According to the Central Pollution Control Board (CPCB), which particulate size in diameter (in micrometres) of the air pollutants is responsible for the greatest harm to human health?

Explanation

Particulate matter consists of soot, fly ash, dust, spores, pollen grains etc. Particulate matter is differentiated into settleable (larger than 10 mm and remaining in the air for less than one day) and suspended (less than 10 mm and remaining in the air for more than one day to several weeks). Particles of 2.5 μm and lesser diameter (PM 2.5) are the most harmful to human health (as per Central Pollution Control Board or CPCB). They pass deep into the lungs causing breathing and respiratory problems, irritation, inflammation and damage to the lungs resulting in pre­ mature death. It cannot directly enter the circulatory system but indirectly through the respiratory system.