particulate matter

Abbreviated way of referring to particulate matter (PM). This name is given to the mixture of tiny particles in liquid or solid phase, of both organic and inorganic origin, that are suspended in the air, contributing to its pollution. These particles include highly varied elements, such as mineral dust, soot, sulfates, nitrates, silicates, ash, pollen and so on. Emission sources can be natural (volcanic eruptions, forest fires) or originate from human activities (traffic, industry, agriculture…). In air quality studies, particulate matter is classified as PM10 or PM2.5, depending on its size. The first category (PM10) corresponds to the larger particles, with diameters between 10 and 2.5 µm, while the second (PM2.5) encompasses fine particles, with diameters smaller than 2.5 µm. The latter are the most dangerous to health, since, when inhaled, they are not retained in the respiratory tract (which does happen with PM10), but manage to reach the pulmonary alveoli -in the outer part of the bronchioles-, going on to pass into the bloodstream. In recent years, studies focused on the so-called ultrafine particles (PM1), with diameters smaller than one micron (1 µm), have begun to appear. See also volcanic ash.