PM2.5 (Particulate Matter ≤ 2.5 μm) are fine particles invisible to the naked eye, originating from vehicle combustion, industry, heating, wildfires, and atmospheric chemical reactions. Being so small, they bypass the nose and trachea, reaching the lung alveoli and bloodstream.
Health impact
The WHO estimates PM2.5 pollution causes 4.2 million premature deaths annually. The 2021 WHO guideline recommends not exceeding 15 μg/m³ daily average and 5 μg/m³ annual average. During Saharan dust episodes in Spain, PM2.5 levels can multiply 5–10 times above normal values.