The WHO air quality guideline (2021) for PM2.5 was revised downward compared to 2005. The revised 24-hour mean guideline value is:
- A 25 µg/m³ (unchanged from 2005)
- B 15 µg/m³ (revised from 25 µg/m³ in 2005) ✓
- C 5 µg/m³ (revised annual mean) — same as 24-hour guideline
- D 35 µg/m³ to align with US-EPA standards
Correct answer: B. 15 µg/m³ (revised from 25 µg/m³ in 2005)
Explanation
The WHO 2021 Global Air Quality Guidelines significantly tightened PM2.5 standards based on evidence of harm at previously considered safe levels. The 24-hour mean PM2.5 guideline was revised from 25 µg/m³ (2005) to 15 µg/m³, and the annual mean from 10 µg/m³ to 5 µg/m³. These revisions reflect accumulating evidence that cardiovascular, respiratory, and carcinogenic effects occur at lower concentrations than previously recognized. India's National Ambient Air Quality Standards remain 60 µg/m³ (24h) and 40 µg/m³ (annual) — far above WHO guidelines.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.