North American fires contaminate Europe

10.22.2025, by

Reading time: 4 minutes

aerial handout photo from the Saskatchewan Public Safety Agency, taken in July/August 2025, shows billowing smoke and flames from the Muskeg, Trail, and Knee fires in northern Saskatchewan, Canada.

A huge fire in northern Saskatchewan, (Canada), in the summer of 2025.

The huge fires that burn down millions of hectares of forest in North America every year have an impact on the other side of the Atlantic. Plumes of smoke and various other pollutants have been detected in the skies over France and beyond, explains the atmospheric scientist Stéphane Sauvage.

How is it that the huge fires that are destroying North America's forests are having an effect on air quality here in France?

Stéphane Sauvage1: Megafires are so fierce that the plumes of smoke they release are carried high into the atmosphere, up to altitudes of around fifteen kilometres, and then drawn into the atmospheric circulation system. Take, for example, the Canadian megafires that devastated 3.2 million hectares2 of forest before the summer, which we've specifically been focusing on (the total area burned in Canada in 2025 now exceeds 8 million hectares – Editor's note). The plumes laden with aerosols, in other words airborne microparticles, took just a few days to cross the Atlantic, and their presence was detected as far away as Frankfurt, Germany.

Satellite image on 10 June, 2025. Next to the clouds (in white), a yellowish-grey veil of pollution produced by the smoke from the Canadian fires can be seen. It covers not only France, but also Italy, Germany and further afield.

More specifically, exactly what sort of pollution are we talking about?

S. S.: In fact, observations are carried out at two different levels: on the ground, where the plumes eventually settle, directly impacting the quality of the air we breathe; and in the upper atmosphere, where the smoke produced by the Canadian megafires in early June 2025 were observed by satellites, as well as by airliners equipped with sensors belonging to the In-service Aircraft for a Global Observing System (IAGOS), an observing network installed on some ten commercial aircraft which has been in operation for the past 20 years.

On 9 June, a flight from Orlando (Florida, USA) to Frankfurt (Germany) detected a sharp increase in carbon monoxide (CO) at an altitude of 10,000 m, and then between 4,000 and 2,000 m while it was landing in Germany. In mainland France, the four lidars3 used to monitor the atmosphere, and which form part of the Aerosol, Clouds, and Trace Gases Research Infrastructure (ACTRIS) network – lasers that can reach altitudes of up to 40 km! – measured high concentrations of soot particles at a height of 15 km. Large quantities of pollutants were also found on the ground at various specific locations. In some places, carbon monoxide levels rose by a factor of 1.5 to 2, while the quantity of fine particles resulting from combustion (soot) grew 4- to 5-fold. Another pollutant detected at ground level, acetonitrile, a gas produced by the combustion of wood, showed a 1.5 increase in concentration.

What about carbon dioxide (CO₂)?

S. S.: The CO₂ concentrations detected over France after the massive fires in June 2025 are somewhat counterintuitive. Measurements actually show a slight fall in CO₂ levels in the plumes, mainly due to the fact that at the end of spring, trees in Canadian forests are in full growth and remove CO₂ from the atmosphere for photosynthesis. The CO₂ emitted by the fires is thus partially offset by the 'carbon sink' effect of the forest.

The SIRTA research observatory, in Palaiseau, near Paris, measures greenhouse gases as well as concentrations of aerosols and reactive gases in the atmosphere, in particular acetonitrile from wood combustion.

We should nonetheless bear in mind that fires, especially huge ones, do contribute to the increase of CO₂ in the atmosphere over the long term, not only due to combustion, but also because they destroy the key role of forests as essential lungs for the planet. However, with climate change, megafires are going to become increasingly frequent. Observing networks like those developed by scientists across Europe in the past few years, as well as the large-scale facilities on which they rely, have a crucial part to play in addressing current environmental challenges.

1. Stéphane Sauvage is an atmospheric physicist and chemist at the Institute of Environmental Geosciences (IGE – CNRS / INRAE / IRD / Université Grenoble Alpes) in Grenoble (southeastern France), and director of the French component of the European Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS).
2. I.e. 32,000 km².
3. Lidar (acronym for Laser Imaging, Detection, and Ranging): a laser remote-sensing technique.