- A fine grain of sand is 90 microns.
- Particles larger than 2.5microns: trapped and filtered by lungs.
- Particles smaller than 2.5 microns: penetrate deeply and enter the blood stream.
- A PM 2.5 concentration of over 100 is unhealthy for the particularly sensitive.
To view updates on PSI and PM2.5 levels: http://www.nea.gov.sg/psi/