Particulate matter is arguably the most danger- ous component of automobile exhaust. Particles are small enough to infiltrate nasal, sinus, and bron- chial passages where they can accumulate and cal- cify. Fine PM can penetrate the deepest portions of the lungs and the very smallest particles can be absorbed into the bloodstream. In the nose, throat, and lungs, particulates act as extreme irritants. Exposure to even low levels of PM can cause na- sal congestion, sinusitis, throat irritation, cough- ing, wheezing, shortness of breath, and chest dis- comfort. Medical studies have associated expo- sure to elevated.
