HIGH-OUTPUT GENERATION OF AEROSOLS WITH NARROW SIZE DISTRIBUTIONS

Two aerosol generators-a small particle generator (SPG) and a large pa rticle generator (LPG)-were designed and fabricated to produce water-s oluble particles with high mass output and narrow size distributions. The mass median aerodynamic diameter (MMAD) of solid particles produce d could be varied by changing operation conditions and using different concentrations of sodium chloride (NaCl) solutions. The aerosol gener ation rate varied from about 0.2 to 24 mg/min depending upon the parti cle size produced as the geometric standard deviation (GSD) was mainta ined below 1.5. The SPG employed a Collison-type nebulizer with multip le nozzles and a solid-plate impactor, which removes generating drople ts larger than the cutpoint diameter for the production of submicromet er aerosols with GSD <1.5. Different combinations of nebulization pres sure/cutpoint diameter were selected to produce solid particles with M MAD in the range of 0.13-1.0 mu m. The LPG was consisted of a Delavan simplex nozzle installed at the bottom of the generation chamber labou r 190 cm in height and 15 cm in diameter) and an improved virtual impa ctor 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 accele ration nozzle and collection probe were used to vary the impactor cut rite. The size-selective droplets were then evaporated to form solid p articles with the MMAD nominally varying from 1 to 10 mu m and GSD <1. 5.