E-Mail Researchers at Scripps Institution of Oceanography at UC San Diego examining 14 years of hospital admissions data conclude that the fine particles in wildfire smoke can be several times more harmful to human respiratory health than particulate matter from other sources such as car exhaust. While this distinction has been previously identified in laboratory experiments, the new study confirms it at the population level. This new research work, focused on Southern California, reveals the risks of tiny airborne particles with diameters of up to 2.5 microns, about one-twentieth that of a human hair. These particles - termed PM2.5 - are the main component of wildfire smoke and can penetrate the human respiratory tract, enter the bloodstream and impair vital organs.