Food for thought
Biofilters
https://en.wikipedia.org/wiki/Biofilter#Control_of_air_pollution
Smoke particle size, filter types
https://www.sciencedirect.com/science/article/pii/B9780081005736000253
“The most striking finding of this study is that the initial efficiency of the cotton-polyester media is poor as compared to the electret media. This means that the new cotton-polyester media removes fewer contaminant particles when it is placed in service as compared to the removal efficiency of the electret media. Less particulate removal translates to more contaminant particles in the air downstream of the filter.”
https://www.jeffjournal.org/INJ/inj03_4/p43-54-myers.pdf
“The electrostatic effects created in an electret-charged media are particularly useful in increasing the capture efficiency for submicron particles. This is because, while submicron particles are much smaller than the void spaces present in most commercial electret media, the electrostatic forces within the media structure allow those particles to be removed with high efficiency. Mechanical-only media, on the other hand, must use extremely fine fibers or dense structures to achieve high efficiency with submicron particles, and this can create airflow resistance in the filter, which can lead to higher energy use/cost.”
Nonwoven fabrics: mechano-electret filter media provides for IAQ advantages
“The virus can spread from human to human. According to the Chinese Center for Disease Control and Prevention, the size of this virus is about 100nm. When airborne or aerosolized, the virus can be attached to nuclei particles, which can be fine particles in the respiratory tracts or saliva and nasal droplets of an infected person, as well as fine particles suspended in air. Regardless, the minimum size of airborne nCoV is about 100nm when attached to a nano-size particle. The 100nm size airborne particle is referred to as nanoaerosol (also known as nanoparticle or ultrafine particle). While the National Institute for Occupational Safety and Health has standardized N95 and N98 at 300nm, there is no standard filtration test for nanoaerosols at 100nm.
In the past 15 years, Prof. Leung and his group in Hong Kong have researched the filtration of airborne nanoaerosols, which are abundant in pollutants and airborne viruses, from the common flu to SARS, MERS, swine flu, bird flu and the most recent nCoV. Nanofiber filters, by virtue of the small diameter of the fibers (typically 100-300nm), have large specific surfaces that are most suitable to capture by diffusion the nanoaerosols that can penetrate deeply into our lungs, causing infection, sickness and even death.
From basic research to commercial realization, multilayer nanofiber technology has been developed to achieve high filtration efficiency while maintaining low pressure drop. It is most suitable for personal protection equipment, such as face masks and respirators. The technology has been tested extensively in laboratory settings using sodium chloride aerosols (50-500nm), and also ‘road-tested’ on real aerosols (10-400nm), such as traffic emissions with a high concentration of nanoaerosols around 100nm, which is also the same size as nCoV.”
Smoke
“Smoke particulates, like other aerosols, are categorized into three modes based on particle size:
- nuclei mode, with geometric mean radius between 2.5–20 nm, likely forming by condensation of carbon moieties.
- accumulation mode, ranging between 75–250 nm and formed by coagulation of nuclei mode particles
- coarse mode, with particles in micrometer range
”
“The naked eye detects particle sizes greater than 7 µm (micrometres).”
https://en.wikipedia.org/wiki/Smoke