Measurements of the size distribution of aerosols produced by ultrasonic humidification

Aerosol number and mass distributions produced by an ultrasonic room humidifier and an ultrasonic medical nebulizer were examined in a limited-scale study. Rapid droplet drying occurred at room humidities and under near saturated conditions. A model was tested describing the diameter of dried particles as a function of the dissolved mineral content of the water and the transducer frequency. Water containing 102 mg/L of dissolved minerals in a humidifier with a 1.6 MHz transducer produced droplets with a mass median diameter of 2.9 μm. The number median diameter of particles after drying was computed to be 0.11 μm. The distribution of particles in a nebulizer tube using a NaCl solution was shown to consist of a mixture of dried salt particles and droplets which included coagulated multiplets.