Worries About Air Pollution from the Unsustainable Use of Studded Tires and Cruise Ships—A Preliminary Study on the Relationship Between Worries and Health Complaints Due to Seasonal Pollution

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper titled "Worries about air pollution from studded tires and cruise ships – a preliminary study on the relationship between worries and health complaints due to seasonal pollution" by Höller et al. investigates the links between public concerns about air pollution from two distinct sources: studded tires and cruise ships, and their association with mental and physical health symptoms such as insomnia, migraines, and eco-anxiety.

However, the limitations of the study, particularly in terms of sample size, self-report biases, hinder its robustness. The original research design aim for 300 participants (line 152 and line 154), it is quite a pity the authors could not get more respondents.

Another criticism of the paper is its reliance on self-reported measures, which may be susceptible to bias and inaccuracies. Individuals might not always accurately report their worries or health symptoms, potentially skewing results. Incorporating objective measures, such as air quality data in conjunction with health assessments, could provide a more comprehensive understanding of the relationship between worries and health outcomes mcv.  

Line 288 18(men)+17(women)+2(NA)=37 it is quite different from 47 participant the author indicated (line 286)

Line 317 the location port, main street, nursery school and school should be described or graphed in the manuscript.  

Line 321 the authors should write the main massage for table 2, otherwise this table can be moved to the appendix.

Line 355 the authors would be benefited from explaining the meaning of V inside the parentheses

Line 346 the authors would be benefited from explaining the meaning of rho in table 4

Line 362-line 364 15 (Oddeyrin) + 27 (Giljahverfi) + 4(live somewhere else )= 46, it seems like one respondent is missing. I also suggest those 4 respondent who live somewhere else should be removed from the statical analysis.  

Author Response

We would like to thank Reviewer 1 for their time taken to review our manuscript and for the valuable comments! Below we answer them point by point:

 

Comments 1: However, the limitations of the study, particularly in terms of sample size, self-report biases, hinder its robustness. The original research design aim for 300 participants (line 152 and line 154), it is quite a pity the authors could not get more respondents.

 

Response 1: We fully agree on this matter. While preparing the manuscript we discussed that publishing this really small study is important to inform researchers in a similar situation. We wanted to research the negative impacts of studded tires in a population where large parts believe they need the studded tires. The study invitation letter wording prevented people from wanting to participate. We explained this better in the revised version of the manuscript:

 

Abstract: The low participation rate limits generalizability but is a result by itself because of the highly controversial topic of studded tires. We hypothesize that participation in studies set out to demonstrate negative effects of particulate matter needs to be strategically planned when the overall opinion of the population to be studied is positive towards the source of the hazardous pollution.

 

Discussion, first paragraph: While the sample size recruited limits generalizability, the recruitment difficulties encountered need to be communicated to other scientists in the field to facilitate better recruitment in other studies. In the following, we will first discuss the possible results based on the limited sample and then attempt to give recommendations how to improve the limited recruitment success in future studies.

 

Discussion, section 4.3 Challenging recruitment: Is it the topic? – We considerable rewrote the section and added references providing evidence for the local opinion that most likely impacted the low participation rate. We copy the whole section here below:

 

