Flow Field Optimization for Inexpensive Optical Aerosol Particle Counting and Sizing

Abstract Optical Particle Sizers (OPSs) are widely used for measuring size distributions of particles larger than ca. 0.2 μm. To do so, they use mirrors or lenses to gather light scattered by particles passing through a focused beam, directing it to a photo-detector to produce electric pulses from individual scattering events. Considering their ability to provide near real-time measurements with minimal attendance and maintenance, and to expand the networks of Particulate Matter (PM) monitoring, several manufacturers have developed low-cost and compact OPS systems. Despite that low-cost OPSs are already available in the market and employed for monitoring PM concentrations, their reported values typically deviate from those of reference-grade instruments, warranting further efforts to improve their performance. In this work, we designed and built a custom-made and low-cost OPS optical system, and optimized its performance using a combination of computational and experimental methods. The performance of the optimized OPS is very similar to that of a reference instrument, exhibiting a counting efficiency of 50% for ca. 320-nm particles and a sizing resolution of below 15%, complying with the ISO 21501-4 standards.