Mikio Kasahara

Characteristics of single particles sampled in Japan during the Asian dust}storm period

Abstract To investigate the characteristics of Asian dust storm particles as single particles in Japan, we measured morphology, composition and concentration of single particles using Scanning Electron Microscope (SEM) coupled with an energy dispersive X-ray microanalyzer (EDX), particle induced X-ray emission (PIXE) and micro-PIXE. Particles were sampled in Kyoto, Japan from the middle of April to the end of July 1999. Mass concentration in Asian dust–storm events was roughly 3–5 times higher than that of the highest concentration measured in non-Asian dust storm seasons. Single particles were generally sharp-edged and irregular in shape and contained mostly crustal elements such as Si, Fe, Ca and Al. Particles which have more than 40% Si content comprised nearly 50% of coarse single particles in Asian dust storm events. Main concentration range of Al in single Asian dust storm particles was 10–20%, and those of Ca and Fe were below 10%. Even though S and Cl in soils of the desert and loess areas in northwest of China were not detected, significant concentration of S and Cl in coarse fraction in Asian dust storm event were detected in single particles. Especially, the maximum concentration of S in Asian dust storm event was about 5 times higher than that in non-Asian dust storm days. Every single particle in coarse fraction existed as the mixing state of soil components and S. Good agreement between the results of SEM–EDX analysis and that of micro-PIXE analysis was obtained in this study.

Wavelength‐dependent aerosol single‐scattering albedo: Measurements and model calculations for a coastal site near the Sea of Japan during ACE‐Asia

Wavelength-dependent optical properties together with the size-resolved elemental and chemical composition of the atmospheric aerosol were measured at Yasaka, Japan, near Wakasa Bay on the coast of the Sea of Japan. Observations were performed as part of the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) campaign during three weeks in March and April 2001. Information about the detailed chemical composition and the size distribution of the aerosol, including absorbing material, was used to model optical properties of the aerosol and compare them with directly measured properties. Continuous, size-resolved measurements of aerosol scattering and backscattering coefficients were made at wavelengths of 450, 550, and 700 nm. Aerosol size distribution measurements were taken three times during the campaign for a period of 3-4 days each, using cascade impactors. One of the measurement periods was influenced by an intense yellow dust event originating on the Asian continent (20-25 March 2001), while the other two data sets were only weakly influenced by dust particles. The size-resolved measurement of aerosol scattering coefficients and the chemical analysis showed that the dust was accompanied by fine accumulation-mode particles during the dust event. The effects of the mineral dust particles on the optical and chemical properties of the aerosol are discussed, and data sets with and without desert dust influence are compared. Before the optical closure calculation a mass closure of the aerosol was performed, and the influence of the nonanalyzed fraction on the calculated optical properties of the aerosol is investigated. In general, good agreement between measured and modeled aerosol optical properties was found for the aerosol scattering and absorption coefficients, while less agreement was found for the backscattering coefficients, especially for the coarse mode of the aerosol. A distinct difference between the dust and nondust periods was found for the wavelength-dependent single-scattering albedo.

A kinetic model of sulfuric acid aerosol formation from photochemical oxidation of sulfur dioxide vapor

Abstract Sulfur dioxide vapor in air is photo-oxidized by u.v. irradiation in sunlight to form sulfuric acid aerosol. The nucleation rate for a system of water and sulfuric acid vapor was calculated at various relative humidities according to Reisss theory. Taking the concentration of sulfuric acid vapor and particles into account, a kinetic model for each component was proposed. Some calculated examples were shown as a function of photo-oxidation rate of sulfur dioxide to sulfuric acid and of relative humidity.

Life-cycle analysis of charging infrastructure for electric vehicles

Life-cycle analysis of a charging station for electric vehicles (EVs) was performed in the three phases, that is, production, transportation and installation of the charging equipment, which consists of charger, battery and stand. We chose parking lots on expressways, commercial parking lots in cities, municipal facilities, shopping centers, etc. throughout the country as the charging sites according to the EV charge program in Southern California. Air-pollutant emissions during the transportation phase were calculated based on the emission factors of vehicles, running speed and the transport distance between one factory of the charging equipment and each site. The share of transporting the charging machines in total emissions of CO2, SOx and CO was less than 15% and the production phase was dominant. In case of NOx, the share of transporting them was over 20%. The relation between gasoline vehicle and gas station was applied to estimate the number of EVs using the charging stations through the country, and the contribution of the charging stations to life-cycle emissions of air pollutants from EV was presented. The share of infrastructure in total emissions of CO2 was 16% in our model case. Thus the development of the charging infrastructure almost did not change the advantage of EV compared to gasoline vehicle (GV) in terms of CO2, NOx, and CO emissions. But an EV emits more life-cycle SOx than gasoline vehicles (GVs).

