Evaluation of a Portable Aerosol Collector and Spectrometer to measure particle concentration by composition and size

We evaluated a newly developed Portable Aerosol Collector and Spectrometer (PACS) in the laboratory. We developed an algorithm to estimate mass concentration by size and composition with a PACS. In laboratory experiments, we compared particle size distributions measured with the PACS to research instruments for multi-modal aerosols: two-mode generated by spark discharge, consisting of ultrafine (fresh Mn fume) and fine particles (aged Cu fume); and three-mode produced by adding coarse particles (Arizona road dust) to the two-mode. Near-real-time size distributions from the PACS compared favorably to those from a scanning mobility particle sizer and an aerodynamic particle sizer for the three-mode aerosol (number, $bias=9.4\%$ and $R^2=0.96$; surface area, $bias=17.8\%$, $R^2=0.77$; mass, $bias=-2.2\%$, $R^2=0.94$), but less so for the two-mode aerosol (number, $bias=-17.7\%$ and $R^2=0.51$; surface area, $bias=-45.5\%$, $R^2=0$; for mass, $bias=-81.75\%$, $R^2=0.08$). Elemental mass concentrations by size were similar to those measured with a nano micro-orifice uniform deposition impactor for coarse-mode particles, whereas agreement was considerably poorer for ultrafine- and fine-mode particles. The PACS has merit in estimating multi-metric concentrations by size and composition but requires further research to resolve discrepancies identified for two-mode aerosol.