Fine atmospheric particulate matter, which is the major pollutant in cities, is made up of a mixture of solid and liquid particles of organic and inorganic substances suspended in the air. The particles are called "fine dust" and identify in particular: Pm10 or particles with an aerodynamic diameter of less than 10 μm capable of penetrating the upper part of the respiratory system.
The World Health Organization recommends an average annual value of 20 µg/cubic meter for PM10 and 10 µg /cubsit for PM2.5 as a threshold for the protection of human health.