Interaction effects of outdoor thermal comfort and air pollution – Nature

Report on the Interaction of Outdoor Thermal Comfort and Air Pollution in Urban Green Spaces

Introduction: Aligning Urban Environmental Quality with Sustainable Development Goals

Rapid urbanization presents dual environmental challenges—the urban heat island effect and severe air pollution—that directly impede progress toward key Sustainable Development Goals (SDGs). Urban haze and thermal pollution pose significant threats to **SDG 3 (Good Health and Well-being)** by increasing the risk of respiratory and cardiovascular diseases. Concurrently, these issues undermine efforts to create inclusive, safe, and resilient urban environments as outlined in **SDG 11 (Sustainable Cities and Communities)**. This report details a study conducted in Xi’an, China, that investigates the interactive effects of the outdoor thermal environment and air quality on human comfort within University Campus Green Spaces (UCGSs). By examining these interactions, the research aims to provide evidence-based strategies for optimizing urban green spaces, thereby enhancing the quality of life and contributing to the achievement of global sustainability targets, including **SDG 4 (Quality Education)** by fostering healthier campus environments.

Research Methodology

Study Design and Location

The study was conducted at the Xingqing Campus of Xi’an Jiaotong University, a site representative of a warm temperate semi-humid continental monsoon climate. Four distinct types of University Campus Green Spaces (UCGSs) were selected to analyze varying environmental conditions:

• Wutong tree-shaded section (SR)
• Empty area (CS)
• Green area (GA)
• Residential area (RA)

Data Collection and Analysis

A comprehensive methodology combined objective field measurements with subjective questionnaire surveys to assess the complex relationship between environmental conditions and human perception. Data was collected across all four seasons to ensure a holistic analysis.

1. Field Measurements: Instruments were used to record key physical parameters, including air temperature, relative humidity, wind speed, black bulb temperature, and PM2.5 concentrations.
2. Questionnaire Surveys: A total of 927 valid questionnaires were collected. The survey gathered demographic data and subjective evaluations from respondents on a 7-point scale for:
   • Thermal Sensation Vote (TSV)
   • Thermal Comfort Vote (TCV)
   • Air Quality Vote (AQV)
   • Breathing Sensation Vote (BSV)
3. Thermal Comfort Assessment: The modified Physiological Equivalent Temperature (mPET) index was calculated using RayMan Pro software to provide a standardized measure of the thermal environment, integrating meteorological data with personal factors like clothing and activity levels.

All research methods received ethical approval, and informed consent was obtained from all participants, ensuring adherence to ethical standards.

Key Findings on Environmental Comfort and Perception

Combined Impact of Thermal Environment and Air Quality

The study revealed a significant interaction between the thermal environment (mPET) and air pollution (PM2.5) on subjective comfort, with effects varying across different types of spaces. Extreme temperatures consistently resulted in discomfort, highlighting a critical challenge for public health management under **SDG 3**. The influence of haze pollution on thermal comfort was most pronounced in high and low-temperature environments. In high-temperature conditions, a PM2.5 concentration above 100 µg/m³ was associated with low respiratory comfort. These findings underscore the need for integrated environmental management to support **SDG 11**.

• Residential Area (RA): Showed the most significant response to temperature changes, with both thermal sensation and comfort being highly sensitive to mPET fluctuations.
• Green Area (GA): Respondents reported moderate comfort, with higher PM2.5 levels diminishing comfort even in thermally pleasant conditions.
• Empty Area (CS): Perceived as slightly warm on average, with comfort decreasing as mPET increased.
• Shaded Road (SR): Respondents were less sensitive to air pollution in this thermally buffered environment, indicating the mitigating potential of urban greenery.

Influence of Demographic and Seasonal Factors

Demographic and seasonal variables were found to significantly mediate perceptions of comfort, providing crucial data for designing inclusive urban spaces that align with **SDG 11**.

