebol, A. E.; Canty, T. P.; Wolfe, G. M.; Hannun, R.; Ring, A. M.; Ren, X. Exploring Ozone Production Sensitivity to NOx and VOCs in the New York City Airshed in the Spring and Summers of 2017–2019. Atmospheric Environment 2024, 324, 120417. https://doi.org/10.1016/j.atmosenv.2024.120417.
(5)Wild, O. & Akimoto, H. Intercontinental transport of ozone and its precursors in a three-dimensional global CTM. J. Geophys. Res. Atmos. 106, 27729–27744 (2001).
(6) Derwent, R. Intercontinental transport and the origins of the ozone observed at surface sites in Europe. Atmos. Environ. 38, 1891–1901 (2004).
(7)WHO global air quality guidelines: particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide. (World Health Organization, 2021); https://apps.who.int/iris/bitstream/handle/10665/345329/9789240034228eng.pdfequence=1&isAllow=y
(8) Achebak, H., Garatachea, R., Pay, M.T. et al. Geographic sources of ozone air pollution and mortality burden in Europe. Nat Med 30, 1732–1738 (2024). https://doi.org/10.1038/s41591-024-02976x
Great job, Gergana! I agree with your 9/10 rating of Chadwick’s article. I thought her article was easily understood and accurate, especially for a general audience. Like you, I think including visual figures from the original study (especially Figure 2) would have significantly strengthened her piece by making the data more tangible for readers.
ReplyDeleteI also appreciated your point about how the article connects scientific findings to a larger global conversation. Your background section, especially the reference to the Montreal Protocol, reminded me of something we discussed in class that early international efforts like the Protocol often centered on industrialized nations, sometimes excluding developing ones. This study and what I was able to take away from it proves that the global pollution conversation must include everyone because, as the data shows, Countries with fewer emissions may still suffer the consequences of pollution from elsewhere. That dynamic seems to open up an ethical conversation about environmental justice at a continental (or even global) scale that the article hints at but doesn’t fully explore..
How do you think the article (or future reporting on similar studies) can go beyond establishing the idea of global accountability, and open up the conversation of environmental justice?
Thank you so much for your insightful feedback! I think the study does an excellent job of connecting the science to everyday impacts. The figures in the peer-reviewed paper all reinforce one central message: ozone levels across Europe are largely transported rather than locally produced.
DeleteWhat stood out most to me was that the highest mortality rate from ozone occurred in my home country, Bulgaria. Despite not being as industrialized as many other European nations, Bulgaria experienced some of the worst outcomes. With one of the oldest populations in Europe and the lowest household welfare (measured by consumption per capita) within the EU, this raises important questions about environmental justice. Countries with fewer economic resources are often the ones most negatively affected by the emissions of more industrialized nations.
Global councils should actively let the impacted countries to have the leading voices in these discussions. At the same time, highly industrialized countries must take stronger action to reduce emissions in order to mitigate ozone formation at its source. The finding that much of the ozone in European countries originates from hemispheric transport underscores the responsibility of outside nations to strengthen infrastructure and implement stricter controls on industrial activity.
This is a great overview and analysis of both articles, Gergana! Your connection back to the Montreal Protocol provides really useful context for our scientific understanding of stratospheric vs tropospheric ozone and how ozone is regulated. I agree that the popular news article does a nice job summarizing the most important statistics and findings from the paper, while ensuring the science is accessible to a general audience. I also really like your point that connecting the research to the news outlet's main audience is helpful, because it makes the findings less abstract and will hopefully help readers understand how this work is relevant to their own lives. Additionally, I think there is a tendency in popular news articles to overstate the findings of a study, but Chadwick's article avoids this pitfall and discusses both the strengths and limitations of the research.
ReplyDeleteAt the end of Achebak et al., the authors acknowledge the impacts of climate warming on ozone formation and argue that "the fight against climate change is key to improvement in air quality." This is one point that was left out of Chadwick's article, but it seems to me like an important one – not only is coordination of global ozone mitigation efforts required, but so are mitigation efforts that account for the changing climate. Do you think including this information in Chadwick's article would help further explain the importance of the research, or would it distract from the main point about the need for international cooperation?
Hi Claire,
DeleteThank you for your feedback and insightful comments! I agree that including this point in Chadwick’s article would have strengthened her coverage of the peer-reviewed paper. One thought I had while analyzing her work is that she could have emphasized that, although O₃ concentrations in Europe are largely hemispheric in origin, this should not discourage regional mitigation efforts. The study clearly cautions against using the data to justify reducing or abandoning local ozone control measures.
