Wildfires and Heatwaves Threaten Global Progress on Cleaner Air

PM2.5 consists of particles and liquid droplets smaller than 2.5 micrometres, allowing them to enter deep into the lungs and reach the bloodstream.

Air pollution driven by extreme wildfires and intense heatwaves could weaken global efforts to protect public health, agriculture and natural ecosystems, according to the World Meteorological Organization's Air Quality and Climate Bulletin No. 6. Released on the International Day of Clean Air for blue skies on 7 September, the report shows that air quality and climate are closely connected, with rising temperatures, wildfire smoke and atmospheric changes creating pollution risks that cannot be addressed through separate policies.

Drawing on scientific articles and information from WMO's Global Atmosphere Watch network, the bulletin calls for stronger monitoring of fine particulate matter, ground-level ozone, black carbon and airborne microplastics. Many of these pollutants can travel across national borders, alter land and water chemistry, harm human health and affect the climate system, yet their movement and environmental impact remain poorly measured in many regions.

Wildfire Smoke Is Becoming a Deadlier Source of Fine-Particle Pollution

PM2.5 consists of particles and liquid droplets smaller than 2.5 micrometres, allowing them to enter deep into the lungs and reach the bloodstream. Industrial operations, transport, residential heating, agriculture, dust storms and wildfires all release these particles, making PM2.5 one of the most complex and dangerous forms of air pollution faced by cities and rural communities.

Concentrations during 2025 remained above the long-term average across northern Canada, parts of the Russian Federation and western-central Africa, largely because of increased fire activity. Exceptional late-summer wildfires also turned north-western Spain into a pollution hotspot, while burning across South American Amazonia was lower than in several previous years. China continued to record below-average levels as pollution from human activities declined, while India remained above average because of biomass burning and other emission sources.

Extreme fire-smoke events have tripled worldwide since the 1990s, according to research cited in the bulletin, contributing to nearly 100,000 additional deaths each year between 2010 and 2018. The true burden may be higher because conventional health-risk models often treat all PM2.5 as equally harmful, even though wildfire particles can carry greater toxicity. One epidemiological study found that standard models may underestimate wildfire-related mortality by as much as 93%.

Heatwaves Create Conditions for Dangerous Ground-Level Ozone

Heatwaves do more than raise temperatures and increase the risk of dehydration or heatstroke; they also encourage the formation of ground-level ozone, a pollutant linked to respiratory illness, premature death, crop damage and wider ecological harm. Hot weather, stagnant air and powerful sunlight create ideal conditions for ozone to build near the surface, particularly when emissions from vehicles, industry and other sources are already present.

Studies covering heatwaves in south-eastern parts of the United States, Europe and China show how these conditions can sharply increase ozone exposure. WMO warns that the resulting pollution could contribute to tens of thousands of additional premature deaths, with health risks expected to grow as heatwaves become more frequent and severe under a warming climate.

Black Carbon and Microplastics Carry Pollution Across the Planet

Atmospheric aerosols can travel across oceans and continents, spreading pollution far beyond the places where it was produced. Black carbon, often called soot, can settle on snow and ice, darkening bright surfaces that would normally reflect sunlight and accelerating melting by increasing heat absorption.

Microplastics present another growing concern. These tiny particles form as discarded plastic breaks down through sunlight, weathering and physical damage, entering the atmosphere from land and ocean sources before being transported into distant environments. One Earth-system simulation estimated that land contains about 51 million tonnes of microplastics and the ocean around 22 million tonnes, though estimates differ greatly because sustained observations remain limited.

WMO says coordinated climate and clean-air policies are essential because measures taken in one area can directly influence the other. Better monitoring, stronger health-risk models and deeper international cooperation will be needed as fire weather intensifies, ozone exposure grows and emerging pollutants spread through the atmosphere.