Thread by @jljcolorado

1/ AIR CLEANERS: recommendations from the scientists of what to use and what to avoid

2/ More details about how to remove the virus from the air (best ventilation, otherwise filtration, UV in some special cases, avoid others): sciencedirect.com/science/articl…

3/ A thread on air cleaners that explains the recommendations:

https://twitter.com/jljcolorado/status/1291758303089852417

4/ A Medium article explaining why spraying disinfectants in the air is a very BAD idea when people are present. These techniques are ONLY useful for surfaces when NOBODY is present and you can ventilate afterwards.

By @EarthMechanic, @ChemDelphine & me

medium.com/@dbc007/the-ai…

5/ Note that since surfaces transmit SARS-COV-2 poorly, and if you ventilate, you already remove the virus from the air, there is little point on spraying a disinfectant for COVID-19.

6/ Filtration is very effective to remove virus-containing aerosols from the air. Either within HVAC systems (with MERV13 when possible), or portable HEPA (great but expensive) or cheap fan-filter combos (works!). Follow @JbcLiftec @JimRosenthal4 @SmartAirFilters for fan-filter

7/ Germicidal UV works, BUT it is more expensive, it is dangerous if shone on people, and needs professional design, installation, and maintenance. So we recommend it only when filtration not possible (e.g. prisons, waiting rooms for Emergency in hospitals etc.)

8/ Avoid air cleaners that "kill" the virus with chemical reactions with its biomolecules (thru ions, plasmas, hydroxyl etc.). The same chemistry reacts with abundant volatile organic compounds (VOCs) indoors, which is expected to form toxic oxidized VOCs and chemical aerosols.

9/ What about controlling humidity?
- Virus survives better if very dry or very humid. Worst 40-60% RH
- Controlling RH is useful, but it just shortens the virus lifetime. We favor removing the virus from the air through ventilation or filtration first.

10/ For ventilation, need to measure CO2 in all shared spaces. Low-cost NDIR $90-$200
- 400 ppm outdoor
- 800 ppm = 1% of the air you air breathing, someone else has breathed it before
- 4400 ppm = 10% rebreathing, very dangerous! Common in classrooms etc. without ventilation

11/ Going forward, and since many more diseases (e.g. flu, next pandemic) transmit via aerosols, we need to mandate visible CO2 meters in all public spaces where we share air. Doable with very limited cost.

12/ An example of bringing a CO2 meter in an aircraft trip in Europe:

https://twitter.com/jljcolorado/status/1328515572187873280

13/ And an example of a poorly ventilated supermarket. Citizens should themselves of CO2 meters and report poor ventilation to those responsible for public spaces.

https://twitter.com/jljcolorado/status/1333219374874963969

14/ With a CO2 meter, natural ventilation (by opening windows) can be managed in shared spaces, so that infection risk is greatly reduced, while thermal comfort is not reduced majorly.

15/ Finally, a reminder that when we think about masks and filters, that the virus is not naked in the air, but it flies in much larger aerosol-vessels. Which still float in the air for some time, but are much easier to filter.

15/ If you want more details, see these top-scientist generated Frequently Asked Questions, which has more info and links to many resources.

tinyurl.com/faqs-aerosol

16/ To see my whole slide deck on this topic, or a recent presentation to @APSphysics (more focused on why we think, based on the science, that this virus is transmitted mainly through the air, and dispelling the misconceptions that plague @WHO et al), see

https://twitter.com/jljcolorado/status/1334633988263206916