GENEVA, Sept. 7 (Xinhua) -- 2025 wildfire and heatwave pollution threatens international air-quality and health efforts, and the better monitoring of PM 2.5, ozone, black carbon and microplastics is urgently needed, said the World Meteorological Organization(WMO) on Monday.
Issued on the International Day of Clean Air for Blue Skies, the 2025 edition of the WMO's Air Quality and Climate Bulletin traces the complex interlinkages between air quality and climate, highlighting the negative impacts of aerosols - including particulate matter - and surface ozone on human health.
The bulletin notes that PM2.5 consists of tiny particles and droplets with a diameter of less than 2.5 micrometers, which pose a health threat because they can penetrate deep into the lungs and enter the bloodstream. Sources of PM2.5 are diverse, ranging from industrial activities, agriculture, residential heating and transport to wildfires and dust storms.
Consistent with recent trends, PM2.5 concentrations in 2025 were above the long-term average in northern Canada, parts of the Russian Federation, western-central Africa and northwestern Spain due to increased fire activity. China continued to record PM2.5 levels below the long-term mean, reflecting a decline in anthropogenic emissions.
Extreme wildfires are becoming more frequent and produce highly toxic smoke, with serious consequences for public health. A study cited in the report showed that extreme fire-smoke events have tripled globally since the 1990s, leading to an estimated nearly 100,000 additional deaths per year between 2010 and 2018. Current air-quality risk assessments often fail to fully account for the enhanced toxicity of wildfire smoke, the report warned.
Ground-level ozone pollution affects human health, agriculture and ecosystems, and is becoming an increasing concern due to more frequent heatwaves. Long-term exposure to ozone is linked to higher mortality, primarily from respiratory diseases. Recent research indicates that rising temperatures, atmospheric stagnation and intense solar radiation jointly promote surface ozone formation during heatwaves, and the resulting increase in ozone exposure could lead to tens of thousands of premature deaths, with ozone-related health risks expected to intensify further in the future.
Aerosol particles can travel long distances from their sources across oceans and continents, altering the way the atmosphere reflects sunlight. They also change the chemistry of land and water bodies and can contaminate previously pristine environments. Given the continued rise in plastic production and inadequate plastic waste management, the bulletin emphasised that monitoring the atmospheric pathway of microplastic deposition in remote environments is crucial for understanding their overall impacts on the Earth system. ■