4.3. Challenging recruitment: Is it the topic?

The main limitation of the present study is the small sample size. But other than being a simple limitation, it might also be a result. In this study, we put more effort and money into recruitment than for other studies we ran in our research group – nevertheless, the recruitment rate was extremely low as compared to other studies we conducted in the area on non-controversial topics. For example, in the EPiC SAD study the response rate was around 20%, but in the present study it was only about 4%. A gradual fall in participation rate in health surveys in Europe has been reported previously. This trend in declining response rates will further limit studies on controversial topics where participation rate is generally lower than the national average participation rate. However, we strongly suspect that the title of the study kept most people from participating. Specifically, when recruiting participants, the title of the study was shown in the advertisement in the newspaper, in the letters sent to potential participant’s homes, and on the study website. The title of the study might have directly impacted the willingness to participate, since it mentioned the potential connection between studded tires, air quality, and health. In Iceland use of studded tires is restricted and in 2023 the City of Reykjavik has declared that their use is undesirable [78]. Thus, there is public effort in inducing a gradual shift towards not using studded tires in Iceland. However, the major part of the population in Akureyri is reluctant to change studded tires out for non-studded winter tires, as the most recent count in Akureyri in April 2025 yielded that 85% of cars run on studded tires [79]. The low participation rate in our study may indicate how controversial the issue of studded tire use is especially in the Northen part of Iceland where winter conditions are harsher compared to the South. Some of the people invited to take part in this study may have feared that just by taking part they could increase the chance of studded tires being banned in Akureyri. In this town, the use of studded tires is restricted to the season 01. November to 14. April. However, even the local police in Akureyri announced not to punish the use of studded tires until May [80,81]. The low participation rate in our study may indicate how controversial the issue of studded tire use is especially in the Northern part of Iceland where winter conditions are harsher compared to the South.

In contrast to the public opinion on studded tires, there is broad consensus in the local population that cruise ships pollute the area [82]. The relatively large group of citizens not benefitting from the narrow economic impact of cruise ships would prefer a drastic reduction in ship arrivals. In contrast, the number of citizens that openly criticise the use of studded tires and would prefer a ban of them is very small. No reliable data on this discrepancy of public opinions exists in Iceland and comparable Nordic regions, warranting future research. Most importantly, with better knowledge on the impact of the title of a study on participation rates in research tackling a highly controversial issue future studies can be designed better in their wording to avoid a low participation rates despite considerable effort as in the present case.

 

Comments 2: Another criticism of the paper is its reliance on self-reported measures, which may be susceptible to bias and inaccuracies. Individuals might not always accurately report their worries or health symptoms, potentially skewing results. Incorporating objective measures, such as air quality data in conjunction with health assessments, could provide a more comprehensive understanding of the relationship between worries and health outcomes mcv.  

 

Response 2: We agree on the limitation arising from the self-report measures. We discussed this issue in the limitation section as follows:

Additionally, it must be noted that the present study relied solely on self-reported health problems, which are somewhat unreliable. Specifically, self-reported health problems associated with increased worries about air pollution are likely to suffer from poor reliability as it was reported that the concerns themselves influence symptom reporting, perceptions of current health, medication use, and visits to health care providers [83]. Thus, the concerns and health reports are not independent, and may be rather driven by the worries than actual health issues.

 

Additionally, we added a note regarding the need for future studies measuring health issues in combination with personal exposure:

Future studies should be designed to accurately measure individual exposure to air pollution combined with objective measurements of health.

 

 

Comments 3: Line 288 18(men)+17(women)+2(NA)=37 it is quite different from 47 participant the author indicated (line 286)

 

Response 3: Thank you very much for this hint, there was a typo and it is actually 27 women, we changed this in the manuscript.

 

Comments 4: Line 317 the location port, main street, nursery school and school should be described or graphed in the manuscript.

 

Response 4: That is an excellent idea, thank you so much! We added a map of the town and marked the locations of measurements.

 

Comments 5: Line 321 the authors should write the main massage for table 2, otherwise this table can be moved to the appendix.

 

Response 5: Thank you very much. We added this table as it is custom to provide the descriptive statistics on all variables used in a manuscript. However, we agree that we missed out on commenting on the meaning of the data. We added a sentence explaining the value of the information as follows:

The data shows that dispersion of symptoms of seasonality, insomnia, migraine, and eco-anxiety was covering well the range of possible answers on the employed scales.

 

Comments 6: Line 355 the authors would be benefited from explaining the meaning of V inside the parentheses

 

Response 6: Thank you, we added the information that we refer with V to “Wilcoxon test statistic”

 

Comments 7: Line 346 the authors would be benefited from explaining the meaning of rho in table 4

 

Response 7: Thank you very much, we added to the note below the table that rho indicates the Spearman correlation coefficient.

 

Comments 8: Line 362-line 364 15 (Oddeyrin) + 27 (Giljahverfi) + 4(live somewhere else )= 46, it seems like one respondent is missing. I also suggest those 4 respondent who live somewhere else should be removed from the statical analysis.

