Kazuhiko Miura

Application of lidar depolarization measurement in the atmospheric boundary layer: Effects of dust and sea‐salt particles

We intensively observed the atmospheric boundary layer with a polarization lidar, a Sun photometer, and a high-volume sampler at a coastal area of Tokyo Bay. The purpose of the observation is to investigate a phenomenon discovered in the past summer: relatively high depolarization ratio events (≃ 10% at peak) in the lower atmosphere associated with sea breeze. From the chemical analyses of the simultaneously sampled aerosols, we found that the depolarization ratio might be related to crystallized sea salt and dust particles. A boundary structure was clearly revealed by the depolarization ratio in the lower atmosphere, which might correspond to the mixed layer (the internal boundary layer) or the sea breeze in which crystallized sea salt and/or dust particles were diffused. We also presented the first numerical calculation on the depolarization ratio of the cubic particles to apply crystallized sea-salt (NaCI) particles by the dipole discrete approximation (DDA) method: the calculation yields 8-22% of depolarization ratio for the effective size larger than 0.8 μm at the investigated wavelength (532 nm).

Variation of concentration of ambient aerosols in Tokyo

Abstract The number concentration of aerosol particles dispersed in the urban atmosphere was measured at Kagurazaka in central Tokyo from January 1980 to December 1987. Aitken particle number concentrations were measured with a Pollak condensation nuclei counter and a diffusion battery. The characteristic radius was deduced, using the DeMarcus equation, from the measured concentrations. Mie particle number concentrations ranging from 0.055 to 2.5 μm in radius were measured with two optical particle counters. Slope and intercept of the Junge distribution were calculated for particles > 0.15 μ m. The main results are as follows. 1. (1) For these 8 yr, there are no long-term trends in the particle number concentrations, characteristic radius, and slope and intercept of the Junge distribution. 2. (2) Aitken particle number concentrations show regular seasonal variations, with a maximum during winter and a minimum during summer. They also show regular diurnal variations, with an increase during daytime and a minimum in the early morning. Detailed discussions suggest that these variations are affected by anthropogenic sources and meteorological conditions. 3. (3) Mie particle number concentrations show neither a clear seasonal nor diurnal variation. The variations are strongly dependent on meteorological conditions. Our careful analysis shows that wind speed is most important of the meteorological elements. Mie particle number concentrations decrease as wind speed increases, often by as much as two-thirds. This effect was observed for all wind directions.

Observation of aerosols in the planetary boundary layer by using kytoon on R/V MIRAI

It is important to know aerosol composition profile in the lower troposphere for the process study of aerosol transport from continental to the remote ocean. There is no data of marine aerosol composition profile in the the planetary boundary layer (PBL), however there are a few data in the free troposphere (FT) by aircraft. In this work, we report the observed results of aerosol profile in the PBL by using kytoon system over the ocean.