After two years of politicized masks debates and antigen tests gaining traction, ventilation and filtration is finally gaining the spotlight it deserves. Improving indoor air is a powerful mitigation tool that has been underutilized throughout the pandemic. Some of the best public health interventions are those happening in the background: institutional-level interventions that work passively and invisibly on the individual level.
So, how can you know if have good ventilation? A CO2 meter will tell you this! CO2 from exhaling builds up in the air. Ambient air is 420 ppm (should be 280, but fossil fuels...) Great ventilation is 600 or lower. Good up to 800. Acceptable up to 1000.
I have an Aranet4. It fits in your pocket. Runs for a year on 2 AA batteries. Has app that connects to your phone via Bluetooth.
Some things I've found... my local supermarkets runs 800-1000 depending on the crowd. Big box home improvement stores about 600. Hotels... 1000-2000 in the rooms, but those aren't "shared air". Airports - 600s in common area like security, 900s in gate lounges. On plane >1000 - but this air is 100% HEPA filtered.
Home HVAC systems rarely have any external ventilation - beware! Your house may have the lowest air quality of anywhere you go.
An cheap DIY alternative to a portables HEPA filter is the Corsi-Rosenthal box. You can make one our of a box fan, MERV 13 furnace filters and duct tape. Higher clean air delivery than many portable HEPA filters. Google it and you'll find tons of instructions and videos.
We can all thank the "aerosol warriors" for finally winning this battle. They had a hard, upstream battle before the medical community accepted what these engineers knew.
Great article, as usual. Readers might also be interested in the DIY air filter system (sometimes known as a Corsi-Rosenthal box, after the inventors) that can be made for around $120 using a box fan, and four 20" MERV-13 air filters. Descriptions and fabrication instructions now available at many sites (google "DIY covid box fan air cleaner"). Data on effectiveness here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8142835/
Thanks for all your articles. Thought for future. Re-address the J&J vaccine, especially in light of yet another mRNA booster. Would mix and match vaccines now be a better idea?
I will be sharing this important post far and wide - thank you.
FLOATING DROPLETS
The terminology used in research is confusing and problematic for all - does the term “floating droplets” include aerosols, droplets and particles in your opinion? We urgently need to clarify those terms to avoid confusion by all.
Based on the dozens of sometimes conflicting papers I’ve reviewed over the last 24 months, I have been using droplet size up to 100 microns as “floating droplets” which can persist up to 16 hours after reviewing dozens of conflicting papers. Above 100 microns fall to the floor within about 6-10 feet - not only sub 20 microns. This seems like a critical factor with quite a bit of variance from authoritative sources.
My understanding is that masks and filtration must handle floating droplets from 0.1 microns up to 100 microns.
I will find those papers and post today.
0.3 microns and below are the “most penetrative particle size” (MPPS) meaning it penetrates deep into the lungs, which is why N95s with electrostatic filters are so effective. MPPS particles of 0.3 microns is the standard size used for N95 certification and is the most difficult to filter.
AIR QUALITY METERS
I believe all public places must have an accurate, publicly available meter showing Air Changes Per Hour (ACH) and perhaps some other way to measure “dead air” building up, like CO2 monitors or an introduced substance/gas that can be measured to warn of poor ventilation.
It should be instantly clear if ventilation is not working, so we know a restaurant is actually safe for instance.
If we can radically improve ventilation and N95 mask use we could withstand a new killer virus/variant without shutting down the economy. Crucial.
Thinking outside the box..could the "sick building" phenomena be reproduced over a larger area by the meteorological phenomena of inversion layers- a condition where normal air mixing is reduced to a minimum and the air over a metropolitan area gets stale and polluted. Here in Portland, this is a frequent winter problem. Given the ability of aerosols to remain suspended in such air, has anyone ever looked at covid infection rates in cities during such conditions and whether there are correlations with upticks in new cases following extended inversions?
