Yes, if you haven’t done anything to keep up the purifying efficiency. On days with bad outdoor air pollution, all purifiers we’ve tested achieved lower percentage reductions. That’s despite the fact that they were running on their highest setting.
There are two things you can do if you live in a really polluted area :
1. Seal up the doors and windows
2. Bring in back up: using a second purifier or buying a machine that is rated for an even bigger room
Click here to read the tests and more details: https://smartairfilters.com/en/blog/purifiers-perform-worse-when-pollution-high/