Non-Optimal Wet-Bulb Temperature and Short-Term Black Carbon Exposure Largely Impact Emergency Department Visits for Cause-Stable Ischemic Heart Disease

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Kindly see my detailed comments on the manuscript below:

Line 31: How do extreme weather events exacerbate pollution levels and their associated health effects?

Lines 65–72: The period considered for the analysis should be clearly stated, along with the population under study (e.g., general population, older adults, or stratification by age and gender).

Introduction: Justify the choice of the distributed lag nonlinear model (DLNM) for the analysis within the introduction.

Lines 60–62: Further specify the characteristics of black carbon (BC) and how it differs from other fine particulate matter, such as PM2.5.

Figure 1 (Map):

Replace the low-resolution satellite image with a cleaner or higher-resolution background. Consider using a simplified topographic or street map instead of satellite imagery.

Increase the font size and apply a white or transparent background for better readability. Add any missing elements (e.g., clarify the “Study Area” symbol shown in the inset map, which is currently not explained in the legend).

Use symbols with stronger contrast against the background. For example, add black outlines to yellow and red triangles or adjust the color scheme to be more colorblind-friendly. Consider using different shapes (e.g., circles for hospitals and triangles for stations) to improve visual distinction.

Reduce the size of the compass rose and position it less prominently. Make the scale bar more visible using a contrasting background or clearer format.

Enlarge the inset map and ensure all fonts are legible. Highlight the study region more clearly, for example by labeling the city or province (e.g., Shanghai).

Make the figure caption more descriptive. Suggested revision: "Geographical locations of air pollution monitoring stations and Renhe Hospital in Shanghai, China."

Line 411: Replace "due to various diseases" with a more specific description of the diseases involved.

Line 428: Expand the discussion in "similar to previous studies" to include specific comparisons or findings from those studies.

Lines 429–435: How do the mechanisms of BC exposure compare with those of other fine particulate matter such as PM2.5?

WBT/BC Lag Effects:
Could you clarify why the effects of extremely low WBT are no longer significant after 5.5 days, while the effects of high WBT appear to be more rapid and short-lived? Additionally, what is the underlying explanation for the prolonged lag effects of high BC exposure, particularly the peak observed on day 9?

Author Response

Question 1: Line 31: How do extreme weather events exacerbate pollution levels and their associated health effects?

Our reply 1: Thanks for your comment. Extreme weather events significantly increase pollution levels and exacerbate their health impacts through processes such as wildfires, heat waves, floods, and droughts. Wildfires release large amounts of particulate matter and toxic gases, heat waves accelerate the formation of ground-level ozone, and floods spread waterborne pollutants. Additionally, droughts trigger dust storms that reduce air quality, while temperature inversions trap pollutants near the ground. These processes can lead to increased respiratory diseases, cardiovascular diseases, infection risks, and increased mortality, highlighting the critical links between extreme climate, pollution, and public health. We have added the description of how extreme weather events can exacerbate pollution levels and their associated health impacts in lines 32-40 of the manuscript.

 

Question 2: Lines 65–72: The period considered for the analysis should be clearly stated, along with the population under study (e.g., general population, older adults, or stratification by age and gender).

Our reply 2: Thanks for your comment. We have added explanations of the period considered in the analysis and the population studied, such that they are clearly stated in lines 81-85 of the manuscript.

 

Question 3: Introduction: Justify the choice of the distributed lag nonlinear model (DLNM) for the analysis within the introduction.

Our reply 3: Thanks for your comment. We have added an explanation of the rationality of choosing the distributed lag nonlinear Model (DLNM) for analysis in the Introduction section in lines 87-95 of the manuscript.

 

Question 4: Lines 60–62: Further specify the characteristics of black carbon (BC) and how it differs from other fine particulate matter, such as PM2.5.

Our reply 4: Thanks for your comment. We have added the description with respect to the characteristics of black carbon (BC) and its distinction from other fine particulate matter such as PM2.5 in lines 69-75 in the manuscript.

 

Question 5: Figure 1 (Map): Replace the low-resolution satellite image with a cleaner or higher-resolution background. Consider using a simplified topographic or street map instead of satellite imagery.

Our reply 5: Thanks for your comment. We have used simplified street map instead of satellite image in Figure 1.

 

Question 6: Increase the font size and apply a white or transparent background for better readability. Add any missing elements (e.g., clarify the “Study Area” symbol shown in the inset map, which is currently not explained in the legend).

Our reply 6: Thanks for your comment. We have addressed this issue in Figure 1.

 

Question 7: Use symbols with stronger contrast against the background. For example, add black outlines to yellow and red triangles or adjust the color scheme to be more colorblind-friendly. Consider using different shapes (e.g., circles for hospitals and triangles for stations) to improve visual distinction.

Our reply 7: Thanks for your comment. We have addressed this issue in Figure 1.