 

Response 8: We are sorry about the misunderstanding. We in fact did exclude those 4 from the neighbourhood analysis. We added this explanation:

(4 indicated to live somewhere else and were excluded from the comparison of neighbourhoods).

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

General comment: The study seeks to determine the association between environmental pollution, caused by land and sea traffic, and the mental health of human populations.

Specific comments:

Introduction: Brief but sufficient

Material and methods: The sample is small. Air quality measuring instruments appear to be adequate and come from official bodies. Mental health assessment questionnaires are validated and appear reliable. The statistical analysis methods are correctly described, although I believe that this study could have had a more rigorous, more comprehensive and broader analysis strategy.

Results: The results should be further explored, as well as their presentation. There are many tables and little commentary on the results. The authors could have explored other association relationships taking into account the diversity of data they collected. In the association relationships studied, confounding factors were not taken into account, such as: alcohol, tobacco, coffee, other health conditions and/or use of medication.

Discussion: The authors summarize their main findings, which they present in results and compare with existing literature. The authors are aware of the limitations of the study, however these limitations are so important that they may call into question the validity of the present study.

Conclusion: The study has the merit of pointing to an important public health problem, already known, which according to the authors, has not been given due attention. However, there appears to be a lack of proven scientific evidence in this study that would suggest we need to raise these concerns. The authors could also propose some corrective measures to minimize the impact of pollution caused by land and sea traffic on human health.

Author Response

We would like to thank Reviewer 2 for their time taken to review our manuscript and for the valuable comments! Below we answer them point by point:

 

Comments 1: Material and methods: The sample is small. Air quality measuring instruments appear to be adequate and come from official bodies. Mental health assessment questionnaires are validated and appear reliable.

 

Response 1: We fully agree on this matter, the sample size is very small. While preparing the manuscript we discussed that publishing this really small study is important to inform researchers in a similar situation. We wanted to research the negative impacts of studded tires in a population where large parts believe they need the studded tires. The study invitation letter wording prevented people from wanting to participate. We explained this better in the revised version of the manuscript:

 

Abstract: The low participation rate limits generalizability but is a result by itself because of the highly controversial topic of studded tires. We hypothesize that participation in studies set out to demonstrate negative effects of particulate matter needs to be strategically planned when the overall opinion of the population to be studied is positive towards the source of the hazardous pollution.

 

Discussion, first paragraph: While the sample size recruited limits generalizability, the recruitment difficulties encountered need to be communicated to other scientists in the field to facilitate better recruitment in other studies. In the following, we will first discuss the possible results based on the limited sample and then attempt to give recommendations how to improve the limited recruitment success in future studies.

 

Discussion, section 4.3 Challenging recruitment: Is it the topic? – We considerable rewrote the section and added references providing evidence for the local opinion that most likely impacted the low participation rate. We copy the whole section here below:

 

Comments 2: The statistical analysis methods are correctly described, although I believe that this study could have had a more rigorous, more comprehensive and broader analysis strategy.

 

Response 2: We thank the reviewer for this suggestion. We see that in the next comment below the reviewer suggested to study confounding factors in the association relationships, we assume this is what the reviewer implied with the “more rigorous, comprehensive, and broader analysis strategy”. We refer to our response nr. 3 with respect to which changes we made to the analysis to address this concern. Additionally, we added analysis of the number of participants exceeding defined thresholds on the employed (mental) health scales in Table 2, and described these thresholds in the methods section.

 

Comments 3: Results: The results should be further explored, as well as their presentation. There are many tables and little commentary on the results. The authors could have explored other association relationships taking into account the diversity of data they collected. In the association relationships studied, confounding factors were not taken into account, such as: alcohol, tobacco, coffee, other health conditions and/or use of medication.

