From the articles:

> A good heuristic is that an increase of 33.3 PM2.5 μg/m³ costs around 1 disability-adjusted life year. Correia et al. (2013) estimated something close to this from different counties in the US, and more recent data from many different countries confirm this. The most polluted cities in the world have levels around 100 PM2.5 μg/m³.

> When inhaled during an 8-hr exposure time, and depending on mineral water quality, humidifier aerosols can deposit up to 100s of μg minerals in the human child respiratory tract and 3–4.5 times more μg of minerals in human adult respiratory tract. > (Yao et al., 2020)

The amount of particles people breathe in in a night of worst case ultrasonic humidifier use is 8x more than the particle level in the air of the most polluted cities in the world.