For my apartment, highest polluters include: dishwasher heating cycle, cooking, neighbor cigarette smoke, and air leaking in from main door. Adding weather stripping on the main door has substantially reduced the ambient pollution levels of my unit.

Adding stripping to my patio door that opens towards the main street helped me a lot. I am also surprised at how much noise isolation this added.

This makes my dwelling more air tight, so it's not good for carbon dioxide but I simply open windows outside traffic hours.

I live in a single family dwelling so it's probably breakfast then.