Study Finds “Synergistic Effect” Between Ozone and Fine Particulate Matter Air Pollution Heart Risks

The health risks of combined particulate matter and ozone pollution were more pronounced in colder weather and climates, researchers found.

The findings of a new study warns that the combined effects of two common air pollutants increase the risk of death from heart disease.

Researchers say ozone and fine particulate matter 2.5 (PM 2.5), can have a synergistic effect, which increases the risk of death from heart-related and respiratory conditions, particularly in cooler weather and climates. The findings were published on August 14 in the journal The BMJ.

A synergistic effect is when one substance works in conjunction with another to enhance the effects. In this case, the effects are negative to human health.

For this new study, a team of international researchers conducted an analysis across 372 cities in 19 countries and regions, using data on mortality from 1994 to 2020.

During the study, the researchers determined 5.3 million deaths were linked to heart disease, and 1.9 million deaths were linked to respiratory illnesses. However, the researchers also noted that when high ozone levels were present at the same time as high particulate matter levels, the rates of death increased.

Researchers noted this synergistic effect between PM 2.5 and ozone was particularly pronounced in high-latitude regions such as the northern parts of the U.S. and Canada. The synergistic effect was also more prominent during cold seasons.

“Regional and seasonal characteristics may modify the interaction between PM_2.5 and O₃ associated with different mortality outcomes, with more pronounced interactions in high latitude regions and during cold seasons,” the researchers concluded. “Our findings indicate a larger disease burden associated with exposure to PM_2.5 and O₃ than the sum of their individual contributions, which provide important evidence for future coordinated control of these air pollutants.”

Particulate Matter and Ozone Air Pollution Risks

Prior studies have indicated more than one-third of the U.S. population lives in areas with unhealthy levels of air pollution, or about 120 million Americans.

Ground-level ozone air pollution, also commonly referred to as smog, is primarily caused by vehicle emissions, but is also caused by fossil fuel production, industrial plants, and the evaporation of paints.

Particulate matter 2.5 consists of tiny particles of soot, dirt, and other droplets of chemicals smaller than 2.5 micrometers or less than 70 times the width of a human hair. The particles are so small they are easily inhaled into the body, where they enter the bloodstream and can lead to widespread inflammation that can cause serious health side effects.

Research has linked exposure to particulate matter and ozone to increased risk of cardiovascular disease and stroke, even for short-term exposure.

Earlier this year, the U.S. Environmental Protection Agency (EPA) proposed new regulations to tighten air quality standards for the U.S. The agency claims the new regulations will help all Americans, but particularly disadvantaged communities, which are disproportionately impacted by air pollution health risks.