OTTAWA – A 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.

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.

Environment and Climate Change Canada scientists reached their conclusion about lower-level ozone formation 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.

“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

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

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.

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.