A direct-reading particle sizer (DRPS) with elemental composition analysis
Date
2023
Authors
Sipich, James Robert, author
Yalin, Azer P., advisor
Volckens, John, committee member
L'Orange, Christian, committee member
Carter, Ellison, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
There is a lack of aerosol measurement technology capable of quantifying, in real-time, the size, concentration, and composition of large inhalable particles with an aerodynamic diameter larger than 20 µm. Aerosols of this size penetrate the upper respiratory system upon inhalation and present surface contamination hazards upon settling. The ability to obtain information on the composition of airborne particles is necessary to identify and control risks from exposure to potentially toxic materials, especially in the workplace. The objective of this work was to validate the performance of a prototype Direct-Reading Particle Sizer (DRPS) that counts and sizes particles via time-of-flight light scattering and determines single-particle elemental composition via Laser-Induced Breakdown Spectroscopy (LIBS). Counting, sizing, and spectral measurement efficiency were evaluated using test aerosols of multiple materials with diameters between 25 and 125 µm. Particle sizing results showed good agreement with optical microscopy images. The relationship between the median aerodynamic diameters measured by the DRPS time-of-flight and optical microscopy was linear (Deming regression slope of 0.998) and strongly correlated (r2 > 0.999). The mean absolute difference between the median aerodynamic diameters measured by the instrument by time-of-flight and microscopy over all 8 test aerosol types was 0.9 µm with a mean difference in interquartile range of 1.9 µm. The prototype sensor uses an optical triggering system and pulsed Nd:YAG laser to generate a microplasma and ablate falling particles. Particle composition is determined based on collected emission spectra using a real-time material classification algorithm. The accuracy of the composition determinations was validated with a set of 1480 experimental spectra from four different aerosol test materials. We have studied the effects of varying detection thresholds and find operating conditions with good agreement to truth values (F1 score ≥ 0.9). Details of the analysis method, including subtracting the spectral contribution from the air plasma, are discussed. The time-of-flight aerodynamic diameter measurement and LIBS elemental analysis capabilities demonstrated by the DRPS provide a system capable of both counting, sizing, and identifying the composition of large inhalable particles.
Description
Rights Access
Subject
aerosol
spectroscopy
laser-induced breakdown spectroscopy (LIBS)
aerodynamic diameter