Averaging over 7 different tests on a polluted day in Beijing, the effect on 0.5 micron particles (left) was basically zero. The effect on 2.5 micron particles (right) was that they actually went down a little.
Our conclusion is wall-mounted air conditioners like this do NOT bring in dirty outdoor air. Instead, they pull air from the top of the machine and recirculate it through the room.
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