 

Response 3: We thank the reviewer for pointing out that the description of the results was rather short. We amended the presentation of results by putting the measured air pollution into perspective on the background of the WHO recommended health limits:

 

According to the measurements of the environmental agency, the overall of PM₁₀ average across all hours and days in the time frame of interest was 17.2 μg/m³, thus, exceeding the WHO recommended health limits for 24h averages ([62]<5 μg/m³ PM_2.5 and <15 μg/m³ PM₁₀). Our point-measurements of PM_2.5 and PM₁₀ in the time frame of recruitment at other places in town were considerably higher and can be found in Table 1. Particulate matter measurements were consistently higher in Oddeyrin as compared to Giljahverfi.

 

Additionally, we explained the descriptives in Table 2 better:

The data shows that dispersion of symptoms of seasonality, insomnia, migraine, and eco-anxiety was covering well the range of possible answers on the employed scales. These ranges were comparable to what would be expected in a community sample according to the literature.

 

We also thank for asking for additional analysis regarding these 5 variables. We added the analsis of alcohol use and caffeine intake to tables 2 and 4 and concluded in the text that there were

“but no significant correlations between any of the worries-subscales with the alcohol consumption index and daily caffeine consumption.”

 

We also compred the neighbourhoods by alcohol and caffeine consumption and found no significant differences. We added this information to the respective chapter.

 

The use of tobacco is not very common in Iceland, hence, further analysis of the 4 individuals in the sample who were using tobacco was not possible from a statistical point of view. We added this to the discussion:

“In relation to the small sample there were several aspects that we could not analyse due to small subsamples. Specifically, only 4 participants were tobacco users. Smoking is not very common in Iceland but the combined impact of particulate matter and smoking especially regarding indoor air quality [85] should be taken into account in future studies with larger sample size. “

 

Regarding self-reported other health conditions and the use of  medication we refrained from further analysis because the reported conditions and medications were quite inhomogeneous. We added this lack of further analysis possibilities to the limitation section as follows:

“Future studies should be designed to accurately measure individual exposure to air pollution combined with objective measurements of health. This is especially relevant as we obtained information on self-reported other health conditions and the regular intake of medication that might be of interest to the presented research questions, but the inhomogeneity of these conditions and pharmaceutical agents paired with the low reliability of self-reported health data prevented us from conducting further quantitative analysis.”

 

Comments 4: Discussion: The authors summarize their main findings, which they present in results and compare with existing literature. The authors are aware of the limitations of the study, however these limitations are so important that they may call into question the validity of the present study.

 

Response 4: We thank the reviewer for the evaluation. We added more emphasis to the conclusions on one of the main messages we would like to convey with the publication of this analysis of a rather small sample:

“Most importantly, the study draws attention of researchers to special care needed when designing surveys on controversial issues. The wording of the study invitation might limit participation, which was likely the reason for the low participation in the present case rate despite considerable recruitment effort.”

 

Comments 5: Conclusion: The study has the merit of pointing to an important public health problem, already known, which according to the authors, has not been given due attention. However, there appears to be a lack of proven scientific evidence in this study that would suggest we need to raise these concerns. The authors could also propose some corrective measures to minimize the impact of pollution caused by land and sea traffic on human health.

 

Response 5: We fully agree that we could have been  more concrete and clear with what we actually wanted to tell the public with this research. We added to the discussion at the beginning a clear statement that air quality measurements are exceeding the recommended health limits:

Air quality in Iceland is said to be good, which is only true for part of the year. According to our data and the data from the environmental agency, levels of particulate matter exceed WHO recommended health limits [62] in urban areas like Akureyri during certain parts of the year.

 

And to the conclusion the respective sentence:

“Finally, we propose corrective measures to minimize the impact of pollution caused by land and sea traffic on human health, such as the permanent ban of studded tires and the limitation of the number of cruise ships.”

 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

COMMENTS TO THE AUTHORS

1. Dear Authors, although the sample size of your study cannot define the situation of the population, it does represent an approximation of the results that could be obtained by extending the study to the different regions of Iceland.
2. The study seems novel and reproducible to me.
3. It would be convenient to analyze the variables related to physical and mental health identified in the population and thus identify that other factors, together with pollution, contribute to discomforts that may be present in the population.

Thank you for your contribution.

