I discovered this when doing a post-assembly indoor test of a Luftdaten air quality sensor I built[0]. I kept it running for few hours and then looked at the data, and saw some ridiculously high levels of PM2.5 and PM5 in the evening. I've decided to investigate it. Over the next two days, I figured out that the increased levels happen at times when our air humidifier is running, which led me to discover that those ultrasonic air humidifiers essentially atomize everything that was mixed with/dissolved in the water - and we were using filtered tap water with ours. With distilled water in the humidifier, the sensor did not show increased particulate levels.

We've mostly stopped using the humidifier now, because I can't find a source of distilled water that doesn't involve buying plastic bottles.

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[0] - https://luftdaten.info/en/home-en/

If it's a cool-mist type humidifier, definitely.

I grabbed an evaporative one from the local big box hardware store and zero 'smoke'. You should get some bacteriostat and you'll have to replace the paper elements every now and again, but it's way better.