Ultrafine particle deposition in humans during rest and exercise.

Ultrafine particles (diameter < 100 nm) may be important in the health effects of air pollution, in part because of their predicted high respiratory deposition. However, there are few measurements of ultrafine particle deposition during spontaneous breathing. The fractional deposition for the total respiratory tract of ultrafine carbon particles (count median diameter = 26 nm, geometric standard deviation = 1.