• Age: Younger respondents (18–25) generally preferred cooler temperatures, whereas older individuals (41–60) favored warmer conditions. The 31–50 age group demonstrated the highest sensitivity to site-specific thermal changes.
• Gender: Females exhibited greater sensitivity to thermal variations than males, with a lower neutral temperature. Males, however, reported higher overall thermal comfort.
• Season: Thermal adaptation behaviors and preferences varied distinctly by season. In summer, respondents preferred lower temperatures and higher wind speeds, seeking shelter and water. In winter, adding clothing was the primary adaptation strategy.

Perception of Air Quality

The perception of air quality was intricately linked to the thermal environment. In spring and summer, higher temperatures were found to alleviate the perception of haze but simultaneously decreased breathing comfort. Conversely, in autumn and winter, higher temperatures exacerbated perceived haze severity but improved breathing comfort. This complex relationship is vital for developing effective public health communications and policies aimed at achieving the clean air targets of **SDG 3** and **SDG 11**.

Implications for Public Health and Sustainable Urban Development

Health Impacts of the Thermal and Air Environment

The study confirmed that adverse thermal conditions and poor air quality have measurable impacts on human health, directly relating to the objectives of **SDG 3 (Good Health and Well-being)**. The findings identify vulnerable populations and specific health risks associated with environmental stressors.

1. Thermal Environment Health Risks:
   • Individuals with pre-existing mental health conditions were found to be the most sensitive to the thermal environment.
   • Respondents with respiratory diseases reported the lowest thermal comfort scores at temperatures above 21°C.
   • Cardiovascular and cerebrovascular patients exhibited the highest neutral physiologically equivalent temperature (29.66°C), indicating a different thermal comfort range.
2. Air Quality Health Risks:
   • Respiratory diseases were the most frequently reported illness associated with haze pollution, affecting 71% of respondents with related conditions.
   • Individuals with immune system diseases were the most sensitive to poor air quality.
   • Respondents with skin diseases were also significantly affected by air pollution, reporting high levels of discomfort.

Conclusion and Recommendations for Achieving SDGs

This study demonstrates the critical and complex interplay between outdoor thermal comfort, air quality, and public health in an urban university setting. The findings emphasize that achieving **SDG 11 (Sustainable Cities and Communities)** and **SDG 3 (Good Health and Well-being)** requires an integrated approach to urban environmental management that addresses both thermal stress and air pollution simultaneously.

Based on the results, the following recommendations are proposed:

• Integrated Urban Planning: Urban design strategies must consider the combined effects of heat and air pollution. The strategic placement of green infrastructure, such as shaded walkways and green areas, can mitigate both heat stress and the perception of poor air quality.
• Targeted Public Health Interventions: Public health policies should be tailored to protect vulnerable groups, including the elderly, individuals with respiratory or cardiovascular conditions, and those with mental health challenges. This includes issuing targeted advisories during periods of extreme heat and high pollution.
• Enhance Urban Green Spaces: Optimizing the design and management of UCGSs and other urban parks is a tangible strategy for advancing multiple SDGs. These spaces improve environmental quality, promote physical activity, and enhance the overall well-being of urban residents.

By addressing these interconnected challenges, cities can create healthier, more comfortable, and more resilient environments for all residents, making significant strides toward a sustainable future.

Analysis of Sustainable Development Goals in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

1. SDG 3: Good Health and Well-being

   • The article extensively discusses the adverse health effects of urban environmental problems. It explicitly links “haze pollution” and “thermal pollution” to human health, stating that “Heat pollution and air pollution will affect human health to varying degrees.” It details specific health issues such as “lung cancer,” “cardiovascular and respiratory diseases,” “mental disorders,” “heart disease,” and “skin diseases” that are exacerbated by poor air quality (high PM2.5 concentrations) and extreme thermal environments.

