PM2.5 (particulate matter ≤ 2.5 µm diameter) is considered more harmful than PM10 primarily because:

• A PM2.5 has a higher chemical reactivity with ozone
• B PM2.5 is exclusively produced by vehicle exhaust, making source attribution easier
• C PM2.5 causes immediate bronchospasm while PM10 causes delayed fibrosis
• D PM2.5 penetrates deeper into the alveoli and can enter the systemic circulation ✓

Explanation

The primary reason PM2.5 is more harmful is its aerodynamic diameter — particles ≤ 2.5 µm penetrate beyond the bronchi into the respiratory bronchioles and alveoli, bypass mucociliary clearance, and can translocate into the systemic circulation causing cardiovascular effects (atherosclerosis, MI). PM10 (coarse) is filtered in the upper airways and tracheobronchial tree. PM2.5 is associated with IHD, stroke, COPD, and lung cancer. WHO ambient PM2.5 guideline is 15 µg/m³ (annual average, revised 2021).

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.