High-Output Generation of Aerosols with Narrow Size Distributions

Abstract

Two aerosol generators–a small particle generator (SPG) and a large particle generator (LPG)–were designed and fabricated to produce water-soluble particles with high mass output and narrow size distributions. The mass median aerodynamic diameter (MMAD) of solid particles produced could be varied by changing operation conditions and using different concentrations of sodium chloride (NaCl) solutions. The aerosol generation rate varied from about 0.2 to 24 mg/min depending upon the particle size produced as the geometric standard deviation (GSD) was maintained below 1.5. The SPG employed a Collison-type nebulizer with multiple nozzles and a solid-plate impactor, which removes generating droplets larger than the cutpoint diameter for the production of submicrometer aerosols with GSD < 1.5. Different combinations of nebulization pressure/cutpoint diameter were selected to produce solid particles with MMAD in the range of 0.13–1.0 μm. The LPG was consisted of a Delavan simplex nozzle installed at the bottom of the generation chamber (about 190 cm in height and 15 cm in diameter) and an improved virtual impactor located at the top of the generation chamber. Gravity was used to remove large droplets and the improved virtual impactor was employed to remove droplets less than the cutpoint diameter. Two sets of acceleration nozzle and collection probe were used to vary the impactor cut size. The size-selective droplets were then evaporated to form solid particles with the MMAD nominally varying from 1 to 10 μm and GSD < 1.5.