2. SDG 11: Sustainable Cities and Communities

   • The article’s central theme is the environmental quality of urban spaces. It addresses issues like “Urban haze pollution,” the “urban heat island effect,” and the quality of “Urban Campus Green Spaces (UCGSs).” The study aims to contribute to “healthy urban development” by investigating the interaction between the thermal environment and air pollution in a city (Xi’an, China), which is directly related to making cities more sustainable, resilient, and inclusive.

3. SDG 13: Climate Action

   • The article addresses the “urban heat island effect” and “thermal pollution,” which are phenomena closely linked to climate change and its impacts on urban areas. By studying outdoor thermal comfort and human adaptation to extreme temperatures, the research contributes to understanding the adaptive capacity of urban populations to climate-related hazards like heatwaves, which is a key aspect of climate action.

2. What specific targets under those SDGs can be identified based on the article’s content?

1. Target 3.9: By 2030, substantially reduce the number of deaths and illnesses from hazardous chemicals and air, water and soil pollution and contamination.

   • The article directly supports this target by investigating the health impacts of air pollution. It states that “increased PM2.5 concentrations pose a serious threat to human health” and mentions studies linking PM2.5 to “the incidence of lung cancer” and “cardiovascular and respiratory diseases.” It also notes that “short-term exposure to high PM2.5 levels increases morbidity and mortality from cardiopulmonary diseases.”

2. Target 11.6: By 2030, reduce the adverse per capita environmental impact of cities, including by paying special attention to air quality and municipal and other waste management.

   • The research focuses on urban air quality as a major environmental challenge. It highlights that in Xi’an, “PM2.5 is the primary pollutant,” and its average concentration in 2022 (52 µg/m³) was “significantly higher than the national standard.” The entire study is an effort to understand and ultimately mitigate the adverse effects of poor urban air quality.

3. Target 11.7: By 2030, provide universal access to safe, inclusive and accessible, green and public spaces, in particular for women and children, older persons and persons with disabilities.

   • The study is conducted within “University Campus Green Spaces (UCGSs),” which are defined as a type of urban green space. The research evaluates the environmental quality (thermal and air) of these spaces to determine their comfort and usability for people. By developing strategies for “optimizing the thermal comfort of urban campus green space environments,” the article contributes to improving the quality and accessibility of these public spaces.

4. Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries.

   • The article’s investigation into the “urban heat island effect” and its impact on “thermal comfort” is directly related to strengthening resilience against climate-related hazards like extreme heat. The study analyzes “thermal adaptation behavior” in summer and winter, providing insights into how urban populations can adapt to thermal stress, which is crucial for building climate resilience in cities.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

1. Indicators for Target 3.9

   • Morbidity and mortality rates from pollution: The article implies the use of morbidity rates for specific diseases as an indicator. It states that “respiratory diseases…account for the highest proportion of haze-related illnesses (71%).” It also refers to studies linking PM2.5 exposure to increased “morbidity and mortality from cardiopulmonary diseases,” which aligns with the official indicator 3.9.1 (Mortality rate attributed to household and ambient air pollution).

2. Indicators for Target 11.6

   • Annual mean levels of fine particulate matter (PM2.5): The article directly uses this indicator. It provides specific measurements, stating that “the average concentration of PM2.5 in 2022 was 52 µg/m³” in Xi’an. The study also categorizes PM2.5 concentrations for its analysis: “0–50 µg/m³ (excellent), 50–100 µg/m³ (good), and 100–150 µg/m³ (slight pollution).” This directly corresponds to indicator 11.6.2.

3. Indicators for Target 11.7

   • Subjective comfort evaluations in green spaces: While not a direct measure of physical access, the article uses qualitative indicators to assess the quality and usability of green spaces. These include the Thermal Sensation Vote (TSV), Thermal Comfort Vote (TCV), Air Quality Vote (AQV), and Breathing Sensation Vote (BSV). These metrics serve as indicators of how safe, inclusive, and welcoming these spaces are from a human comfort perspective.

4. Table of SDGs, Targets, and Indicators

Source: nature.com