Environmental Chemistry Lab, Department of Applied Chemistry,
Faculty of Science and Technology, Keio University

Led by Tomoaki OKUDA, Ph.D.


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Particle Charging State

Several laboratory experiments and numerical simulations have shown that the aerosol charging state influences particle deposition on human airway surfaces. However, the actual charging state of ambient aerosol particles is still quite unknown. We try to elucidate the mechanisms of aerosol charging and its impact on the surrounding environment including human body by measuring several parameters of atmospheric aerosols through the development of original measurement methods based on atmospheric chemistry and aerosol engineering.

The content of this research was featured in “KEIO RESEARCH HIGHLIGHTS”, which introduces the research activities conducted at the entire Keio University.


Elucidation of Charging Mechanism of the Actual Atmospheric Aerosols

We measured the charging state of real-world atmospheric aerosols to elucidate their charging mechanisms using the K-MACS (Keio-Measurement System of Aerosol Charging State) based on the principle of electric mobility.

Snap Shots

The photo of the K-MACS developed by our laboratory. This device is used for obtaining the charge distribution of actual ambient aerosol particles. Publication #67 includes the detailed description of K-MACS, and it was selected as an Aerosol Science & Technology Most 10 Top Downloaded Articles for two consecutive months.

An experimental setup to measure the charging state of ambient aerosol.

Results of charging state of atmospheric aerosol measured using K-MACS.

Measurement of Particle Charging State using a Tandem DMA

Several studies have been conducted on nanoparticles because particle charging caused by collisions with atmospheric ions is important in particle generation/growth and removal mechanisms. However, charging state of submicron particles have not been elucidated so far. We have been investigated the charging state of submicron aerosols to evaluate toxicity of ambient particulate matter.

Snap Shots

The aerosol charging state is analyzed by tandem DMA, which connects two DMAs in series.

The charging state of aerosol particles is analyzed by generating particles derived from combustion in an aluminum container.

This is a measurement of the charging state of particles using a tandem differential type electric mobility classifier. We develop our own programs to control various devices and investigate the particle characteristics.

Elucidation of Electrostatic Charging Characteristics of Radioactive Cs-Bearing Particles by Kelvin Probe Force Microscopy

After several years have passed from the Fukushima Daiichi Nuclear Power Plant accident, insoluble radioactive Cs-bearing particles have been found in some regions in Japan. These insoluble particles remain as a particle in human airways and continue emitting radiation. Therefore, there could be a concern about health effects. The particles have seemed to be present in contaminated nuclear reactors and the surrounding areas of F1NPP. To eliminate the hazard of the particles, it is necessary to understand and utilize the physical properties of the particles, which is not yet understood.
Because of the continuous emission of the electron beam, we hypothesized that the radioactive Cs-bearing particles have specific electrostatic charging characteristics. In this study, we attempt to apply the technique of Kelvin Probe Force Microscopy (KPFM) to measure electrostatic charging state of radioactive Cs-bearing particles. KPFM is a method that enables imaging of nanometre-scale surface topography, and also the surface potential of a sample. KPFM scans a sample with an oscillating probe to detect interatomic force between the probe and the sample. In addition, contact potential differences between the probe and sample are detected.

Snap Shots

By attaching a dedicated KPFM module owned by our laboratory to a normal AFM (Atomic Force Microscopy) owned by our university, measurement can be performed as a KPFM.

We analyzed a radioactive Cs-bearing particle by KPFM, and there was the distribution of potential in the surface of the particle. These images were obtained by FE-SEM, topography, and surface potential in an order from left.



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