Table 1 Aerosol generators

Nebulizer

Droplets are formed with an atomizer or in a fountain formed by ultrasonic sound. Dried droplet residue forms the particles.

Liquids containing dissolved or suspended solids

0.43–16.2 μm

Optimal for 6-h durations

0.01–5 mg/m³

[34]

Electro spray Generator

High voltage is applied to a metal capillary end containing flowing liquid. Expelled charged droplets fragment when electrostatic forces exceed surface tension. Dried droplet residue forms the particles.

Liquids containing dissolved or suspended solids

2- 100 nm

Optimal for 4 h

5 ng/cm²/min for in vitro and 2 mg/m³ for in vivo

[35]

Fluidized bed

Small beads are fluidized by air, and the turbulent motion and bead interaction disperses powder added to the bed.

Solid

20–500 μm

Greater than 3 h

0.5–40 mg/m³

[31], [36]

Acoustic

Includes an acoustic energy source and a diaphragm(s) that produce a pressure gradient.

Solid

Same as the original particle size

Greater than 30 h

15 mg/m³ or more

[37]

Brush feed

Composed of a screw feeder, rotating brush, and a cyclone designed to remove larger particles to aerosolize carbon fibers.

Solid

Same as the original particle size

In 6 h increments

5 mg/m³

[38]

Dust feeder

The surface of a cake of compacted powder is scraped at a controlled rate, by mechanical scraping and blown by compressed air.

Solid

Same as the original particle size

>20 h

Concentration of the output aerosol can be controlled by adjusting the air-flow rate

[27, 39], [40]