Maybe it's time to revisit the "vaccine passport" but in reverse. An issuing authority, like a city government, issues a grade to a building, along with a QR code posted prominently somewhere. People would be able to scan the code with their phones, to verify its validity. Wouldn't be too hard to extend the functionality of some of the SMART Health Cards to encompass this - the issuer/holder/verifier abstraction is the same
Is there a "sweet spot" where proper ventilation also means maskless? My workplace has a rule in place that even with the air filtration running, we should only take our mask off if we are alone with the door shut, and we also require everyone to be vaxxed and boosted.
This is mostly excellent, thank you, but you’re repeating the error that aerosols are particles less than 5 microns. Particles as large as 100 microns can remain suspended in the air. See Jose-Luis Jimenez, Kimberly Prather, Linsey Marr, and this summary in Wired. https://www.wired.com/story/the-teeny-tiny-scientific-screwup-that-helped-covid-kill
Remember the spate of mass infections in meat packing facilities in the first year of the epidemic? At the time it appeared to me to probably be an aerosol problem caused by the power saws used in such places and the probability that the source was infected livestock, i.e. a form of zoonotic transfer mediated by meat processing technology. The media explanation at the time was close quarters of infected workers, but I don't think the workers were the real carriers initially. Has anyone looked into this?
Great article. Thanks. You mentioned: "Places with high ceilings, like gyms, should use another metric (not ACH) to measure adequate ventilation." Can you recommend any of those other metrics?
Not directly related to filtration, but I'm not seeing where to submit questions - we're starting to see folks getting Covid significantly for the 2nd time as BA2 increases, especially teachers and parents of young kids. What are the plans for actually addressing the issue of "living" with the virus? We had employees sick for 8-10 weeks in round 1 of their illness. It is not sustainable economically or personally to have people sick for up to 4 months of a 6 month time period. These are fully vaccinated and boosted individuals. Are we ever going to get a more variant specific vaccine? How do we even plan as parents, employers, and teachers for a world with this much infection and illness?
So, how can you know if have good ventilation? A CO2 meter will tell you this! CO2 from exhaling builds up in the air. Ambient air is 420 ppm (should be 280, but fossil fuels...) Great ventilation is 600 or lower. Good up to 800. Acceptable up to 1000.
I have an Aranet4. It fits in your pocket. Runs for a year on 2 AA batteries. Has app that connects to your phone via Bluetooth.
Some things I've found... my local supermarkets runs 800-1000 depending on the crowd. Big box home improvement stores about 600. Hotels... 1000-2000 in the rooms, but those aren't "shared air". Airports - 600s in common area like security, 900s in gate lounges. On plane >1000 - but this air is 100% HEPA filtered.
Home HVAC systems rarely have any external ventilation - beware! Your house may have the lowest air quality of anywhere you go.
An cheap DIY alternative to a portables HEPA filter is the Corsi-Rosenthal box. You can make one our of a box fan, MERV 13 furnace filters and duct tape. Higher clean air delivery than many portable HEPA filters. Google it and you'll find tons of instructions and videos.
We can all thank the "aerosol warriors" for finally winning this battle. They had a hard, upstream battle before the medical community accepted what these engineers knew.
Great article, as usual. Readers might also be interested in the DIY air filter system (sometimes known as a Corsi-Rosenthal box, after the inventors) that can be made for around $120 using a box fan, and four 20" MERV-13 air filters. Descriptions and fabrication instructions now available at many sites (google "DIY covid box fan air cleaner"). Data on effectiveness here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8142835/
This makes so much sense!
Thanks for all your articles. Thought for future. Re-address the J&J vaccine, especially in light of yet another mRNA booster. Would mix and match vaccines now be a better idea?
I will be sharing this important post far and wide - thank you.
FLOATING DROPLETS
The terminology used in research is confusing and problematic for all - does the term “floating droplets” include aerosols, droplets and particles in your opinion? We urgently need to clarify those terms to avoid confusion by all.
