Older adults who breathe in very small particles from air pollution for even a day or two are more likely to be hospitalized for many diseases, a recent U.S. study suggests. Researchers examined particles called PM2.5, a mixture of solid particles and liquid. The particles are too small for the eye to see; each one is about three percent of the size of a human hair or smaller. PM2.5 can include dust, dirt, soot, and smoke. The researchers confirmed earlier links between short-term exposure to PM2.5 and a higher risk of hospitalization and death from some diseases. Those include heart and lung diseases, diabetes, and blood flow blockages in the legs.