Virus-containing particles can be very small, even submicron (less than 1 micron in diameter), but it wasn’t known if viable SARS-CoV-2 virus could be cultured from such tiny particles suspended in air.
If culturable, there is indication that those tiny particles are contagious, because they have enough viable virus to grow, after being incubated into cells.
A 2021 study revealed that most of the culturable SARS-CoV-2 taken from ambient air samples comes from submicron particles — and none of the ambient COVID-containing particles which were over 4.1 microns in diameter were culturable.
If large droplets are not culturable, it stands to reason that they are not contagious.
This is important because places like Philadelphia are “going back to masks” — but mask mandates directed at large-particle transmission do not have good science to support them.
As you can see, typical gaps in facemasks are 80 times larger than necessary in order for COVID to get through. Not only can COVID get through facemasks, it can get through at a rate of at least “80-at-a-time.”
Even the pores in the filter layer of a surgical mask are still 12 times larger than needed for COVID to get through — although electrostatic charges may help draw most of the tiny COVID particles to the sides of the pores.
Evidence suggests that facemasks are approximately useless regarding COVID transmission. Gaps and pores are several times larger than would be needed in order for COVID to get through.
Because long (>90 minute) use of masks can super-concentrate oro-nasal pharangeal bacteria counts, possibly enough to increase the risk of bacterial pneumonia, the use of masks for COVID should be medically contraindicated (as they are unlikely to help; and even somewhat likely to cause harm).
Wearing the same mask for 4 hours in a row can even ‘more-than-triple’ the bacterial counts in the mouth, nose, and throat. Who in their right mind wants to walk around with more than 3 times the typical count of bacteria in their mouth, nose, and throat?
Do the people of Philadelphia want that?
The improper handling and disposal of worn masks also increases the risk of fomite transmission so, by nearly all counts, facemasks are contraindicated by the medical/scientific evidence for and against them.
Reference
[most suspended COVID particles were submicron (less than 1 micron); and all 'infective" or culturable COVID particles were under 4.1 microns] Santarpia JL, Herrera VL, Rivera DN, Ratnesar-Shumate S, Reid SP, Ackerman DN, Denton PW, Martens JWS, Fang Y, Conoan N, Callahan MV, Lawler JV, Brett-Major DM, Lowe JJ. The size and culturability of patient-generated SARS-CoV-2 aerosol. J Expo Sci Environ Epidemiol. 2021 Aug 18:1–6. doi: 10.1038/s41370-021-00376-8. Epub ahead of print. PMID: 34408261; PMCID: PMC8372686. Available: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8372686/
[micrograph of filter layer in surgical mask, SM1 (Filter Layer 2) in Figure 7 shows a pore in the upper right quadrant that is approximately 12 microns in diameter, while the zoomed-in inset at bottom right in the image shows another pore about 5 microns wide] Evaluation of survival rates of airborne microorganisms on the filter layers of commercial face masks. Sang Bin Jeong, Ki Joon Heo, Hyun Sik Ko, Jae Pyoung Ahn, Seung-Bok Lee, Jae Hee Jung. First published: 08 March 2021. https://doi.org/10.1111/ina.12816. Available: https://onlinelibrary.wiley.com/doi/10.1111/ina.12816
[after approximately 90 minutes of wearing them, masks begin to super-concentrate bacterial counts] Zhiqing L, Yongyun C, Wenxiang C, Mengning Y, Yuanqing M, Zhenan Z, Haishan W, Jie Z, Kerong D, Huiwu L, Fengxiang L, Zanjing Z. Surgical masks as source of bacterial contamination during operative procedures. J Orthop Translat. 2018 Jun 27;14:57-62. doi: 10.1016/j.jot.2018.06.002. PMID: 30035033; PMCID: PMC6037910. Available: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6037910/