Size-Resolved Performance Evaluation of the Portable Mini Wide-Range Aerosol Spectrometer (MiniWRAS)

Real-time aerosol characterization across ultrafine, fine, and coarse particle fractions remains technically challenging, particularly in portable platforms intended for field deployment. The MiniWRAS portable wide-range aerosol spectrometer combines an electrometer-based NanoSizer with an optical particle counter to provide continuous size-resolved aerosol measurements in a compact platform. Although the MiniWRAS is increasingly used as a laboratory reference instrument, direct evaluation against established Scanning Mobility Particle Sizer (SMPS) and Aerodynamic Particle Sizer (APS) reference measurements remains limited. This study evaluated the MiniWRAS against a combined SMPS + APS system using polydisperse sodium chloride, Arizona road dust (ARD), and kerosene oil aerosols at environmental and occupational concentrations, along with monodisperse Di-ethyl-hexyl-sebacate (DEHS) particles from 0.1 to 5.0 µm. For monodisperse aerosols, MiniWRAS detection efficiency was near 100% at 1.0 µm and 2.0 µm, measuring 95.2% and 97.1%, respectively, but deviated (overestimated) substantially at the size extremes, reaching 616.7% at 0.1 µm and 265.5% at 5.0 µm. The MiniWRAS systematically underestimated mass median diameter (MMD) for monodisperse particles at and above 1.0 µm, recording 0.595 µm and 4.234 µm at the 1.0 µm and 5.0 µm targets, respectively, compared with 0.929 µm and 4.915 µm for the SMPS + APS. For particles 0.2 µm and larger, MiniWRAS geometric standard deviation (GSD) values were larger than those from the SMPS + APS, indicating broader size classification precision. For polydisperse aerosols, agreement varied by aerosol type and concentration range. Salt showed the closest MMD agreement between instruments at environmental concentrations, while ARD showed the largest MMD overestimation. Kerosene oil showed the closest agreement between instruments in number concentration distribution, particularly at occupational concentrations. Across the aerosols and conditions evaluated, the MiniWRAS performed most reliably in the 1.0–2.5 µm particle size range, but overcounted ultrafine particles, underestimated MMD for larger monodisperse particles, and produced broader or irregular mass distributions for some polydisperse aerosols.