According to Central Pollution Control Board $\left[\mathrm{CPCB}\right]$ what size (in diameter) of particulate is responsible for causing greater harm to human health?

According to Central Pollution Control Board ($\mathrm{CPCB}$), particulate matter size 2.5 micrometres or less in diameter are responsible for causing the greatest harm to human health. These fine particulate matter can be inhaled deep into the lungs and can cause irritation, breathing and respiratory symptoms, inflammations and damage to the lungs and premature deaths.