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.
Click here to read the full article: https://smartairfilters.com/en/blog/does-ac-bring-in-pm2-5/
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