Numerical-simulation-based improved measurement of submicron-sized particle charge distribution with high temporal resolution

This study designed an improved parallel-plate particle separator, the Keio Measurement System of Aerosol Charging State (K-MACS), using numerical simulations to achieve a stable laminar flow field in practical devices. Combined with optical particle counters (OPCs), the system enables high-temporal-resolution (20 s) measurements of number concentrations of positively charged, uncharged, and negatively charged particles, allowing estimation of charge distributions for submicron particles (0.3–0.5 µm). The average particle charge number ( p ave ) and standard deviation (1 σ ) were obtained by fitting the distributions to a Gaussian function. Experimental evaluation demonstrated that multiply charged particles moved toward oppositely charged electrodes and identified an optimum voltage of approximately 5.4 kV, where experimental and theoretical charge distributions agreed well. Measurement uncertainties for 1 σ and distribution amplitude were reduced to ~ 5%, significantly lower than ~ 15% in the previous system. An application to indoor air revealed that p ave and charged particle number concentrations varied with ion concentrations, confirming the importance of ion–aerosol interactions. The high temporal resolution of the K-MACS/OPC system enables the capture of rapid changes in particle charging states, thereby providing a powerful tool for advancing our understanding of atmospheric electrical processes and their impact on particle deposition in the human respiratory system.