Wildfire Smoke Is Erasing Clean-Air Gains—and Raising New Health Risks

Cleaner factories, power systems and vehicles can lower everyday air pollution. But climate-driven heatwaves and wildfires are creating a harder-to-control source of pollution: smoke. Fine particles can travel across regions and oceans, while heat and sunlight help form harmful ground-level ozone downwind. The result is a growing risk that progress in cutting industrial and transport emissions will not translate into consistently cleaner air.2250

Why heat and fires can reverse clean-air progress

Wildfires release large amounts of fine particulate matter, known as PM2.5, as well as gases that contribute to ground-level ozone formation. PM2.5 is especially consequential because particles 2.5 micrometres or smaller can reach deep into the lungs and enter the bloodstream.5152

Heat compounds the problem. It creates conditions that can dry vegetation and intensify fire weather, and it accelerates atmospheric chemistry involved in ozone production. Unlike the protective ozone layer high in the atmosphere, ground-level ozone is an air pollutant. Fires supply precursor gases, and ozone can form downwind rather than only at the fire itself.52

This pollution is not confined to the burn zone. Copernicus tracked Canadian wildfire plumes across the North Atlantic in 2025, with smoke reaching southern Europe, the Mediterranean, the Azores and northwestern Europe.17 That long-range transport means a city can experience a serious smoke episode even when its own local emissions are falling.

The health risks of wildfire PM2.5

Evidence is strongest for respiratory harm. A systematic review and meta-analysis found wildfire-specific PM2.5 was associated with higher same-day all-cause mortality, respiratory hospital admissions and respiratory emergency-department visits. Earlier reviews also found consistent evidence of asthma and chronic obstructive pulmonary disease exacerbations, with growing evidence for respiratory infections and mortality.3436

The major implications are clear:

• Smoke is not just a visibility problem. PM2.5 can be inhaled deeply into the body, and extreme fire events can push concentrations to 10–20 times the World Health Organization’s air-quality guideline levels.51
• Risk is not evenly distributed. People with respiratory disease, older adults, children, pregnant people and those unable to access clean indoor air may be particularly vulnerable during smoke episodes. The evidence base also supports concern for people with cardiovascular disease, although some cardiovascular findings are less consistent than respiratory findings.3436
• Wildfire particles may not behave like average urban PM2.5. Their composition can include higher levels of carbonaceous and polar organic compounds; studies describe wildfire PM2.5 as potentially more toxic than non-smoke PM2.5. Effects can also be compounded when smoke coincides with extreme heat.3941

Mortality estimates should be read carefully because methods, exposure estimates and time horizons differ. Still, a 2026 study estimated that wildfire-smoke PM2.5 was associated with roughly 24,100 all-cause deaths per year in the contiguous United States. That is an estimate for one country and study design—not a global total—but it illustrates the scale of the potential burden.33

Ozone is the second pollution threat

Wildfire smoke is often discussed in terms of particles, but fires also matter for ozone. Ground-level ozone can irritate and impair the respiratory system, and ozone exposure has been linked to respiratory and cardiovascular illness and mortality. Research specifically isolating wildfire-related ozone is newer and less developed than the PM2.5 literature, so its source-specific health burden is less certain.38

That uncertainty is not a reason to dismiss the risk. It is a reason to improve measurements and forecasting during hot, smoky periods, when particle pollution and ozone can occur together.

What recent fire and smoke data show

The World Meteorological Organization reports that exposure to fire-related PM2.5 has increased even as regulations have reduced industrial and transport PM2.5 emissions in parts of Europe and North America.22

Its 2025 assessment identified above-average PM2.5 in northern Canada, parts of the Russian Federation and western-central Africa in connection with increased fire activity. Exceptional late-summer fires also made northwestern Spain a pollution hotspot.22

Europe’s 2025 summer brought widespread fire-related air-quality impacts, particularly in the southwest and southeast. Copernicus reported major fires in Greece, Türkiye and Cyprus in late June and early July, followed by rapidly escalating fires in Portugal and northwestern Spain in August.18

The following year remained severe. The European Commission’s Joint Research Centre reported 650,458 hectares burned in the EU from 1 January to 6 September 2026, across 1,940 detected fires. This was a live cumulative estimate, not a final annual total; it was below the same-date figure for 2025 but above the 20-year average for that point in the season.2

Why wetter and northern regions cannot assume they are protected

Annual rainfall alone does not determine fire danger. What matters during a fire episode is whether vegetation and soils become dry under hot, low-humidity and windy conditions. Research on the exceptional 2025 European fire season found strong trends toward drier summers and unusually high vapour-pressure deficit—a measure of atmospheric drying demand. It concluded that this drying was a key reason hot, dry and windy fire-weather conditions had become more frequent than expected from natural variability.19

This does not mean every northern or wetter region will see more fire every year. Ignition sources, land management, fuel conditions, suppression and weather variability remain important. But forests, peatlands and other fuel-rich landscapes can become highly flammable during intense dry spells, so historic wetness is not a reliable shield against acute smoke risk.

The monitoring gaps: mass alone is not enough

Most routine air-quality systems focus on pollutant concentrations such as PM2.5 and ozone. Those measurements are essential, but they do not fully show what is in smoke, where it came from or how it affects climate and health.

The WMO specifically highlights inadequate observations of black carbon and emerging aerosols such as microplastics, alongside the need for stronger monitoring of PM2.5 and ground-level ozone.50

Three gaps matter most:

• Black carbon: Better observations can help distinguish combustion sources and improve understanding of a pollutant that affects both air quality and climate.
• Smoke composition: A PM2.5 mass reading does not reveal the mixture of organic compounds, soot and particle sizes that may influence toxicity.
• Coverage and calibration: Satellites and models extend visibility over remote areas and moving plumes, but ground observations remain vital for accurate local assessment and forecasting.

Improved monitoring is therefore not merely a scientific upgrade. It supports public warnings, health decisions and more targeted emissions policy.

Why the WMO wants climate and clean-air policy combined

The WMO’s argument is practical: air pollution and climate change share sources, chemistry and consequences. Heat and drought can promote wildfire smoke; fires release particles and gases; and the smoke can worsen health far beyond the ignition zone. At the same time, many measures that reduce combustion-related pollution can deliver health benefits while also helping limit warming.5052

A coordinated approach should connect emissions reduction with fire-weather forecasting, smoke prediction, public-health alerts, cleaner indoor-air options during severe episodes and stronger atmospheric observations. Cross-border coordination is essential because smoke does not respect national boundaries.5051

Cleaner transport and industry still matter. But the wildfire era changes the definition of clean-air policy: it must reduce routine pollution while preparing communities for climate-amplified smoke and ozone episodes that local controls alone cannot prevent.