Based on the dozens of sometimes conflicting papers I’ve reviewed over the last 24 months, I have been using droplet size up to 100 microns as “floating droplets” which can persist up to 16 hours after reviewing dozens of conflicting papers. Above 100 microns fall to the floor within about 6-10 feet - not only sub 20 microns. This seems like a critical factor with quite a bit of variance from authoritative sources.
My understanding is that masks and filtration must handle floating droplets from 0.1 microns up to 100 microns.
I will find those papers and post today.
0.3 microns and below are the “most penetrative particle size” (MPPS) meaning it penetrates deep into the lungs, which is why N95s with electrostatic filters are so effective. MPPS particles of 0.3 microns is the standard size used for N95 certification and is the most difficult to filter.
AIR QUALITY METERS
I believe all public places must have an accurate, publicly available meter showing Air Changes Per Hour (ACH) and perhaps some other way to measure “dead air” building up, like CO2 monitors or an introduced substance/gas that can be measured to warn of poor ventilation.
It should be instantly clear if ventilation is not working, so we know a restaurant is actually safe for instance.
If we can radically improve ventilation and N95 mask use we could withstand a new killer virus/variant without shutting down the economy. Crucial.
Thinking outside the box..could the "sick building" phenomena be reproduced over a larger area by the meteorological phenomena of inversion layers- a condition where normal air mixing is reduced to a minimum and the air over a metropolitan area gets stale and polluted. Here in Portland, this is a frequent winter problem. Given the ability of aerosols to remain suspended in such air, has anyone ever looked at covid infection rates in cities during such conditions and whether there are correlations with upticks in new cases following extended inversions?
Maybe it's time to revisit the "vaccine passport" but in reverse. An issuing authority, like a city government, issues a grade to a building, along with a QR code posted prominently somewhere. People would be able to scan the code with their phones, to verify its validity. Wouldn't be too hard to extend the functionality of some of the SMART Health Cards to encompass this - the issuer/holder/verifier abstraction is the same
Is there a "sweet spot" where proper ventilation also means maskless? My workplace has a rule in place that even with the air filtration running, we should only take our mask off if we are alone with the door shut, and we also require everyone to be vaxxed and boosted.
Should municipalities have grading systems like they do for energy efficiency?
This is mostly excellent, thank you, but you’re repeating the error that aerosols are particles less than 5 microns. Particles as large as 100 microns can remain suspended in the air. See Jose-Luis Jimenez, Kimberly Prather, Linsey Marr, and this summary in Wired. https://www.wired.com/story/the-teeny-tiny-scientific-screwup-that-helped-covid-kill
Remember the spate of mass infections in meat packing facilities in the first year of the epidemic? At the time it appeared to me to probably be an aerosol problem caused by the power saws used in such places and the probability that the source was infected livestock, i.e. a form of zoonotic transfer mediated by meat processing technology. The media explanation at the time was close quarters of infected workers, but I don't think the workers were the real carriers initially. Has anyone looked into this?
Please comment on the adequacy of ventilation on airplanes and inside gyms or other buildings with extremely high ceilings.
Do you have a view on 222 nm technology?
https://www.nature.com/articles/s41598-020-67211-2
Great article. Thanks. You mentioned: "Places with high ceilings, like gyms, should use another metric (not ACH) to measure adequate ventilation." Can you recommend any of those other metrics?
Not directly related to filtration, but I'm not seeing where to submit questions - we're starting to see folks getting Covid significantly for the 2nd time as BA2 increases, especially teachers and parents of young kids. What are the plans for actually addressing the issue of "living" with the virus? We had employees sick for 8-10 weeks in round 1 of their illness. It is not sustainable economically or personally to have people sick for up to 4 months of a 6 month time period. These are fully vaccinated and boosted individuals. Are we ever going to get a more variant specific vaccine? How do we even plan as parents, employers, and teachers for a world with this much infection and illness?