From an HVAC engineering perspective, here's what I've learned about coronavirus prevention - the key is to control the amount of outside air brought into a building as well as to control the humidity. https://twitter.com/BDNbiz/status/1275411901099499520

Almost all buildings have air supply into them. Your office probably has a couple of grilles in the ceiling that blow air in and pull air out. That air is not all fresh air from outside. Buildings recirculate 75-90% of the building air movement, with some stale air exhausted out.

Increasing the amount of stale air exhausted and increasing fresh air into a building helps flush out contaminants and particulate. Some buildings will use HEPA filters instead of increasing fresh air. The key is to get clean air into a room and dirty air out of the building.

The problem is that more fresh air costs money. You need to heat it in winter and condition it in summer. HEPA filters also cost more money as it requires bigger fan motors to push air through that filter.

Humidity is a surprising item. When a person coughs or sneezes they expel moisture from their mouth. If those moisture droplets are large, they generally fall to the floor fairly quickly. If the droplets are small, they can stay afloat for hours, even days.

Those droplets can contain the virus. If the droplet is aerosolized (if the droplet becomes very small), the virus literally floats in the room waiting for someone to breath it in. That's where increasing outside air flow rates help to flush out the bad air.

But, if the relative humidity is low, more of the large droplets dry out and become aerosolized. This starts to happen at 40% relative humidity. As humidity drops, and the air becomes more dry, more droplets become aeresolized.

That's why I worry about the coming fall and winter. Right now most buildings are around 40-50% RH inside, even with air-conditioning. That's actually the sweet spot to reduce airborne transmission of disease while also preventing mould. But, this fall, the air will begin to dry.