3. Just some fun facts: nearly 1000 dust particles per square centimeter settle on domestic surfaces every hour (same source as before). Also, some dust consists of human skin; it is estimated that the entire outer layer of skin is shed every day or two at a rate of 7 million skin flakes per minute, which corresponds to a mass emission rate of about 20 mg/minute (Heinsohn, R., Cimbala, J., (2003) Indoor Air Quality Engineering: Environmental Health and Control of Indoor Pollutants. page 146. CRC Press.) From the same, the average size of a skin flake is about 14 micrometers or microns, with a range of 10-24 micrometers. Remember, any home filter would have to have air pores smaller than this. A HEPA filtration device is sufficient.
6. Human hair averages 80-100 micrometers in diameter.