The WHO Air Quality Guidelines (AQG) 2021 reduced the annual mean PM2.5 standard to 5 µg/m³. The primary reason PM2.5 is more hazardous than PM10 is:
- A PM2.5 reflects sunlight causing urban heat islands
- B PM2.5 contains more sulfur dioxide per particle than PM10
- C PM2.5 particles penetrate to the alveolar level and enter systemic circulation, causing cardiovascular and neurological effects ✓
- D PM2.5 is exclusively produced by vehicular emissions and is therefore more toxic
Correct answer: C. PM2.5 particles penetrate to the alveolar level and enter systemic circulation, causing cardiovascular and neurological effects
Explanation
PM2.5 (aerodynamic diameter ≤ 2.5 µm) bypasses upper respiratory mucociliary clearance and deposits in terminal bronchioles and alveoli; the smallest fraction (ultrafine, < 0.1 µm) can translocate across the alveolar membrane into blood, reaching the heart, brain and other organs, causing endothelial inflammation, oxidative stress and accelerated atherosclerosis. PM10 is largely trapped in the upper airway. The 2021 AQG update reflects the dose-response evidence showing harm even below previous 10 µg/m³ thresholds.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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Written and medically reviewed by the StethoPrep medical team.