What comes to mind for me is the idea that prevention is always better than cure. Continued efforts to improve air quality will undoubtedly have far-reaching impacts in lowering ozone levels. Including this perspective in Chadwick’s coverage would not have distracted from her overall argument, especially given that domestic ozone still contributes to mortality.
I appreciate your critique that the journal article should have included information about the economic status of each nation because that is relevant to surface-level ozone concentrations. Additionally, I appreciated that both articles use the term “imported” to describe how ozone pollution moves from one area to another. I think that term grabs the reader’s attention and emphasizes the study’s findings to clearly convey the study’s results in an easy-to-understand way in both the journal and news article. You made the point that news article includes important statistics in the appropriate context, and I think this further emphasizes the study’s findings and showcases the significance of ozone emitted from other countries. I appreciate your point that the news article should have included at least one figure from the journal article. I think a visual, especially when talking about lots of data, helps the reader better understand the data.
ReplyDeleteOne question I have after reading both articles is whether the EEA has any feedback or pushback on the study’s findings since they differ from their own. I hope that going forward, the EEA can be more specific in their estimates instead of using a uniform mortality level per country because I think it could aid in mitigating ozone pollution on a global scale.
Hi Caroline,
DeleteI wasn’t able to find any direct feedback from the EEA on this article, but I do think the methodology presented could be very useful for them in the future. The EEA typically provides a more generic baseline value for ozone that is averaged across multiple countries and regions. By contrast, CALIOPE offers much higher resolution data that can identify ozone hotspots rather than smoothing them over broad areas. This kind of detail could give the EEA deeper insights into how ozone is impacting populations across Europe, which is central to the institution’s mission.
It would be especially valuable if the EEA collaborated with the scientists behind this study, as their high-resolution modeling could complement the EEA’s existing monitoring framework and strengthen the overall assessment of ozone’s health impacts across Europe.
Nice job, Gergana! As far as your rating for Chadwick's article I may lean more towards an 8/10. I did like how the article was broken up into the 2 sections about the logistics and necessary info about the study and then telling the story about how ozone contributes to death in neighboring countries. I also found it useful that Chadwick made the distinction of O3 in the stratosphere vs troposphere (as I was confused at first too learning about O3 in the atmosphere). I do think the lack of visuals and failing to include the paper link are issues.
ReplyDeleteYour background section serves as an excellent precursor to the article and the topic of ozone mortality. Again, I love the distinction between the stratospheric vs tropospheric ozone. When reading your descriptions of the air quality monitoring systems and O3 concentration measurements, I was trying to keep track of the other models that you said were integrated and their functions. Therefore, it was great to have a visualization (your Figure 1) that quickly summarizes this for the reader.
I also liked the flow of your summary, adding Figure 2 after explaining the percents of ozone that were responsible for the deaths (between national, other countries, and outside sources as well). I like this study in particular because it provides clear evidence that this ozone problem is a global one, and can effect anyone as ozone knows no boundaries.
The peer-reviewed article points to the need to keep national coordinated efforts, but also ramp up global efforts to tackle this ozone issue. Why do you think that global efforts are lacking, when studies like these prove that there is a clear issue here. Additionally, what do you think some first steps could be in getting more countries on board with efforts like these?
Hi Gregana! I really liked your review of the two articles. I especially liked how you explained the distinction between tropospheric and stratospheric ozone. Your description of why ozone in the troposphere is harmful and the effect of transboundary transport on ozone concentrations in the troposphere was helpful in understanding your review. I agree with your rating of 9/10 for the Euronews article. With Euronews being a multilingual news outlet, the article was written well for its wide range of readers and most importantly, was able to increase education about tropospheric ozone pollution to the general public. However, as you mentioned, inclusion of figures and a link to the peer-reviewed article would have greatly improved the news article as it would have aided readers in learning more about this subject. I also liked how the news article mentioned limitations to the study as well.
ReplyDeleteGergana, well done on this very detailed analysis! The journal and news articles you have chosen are very interesting. You have covered the background well, and the summary is very digestible. I just have a few questions:
ReplyDelete1. What is the definition of “Europe” in this study, given that parts of Russia are geographically in Europe but have not been included?!
2. What incentives for the countries that produce O3 – yet experience fewer of its harmful effects compared to neighboring countries – have to reduce their O3 emissions?
3. Additionally, it is not clear how coupling he CMAQ-derived O3 concentrations with Eurostat mortality data allows for the calculation of O3-linked deaths. I do appreciate that the news article, at least, acknowledges there is no fixed link between ozone and mortality rate.
Hi Frozan!