Author Response

We would like to thank reviewer 3 for their time taken to read our manuscript and for giving us valuable hints on how to improve the text.

 

Comments 1: Dear Authors, although the sample size of your study cannot define the situation of the population, it does represent an approximation of the results that could be obtained by extending the study to the different regions of Iceland.

 

Response 1:  We thank the reviewer for this assessment. We added the following text to the limitations section:

“The main limitation of the study is the small sample size, which prevents generalizations to the population of Iceland and beyond. However, the study results can be seen as a pilot indicator for results that could be obtained by extending the study to different regions in and outside of the country.”

 

Additionally, we would like to point to the extensive changes made in sections

4.3. Challenging recruitment: Is it the topic?

and

 

5. Conclusions

 

Where in both chapters we emphasized the relevance of the publication of our difficulties in gathering a significant sample. the small sample size is not a result from insufficient efforts or coincidence. Rather it is mostly caused by the wording of the invitation to participate in the study. See for example the amended text:

“However, the major part of the population in Akureyri is reluctant to change studded tires out for non-studded winter tires, as the most recent count in Akureyri in April 2025 yielded that 85% of cars run on studded tires [80]. The low participation rate in our study may indicate how controversial the issue of studded tire use is especially in the Northen part of Iceland where winter conditions are harsher compared to the South. Some of the people invited to take part in this study may have feared that just by taking part they could increase the chance of studded tires being banned in Akureyri. In this town, the use of studded tires is restricted to the season 01. November to 14. April. However, even the local police in Akureyri announced not to punish the use of studded tires until May [81,82]. The low participation rate in our study may indicate how controversial the issue of studded tire use is especially in the Northern part of Iceland where winter conditions are harsher compared to the South.“

 

Comments 2: The study seems novel and reproducible to me.

 

Response 2: Thank you very much for your encouraging words.

Comments 3: It would be convenient to analyze the variables related to physical and mental health identified in the population and thus identify that other factors, together with pollution, contribute to discomforts that may be present in the population.

 

Response 3: We agree that this would be the most important contribution. WE hope that we can provide systematic data on this in the future, as we are currently running another large study in Iceland which meausres also individual exposure to particulate matter (the EpiC SAD study). For the present study we added the following to the discussion:

“Population-level data has been analyzed with respect to the impact of volcanic activity on respiratory diseases and deaths [62]. In contrast, a systematic estimation of the negative health impact of high levels of particulate matter caused by the use of studded tires as measured by the environmental agency (Figure 1) on the urban population in Iceland is lacking. Given the comparably high levels of pollution the effects on physical and mental health can be assumed to be comparable to other regions in the world where other sources of particulate matter lead to a wide variety of negative health consequences.”

 

Author Response File: Author Response.docx

Reviewer 4 Report

Comments and Suggestions for Authors

The submitted study concentrates on a small Icelandic town with transient high PM levels due to studded tires and cruise ship emissions at the port, i.e. two outdoor pollution sources. The authors noticed themselves that a sample of 47 citizens due to a low participating rate is not sufficient for generalizations. This initial shortcoming could be improved by continuing the study for a longer time.

However, a more serious shortcoming not pointed out properly in the manuscript is the subjective overrating of outside air pollution compared to indoor air pollution. The United States Environmental Protection Agency (EPA) showed repeatedly (see literature below) that indoor pollution at home, at work, and in school lies 2-5 times over the outdoor pollution level and can get even 100 times more worse. Although it has to be taken into account that public discussions and media contributions about studded tires and cruise ship pollution raised citizen's subjective awareness of these phenomena with resulting psychosomatic effects, a true empirical cross-check about local indoor pollution is missing and would show the local balance. The referee does not know whether additional empirical data on Icelandic indoor pollution are available in this context, but the EPA-published magnitude discrepancy of the two environmental stressors makes a casual treatment of their relationship look rather problematic. This very issue needs revision and additional references and would set the original study into a better, more balanced perspective.

References 

United States Environmental Protection Agency. (2018). Indoor air quality.  

