Typical Particle Diameters (um) Photochemical aerosols 0.01-1 Tobacco smoke 0.25 Coal fly ash 1-50 Flour dust 15-20 Pollens 15-70 Human hair: 25-100 umTypical Particle Diameters (mm) Photochemical aerosols 0.01-1 Tobacco smoke 0.25 Coal fly ash 1-50 Flour dust 15-20 Pollens 15-70 Human hair: ~25-100 mm