 

Question 8: Reduce the size of the compass rose and position it less prominently. Make the scale bar more visible using a contrasting background or clearer format.

Our reply 8: Thanks for your comment. We have addressed this issue in Figure 1.

 

Question 9: Enlarge the inset map and ensure all fonts are legible. Highlight the study region more clearly, for example by labeling the city or province (e.g., Shanghai).

Our reply 9: Thanks for your comment. We have addressed this issue in Figure 1.

 

Question 10: Make the figure caption more descriptive. Suggested revision: "Geographical locations of air pollution monitoring stations and Renhe Hospital in Shanghai, China." 

Our reply 10: Thanks for your comment. We have modified the caption of the figure to " Geographical locations of air pollution monitoring stations and Renhe Hospital in Shanghai, China." in lines 142-143 of the manuscript.

 

Question 11: Line 411: Replace "due to various diseases" with a more specific description of the diseases involved.

Our reply 11: Thanks for your comment. We have changed “due to various diseases” to be more specific with respect to the diseases involved in lines 439-440 of the manuscript.

 

Question 12: Line 428: Expand the discussion in "similar to previous studies" to include specific comparisons or findings from those studies.

Our reply 12: Thanks for your comment. We have added discussions with similar previous studies, including specific comparisons or findings of those studies in lines 458-463 of the manuscript.

 

Question 13: Lines 429–435: How do the mechanisms of BC exposure compare with those of other fine particulate matter such as PM2.5?

Our reply 13: Thanks for your comment. We have supplemented the description of the mechanism of exposure to BC compared with other fine particulate matter (such as PM2.5) in lines 466-470 of the manuscript.

 

Question 14: WBT/BC Lag Effects: Could you clarify why the effects of extremely low WBT are no longer significant after 5.5 days, while the effects of high WBT appear to be more rapid and short-lived? Additionally, what is the underlying explanation for the prolonged lag effects of high BC exposure, particularly the peak observed on day 9?

Our reply 14: Thanks for your comment. The effect of extreme low WBT is no longer significant after 5.5 days, while the effect of high WBT seems to be more rapid and short-lived. This is mainly because the individual's reaction to heat exposure is relatively faster than that to cold exposure, and the duration of the effect of cold exposure is longer. The prolonged lag effect of high BC exposure, especially the peak observed on the 9th day, was interpreted as the significant and persistent health effects of high BC exposure on individuals. This is similar to previous studies on air pollution and health outcomes. We have supplemented the explanations and clarifications regarding these aspects in lines 492-499 of the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The present study aimed to investigate whether non-optimal wet bulb temperature (the lowest temperature to which air can be cooled by the evaporation of water into the air at a constant pressure) and short-term black carbon (linked to increased risk of cardiovascular diseases) exposure largely impact emergency department visits for cause‑stable ischemic heart disease. This field of study is relevant since climate change and global warming have been reported to play an insidious role in the manifestation of several infectious and non-infectious diseases, including cardiovascular disease.

Comments:
1) I find the manuscript written well and informative. The Introduction, Methodology, Results, Discussion and Conclusion seems well-written and presented. 

2) “Methodology section”: 
- The authors stated in Page 3, Lines 117 – 123: “2.4. Emergency department visits of cause‑stable ischemic heart disease (CSIHD). Emergency department attendance records were extracted from Renhe Hospital, Baoshan District, Shanghai, China, from January 1, 2013 to December 31, 2020 (Fig. 1)”. The COVID-19 pandemic, which originated in Wuhan China, began in December 2019 onwards. The authors collected data up till 31 December 2020 (during the COVID-19 pandemic). My point raised is whether the authors excluded patients that presented with COVID-19 from this study – COVID-19 contributed to cardiovascular issues during the COVID-19 pandemic (which raises the question whether CSIHD was associated with COVID-19 or CSHID was associated with wet bulb temperature and black carbon or CSIHD was associated with COVID-19+wet bulb temp+black carbon)? If not, this should be a limitation in study. Also, during 01 December 2019 till 31 December 2020 lockdowns were implemented which could have caused a reduction in air pollutants and black carbon emission, as well as optimal wet bulb temperature – this could have affected the results obtained?

In addition, indoor exposures from secondhand tobacco smoke, cooking with solid fuels and gas stoves, heaters, gas leaks, or blocked chimneys that produce carbon monoxide, and molds, fungi and mycotoxins also play a role in heart disease – In this study the authors only considered outdoor exposures. This should be a limitation in study. Other issues, chronic stress issues and mental health issues also affect heart disease. 

- The authors need to mention the inclusion and exclusion criteria for patient selection for this study.

- The mathematical models used and presented seem acceptable

3) Results section: Upon scrutinizing this section, I found no issues with the presentation and interpretation of the results.

Overall, I approve publication of the manuscript after my comments are addressed.

