Particulate
Composed of distinct particles. Smoke is particulate; pure gases are not.
PM2.5
Particles measuring 2.5µm or less. These are the fraction of the particulates which are thought to be the most dangerous.
PM10
Particles measuring 10µm or less. Due to their size they are readily inhaled and are not filtered. They penetrate deep into the cardiovascular system where they cause damage.
See also: Smog.
