Particles less than 2.5 micrometers in diameter (PM2.5) pose the greatest health risks due to their small size (1 / 30th diameter of a human hair and not visible to the human eye), is created from combustion from cars, power plants, forest fires and others. (sciencedaily.com)
Even at temperatures below -400 degrees Fahrenheit, the backplane is steady down to 32 nanometers, or less than a thousandth the diameter of a human hair. (discovermagazine.com)
«That means things that are smaller than the diameter of a human hair, like cells, parts of cells or the fine structure of fibers.» (sciencedaily.com)