Actual Microscopic Images of Covid
https://www.cdc.gov/sars/lab/images.html
How small is a micron, and why does it matter?
One micron is 1/1000 mm (1/25,000 of an inch). Airborne particles are usually described in microns. Generally speaking, the human eye can see debris and dust that are approximately 25 microns in size. To understand just how small this is, consider that a single hair from your head averages about 70 microns in diameter or 30 times larger than the largest fine particle. The size of a given particle helps to determine the degree of potential threat to human health.
Particles ranging from 0.3 to 0.9 micron present the greatest health concern because they are small enough to get past the tiny hairs that line our breathing passages and are too large to be easily exhaled. These irritating mid-range particles include house and textile dust, pollen, pet dander, dust mites and their feces, many bacteria, auto exhaust, mold spores, and particles from laser printers and copiers.
0.1 to 0.3 micron = Dust mites and allergens
0.3 to 1 micron = Tobacco smoke, metallic fumes and bacteria such as staphylococcus
1 to 5 micr>5 to 10 micr>10 micr>
Because mid-range particles are more likely to become lodged in lung tissue, they are suspect in a wide range of health problems related to indoor air pollution, from headaches and dizziness to cardiovascular disease and cancer. In particular, pollen, pet dander, mold spores and dust mite particles are known to trigger asthma episodes and allergy attacks.
While smaller particles (0.1 to 0.3 micron) can be inhaled and exhaled more easily than mid-range particles, even these minute particles may irritate breathing passages and lungs. Smaller particle filtration is particularly beneficial to people living with allergies, asthma, other respiratory conditions, or cardiovascular disease.
More information here: https://www.mpic.de/4763581/drewnick_et_al_ast_2020_final.pdf
Methods
We characterized the surface of twenty different types of CMs using optical image analysis method. The filtering efficiency of selected cloth face masks was measured using the particle counting method. We also studied the effects of washing and drying and stretching on the quality of a mask.
Results
The pore size of masks ranged from 80 to 500 μm, which was much bigger than particular matter having diameter of 2.5 μm or less (PM2.5) and 10 μm or less (PM10) size. The PM10 filtering efficiency of four of the selected masks ranged from 63% to 84%. The poor filtering efficiency may have arisen from larger and open pores present in the masks. Interestingly, we found that efficiency dropped by 20% after the 4th washing and drying cycle. We observed a change in pore size and shape and a decrease in microfibers within the pores after washing. Stretching of CM surface also altered the pore size and potentially decreased the filtering efficiency. As compared to CMs, the less frequently used surgical/paper masks had complicated networks of fibers and much smaller pores in multiple layers in comparison to CMs, and therefore had better filtering efficiency. This study showed that the filtering efficiency of cloth face masks were relatively lower, and washing and drying practices deteriorated the efficiency. We believe that the findings of this study will be very helpful for increasing public awareness and help governmental agencies to make proper guidelines and policies for use of face mask.