Aerosol emissions from an evaporative humidifier.

The widely used evaporative humidifier can be a source of airborne particulate hazards. Available knowledge about the aerosol emissions from an evaporative humidifier is lacking. We measured the particle/droplet emission rates and particle size spectra from an evaporative humidifier, and examined key factors affecting the particle emissions. We found most of the emitted aerosols from an evaporative humidifier are from its reservoir. The formation of reverse water jets and their fragmentation into secondary droplets after the impaction of the dripping water on the reservoir constitute the primary particle emission. The particle emission rate increases sharply when the Froude number of the dripping water drops exceeds 100. The presence of waterborne Pseudomonas aeruginosa remarkably increases both the total particle emissions and the airborne bacteria numbers. These findings are vital for developing scientific strategies to reduce the probability of airborne contamination by an evaporative humidifier.