When weather and air quality conditions allow, check with school administrators about increasing fresh outdoor air by opening windows and doors. Do not open windows and doors if doing so poses a safety or health risk for students (e.g., risk of falling, triggering asthma symptoms).
An air purifier can clean the air with the windows open, but it cannot work as well as it would with the room sealed. Leaving a window open means the air purifier is not just cleaning the air in the room. It must also clean the air entering the room from the outdoors as well and will never have fully purified air inside. When we limit the amount of air an air purifier must clean, we increase its efficiency and the amount of time it will take to freshen an entire room.