SUBMICROMETER AEROSOL GENERATOR DEVELOPMENT FOR THE UNITED-STATES-ENVIRONMENTAL-PROTECTION-AGENCY HUMAN EXPOSURE LABORATORY

A submicrometer aerosol generation unit was developed for use in the U .S. Environmental Protection Agency's new air pollution exposure chamb ers located on the campus of the University of North Carolina at Chape l Hill. The aerosol mass median aerodynamic diameter and mass concentr ation are operator-selected, ranging from 0.1 to 1.0 mum and from 0 to 2 mg/m3, respectively. The aerosol was to have a geometric standard d eviation (GSD) of < 1.5. Two-fluid nebulization was selected to genera te water-soluble aerosols. Multiple Collison-type nozzles are used to create a polydisperse droplet cloud. Aerosol uniformity is improved by removing the large droplets from the original distribution by passing the aerosol through an external impaction device. Variations in the s olvent-solute ratio, nebulizer driving pressure, impactor cut-point si ze, and number of nozzles are used to control the final aerosol size a nd mass concentration. Aerosol size distributions were determined with an electrical aerosol analyzer and a low-pressure impactor. By means of data obtained by testing several experimental nebulizers, a 48-nozz le prototype submicrometer aerosol generator was designed, constructed , and tested. The GSD of the aerosol produced ranged from 1.4 to 1.6 a nd the mass output, upon generator replication, can satisfy maximum ex posure chamber demands.