Do you want to open the window for air in foggy weather?

I have carefully read your question, and my suggestions are as follows:

First of all, you must distinguish whether it is fog or haze outside. You can call the weather app that comes with your mobile phone to view it.

If it is foggy outside, don't open the window to breathe, because inhaling too much smog is harmful to your health and may lead to serious diseases such as lung disease.

If it is foggy outside, it is best not to open the window for ventilation, because the humidity is generally heavy in foggy days, and the essence of fog is also some small water vapor in the air, so opening the window may lead to moisture entering the room.

To sum up, it is best not to open the window in foggy days. If it is fog instead of smog, the sun will disperse quickly after it comes out, and it is advisable to open the window for ventilation after the fog clears.