11:15 AM - 11:30 AM
[AAS11-14] Evaluation of the Polarized Complex Amplitude Aerosol Sensor using Two-Sphere Clusters
1. Background
Complex Amplitude Sensing version 2 (CAS-v2)1 has recently been developed for detailed, yet fast inline analyses of single particles suspended in environmental fluids (air/water). The polarized complex forward-scattering amplitude, 4-dimensional single-particle data acquired by CAS-v2, contains information on particle volume, shape, and complex refractive index. However, the full analytical capability of CAS-v2 has not yet been experimentally evaluated due to the unavailability of nonspherical particles with well-defined and homogeneous properties. Here, we evaluate the measurement accuracy of CAS-v2 for nonspherical particles for the first time using two-sphere clusters of polystyrene prepared by a novel aerosol-generation method.
2. Method
Droplets were generated by nebulizing a suspension of PS (Polystyrene) standard particles, and aerosol particles were extracted as residue within the droplets by evaporating the water in a heating chamber. When a droplet contains n PS particles, an aerosol particle consisting of an aggregate of n PS particles is formed during drying (n=0, 1, 2, ...). These aerosols were electrically charged through a 241Am neutralizer, and only particle groups with specified mass-to-charge ratios were extracted using an Aerosol Particle Mass analyzer (APM). In this experiment, the APM voltage was set to simultaneously allow the transmission of single spheres (charge 1) and two-sphere clusters (charge 2) of known mass. For PS samples with diameters of 303, 345, 401, and 453 nm, data from tens of thousands of single spheres and hundreds of two-sphere clusters were acquired using CAS-v2. The former was compared with Mie theory, while the latter was compared with exact theoretical distributions calculated using the Multi-Sphere T-matrix Method (MSTM) assuming random orientation in air.
3. Results and Discussion
The figure 1 shows a comparison between measured and theoretical values of the complex scattering amplitude (average of two orthogonal polarizations) for PS particles with a diameter of 401 nm. Not only for single spheres but also for two-sphere clusters, the measured distribution showed good agreement with theoretical distributions. Similar agreement was obtained for other PS diameters as well. These results provided the first verification that CAS-v2 can accurately measure the polarized complex scattering amplitude of non-spherical particles.
ReferencesMoteki, N., & Adachi, K. (2024). Measuring the polarized complex forward-scattering amplitudes of single particles in unbounded fluid flow: CAS-v2 protocol. Optics Express, 32(21), 36500-36522.
Complex Amplitude Sensing version 2 (CAS-v2)1 has recently been developed for detailed, yet fast inline analyses of single particles suspended in environmental fluids (air/water). The polarized complex forward-scattering amplitude, 4-dimensional single-particle data acquired by CAS-v2, contains information on particle volume, shape, and complex refractive index. However, the full analytical capability of CAS-v2 has not yet been experimentally evaluated due to the unavailability of nonspherical particles with well-defined and homogeneous properties. Here, we evaluate the measurement accuracy of CAS-v2 for nonspherical particles for the first time using two-sphere clusters of polystyrene prepared by a novel aerosol-generation method.
2. Method
Droplets were generated by nebulizing a suspension of PS (Polystyrene) standard particles, and aerosol particles were extracted as residue within the droplets by evaporating the water in a heating chamber. When a droplet contains n PS particles, an aerosol particle consisting of an aggregate of n PS particles is formed during drying (n=0, 1, 2, ...). These aerosols were electrically charged through a 241Am neutralizer, and only particle groups with specified mass-to-charge ratios were extracted using an Aerosol Particle Mass analyzer (APM). In this experiment, the APM voltage was set to simultaneously allow the transmission of single spheres (charge 1) and two-sphere clusters (charge 2) of known mass. For PS samples with diameters of 303, 345, 401, and 453 nm, data from tens of thousands of single spheres and hundreds of two-sphere clusters were acquired using CAS-v2. The former was compared with Mie theory, while the latter was compared with exact theoretical distributions calculated using the Multi-Sphere T-matrix Method (MSTM) assuming random orientation in air.
3. Results and Discussion
The figure 1 shows a comparison between measured and theoretical values of the complex scattering amplitude (average of two orthogonal polarizations) for PS particles with a diameter of 401 nm. Not only for single spheres but also for two-sphere clusters, the measured distribution showed good agreement with theoretical distributions. Similar agreement was obtained for other PS diameters as well. These results provided the first verification that CAS-v2 can accurately measure the polarized complex scattering amplitude of non-spherical particles.
ReferencesMoteki, N., & Adachi, K. (2024). Measuring the polarized complex forward-scattering amplitudes of single particles in unbounded fluid flow: CAS-v2 protocol. Optics Express, 32(21), 36500-36522.