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Lab Experiments to Optimize a Newly Developed Ultrafine Particle Counter

Ultrafine particles (< 0.1 μm in size) are much smaller than the EPA-regulated PM2.5 (< 2.5 μm) and pose even stronger health risks because they are small enough to penetrate deep into the lungs. Ultrafine particles are challenging to measure. Currently available condensation particle counters (CPCs) capable of detecting them are expensive (>$25,000), which limits the extent of further research. Collaborators at the University of Arizona developed a new style of ultrafine particle counter which utilizes inexpensive components. The Arizona ultrafine particle counter (AUPC) uses an expansion-based approach for forced condensation of water vapor onto condensation nuclei, which scatter light from a green diode laser as they fall and are recorded by the instrument’s camera. The thesis project involved laboratory experiments comparing number concentrations measured by both a commercial CPC and the AUPC. Experiments focused on changing particle size and particle composition. Particle size experiments compared counting efficiency of each instrument by aerosolizing sizing standard polystyrene latex beads to verify the AUPC counting capability over a range of particle diameters.

The AUPC matched the relative trend of the commercial CPC, but with a lower counting efficiency over particle sizes 25 - 345 nm. The composition-based experiments included aerosolizing a solution with particles of differing chemical properties. Particles composed of either pure ammonium sulfate (more polar and hygroscopic) or oleic acid (less polar, more hydrophobic) were chosen to represent materials with opposite water adsorbing properties. Results again showed the AUPC can reproduce the behavior of the CPC, but at lower count efficiency. The AUPC may represent a useful approach toward providing information about ultrafine particles in a variety of indoor and outdoor environments at dramatically lower cost (est. <$2,000), but the instrument will require further improvements to more closely compete with commercial CPCs.