Comparison of Particle Number Counts Measured with an Ink Jet Aerosol Generator and an Aerodynamic Particle Sizer

Abstract

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.

On the Feasibility of a Number Concentration Calibration Using a Wafer Surface Scanner

“…The sheath flow of clean air at a flow of about 15 cm 3 /s compared to an aerosol flow of about 2 cm 3 /s minimizes the deposition of the 3 mm spheres on the walls of the diluter and on the outlet tubing. Kesavan et al (2014) obtained an average wall loss of 0.7% for 2.7-mm aerodynamic fluorescein particles in a flow adapter with sheath flow and overall dimensions similar to our diluter. We expect our losses to also be less than 1%, which would have a negligible effect on our uncertainty.…”

Toward biological aerosol reference standards

“…More recently, the degree of damage to organisms caused by aerosolization using a Collison has been quantified (Zhen et al 2013); (Ibrahim et al 2015) as well as comparison among selected devices (Zhen et al 2014). Additionally, there are a number of methods (and some commercial devices) designed to provide very narrow or monodisperse (geometric mean standard deviation <1.25) initial droplets and provide a degree of control over the nominal droplet size (see, e.g., Lin, Eversole, and Campillo 1990;Kesavan et al 2014;Waldrep and Dhand 2008;Kuo et al 2019). Electrospray devices can also be operated in a monodisperse droplet mode (cone jet mode) (Tang and Gomez 1994;Eninger et al 2009).…”

Laboratory Validation and Initial Field Testing of an Unobtrusive Bioaerosol Detector for Health Care Settings

“…A detailed description of the IJAG is provided in Kesavan et al (2014) and a brief description is provided below. The IJAG dispenser contains a liquid solution of bacteria.…”

“…The IJAG has been utilized in many studies, especially to calibrate the Aerodynamic Particle Sizer (APS) using 0.95 to 13.3 µm solid and liquid particles (Kesavan et al, 2014). Kesavan et al (2013) employed the IJAG system to generate near-monodisperse clusters (geometric standard deviation ≈ 1.15) of Bacillus atrophaeus spores in the size range of 2.8 to 4.4 µm for Ultraviolet C inactivation studies.…”