Tatsuhiro Mori

Mineral dust accounts for a significant fraction of the atmospheric aerosol burden, impacting climate through its interactions with radiation and clouds. However, limited observations of dust particles in the free troposphere hinder our understanding of its spatial distribution and climatic impacts. In this study, aerosols were collected on filters using aircraft over the western North Pacific at 0.2–8 km altitudes in summer 2022. Individual water‐insoluble particles dispersed in water were analyzed using a complex amplitude sensor (CAS), which enabled classifying particle type, sizing, and counting from the particle's complex amplitude data. During the eight observation flights, the number and mass concentrations of dust were 1.2 ± 1.0 cm⁻³ and 0.6 ± 0.4 μg m⁻³ (mean ± 1σ), respectively, in the 0.3–2.5 μm diameter range, which were 2–3 orders of magnitude lower than previously reported values near the major dust sources in East Asia. A comparison with the total aerosol data from an optical particle counter onboard aircraft suggested that dust dominated aerosols larger than 0.8 μm, consistent with electron microscopy analyses. The observed dust size distributions implied more efficient removal of larger dust during transport. Since our samples were collected at −18°C to 21°C, the free tropospheric dust could contribute to ice formation in clouds. Our observation using the CAS revealed microphysical properties of dust over the western North Pacific when no distinct Asian dust events were observed near the ground, aiding in the validation of models that assess the climatic impacts of dust.

1. Black carbon (BC) particles, which are emitted by incomplete combustion of carbon-based fuels, impact the radiation budget in the Arctic and globally (AMAP 2021; Bond et al. 2013; Oshima et al. ...

The charging state of submicron particles strongly affects the number of particles deposited on the inner surface of human airways during inhalation, and an increase in this number leads to adverse effects on human health. However, the key factors controlling the charging state of particles are poorly understood because of the limited measurements of the number concentrations of charged submicron particles. In order to experimentally investigate the key factors controlling the number concentration of charged particles, the technique for accurately measuring the number concentration of non-charged particles (Nnon-charge) was improved based on a system consisting of optical particle counters and a parallel-plate particle separator to which a high voltage (1.0–1.5 kV) was applied. The ratio of the Nnon-charge to the total number concentration of particles (Ntotal), with diameters 0.3–0.5 μm, was used as a metric of the number fraction of non-charged particles. A decrease in the Nnon-charge/Ntotal ratio with an increase in the negative ion concentration (nion−) and the nion−/Ntotal ratio under stable meteorological conditions showed an increase in the number of charged particles by collisions between aerosols and ions. Under fluctuating humidity conditions, the Nnon-charge/Ntotal ratio also decreased with an increase in the nion− and the nion−/Ntotal ratio. Particularly, the decrease rate in the Nnon-charge/Ntotal ratio was greater at higher nion− and nion−/Ntotal ratio values than that under stable meteorological conditions. This suggests that the generation of water vapor drives an increase in ion concentration, leading to frequent collisions between excessive negative ions and aerosols. A quantitative understanding of the changes in the number fraction of charged particles with increasing humidity and nion− can assist in estimating the number of particles deposited on the inner surface of human airways.