The Impact of Sporting Events on Air Pollution: An Empirical Examination of National Football League Games

Round 1

Reviewer 1 Report

Thank you for the opportunity to review and engage with this paper. I enjoyed reading it. I have only minor comments for improving the manuscript, I hope these will be received in the spirit of constructive feedback.

• INTRO: I would've liked to see a focus on air quality here: why is this an issue, how important is AQI to health/wellbeing? Perhaps a paragraph could be added to explain the importance of this, because it's not as clear to people as emissions, and still quite new in sports. Maybe point to it as one of the the UN's 'triple planetary threats' - climate change, pollution, nature and biodiversity loss - which overlap but are distinct and thus require specific attention be paid to each.
• There's no justification for the NFL focus, but I genuinely think this is one of the most important pieces of this contribution. The NFL, college football, and the MLB have very different locations, customs, playing schedules, etc. If previous research on AQI in sport has focused on other contexts, explain this one. 
• The argument is advanced on p.8 that MLB has more games in a season, and so even with smaller impacts on AQI in each game, that league is worse for air pollution. I would argue this should be more nuanced. Air quality is consistently changing and hyper-local: you can have measurably different readings of AQI in the same spot, just a few minutes apart, and readings differ from as close as a few yards apart. So, it's hyper local, and immediate, and can dissipate or change quickly. A kid with asthma doesn't get an asthma attack because it was exposed to a little bit of ozone on several nights over the baseball season, because the pollution will dissipate rather quickly and is too low to have any measureable health effect, but that kid could suffer an attack on a Sunday if they live close to an NFL stadium hosting a game. All this to say - overall air pollution across a season is the key indicator to investigate from an emissions/climate standpoint, and so MLB is worse from that perspective. But from a health/population perspective, the comparison between types of sport event is most critical on a game-to-game basis (how bad is the AQI in one event and is it bad enough to trigger asthmatics or other breathing deficiencies), and so NFL games are worse for health.
• I think generally the language in the paper is passive and long. I encourage the authors to do a full read-through and cut any filler words, restructure sentences to be shorter and more declarative, and shift to active voice.

Overall, really interesting work. Well done.

Author Response

Reviewer 1

Thank you for the opportunity to review and engage with this paper. I enjoyed reading it. I have only minor comments for improving the manuscript, I hope these will be received in the spirit of constructive feedback.

Reply: Thank you for your comments and suggestions in helping us to improve your papers. We have made significant adjustments to the manuscript and re-written several sections based on your feedback.

• INTRO: I would've liked to see a focus on air quality here: why is this an issue, how important is AQI to health/wellbeing? Perhaps a paragraph could be added to explain the importance of this, because it's not as clear to people as emissions, and still quite new in sports. Maybe point to it as one of the the UN's 'triple planetary threats' - climate change, pollution, nature and biodiversity loss - which overlap but are distinct and thus require specific attention be paid to each.

REPLY: Based on these comments, we have added further sections to the introduction of the paper to highlight the issues that air pollution presents for us based on the UN’s Framework Convention on Climate Change. From this, we pose the severe ecological and health issues that come about from having higher levels of air pollution.

• There's no justification for the NFL focus, but I genuinely think this is one of the most important pieces of this contribution. The NFL, college football, and the MLB have very different locations, customs, playing schedules, etc. If previous research on AQI in sport has focused on other contexts, explain this one. 

REPLY: We agree that we did not do enough to motivate this paper in terms of why we should examine the NFL. We have rewritten the introduction to strengthen our argument as to why we are focused on the NFL in this paper, and why it is important to consider beyond the existing work focused on professional baseball.

• The argument is advanced on p.8 that MLB has more games in a season, and so even with smaller impacts on AQI in each game, that league is worse for air pollution. I would argue this should be more nuanced. Air quality is consistently changing and hyper-local: you can have measurably different readings of AQI in the same spot, just a few minutes apart, and readings differ from as close as a few yards apart. So, it's hyper local, and immediate, and can dissipate or change quickly. A kid with asthma doesn't get an asthma attack because it was exposed to a little bit of ozone on several nights over the baseball season, because the pollution will dissipate rather quickly and is too low to have any measureable health effect, but that kid couldsuffer an attack on a Sunday if they live close to an NFL stadium hosting a game. All this to say - overall air pollution across a season is the key indicator to investigate from an emissions/climate standpoint, and so MLB is worse from that perspective. But from a health/population perspective, the comparison between types of sport event is most critical on a game-to-game basis (how bad is the AQI in one event and is it bad enough to trigger asthmatics or other breathing deficiencies), and so NFL games are worse for health.

