Not according to my uHoo air quality monitor. I have had one running a few feet from the monitor for over a week and there hasn't been any notable increase in PM2.5 particles.
In the next room (where there were none) it was 6.
Depends on the water, I guess.
I have a couple ultrasonic humidifiers, if tap water is put in them it immediately sends the AQI on my air quality monitor into the "Dangerous" level. I have the monitor upstairs and it detected it when my girlfriend put tap water in the humidifier downstairs.
Purified or distilled water works fine. I bought a counter top water distiller because it was a pain lugging 15 gallons of water into the house every week all winter. You can see the residue of whatever was in the tap water at the bottom of the distiller after it runs and it doesn't look like anything I would want to be breathing.
What's your PM2.5 baseline, and did you measure TDS in the water?
I haven't checked the TDS but when I used a water test strip for an aquarium early this year it was in the hard water range.