Particulate matter (PM) is very small inhalable liquid and solid particles floating in the air. Particulate is extremely small; a single human hair is 7 times thicker than particulate. An an extra fine particulate is even smaller; about 700 hundred times smaller than a human hair.
The World Health Organization states that particulate matter in the air can penetrate deep into the lungs and enter the body systematically, affecting the cardiovascular and other major organ systems. Chronic exposure to particulate matter leads to increased risks of premature mortality from heart attack, stroke, respiratory infections, and lung cancer. To expand on that, a 2012 study by EPA researchers estimated that there were some 130,000 premature deaths per year of exposure that are attributable to elevated PM2.5 levels. www.epa.gov
The California Environmental Protection Agency (CALEPA) says a primary source of outdoor PM is motor vehicles. Other sources include dust from construction, landfills, and agriculture, wildfires and brush/waste burning, industrial sources, and windblown dust from open lands. Most Americans, however, spend nearly 90 percent of their time indoors and about 70 percent of their day at home, so indoor exposure to PM is likely to be an important contributor to the adverse health effects caused by PM exposure.