A local optical closure experiment in Vienna

Abstract In a campaign in Vienna, the horizontal extinction over the central part of Vienna, the size dependent light absorption, and the mass size distribution have been measured and a size resolved PIXE analysis has been performed. PIXE did not give a complete chemical analysis; therefore the chemical compounds and the amount of nitrogen and organic carbon had to be guessed. The extinction coefficient has been determined by Mie calculation using the measured size distribution, density and refractive index from the chemical compounds. The closure was successful and a linear relationship between measured and calculated extinction coefficient was found, with the measured extinction coefficient about 20% higher than the calculated one. The Angstrom exponent was also compared, the averages agreed but the measured values were more variable than the calculated ones. A sensitivity analysis shows that the accuracy of the determination of the optical properties of the aerosol is governed by the accuracies of all input parameters and the generally unknown state of mixing. This leads to uncertainties of the optical parameters of at least ±20%. The accumulation mode makes a considerable contribution to the extinction coefficient; therefore knowledge of the size distribution, mass density and refractive index is critical. Lack of information in the coarse mode or the nucleation mode is less critical. Usually extinction coefficients are not measured on a routine basis, instead they are calculated using available aerosol data such as size distributions obtained from models, and densities and refractive indices obtained from chemical analyses or models. In that case larger uncertainties are to be expected.

Characterization of the winter atmospheric aerosols in Kyoto and Seoul using PIXE, EAS and IC

Abstract Characteristics of atmospheric aerosols in Kyoto, Japan and Seoul, Korea were investigated using particle-induced X-ray emission (PIXE), elemental analysis system (EAS) and ion chromatograph (IC). Atmospheric aerosols were collected into fine and coarse fractions using a two-stage filter pack sampler in Kyoto and Seoul in winter of 1998. PIXE was applied to analyze the middle and heavy elements with atomic number greater than 14 (Si), and EAS was applied to analyze the light elements such as H, C and N. The total mass concentration in Seoul was about two times higher than in Kyoto and the concentration of Ca, Si, and Ti that are mainly originated from soil were remarkably higher in Seoul. During an Asian dust storm event, the concentration of soil components increased dramatically and amounted to about 15 times higher than average concentration. The fine/coarse ratios of NH4+, NO3−, and SO42− were extremely high in both sites. The fact that nearly 70% of fine particles in both Kyoto and Seoul consist of the light elements (N, C, and H) suggests the importance of light elements measurement. Good mass closure for fine particles with light element data was achieved.

A theoretical study of the equilibrium particle size distribution of aerosols

Changes in the size distribution of small aerosol particles were computed for nineteen cases with various initial size distributions, patterns of particle generation, and mechanisms of particle aging. It was proven that, for the majority of the cases, the equilibrium size distribution for the larger particle sizes may be expressed as n (v) = Cv−β, and that the self-preserving function may also be expressed in the same form, [n (v) is the number concentration of particles of volume v.]

Effects of electric vehicles (EV) on environmental loads with consideration of regional differences of electric power generation and charging characteristic of EV users in Japan

In order to evaluate the reduction effect of electric vehicles (EVs) on various atmospheric environmental loads, we have performed a life-cycle inventory analysis (LCI), including the installation of charging stations and regional, seasonal and temporal difference of the energy mix of electricity generation. For an EV converted from a small gasoline vehicle, a regional LCI analysis was carried out in the following steps: (1) location of the charging stations, (2) modeling of charging characteristics of station users, (3) calculation of temporal life-cycle emission intensities of CO2, NOx and SOx by region, season and day. Assuming that total traveling distance is 100,000 km, the electricity consumption rate is 0.119 kWh/km and the charging/discharging efficiency is 70%, the average life-cycle emission of CO2 for that EV was 3.6 t-C throughout Japan. However, if we took regional difference into account, the emission ranged over 70-160% of the average amount. It was revealed that the regional difference of the primary energy mix significantly affected the emissions of EVs during the operation phase.

Standard samples and calibration of PIXE analysis

Abstract Standard samples were prepared by the vacuum evaporation method to calibrate the PIXE analysis. The sensitivities for each standard element were determined experimentally first using the standard samples and then the sensitivities for other than standard elements were determined theoretically based on the experimental results. It is confirmed that the high purity carbon plate was useful as the backing for PIXE standard samples and that the single element samples prepared in this study can be effectively applied to the PIXE calibration.

Experimental studies on aerosol particle formation by sulfur dioxide

The formation and growth of aerosol particles of dilute sulfuric acid produced by photochemical oxidation of SO2 (0.05–10 ppm. by volume) in purified air has been studied qualitatively in laboratory apparatus. The number of particles formed is strongly dependent on SO2 concentration, relative humidity (< 10–80%) and u.v. light intensity. The number concentration increases rapidly to a maximum within a few minutes after the start of irradiation and then decreases slowly during the next 10 min. Particle size increases with irradiation time and is dependent on SO2 concentration, and on relative humidity when the SO2 concentration is less than 0.1 ppm. In the conditions employed the volumetric rate of formation of particles ranged from 0.15 to 18.7μm3 cm−3. The overall quantum yield of photochemical reaction was 8 × 10−3. The oxidation rate was 0.04% h−1: extrapolation of this rate to noonday sunlight in summer at latitude 35°N gives 0.7% h−1.