Errors in Measurement and Counting of Particles Using Light Scattering

An indirect Raman spectroscopy method for the quantitative measurement of respirable crystalline silica collected on filters inside respiratory equipment

“…The counting errors made by optical particle number concentration instruments like the Portacount® and the optical detector in the miniWRAS, used for the larger sized particles, are well established. 33 Optical particle sizing instruments are calibrated using uniform spheres with a specic refractive index. The calibration particles' characteristics may differ from the those measured from a workplace aerosol and the instruments oen need a calibration that is specic for the expected matrix due to the nature of light scattered by the particles.…”

“…34 Large counting errors are also attributed to the coincidence of particles at high concentrations, the uctuation of concentrations of particles in the size range just smaller than the lowest detectable particle size and Rayleigh scatter. 33 The miniWRAS uses an electrical mobility spectrometer to count particles at the lowest sizes, for particle sizes below 1 mm, however, counting errors can also occur from multiply charged particles. 35 For this study, particle number concentrations were kept below thresholds specied by the manufacturer that cause an increase in the risk of particle coincidence, and a deionising fan was also included to reduce the potential for agglomeration of multiple charged particles.…”