Cathy S. Scotto, Matthew B. Hart, Jozsef Czege, JAY D. EVERSOLE, Steven Hill, Dan Mackowski, Jana Kesavan, Vipin Rastogi, Naval Research Laboratory
Abstract Number: 303 Working Group: Bioaerosols
Abstract We provide updated results from a continuing bioaerosol radiation exposure study first described at IAC 2018. Ultraviolet photo-degradation data for aerosol particles consisting of Bacillus anthracis, Sterne strain spores are being obtained. Viability of total sample spores pre- and post- exposure are determined by collection onto filters, recovery into liquid, serial dilution and plating. Observed decay rates depend on the mean aerosol particle “size” (spore cluster number) due to shielding effects that have been predicted by numerical modeling.
A significant aspect of this experimental approach, is the control over which sample bioaerosol particles are generated, suspended, exposed, and collected. We have previously described our linear electrodynamic quadrupole (LEQ) trap used to confine and hold particles for long time periods.[1, 2] Concentration of the sample suspension is determined prior to the experiment, and the droplet diameters are measured by video at the capillary tip. Diameters can vary slightly from experimental run to run, but are constant during a given run, (typically about 70 µm). As the solvent component quickly evaporates, resulting residue particle “sizes” depend on spore concentration of the sample suspension.
The total number of aerosol particles for a given run also varies from run to run, typically between 300 to 500. After a sample exposure, or control, is completed, the particles are recorded as they pass through a focused laser beam on their way to a collection filter. Knowing the average number of spores per particle, and the particle number provides an accurate estimate of the total number of spores collected per run. The viable fraction is the ratio of the sample plate count to the total spore number. A significant advantage of this novel approach is that very long exposure times can be achieved with no particle loss even for relatively large particles that would normally experience gravitational settling.
[1] M. B. Hart, J. D. Eversole, et. al. Presented at the Tenth International Aerosol Conference 2018; Poster 10BA.17; American Association for Aerosol Research: St. Louis, MO, Sept. 6, 2018. [2] M. B. Hart, et, al., Appl. Opt. 54, F174-F181 (2015).