Bore a small hole in the wall to the outside in the room where pure air is required.
Place a section of plastic water pipe in the hole which extends all the way through the wall.
Use some filter material on the outside of the pipe to prevent insects etc from getting into the pipe.
On the inside of the room, mount a box on the pipe, the box must contain high-quality HEPA filter.
Cut a hole in the box and mount a quiet fan inside the box which will draw outside air into the box through the HEPA filter and then blow the clean air into the room.

The best room to do this in is the bedroom as this will clean out the lungs at night of all of the pollution which was drawn in during the day.

Leave the bedroom door open during the day and the entire house or apartment air will eventually be cleaned.

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