A direct-reading particle sizer with elemental composition analysis for large inhalable particles

There is a lack of aerosol measurement technology capable of quantifying, in real time, the size, concentration, and composition of large inhalable particles - specifically those with aerodynamic diameter larger than 20 mu m. Aerosols of this size penetrate into the upper respiratory system upon inhalation and present surface contamination hazards upon settling. 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 in the size range 25-125 mu m. Particle sizing results showed good agreement with optical microscopy images, and LIBS measurements allow simultaneous elemental composition measurements. 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 (r(2) > 0.999). The mean absolute difference between the median aerodynamic diameters measured by the instrument by time-of-flight and microscopy over all eight test aerosol types was 0.9 mu m with a mean difference in interquartile range of 1.9 mu m. LIBS spectra have been collected and analyzed to reveal spectral features of species from silver-coated glass and titanium samples. The expected system performance for future field use is considered through numeric simulations based on the instrument parameters and assumed particle size distributions. Finally, potential hardware changes to optimize detection efficiency and facilitate field use are discussed.