The size of contaminants and particles are usually described in microns, a metric unit of measure where one micron is one-millionth of a meter. There are 25,400 microns in one inch. The eye can see particles to about 40 microns.
The size of some Contaminants and Particles are Indicated in the Table Below.
| Particle | Particle Size (microns) |
| one inch | 25400 |
| dot (.) | 615 |
| Eye of a Needle | 1230 |
| Glass Wool | 1000 |
| Spanish Moss Pollen | 150 – 750 |
| Beach Sand | 100 – 10000 |
| Mist | 70 – 350 |
| Fertilizer | 10 – 1000 |
| Pollens | 10 – 1000 |
| Cayenne Pepper | 15 – 1000 |
| Textile Fibers | 10 – 1000 |
| Fiberglass Insulation | 1 – 1000 |
| Grain Dusts | 5 – 1000 |
| Human Hair | 40 – 300 |
| Human Hair | 60 – 600 |
| Dust Mites | 100 – 300 |
| Saw Dust | 30 – 600 |
| Ground Limestone | 10 – 1000 |
| Tea Dust | 8 – 300 |
| Coffee | 5 – 400 |
| Bone Dust | 3 – 300 |
| Hair | 5 – 200 |
| Cement Dust | 3 – 100 |
| Ginger | 25 – 40 |
| Mold Spores | 10 – 30 |
| Starches | 3 – 100 |
| Red Blood Cells | 5 – 10 |
| Mold | 3 – 12 |
| Mustard | 6 – 10 |
| Antiperspirant | 6 – 10 |
| Textile Dust | 6 – 20 |
| Gelatin | 5 – 90 |
| Spider web | 2 – 3 |
| Spores | 3 – 40 |
| Combustion-related – motor vehicles, wood burning, open burning, industrial processes |
up to 2.5 |
| Fly Ash | 1 – 1000 |
| Milled Flour, Milled Corn | 1 – 100 |
| Coal Dust | 1 – 100 |
| Iron Dust | 4 – 20 |
| Smoke from Synthetic Materials | 1 – 50 |
| Lead Dust | 2 |
| Face Powder | 0.1 – 30 |
| Talcum Dust | 0.5 – 50 |
| Asbestos | 0.7 – 90 |
| Calcium Zinc Dust | 0.7 – 20 |
| Paint Pigments | 0.1 – 5 |
| Auto and Car Emission | 1 – 150 |
| Metallurgical Dust | 0.1 – 1000 |
| Metallurgical Fumes | 0.1 – 1000 |
| Clay | 0.1 – 50 |
| Humidifier | 0.9 – 3 |
| Copier Toner | 0.5 – 15 |
| Liquid Droplets | 0.5 – 5 |
| Insecticide Dusts | 0.5 – 10 |
| Anthrax | 1 – 5 |
| Yeast Cells | 1 – 50 |
| Carbon Black Dust | 0.2 – 10 |
| Atmospheric Dust | 0.001 – 40 |
| Smoldering or Flaming Cooking Oil | 0.03 – 0.9 |
| Corn Starch | 0.1 – 0.8 |
| Sea Salt | 0.035 – 0.5 |
| Bacteria | 0.3 – 60 |
| Bromine | 0.1 – 0.7 |
| Lead | 0.1 – 0.7 |
| Radioactive Fallout | 0.1 – 10 |
| Rosin Smoke | 0.01 – 1 |
| Combustion | 0.01 – 0.1 |
| Smoke from Natural Materials | 0.01 – 0.1 |
| Burning Wood | 0.2 – 3 |
| Coal Flue Gas | 0.08 – 0.2 |
| Oil Smoke | 0.03 – 1 |
| Tobacco Smoke | 0.01 – 4 |
| Viruses | 0.005 – 0.3 |
| Typical Atmospheric Dust | 0.001 to 30 |
| Sugars | 0.0008 – 0.005 |
| Pesticides & Herbicides | 0.001 |
| Carbon Dioxide | 0.00065 |
| Oxygen | 0.0005 |
- one micron is one-millionth of a meter
Airborne particles
Airborne particles are solids suspended in the air.
Larger particles – larger then 100 μm
- terminal velocities > 0.5 m/s
- fall out quickly
- includes hail, snow, insect debris, room dust, soot aggregates, coarse sand, gravel, and sea spray
Medium-size particles – in the range 1 to 100 μm
- sedimentation velocities greater than 0.2 m/s
- settles out slowly
- includes fine ice crystals, pollen, hair, large bacteria, windblown dust, fly ash, coal dust, silt, fine sand, and small dust
Small particles – less than 1 μm
- falls slowly, take days to years to settle out of a quiet atmosphere. In a turbulent atmosphere they may never settle out
- can be washed out by water or rain
- includes viruses, small bacteria, metallurgical fumes, soot, oil smoke, tobacco smoke, clay, and fumes
