When the heat rises, so does air pollution.

Every year extreme heat waves across the globe cause fatalities and a rise in hospitalizations from cardiovascular and respiratory ailments, heat stress conditions such as heat stroke, and other heat-related illnesses.

In recent years, high temperatures in North America, Europe, and South Asia produced dangerous air pollution levels (1). One reason for that is heat acts as a chemical catalyst and converts existing elements in the air into ozone and other harmful byproducts.

What is ozone?

For most people, the mention of ozone calls to mind the ozone layer, also known as stratospheric ozone. It exists naturally in the Earth’s upper atmosphere and protects us from the sun’s ultraviolet rays by absorbing them. Stratospheric ozone makes up 90% of the Earth’s ozone.

The harmful ozone is ground-level or tropospheric ozone. It is a chemical pollutant that results from a reaction between sunlight, two groups of airpollution particles: nitrogen oxides and volatile organic compounds (VOCs). Ground-level ozone is the main ingredient in smog (2).

So, heat waves and soaring ozone levels go hand in hand, and that should be a cause for concern as summer heat waves occur.

Sources of ozone’s components

We all know where sunlight and oxygen come from. There are several sources of the nitrogen oxides and VOCs that help create ozone.

For nitrogen oxides, these sources include (3):

• motor vehicles
• power plants
• other combustion sources
• lightning strikes
• volcanoes
• oceans
• biological decay

Sources of VOCs include (4):

• motor vehicles
• wood burning
• industrial emissions
• chemical plants
• refineries
• cleaners and disinfectants
• paints, paint strippers, varnishes, and finishes
• tobacco smoke

Health impacts of ozone

Ozone is a lung irritant. When inhaled, ground-level ozone can cause short-term and long-term harm to your health. People who are most vulnerable to the dangerous effects are children, older adults, asthma sufferers, people with lung diseases, and people who work or exercise outdoors.

The short-term symptoms include:

• shortness of breath
• pain during deep breaths
• lung and throat irritation
• wheezing and coughing

Long-term, the effects from ozone exposure can include:

• increased asthma attacks
• reduced lung function
• exacerbation of respiratory diseases
• cardiovascular disease

What does ozone do to your lungs?

Ozone acutely damages the tissue lining your lungs (5). Chronic exposure to ozone has been linked to premature death from respiratory diseases (6).

High levels of ozone exposure have been associated with poor outcomes, including mortality and increased hospital visits, in patients with two respiratory diseases: chronic obstructive pulmonary disease and interstitial pulmonary fibrosis (7) (8).

Children with asthma who live in areas with high concentrations of ozone have a greater risk of hospitalization from asthmatic episodes than children who live in areas with lower concentrations (9).

And newborns whose mothers had high levels of ozone exposure while pregnant were found to have decreased lung function (10).

What does ozone do your heart?

A study from the American Heart Association details the link between ozone and heart attacks (11).

According to the research, exposure to ozone causes physiological changes that are linked to heart attacks. Those changes include:

• increased inflammation
• a decrease in blood-clotting agents
• a measurable change in heart rhythm

The researchers observed these changes in young and healthy adults after only two hours of exposure. The results of the ozone exposure were not permanent; most effects were gone after 24 hours.

In the study, 23 young adults were exposed to 0.3 parts per million (ppm) of ozone, which is actually higher than the EPA'a eight-hour exposure standard. However, because of the shorter exposure time, the total exposure was about the same as the EPA standard.

“This study provides a plausible explanation for the link between acute ozone exposure and death,” said Robert B. Devlin, Ph.D., the lead author of the study and a senior scientist at the U.S. Environmental Protection Agency.

The American Heart Association also noted that airborne particulate matter has been linked to death in elderly people with cardiovascular disease. The researchers said ozone and particulate airborne pollution may be causing deaths through similar mechanisms.

Heat waves spark wildfires – a major source of ozone’s components

More frequent heat waves create dangerous knock-on effects on our environment. Higher temperatures increase and prolong drought conditions. Brush, grass, and woodland areas become drier. Those tinderbox conditions can lead to massive wildfires as have occurred in 2022 in New Mexico and the U.S West Coast.

While heat waves are well known in the southwestern United States, extreme heat events are also creating more favorable conditions for wildfires in temperate parts of Europe and in Alaskan and Northern Canadian tundra.

Wildfires generate plumes of billowing smoke that contain key elements of ozone - volatile organic compounds and nitrogen oxides (12).

The dangerous air quality caused by wildfires isn’t restricted to the immediate area. Wildfire smoke can travel thousands of miles. Poor air quality from western wildfires impacted cities on the U.S. and Canadian East Coasts in recent years.

The takeaway

A statistical model created recently theorized that summer heat waves in the United States will increase through 2050 as will the number of days of unhealthy ozone levels, especially in the southwestern and northeastern regions (13).

One way to prevent future increases of poor air quality days from high ozone levels is to reduce the atmospheric amounts of its two main components, nitrogen oxides and volatile organic compounds. This can be done by limiting or eliminating their sources – especially fossil fuel combustion and wood burning.

Individually, you can help in this effort by advocating for stronger air quality regulations and transitioning to renewable energy sources to power your vehicles, homes, and businesses.