The health effects of particulate matter are significant. From epidemiological studies it has shown that there is a correlation between the presence of particulates in the atmosphere, and an increase of the levels of mortality and hospitalization. Consider that in London, in 1952, they were recorded mortality increases on the order of 4000 deaths a week to a concentration of particles in the order of 4 mg / m3.
Today, fortunately, thanks to technology development of production processes, the concentration of dust in the air has been drastically reduced. It is also true that the current pollution levels are not harmless: nevertheless have consequences for health, and in particular, some studies have shown that the most significant consequences were related to smaller particles. The size of the particles are the same, therefore, the main parameter to consider its harmfulness to human health. The cells in fact react with the surface of the particles, rather than with their volume: the presence of adsorbed materials on the surface can then depositing harmful compounds in the same cells.
As you can imagine, the apparatus hardest hit by this category of pollutants is the breathing. The size of the particles considerably influence their degree of penetration into the respiratory tract. In particular, the particles having a size greater than 1 micron are easily intercepted and deposited in the nose and throat, and then be duly expelled. The particles between 100 nm and 1 micron can reach up to the bronchioles, there they are conveyed to the throat and be removed in a relatively short time.