According to CPCB, which size of particulate matter are responsible for causing the greatest harm to human health?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 2.5 micrometers or less in diameter
Option (1) 2.5 micrometers or less in diameter — Correct. The Central Pollution Control Board says that particles 2.5 micrometres or less in diameter (PM 2.5) cause the greatest harm, because they are breathed deep into the lungs.
Option (2) 5.0 micrometers or more in diameter — Incorrect. Larger particles, 5 micrometres or more, are trapped in the nose and throat and do not reach deep into the lungs. The greatest harm comes from fine particles of 2.5 micrometres or less.
Option (3) 10.0 micrometers or more in diameter — Incorrect. Particles of 10 micrometres or more are too big to be inhaled deep into the lungs. The CPCB names PM 2.5 (2.5 micrometres or less) as the most harmful.
Option (4) 100 micrometers or more in diameter — Incorrect. Particles of 100 micrometres are very coarse and settle quickly or are filtered in the upper airways. The harmful size is the fine PM 2.5, which reaches deep into the lungs.
Note: This question is from Chapter 16, Environmental Issues, of the pre-rationalised NCERT book. This chapter is not in the present NCERT book (2026-27). The extract below is from the pre-rationalised edition.
NCERT Extract (Pre-rationalised edition, Chapter 16, Environmental Issues):
Air Pollution and Its Control – “… Recently we have realised the dangers of particulate matter that are very very small and are not removed by these precipitators. According to Central Pollution Control Board (CPCB), particulate size 2.5 micrometers or less in diameter (PM 2.5) are responsible for causing the greatest harm to human health.”