German aerosol scientists say these 6 indoor air guidelines will reduce COVID-19 spread

Finally, experts are addressing the contagious elephant in the room: How to actually make indoor air safe in the age of the coronavirus. This week a top cohort of German scientists released surprisingly straight-forward indoor air guidelines to prevent COVID-19 spread. They are:

• N95 masks. “They should be mandatory in many sectors, instead of the simple hygiene masks,” write the authors.
• Window ventilation. The more, the better. It’s effective and cheap.
• Exhaust ventilation systems. The air must be extracted upwards through an overhead exhaust suction, and appropriately filtered if recirculated. The group advises that these ventilation systems be installed immediately in places like classrooms, restaurants, hospitals, buses, and trains.
• Air purification systems. The use of appropriate purifiers for the size and space are critical. Portable is fine.
• CO2 monitoring. The results are proxy for how well ventilation is working. If CO2 levels are extremely low in buildings like museums, for example, reopening could be reasonable.
• No fans. Ceiling fans recirculate air, likely keeping virus particles in the air for longer.

If all guidelines are employed simultaneously, together they would remove about 90% of all viral aerosols, say the scientists.

A key detail: Small aerosol particles rise with the warm air we breathe out, and eventually float below the ceiling. This means that ceiling ventilation systems that supply fresh air from the top-down are potentially recirculating virus particles. Think about airplane seats, with the air blowing down from above your head: not good. (The scientists note that some of these extraction systems could eventually be reversed.)

The group is called the German Working Committee on Particulate Matter, and includes physicists, chemists, engineers, biologists, meteorologists, and doctors from three scientific associations, as well as support from the Leibniz Institute for Tropospheric Research. The guidelines also include a helpful summary of current understandings of COVID-19 aerosol particulates. The 5-page, single-space document is well-worth a read.