PM2.5: Sources, sizes, exposure routes and affected organs. 

PM is classified, based on the aerodynamic diameter of particles, into PM10 (<10 μm), PM2.5 (<2.5 μm) and UFP (<0.1 μm). The size of fine beach sand is depicted for comparison. PM2.5 has natural and anthropogenic sources, resulting in a heterogeneous composition. PM2.5 enters the body through dermal absorption, gastro-intestinal ingestion and inhalation. The significance and contribution of absorption and ingestion is not fully unravelled. After inhalation particles deposit in the deep airways, leading to pulmonary inflammation and spill-over of inflammatory cytokines into the systemic circulation. Combined with translocation of particles to the bloodstream, this leads to distant organ damage.