WHO officially stated that COVID-19 can be spread by airborne particles on July the 9th. In a closed room without proper ventilation, the coronavirus can be transmitted from person to person, usually after close contact with an infected patient.
WHO defines airborne transmission cause by spread of aerosol (suspension of fine solid particles or liquid droplets in the air) stay for eight hours. The coronavirus will come out if they find proper ventilation or air circulation.
In other words, in a closed rooms or spaces without proper ventilation, the coronavirus can stay up to eight hours, then if people who stay in the rooms or spaces and breathe the aerosol which contains virus particles can be infected with coronavirus.
If rooms get colder, aerosol stay longer, making the particles last even longer (to dry) and disappear. As reported from The New York Times, some of the highest risk places for spreading the virus are nightclubs, offices, restaurants, places of worship and other places where so many people talking and spending time in same rooms.
Regardless of how frightening the possibility, WHO and researchers were still finding out the information of droplet size which can be exhaled when they produce due to evaporation, breathe normally, and speak.
Hence, people are still required to apply the health protocol to prevent for getting and spreading the virus including mask wearing, washing hands, keep safe distance and not to stay in rooms or places for long time.
If you need to stay in an AC room or space in long time, try to take a break as often as possible. Go out from your zone, breathe fresh air outside, do it as often as you can.