Particulate matter (PM) is the generic term used for a type
of air pollutants, consisting of complex and varying mixtures
of particles suspended in the breathing air, which vary in
size and composition, and are produced by a wide variety of
natural and anthropogenic activities (Poschl, 2005). Major
sources of particulate pollution are factories, power plants, refuse
incinerators, motor vehicles, construction activity, fires,
and natural windblown dust. The size of the particles varies
(PM2.5 and PM10 for aerodynamic diameter smaller than
2.5 mm and 10 mm respectively) and different categories
have been defined: Ultrafine particles, smaller than 0.1 mm
in aerodynamic diameter, Fine particles, smaller than 1 mm,
and Coarse particles, larger than 1 mm.