United States Environmental Protection Agency. (2020). The inside story: A guide to indoor air quality. 

Author Response

We thank the reviewer for their effort and time taken to read our manuscript and provide important recommendations. We sought to follow them as well as we could. Here are our replies to the highly appreciated comments:

 

Comments 1: The submitted study concentrates on a small Icelandic town with transient high PM levels due to studded tires and cruise ship emissions at the port, i.e. two outdoor pollution sources. The authors noticed themselves that a sample of 47 citizens due to a low participating rate is not sufficient for generalizations. This initial shortcoming could be improved by continuing the study for a longer time.

 

Response 1: We thank the reviewer and fully agree with this assessment. Indeed, we did put considerable effort into recruitment but faced a situation like never before, which would not have been possible to be remediated by continuing the study. Specifically, we are convinced that the wording of the study invitation prevented a larger sample to accumulate in this study on a highly controversial issue. We elaborated further on this situation, that is an important message for the scientific community trying to gather data that could inform policy makers. If study invitations for particiation in studies on controversial issues are not phrased in the best way, the collection of sufficient amounts of valid data might be highly compromised:

 

4.3. Challenging recruitment: Is it the topic?

However, the major part of the population in Akureyri is reluctant to change studded tires out for non-studded winter tires, as the most recent count in Akureyri in April 2025 yielded that 85% of cars run on studded tires [81]. The low participation rate in our study may indicate how controversial the issue of studded tire use is especially in the Northen part of Iceland where winter conditions are harsher compared to the South. Some of the people invited to take part in this study may have feared that just by taking part they could increase the chance of studded tires being banned in Akureyri. In this town, the use of studded tires is restricted to the season 01. November to 14. April. However, even the local police in Akureyri announced not to punish the use of studded tires until May [82,83]. The low participation rate in our study may indicate how controversial the issue of studded tire use is especially in the Northern part of Iceland where winter conditions are harsher compared to the South.

 

Comments 2: However, a more serious shortcoming not pointed out properly in the manuscript is the subjective overrating of outside air pollution compared to indoor air pollution. The United States Environmental Protection Agency (EPA) showed repeatedly (see literature below) that indoor pollution at home, at work, and in school lies 2-5 times over the outdoor pollution level and can get even 100 times more worse. Although it has to be taken into account that public discussions and media contributions about studded tires and cruise ship pollution raised citizen's subjective awareness of these phenomena with resulting psychosomatic effects, a true empirical cross-check about local indoor pollution is missing and would show the local balance. The referee does not know whether additional empirical data on Icelandic indoor pollution are available in this context, but the EPA-published magnitude discrepancy of the two environmental stressors makes a casual treatment of their relationship look rather problematic. This very issue needs revision and additional references and would set the original study into a better, more balanced perspective.

References 

United States Environmental Protection Agency. (2018). Indoor air quality.  

United States Environmental Protection Agency. (2020). The inside story: A guide to indoor air quality. 

Response 2: We thank the reviewer for this extremely important comment! Indeed, we realize we did not deem the assessment of indoor air pollution as important but failed to give reasons for this. The study focused mainly on these two outdoor air pollution sources, which is the main reason we did not further describe potential indoor-air pollution. However, we added the following abstract to section 4.1 in the discussion:

 

The subjective overrating of the hazards from outdoor air pollution compared to indoor air pollution stands in strong discrepancy to research from other areas in the world where indoor air quality is often a much more serious problem [62]. Not all common sources for poor indoor air quality are relevant in Iceland, where radon activity is generally lower [63], cigarette smokers are rare in international comparison [64], and where houses are heated with green geothermal energy which is also used to produce electricity, thus, indoor-pollution from unvented kerosene and gas space heaters, woodstoves, fireplaces, and gas stoves is almost non-existent. However, associations between unhealthy indoor air quality due to mold-infested building materials and self-assessed health have been documented previously in Iceland [65]. Data on indoor pollution from chemicals is less well researched in Iceland and, hence, less described in the media, which is possibly the reason why indoor air pollution was perceived less important by the study participants.

 

Author Response File: Author Response.docx