DeleteThank you for the wonderful questions! I will attempt to answer each of them below:
1. In this paper, “Europe” refers specifically to the 34 countries for which harmonized mortality data were available from Eurostat (covering 813 contiguous regions). This includes the EU member states plus some neighboring non-EU countries, but not Russia, even though part of its territory is geographically European. The exclusion is due to data availability- not necessarily a scientific definition of Europe.
2. This is such a great point. I really think had the authors actually included an economic analysis on how mortality rates due to air pollution impact Europe would've helped fuel motivations of countries that are not as impacted. Furthermore, with the existence of the EU- there are shared common interests between most of the countries that are listed in the peer-reviewed paper that could hopefully motivate collaboration on international policies for ozone mitigation.
3. These concentrations are linked with a published exposure-response function derived from epidemiological studies that estimates the relative increase in mortality risk per µg/m³ of O₃ exposure. You are so right! There is no fixed link between ozone and mortality. These estimates are based on epidemiological associations not clinically reported cause-of-death records. The numbers represent statistical excess mortality consistent with observed population-level risks.
Thanks Gerganan for taking the time to answer my questions! Appreciate it!
DeleteNice work! This was a great choice and a really interesting article and paper. There really doesn't seem to be enough focus on how the actions of one country will impact those nearby, or even those across the globe. Also, I really like your workflow of the model and how it works. With this model, do you think it could be expanded to a global scale? And if it, or a different model, could predict this on a global scale, how useful do you think it would be for informing and making policies?
ReplyDeletePlus, the article could definitely use some form of graphic, but the maps in figure 4 or 5 might be better for a general audience and easier to digest.
I think the background does a really great job of not only explaining the importance of O3 but also including the policy and health components. I was able to quickly find more information about interesting parts of you blog in the Nature paper based on the figures you included. With so much data and complex methods, you did a great job summarizing the important takeaways and describing how the study was done. Reading the Euronews article, I appreciated your description that provided important context that you might not expect to be included for a wider audience.
ReplyDeleteI was really interested to see that they were able to reproduce O3 concentrations within +/- 10 ug/m3, which is down to roughly 2 ppb. While I think focusing on 35 different countries does show a very wide-spread distribution, I noticed in Figure 1 of the Nature paper that the countries not included (specifically Bosnia and Herzegovina, Kosovo, and Macedonia) surrounded by regions with higher mortality and may be especially significant. I think seeing data from Northern Africa (specifically Morocco, which is so close to the high ozone levels in Spain) would have been useful and not necessarily deter from the focus on Europe since not all of Europe is actually included in the study. With the majority of ozone being transported from outside the current countries used in the study, it would be interesting to see ozone concentrations in the neighboring regions. I think you touched on this when you addressed the limitations and how this fits within European policy, particularly with how socioeconomic factors of countries not included in this study seem significant.
Great Job! Your background information provided was very informative especially the distinction between stratospheric and tropospheric ozone that you provided. In your analysis of the peer reviewed article I thought the inclusion of CALIOPE's novel way of simulating ozone concentration compared to the brute force method of previous studies added to the credibility of the study.
ReplyDeleteI agree With your rating of 9/10 for the news article. The article did a great job summarizing the findings of the peer reviewed article without making any incorrect or overreaching claims. The article also provided a simplistic background on the photochemical formation of ozone with common industrial pollutants without getting too in depth and discouraging the average reader. I do believe that adding a graphic of some sort to the news article could increase its accessibility to wider audiences.
Overall, this study and related news article demonstrate how pollution in general is not just a national issue but a global one. Countries that strive to reduce their emissions can still incur the negative effects from other countries that are over polluting
Great analysis, Gergana! I appreciated that you talked about the Montreal Protocol because it is useful in contextualizing ozone regulation that you discuss later in your summary. Overall, the background you provided was well written and included relevant information that made the paper's findings more meaningful.
ReplyDeleteI agree with your 9/10 rating of the article and think that it reports the journal's findings in a way that is digestible to the general public. I liked that the article did not sensationalize the study's results, but agree that including a link to the original paper and figures from the paper would have been beneficial.
I noticed that, while the original paper makes the claim that both global and regional ozone mitigation efforts are necessary after reporting its results, Chadwick does not include that claim in the article reporting on the study. Do you think that the article would have benefitted from the inclusion of this information?
