The suspended particulate matter (PM) is not a single pollutant, but rather is a mixture of tiny solid particles and liquid droplets found in the air. PM includes organic chemicals, metals, smoke, and soil or dust particles. Many of them are so tiny and it is hard to be seen with our naked eyes. This kind of small particles can be only detected using an electron microscope.

For those particles less than 2.5 microns in diameter, they have a generic name called “PM2.5”. The particles size between 2.5 and 10 microns in diameter are called “PM10”.

Size comparisons for PM particles

PM2.5 is made up of more toxic compounds than PM10, such as heavy metals and cancer-causing organic compounds. Since PM2.5 are smaller than PM10, they can travel deeper into the lung, causing even more damage to the respiratory system. These tiny particles can also damage heart and cause cancers.

Many global research studies have shown the association between an increase in PM concentration and an increase in daily hospital admissions and premature deaths from respiratory and cardiovascular diseases.

The main source of PM is burning fuel in power plants, factories, cars and trucks, as well as dust from roadways and construction sites.

Photo/ US Environmental Protection Agency