Canadian scientists discover how forests reduce air pollution

Camera looking up at trees in a forest captured by GTA weekly Toronto news

The Government of Canada relies on sound science to provide information needed to take action and protect the air we breathe. Clean air means healthier Canadians, and it contributes to increased economic prosperity through lower health-care costs and less damage to our natural environment.

Ozone in the lower part of the atmosphere is a short-lived climate pollutant linked to respiratory health problems, smog, climate change, and crop damage. The amount of ozone in the atmosphere is also a challenge for experts to predict. Past predictions using air quality and climate models often overestimated amounts of this harmful air pollutant. This problem suggested there may have been missing atmospheric processes in understanding how ozone in the lower part of the atmosphere forms.

A new study recently published in Nature Communications by scientists at Environment and Climate Change Canada discovered a missing link in lower-atmosphere ozone formation: our forests. The shaded and relatively stagnant air of the forest ecosystem modifies the chemistry of air pollution, resulting in much less ozone formation than had been previously believed to take place. The study also showed that in the absence of forests, ground-level ozone levels would be as much as 50 percent higher.

Environment and Climate Change Canada scientists reached this conclusion after conducting atmospheric measurements, which showed substantial decreases in ozone under forest canopies. They then carried out high-tech computer modelling, which showed that these air-quality benefits from forests extend far above and downwind of the forests themselves and contribute to improved air quality in our communities.

This scientific discovery reminds Canadians of the importance of protecting our parklands, wooded spaces, and even small urban forests since they help to lower ozone levels. Lower ozone levels mean better air quality and healthier Canadians.

The media, fellow scientists, and interested Canadians are invited to contact lead researcher Paul Makar (, for additional information on this study.



“Congratulations to our scientists for their excellent research that is helping us understand the importance of maintaining healthy forests in Canada. The Government of Canada believes in evidence-based policy making, and we depend on our scientists to provide objective information to inform decisions supporting the protection of our environment.”

– Catherine McKenna, Minister of Environment and Climate Change

Quick Facts

  • The Government of Canada is committed to reducing short-lived climate pollutants—including ozone—and providing clean air for Canadians.
  • This research is part of Environment and Climate Change Canada’s ongoing efforts to improve the computer modelling behind our daily Air Quality Health Index forecasts for Canadians.
  • This report is one of several noteworthy papers recently published by one of our scientists. Studies focusing on the reporting of emissions from the oil sands region and on detecting sources of under-reported air pollution using NASA satellites attracted international media interest.
  • Ground-level ozone along with nitrogen dioxide and fine particulate matter are the key common air pollutants used in creating Environment and Climate Change Canada’s daily Air Quality Health Index forecast.

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