Combined Health Effects of Heat Waves and Outdoor Air Pollution

“The theory that hot weather and outdoor air pollution interact together to produce health difficulties is well-supported by scientific research.”

The adverse effects of both hot weather and air pollution on human health are now well-acknowledged. On one hand, outdoor air pollution is a major environmental threat to global public health. On the other hand, extreme heat events, sometimes referred to as heat waves, are one of the primary causes of weather-related mortality in the United States. In addition to increasing mortality, hot weather and heat extremes are also linked to an increase in hospital admissions, emergency department visits, and fatalities from cardiorespiratory and other illnesses. 

Less is known about the health effects on dangerously polluted air in various weather and climatic conditions—namely, heat waves. However, several recent studies have shown the potential combined effects of air pollution and extreme heat on human health.  

Potential synergy on human health 

The theory that hot weather and outdoor air pollution (such as particulate matter [PM], CO, O3, SO2, and NO2) interact together to produce health difficulties is well-supported by scientific research. The severity of these impacts on respiratory illness varies depending on the condition and the individual. More susceptible populations include children and the elderly. Cardiorespiratory illness, asthma, acute bronchiolitis-related illness, and chronic obstructive pulmonary disease (COPD) are the primary symptoms. It is important to note that the combined impact differs based on local climatic idiosyncrasies, activity patterns, and physical adaptations towards hot weather. 

Particularly concerning are any potential correlations between temperature, ozone, and PM. One of the mechanisms behind the combined health impacts of air pollution and heat is oxidative stress and inflammation. Oxidative stress is caused by an imbalance between the production of reactive oxygen species (ROS) in cells and tissues and the available detoxifying defense against them, and it plays a significant role in chronic diseases such as cardiorespiratory disease, Alzheimer's disease, autoimmune diseases, and cancer. Because ozone synthesis in the troposphere can occur concurrently with heat waves, and because heat stress, PM, and ozone are environmental factors that enhance ROS creation, they may cause further oxidative damage by disrupting mitochondrial homeostasis and shutting down cellular activities. Therefore, co-exposure to heat and ozone is already common in Europe. During heat waves, record-breaking temperatures, high ozone and PM concentrations, and rising cardiovascular and pulmonary morbidity and mortality can all occur at the same time. 

What are our options? 

Because of climate change, the prevalence of extreme weather conditions and air pollutants is predicted to worsen respiratory conditions. In order to combat this, proper mitigation policies and public health measures are necessary. 

The goal of public health solutions should be to stop this extra burden of sickness throughout the summer, especially during heat waves. It is critical to identify both the sources and amounts of air contaminants, as well as population groups that are more vulnerable to hot weather fluctuation. Vulnerable populations should be the focus of short-term public health initiatives by way of providing access to cooling devices, such as fans and evaporative coolers, and proper hydration. Additionally, air pollution management that focuses on emissions from motor vehicles may be beneficial, particularly during high-temperature seasons.

Main criteria pollutants, sources, and health effects on respiratory system

• Particulate matter (PM10 and PM2.5)

  Sources

  Automobile, bus, and truck exhaust; fuel-burning (wood stoves and fireplaces); industry; construction

  Human Health Effects on Respiratory System

  • Increasing infant respiratory mortality

  • Decreasing lung function
    

  • Decreasing lung growth
    

  • Increasing symptoms in asthmatics

• Ozone (O3)

  Sources

  Chemical reaction of nitrogen oxides (vehicle emissions) and volatile organic compounds under sunlight.

  Human Health Effects on Respiratory System

  • Decreasing lung growth
    

  • Increasing asthma exacerbation
    

  • Increasing all respiratory hospitalization
    

  • Increasing asthma hospitalization
    

  • Increasing asthma emergency department visit
    

  • Increasing school absence for respiratory illness

• Nitrogen dioxide (NO2)

  Sources
  
  High-temperature fuel combustion and atmospheric reactions.
  
  Human Health Effects on Respiratory System

  • Increasing symptoms in asthmatics
    Decreasing lung growth
    

• Carbon monoxide (CO)

  Sources

  Incomplete burning of carbon-containing fuel, mainly emitted by motor vehicles and gas stove.

  Human Health Effects on Respiratory System

  • Increasing asthma hospitalization
    

  • Increasing clinic visits for lower respiratory tract disease headache

• Sulfur monoxide (SO)

  Sources

  Industrial sites such as smelters, paper mills, power plants, and steel manufacturing plants.

  Human Health Effects on Respiratory System

  • Increasing asthma hospitalization
    

  • Increasing clinic visits for lower respiratory tract disease

Read more on Air Pollution and Health and how does the Extreme Heat Continues to Alter Our Planet  from other The Climate Club writers.