(I know little science so please help me if I'm in the wrong place or if my question needs editing. I could use help with tagging, for example.)
I use two devices that measure PM2.5:
- Kaiterra LaserEgg 2+, an air monitor which uses laser-based light scattering technology
- Blueair Classic 280i, an air purifier which measures PM2.5 but doesn't say how
Generally, their PM2.5 measurements are within 20% of each other and the readings go up and down together.
Both devices are in a room measuring about 40sqm.
It's winter so the windows are closed and I keep the Blueair Classic on automatic mode, which varies the fan speed depending on the level of PM2.5 it measures. It is rare for the fan speed to increase above the lowest level.
The level of PM2.5 is usually under 10μg/m3 (safe, according to the WHO), as measured by the LaserEgg and the Blueair Classic.
A few days ago we felt that the air was dry (cracked skin, etc.) and our humidity sensors reports humidity around 25%, so we turned on an ultrasonic humidifier (https://www.amazon.co.uk/Humidifier-Improves-Health-Sleep-Focus/dp/B01C5YHFWO). We use tap water in the humidifier.
Within a few minutes the LaserEgg and the Blueair Classic reported a massive increase in PM2.5, to about 400μg/m3 (very unsafe according to the WHO). The Blueair Classic changed its fan speed to maximum but it seemed to have little effect. Perhaps the output of the humidifier is greater than the cleaning capacity of the purifier.
We have reproduced this situation several times since - every time the humidifier is turned on.
What could be causing the PM2.5 increase?
Could it be harmful?