Increasing pollution from wildfires and heatwaves risks undermining international efforts to improve air quality and protect human and ecosystem health, according to a new report from the World Meteorological Organization (WMO).
The Air Quality and Climate Bulletin, released for International Day of Clean Air for Blue Skies on September 7, highlights the need for improved atmospheric observations of pollutants including fine particulate matter, ground-level ozone, black carbon and microplastics, which the WMO says remain insufficiently monitored despite being widespread and potentially harmful. The report is based on data from WMO’s Global Atmosphere Watch network and draws on articles from the scientific community that advises WMO on air quality.
In 2025, concentrations of PM2.5 – fine particulate matter that can penetrate deep into the lungs and bloodstream – remained above the long-term average in northern Canada, part of the Russian Federation, western-central Africa and northwestern Spain, driven by increased fire activity. Burning in South America’s Amazonia was relatively lower than in previous years. PM2.5 levels stayed below the long-term average in China, reflecting reduced emissions from human activity, while India continued to see above-average levels due to biomass burning and other pollution sources.
The bulletin cites a study indicating that extreme fire-smoke events have tripled globally since the 1990s, contributing to an estimated nearly 100,000 additional deaths per year between 2010 and 2018, a figure the report says may be an underestimate. It also notes that conventional risk models based on total PM2.5 concentrations may underestimate wildfire-attributable mortality by up to 93%, since they don’t account for the higher toxicity of fire-derived particles.
“Meeting the World Health Organization air quality guidelines will become progressively more difficult, since extreme fire weather is expected to increase in the future,” the bulletin says.
On ozone, the report links rising temperatures, stagnant atmospheric conditions, and intense solar radiation during heatwaves in the southeastern USA, Europe and China to increased ground-level ozone formation, which it says could lead to tens of thousands of additional premature deaths.
“Looking forward, ozone-related health risks are expected to intensify,” the bulletin warns.
The report also addresses aerosols including black carbon, which can accelerate snow and ice melt when deposited on those surfaces, and atmospheric microplastics, for which estimates vary widely due to insufficient monitoring.
“As plastic production and, critically, mismanaged plastic waste continues to increase, monitoring atmospheric pathways of deposition of microplastics to remote environments will be crucial toward understanding their overall impacts on the Earth system,” the bulletin says.
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