Particulates are extremely tiny bits of material suspended in the air that form a major hazard of air pollution . The term aerosol refers to both particulates and the gas in which they are suspended. Particulates, also known as particulate matter or particles, come from many sources. They come from natural soil dusts as well as sources related to human activities, including automobile and factory exhaust. Particulates range in size, even among particulates from the same source. Larger particulates have diameters greater than 2.5 microns. A micron is 0.000001 meter, or 1/25,400 inch. Small particulates have diameters of 2.5 microns or less. Such small particles are known as fine particles or PM2.5.
People take in particulates through breathing. Particulates larger than 10 microns usually become trapped by mucus in the nose , trachea (windpipe), and bronchi (tubes leading to the lungs ). Tiny hairlike projections called cilia sweep them to the back of the throat, where they are coughed out or swallowed. Smaller particles, on the other hand, can move further into the lungs without getting caught. There, they can deposit in the alveoli . The alveoli are tiny sacs where the gas exchange involved in breathing takes place. From the alveoli, PM2.5 particles can enter the bloodstream. Experts believe smaller particulates pose the greatest health threat. Automobile engines, factories, and fires produce most of the particulates that directly affect human health.
When concentrations of particulates increase, people are more likely to have respiratory or heart problems. Scientists have not found strong links between such health problems and the particular chemical composition of any particulates. Instead, experts believe that the particulates themselves are the major concern, and that it is most important to decrease exposure to all particulates, whatever their composition.