I thought you did a great job representing both the original journal article and the news article. The background information was relevant and was good context before getting into the articles. I felt this news article was much less sensational than I would expect and did a great job representing the findings of the journal article. While you said the news article did a good job explaining the background science clearly, I felt Chadwick was a bit unclear with how they determine the ozone is imported and not local, Chadwick says they track and trace the precursor species which when I was reading her article just seemed like generic ways of saying they monitored them, but it clicked when I read in the journal article that they chemically tagged them. That was the only gripe I had with the article, which was cleared up after reading the source, although that could have been cleared up by reading the journal article first, but that defeats the purpose of there being a shorter and less scientific news article.
ReplyDeleteHi Zackary,
DeleteI definitely think the most challenging aspect for Chadwick was conveying the methodology. The way the models work is quite complex, and simplifying that for a general audience is not easy. Even when I read through the article, it took me some time to fully understand how the figures were derived. While I agree that the methodology was more nuanced than what Chadwick presented, I think her explanation was sufficient for the purposes of a general audience. I also appreciate that she included a quote from one of the paper’s co-authors, which helped clarify how they approached following ozone formation.
I really enjoyed reading your analysis! You clearly have a strong understanding of the technicalities of the paper and did a good job explaining the methods used in the research.
ReplyDeleteI agree with your assertion that the news article did a surprisingly accurate job presenting the information from the research paper to a more general audience. I appreciated that the article addressed the serious health concerns the paper attributes to the high ozone concentration in the troposphere over Europe.
I am very curious that although it was known that 52% of the ozone was imported from outside of Europe, the paper didn't mention where some of these big sources of ozone outside of Europe actually is. I wonder if the researchers plan to do further studies into these ozone sources, which were outside of this study's domain, in the future.
Amazing summaries Gregana. Your dissection of the important data from the paper was very well done and identifying the link between latitude and high levels of ozone was very important. I also appreciate how both you and the article address the disparity between SouthEastern countries having the highest rates of motality and levels of ozone whilst simultaneously being less industrialized and thus not producing the ozone themselves. I think it is important to emphasize this distinction because I find many articles shy away from talking about Eastern Europe and the differences of Developing vs Developed countries and their roles they could play in scientific efforts.
ReplyDeleteI also appreciate, as you point out, how the article goes into detail with all the data and even directly quotes someone involved in the study giving credence to the report as a whole and how it could possibly influence policy. While i agree the article is quite good in deciphering the data I do wish it indicated more of a call to action or possible way to raise at least European attention to addressing this issue. Possibly calling for it to be discussed in the EU or UN or even further studies into the classification of the "hemispheric sources". A dialogue of how neighboring countries that are industrialized are effecting an ozone importing country should have been addressed further as well, as they address it a bit in the paper. Overall I still agree very solid article and analysis by yourself.
Very compelling article and analysis! The study introduced a concept that is very relevant and I like that your background explained why ozone on the tropospheric level is important to study. I think emphasizing that ozone from other countries is often the main cause for ozone air pollution in Europe was a good decision.
ReplyDeleteI appreciated that you explained how the air quality monitoring systems work, and how they were able to find the most ozone-affected areas of the troposphere. Mainly, I was impressed with your review of the article's weak points, like how you said it was a mistake that the authors did not mention anything about economics and their relation to policy choices. Also, that the EEA was not accurate in their depiction of deaths.
My favorite part of your post was the call to action. You did a nice job hammering down the point that if we are to reduce ozone concentrations in any country, we must all work together globally because of the effect of the imported gases. I agree with your rating because the article interested me very much, and made sure to quell any assumptions readers might be having about the troposphere and ozone.
This is an interesting analysis. I liked that the article made a distinction between tropospheric and stratospheric ozone and why we want ozone in one layer but not in the other layer. It was also interesting to analyze how pollution can move from one country to another because this is a topic that I find very interesting. One thing I wish the paper and the article went more into was were this outside ozone pollution was coming from. I wonder what specific countries or regions of the world are contributing the most to ozone pollution. I also think its interesting how they talk about how certain european countries contribute a lot of ozone pollution to their european neighbors and how different countries need to cooperate to fix this issue.
ReplyDeleteGreat analysis. I agree with your rating of the news article. Mostly while reading through I had questions about the impact of this research since the study was from 2015-2017 and the news article was from 2022. I think it would be interesting to see how the COVID-19 pandemic changed ozone levels in the troposphere over different industrialized countries.
ReplyDeleteI noticed some differences between the two maps in Figure 1 of the journal article. There is shown to be more deaths related to Ozone in Portugal than Spain, but Spain has a higher daily mean O3 maximum. The mortality related to O3 is also high at the the border of Serbia and Bulgaria, which does not totally line up with the daily mean O3 map. I wonder if there are healthcare disparities or other sociological factors that contribute to these differences between the maps. Therefore, are some of these deaths preventable without lowering the O3 levels?