#2 What does PSI really measure?
According to Singapore’s National Environment Agency, PSI values take into account a variety of toxic matters and gas pollutants. They include particulate matter (PM10), fine particulate matter (PM2.5), carbon monoxide, sulfur dioxide, nitrogen dioxide and ozone. PM10 are particles in the air that are between 2.5 to ten microns, while PM2.5 are ultrafine particles that are smaller than 2.5 microns, which is roughly 30 times thinner than the diameter of a human hair.