REPLY: Thank you for these comments, we believe that is indeed a critical part of the implications of our research that needed to be discussed in further detail. Along these lines, we have added more into the results and discussion section to emphasize these points. As you have noted, the increases in short-term air pollution can have dire consequences, and thus we further engage with the existing research to discuss some of the potential issues that could come about because of increases in short-term air pollution due to NFL games.

• I think generally the language in the paper is passive and long. I encourage the authors to do a full read-through and cut any filler words, restructure sentences to be shorter and more declarative, and shift to active voice.

REPLY: Thank you for the suggestions. We have undergone significant revisions of the writing in the paper, including having two native English speakers edit the manuscript to help improve the flow and writing.

Overall, really interesting work. Well done.

REPLY: Thank you again for the time and consideration of our work. We appreciate the comments and suggestions.

Reviewer 2 Report

Thank you for the opportunity to review your research. This is an overall exceptional paper that deserves to be published. I want to thank the authors for the cleanliness of their manuscript as well.

Normally, I would offer my feedback broken into the sections of the paper, but since my feedback is more holistic, I am not going to do that and instead off my comments based on various themes from the paper.

Re: title: from the start, I might consider a title change as I do not think that “is professional sport environmentally sustainable?” is really the question you were asking and addressing even though I might agree that at a higher level, yes, you are addressing this question. The second half of your title is fine. This paper examines the environmental harms of these events rather than the holistic relationship with the environment, society, and economy and whether that relationship can be maintained. I hope that makes sense.

Re: justification of your study in light of the MLB study: I am struggling to see the difference in your research aside from replication (which does have merit) and comparison of contexts. I did go and read that MLB paper myself as part of this review, so I need this to be made clearer in the rationale for this paper. To my reading, it seems the MLB paper focused more on AQI as a whole and ozone (O3) in particular in comparison to your examination of the individual gases/compounds/particles within AQI. It was mentioned that the profile of an MLB fan was different than NFL fans, but why is there reason to believe in differences between these two sets of fans when it comes to environmental behaviours? In the results section, there is a conjecture offered about tailgating behaviours or vehicle preferences. However, could the difference really be that MLB stadiums might (emphasis: might) be located in dense urban areas whereas NFL stadiums are outside urban areas with parking lots surrounding them?

Re: other variables: the authors did a wonderful job moderating the effects of a variety of variables from weather, to distance, to domed venues. Commendable work there. One other factor that jumps to my mind in reading this would have been a cross check against other events held in the vicinity of the stadiums on the day of the games? I know that NFL games tend to suck the metaphorical air out of communities and focus all resources and attention onto their events, so it is possible that other events were not held at the same time. However, some venues might be in event districts that could have theoretically hosted other events around the time of an NFL game. Would the explanation here be that the number of times that could have happened is insignificant to the data? Of course, all else is background pollution data from an air quality standpoint. I am not asking for the study to be re-done, but more of a thought to consider addressing in the writing.

Re: metrics: were the metrics for temperature, wind speed, and precipitation collected in imperial units (given the United States context this would make sense)? If so, that is fine, but I question why these were not offered in scientific units or metric. Just a note needed in the manuscript rather that the data re-presented.

Other thoughts for future directions: A) I appreciated the discussion of parking lots versus public transit being offered (especially in light of the smog impacts of vehicles noted in the results for O3 and NO2), so I hope this is pursued. B) domed stadiums could be running air conditioning or heat leading to higher levels of the gases/compounds measured? C) The noted temperature increases in relation to air pollution is interesting but align with other air quality research.

Author Response

Reviewer 2

Thank you for the opportunity to review your research. This is an overall exceptional paper that deserves to be published. I want to thank the authors for the cleanliness of their manuscript as well.

Normally, I would offer my feedback broken into the sections of the paper, but since my feedback is more holistic, I am not going to do that and instead off my comments based on various themes from the paper.

