It is widely known that air quality contributes to health conditions thanks to nationwide studies of particulate matter (PM). However, there is growing evidence that the most toxic particles are ultrafine particles (UFP), those smaller than 1/50th the diameter of a human hair. Studies on the health effects of ultrafine particles have been inconclusive and inconsistent due to the lack of a national-scale UFP study, but a team led by Carnegie Mellon University professors Albert Presto and Allen Robinson, postdoctoral researcher Provat Saha, and collaborators from the University of Washington and Virginia Tech, worked to change that.