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 chambers located on the campus of the University of North Carolina at Chapel Hill. The aerosol mass median aerodynamic diameter and mass concentration 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 deviation (GSD) of < 1.5. Two-fluid nebulization was selected to generate 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 solvent-solute ratio, nebulizer driving pressure, impactor cut-point size, and number of nozzles are used to control the final aerosol size and 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-nozzle prototype submicrometer aerosol generator was designed, constructed, and tested. The GSD of the aerosol produced ranged from 1.4 to 1.6 and the mass output, upon generator replication, can satisfy maximum exposure chamber demands.