REPLY: Thank you for the time and consideration of our manuscript. We have rewritten many portions of the manuscript based on the feedback and comments that you have provided us. We believe that this has helped to significantly improve the argument and contributions of our manuscript.

Re: title: from the start, I might consider a title change as I do not think that “is professional sport environmentally sustainable?” is really the question you were asking and addressing even though I might agree that at a higher level, yes, you are addressing this question. The second half of your title is fine. This paper examines the environmental harms of these events rather than the holistic relationship with the environment, society, and economy and whether that relationship can be maintained. I hope that makes sense.

REPLY: Thank you for the suggestion. We agree the title was probably a bit too broad. We have changed it to try and better reflect what is being examined within our manuscript.

Re: justification of your study in light of the MLB study: I am struggling to see the difference in your research aside from replication (which does have merit) and comparison of contexts. I did go and read that MLB paper myself as part of this review, so I need this to be made clearer in the rationale for this paper. To my reading, it seems the MLB paper focused more on AQI as a whole and ozone (O3) in particular in comparison to your examination of the individual gases/compounds/particles within AQI. It was mentioned that the profile of an MLB fan was different than NFL fans, but why is there reason to believe in differences between these two sets of fans when it comes to environmental behaviours? In the results section, there is a conjecture offered about tailgating behaviours or vehicle preferences. However, could the difference really be that MLB stadiums might (emphasis: might) be located in dense urban areas whereas NFL stadiums are outside urban areas with parking lots surrounding them?

REPLY: We agree that in the previous version of the manuscript we did not do enough to motivate the importance and contributions of specifically examining the NFL. Based on this we have rewritten the introduction of the manuscript to provide a better explanation of why there is the need for a study focused on the impact that NFL games have on air pollution. We believe the revised version of the manuscript now provides a stronger argument for the importance and contribution of this paper.

Re: other variables: the authors did a wonderful job moderating the effects of a variety of variables from weather, to distance, to domed venues. Commendable work there. One other factor that jumps to my mind in reading this would have been a cross check against other events held in the vicinity of the stadiums on the day of the games? I know that NFL games tend to suck the metaphorical air out of communities and focus all resources and attention onto their events, so it is possible that other events were not held at the same time. However, some venues might be in event districts that could have theoretically hosted other events around the time of an NFL game. Would the explanation here be that the number of times that could have happened is insignificant to the data? Of course, all else is background pollution data from an air quality standpoint. I am not asking for the study to be re-done, but more of a thought to consider addressing in the writing.

REPLY: This is a good point. We have begun trying to trace events that occurred in similar time frames in the same metro area while NFL contests were being played. In general, we have found very few events, and in most cases those events are either hosted in facilities that are far away from the NFL games (and the air quality monitors) or many hours before/after an NFL game. As such, we believe that there is not much impact from other events within our dataset. However, because we cannot get a complete list of all events in a metro area (there could be small concerts, clubs, trade shows, conventions, etc) there is need to acknowledge this as a potential limitation of our study. Thus, we have included a few sentences within the discussion of the limitations to highlight this potential issue, as well as the fact that we believe it should not have a significant impact on air pollution levels.

Re: metrics: were the metrics for temperature, wind speed, and precipitation collected in imperial units (given the United States context this would make sense)? If so, that is fine, but I question why these were not offered in scientific units or metric. Just a note needed in the manuscript rather that the data re-presented.

REPLY: Thank you for the suggestion. Indeed, the US EPA reports their weather data in Imperial units. We have included a sentence to further clarify this for readers.

Other thoughts for future directions: A) I appreciated the discussion of parking lots versus public transit being offered (especially in light of the smog impacts of vehicles noted in the results for O3 and NO2), so I hope this is pursued. B) domed stadiums could be running air conditioning or heat leading to higher levels of the gases/compounds measured? C) The noted temperature increases in relation to air pollution is interesting but align with other air quality research.

REPLY: Once again, thank you for the time and consideration provided to our manuscript. We have added additional discussion in regards to parking lots and public transit in the conclusion. That is, the very existence of parking lots themselves presents fans the opportunity to use them, and hence create pollution as they travel to games. We believe that this point was critical and need to be addressed further within the paper. Additionally, we have added notes about results for domed stadiums and temperature within the results section suggesting topics that future research should focus on.