Doors and windows are closed and healthy.

If you don't open the window for a long time, the content of carbon dioxide in the air will become high, making people dizzy, disgusting and uncomfortable. Although it is cloudy outside and the air is not clean, it is harmful not to take a breath. Your dormitory does not have the conditions to install an air purifier. You can discuss with your classmates to open a small gap in the window. If your school is safer, there is really no discussion. You need to buy some good green plants and oxygen plants like green radish to purify the air.