"Toxic Mix": Forest fires are damaging air quality thousands of kilometers away, says the UN

Forest fires release a "toxic mix" of pollutants that can end up deteriorating air quality thousands of kilometers away, the World Meteorological Organization (WMO) said Friday, September 5, 2025.

The UN agency explained that the quality of the air people breathe is closely linked to climate change and that the two issues must be addressed together.

Fires in the Amazon, Canada and Siberia have provided insight into how air quality can be affected on a large scale, the WMO said in its fifth annual Air Quality and Climate Bulletin.

"Climate change and air pollution respect no national borders, as evidenced by the intense heat and drought that fuel wildfires and degrade air quality for millions of people," said the organization's deputy secretary-general, Ko Barrett.

The WMO has been looking at the interaction between air quality and climate, highlighting the role of microscopic particles called aerosols in these fires, the formation of winter fog, emissions from shipping and urban pollution.

Particles with a diameter of less than 2.5 micrometers (PM 2.5) are considered particularly harmful because they can penetrate deep into the lungs or the cardiovascular system.

However, forest fires in 2024 led to above-average PM 2.5 levels in Canada, Siberia, and Central Africa, the WMO said. However, the largest increase in PM 2.5 was recorded in the Amazon Basin.

Intercontinental consequences

"The wildfire season tends to be more severe and longer each year due to climate change," said Lorenzo Labrador, chief scientist of the World Meteorological Organization, which edited the bulletin.

For example, forest fires in Canada have ended up causing air pollution in Europe . "That was the case last year and this year as well. So you have a deterioration in air quality across continents when the weather conditions are right," Labrador said during a press conference.

"These fires essentially produced a toxic mixture of components that pollute the air," he summarized.

According to the World Health Organization (WHO), ambient air pollution causes more than 4.5 million premature deaths each year worldwide , with considerable environmental and economic costs.

The WMO called for improved monitoring and better policies to protect human and environmental health and reduce agricultural and broader economic losses.

The bulletin also highlighted pollution hotspots in northern India. It said the Indo-Gangetic Plain, home to more than 900 million people, has seen a marked increase in air pollution, particularly from agricultural biomass burning , which has caused an increase in the number and duration of winter fog episodes.

"The persistence of fog is no longer just a seasonal weather event: it is a symptom of the growing impact of human activities on the environment," according to the World Meteorological Organization.

Dramatic improvements in China

PM 2.5 levels continued to decline in eastern China last year, which the WMO attributes to sustained policies.

When countries take action to address poor air quality, the improvement is clearly visible in weather data, said Paulo Laj, the organization's global atmosphere officer.

"Look at Europe, Shanghai, Beijing, cities in the United States... Many cities have taken measures and over the long term we are seeing a significant decrease " in recorded air pollution, he told AFP.

"Over a 10-year period, Chinese cities have significantly improved their air quality. What they have accomplished is truly impressive," he noted.

According to him, there are no universal measures that can bring about radical change, such as switching to electric cars, "but when measures are taken, it works."

In Europe, he concluded, "we don't realize that what we were breathing 20 years ago was much worse than it is today."