The results of this study demonstrate that the decay rate of spores contained in clusters is proportional to the overall particle size, and that it is harder to inactivate large clusters on surfaces.

Four commercially available batch-type bioaerosol samplers, which collect time-integrated samples in liquids, were evaluated. Sampling efficiency was characterized as a function of particle size using near-monodisperse polystyrene spheres (sizes of 1-5 µm) and oleic acid droplets (3-10 µm). Results show the sampling efficiency of AGI-30 impingers range from 4-67% for particle sizes of 1 to 5.1 µm with significant variations between units; those of SKC BioSampler impingers range from 34-105% for particle sizes from 1 to 9 µm; those of a batch-type wetted wall cyclone with compensation for evaporation (BWWC-EC) range from 5 to 65% for particle sizes 1 to 10 µm; and, those of a batch-type wetted wall cyclone with no evaporation compensation (BWWC-NC) range of 55 to 88% for particle sizes of 1-8 µm. Retention efficiency was measured for 1 and 10 µm polystyrene spheres. For the AGI-30 and BWWC-EC, the retention efficiency of 1 µm particles after 1 h was less than 30%, while that of the SKC BioSampler was 59%. Due to liquid evaporation, the BWWC-NC could not be operated for 1 h. Retention efficiencies for Bacillus atrophaeus spores and Pantoea agglomerans vegetative cells were measured for the AGI-30 and the SKC BioSampler. Results for the spores were about the same as those for 1 µm non-viable polystyrene particles; however, the vegetative bacteria lose culturability and consequently show lower retention efficiencies. For the impingers, significant performance differences were observed in units delivered by vendors at different times.

Aerodynamic particle sizer (APS) users typically calibrate the particle sizing capabilities, but not the counting efficiency upon which aerosol concentration results are based. Herein, comparisons were made between the counts provided by an ink jet aerosol generator (IJAG) with those measured by an APS. Near-monodisperse (geometric standard deviation of about 1.06) liquid or solid aerosols in the size range of 0.95 to 13.3 μm aerodynamic diameter (AD) generated with an IJAG were released into the inner inlet-tube of the APS in a manner that rendered APS wall and aspiration losses negligible. For most experiments, the IJAG generated 75 particles/s, which rate was maintained by the IJAG system through control of electrical pulses applied to its ink jet cartridge. For particles in the size range of 2-13.3 μm AD, the ratio of relative detection efficiency (ratio of the number of particles counted by the APS to the number reported as generated by the IJAG) was 99.3 ± 1.4%; however, for test particles between 0.95 and 2 μm AD, the relative detection efficiency was somewhat lower, but the drop off was less than about 2%. This slight drop off is likely associated with the light scattering detection approach and corresponding counting algorithm of the APS. Tests were conducted where the IJAG produced 7.0 μm AD particles at rates of 1 to 500 s -1 and the results showed essentially a 1:1 correspondence between IJAG and APS counts. The presence of smaller-sized background particles did not affect the measured APS counts of larger-sized challenge particles.

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Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. SPONSORING I MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S) SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION / AVAILABILITY STATEMENTApproved for public release; distribution is unlimited. SUPPLEMENTARY NOTES ABSTRACTCharacteristics and aerosol sampling efficiencies of four Omni 3000 aerosol samplers (Sceptor Industries, Inc., Kansas, MO) were determined at ECBC. These samplers have nontraditional wetted-wall cyclones to collect and concentrate aerosols into liquid. The sampling efficiency tests were conducted with monodisperse 0.5-, 1-, 3-, and 5-pm fluorescent polystyrene latex (PSL) microsperes and 2.9-, 5.8-, and 8-pm fluorescent oleic acid particles. The results showed the highest sampling efficiency of 91% for 3-prm particles using the fluorescent PSL microspheres and 70% for 2.9-pm liquid fluorescent oleic acid particles. Omni aerosol samplers have approximately 277 L/min of air flowrate, use 83 W of power, depending on the attachments, and they are small in size. They give approximately 11 mL of liquid after each sampling. These samplers are portable, battery operated, and easy to use and decontaminate.