Author Response

Question 1: The present study aimed to investigate whether non-optimal wet bulb temperature (the lowest temperature to which air can be cooled by the evaporation of water into the air at a constant pressure) and short-term black carbon (linked to increased risk of cardiovascular diseases) exposure largely impact emergency department visits for cause‑stable ischemic heart disease. This field of study is relevant since climate change and global warming have been reported to play an insidious role in the manifestation of several infectious and non-infectious diseases, including cardiovascular disease.

Our reply 1: Thanks very much for the positive comments. We have addressed all of your comments and suggestions, and correspondingly revised the main manuscript and Supplementary Material.

 

Question 2: I find the manuscript written well and informative. The Introduction, Methodology, Results, Discussion and Conclusion seems well-written and presented.

Our reply 2: Thanks very much for the positive comments.

 

Question 3: “Methodology section”: The authors stated in Page 3, Lines 117 – 123: “2.4. Emergency department visits of cause‑stable ischemic heart disease (CSIHD). Emergency department attendance records were extracted from Renhe Hospital, Baoshan District, Shanghai, China, from January 1, 2013 to December 31, 2020 (Fig. 1)”. The COVID-19 pandemic, which originated in Wuhan China, began in December 2019 onwards. The authors collected data up till 31 December 2020 (during the COVID-19 pandemic). My point raised is whether the authors excluded patients that presented with COVID-19 from this study – COVID-19 contributed to cardiovascular issues during the COVID-19 pandemic (which raises the question whether CSIHD was associated with COVID-19 or CSHID was associated with wet bulb temperature and black carbon or CSIHD was associated with COVID-19+wet bulb temp+black carbon)? If not, this should be a limitation in study. Also, during 01 December 2019 till 31 December 2020 lockdowns were implemented which could have caused a reduction in air pollutants and black carbon emission, as well as optimal wet bulb temperature – this could have affected the results obtained?

Our reply 3: We sincerely thank the reviewer for the thoughtful and important comments. We fully agree that the COVID-19 pandemic may have influenced our study results through multiple pathways. First, regarding the inclusion of patients with COVID-19: during data extraction, we did not specifically exclude patients who may have been infected with COVID-19. As the reviewer pointed out, COVID-19 infection itself can lead to cardiovascular complications, including ischemic heart disease, which may confound the observed associations between environmental exposures (wet bulb temperature and black carbon) and cause-stable ischemic heart disease (CSIHD). We acknowledge this as an important limitation of our study. Second, during the period from December 2019 to December 2020, pandemic-related interventions such as lockdowns could have substantially altered air pollution levels, including black carbon concentrations, and could also have affected population exposure to ambient temperature. These changes may have influenced both exposure patterns and the observed health outcomes, thereby impacting the generalizability and interpretation of our results. We have now explicitly acknowledged these limitations in the Discussion section in lines 514-528 of the revised manuscript.

 

Question 4: In addition, indoor exposures from secondhand tobacco smoke, cooking with solid fuels and gas stoves, heaters, gas leaks, or blocked chimneys that produce carbon monoxide, and molds, fungi and mycotoxins also play a role in heart disease – In this study the authors only considered outdoor exposures. This should be a limitation in study. Other issues, chronic stress issues and mental health issues also affect heart disease.

Our reply 4: We sincerely appreciate the reviewer’s insightful comment. We fully agree that indoor environmental exposures, such as secondhand tobacco smoke, the use of solid fuels and gas stoves, carbon monoxide from heaters or blocked chimneys, as well as molds, fungi, and mycotoxins, are important contributors to cardiovascular disease risk. In addition, chronic stress and mental health conditions also play a significant role in the development and exacerbation of heart disease. In this study, due to data availability, we focused exclusively on outdoor environmental exposures, specifically wet bulb temperature and black carbon concentrations. We were unable to capture information on indoor exposures or individual-level psychosocial factors. We acknowledge that the omission of these factors may have introduced residual confounding, and it represents a limitation of our study. We have added this point to the Discussion section of the revised manuscript in lines 528-538 to ensure a more balanced interpretation of our findings.

 

Question 5: The authors need to mention the inclusion and exclusion criteria for patient selection for this study.

Our reply 5: Thanks for your comment. We have supplemented the description of the inclusion and exclusion criteria for patient selection in this study in lines 146-150 of the manuscript.

 

Question 6: The mathematical models used and presented seem acceptable.

Our reply 6: Thanks for your positive comment.

 

Question 7: Results section: Upon scrutinizing this section, I found no issues with the presentation and interpretation of the results.

Our reply 7: Thanks for your positive comment.

 

Question 8: Overall, I approve publication of the manuscript after my comments are addressed.

Our reply 8: Thanks for your comment. We have addressed all of your comments and suggestions, and correspondingly revised the main manuscript and Supplementary Material.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for the responses. I have no further contributions.