Few studies have investigated the independent health effects of different size fractions of particulate matter (PM), in multiple locations, especially in Europe. The researchers estimated the short-term effects of PM with aerodynamic diameter less than 10μm (PM10), less than 2.5μm (PM2.5), and between 2.5 and 10μm (PM2.5-10) on all-cause, cardiovascular and respiratory mortality in 10 European Mediterranean metropolitan areas within the MED-PARTICLES project.