Kanji Takahashi

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.

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.]

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.

Source contribution of atmospheric aerosols in Japan by chemical mass balance method

Abstract The seasonal variation and regional features of source contributions to atmospheric particulates in Japan were investigated using a Chemical Mass Balance (CMB) method. The elemental concentrations of aerosol particles measured at the nine different National Air Surveillance Network from April 1977 to March 1985 were used in this study. Variations of estimated source contributions were also discussed for various analytical conditions regarding the types of release source and chemical species employed in the CMB analysis. When elements other than indicator elements of the assumed source types were added in the analysis by the CMB method, the contributions of some of source types were strongly affected. Soil source contribution was most significant among the five assumed sources at every site and was elevated in spring every year. On the other hand, the contributions of anthropogenic sources had peaks in early winter.

Electrical charging of aerosol particles by bipolar ions in flow type charging vessels

Abstract The process of charging aerosol particles in a flow type electrical charger is investigated theoretically and experimentally, and the conditions necessary for attaining Boltzmann charge equilibrium are examined. The relationship between the strength of the source of ions and the critical retention time in the charger is found in terms of particle concentration by number and particle size. For normal charging the ion concentration should exceed 107 ion pairs/cm3.

The temperature dependence of nucleation of sulfuric acid-water mixture in air

The temperature dependence of the nucleation rate of H2SO4-H2O vapor mixture is calculated using the Reiss-Doyle method. A large dependence of nucleation rate on temperature is shown when the absolute vapor pressures are kept constant for the mixture, while the dependence is slight if the relative vapor pressures are kept constant. A suggestion is made that apparent nucleation in a smog chamber may differ from that in a cloud chamber. The saturated vapor pressure of sulfuric acid is also discussed, comparing the theoretical results with experimental data on aerosol formation rate by photochemical oxidation of sulfur dioxide.

Estimation of size distribution of small aerosol particles by light-scattering measurement

The size distributions of very small aerosol particles (0.5 < α < 1.9) were determined by means of polarization ratio and/or dissymmetry factor measurements. The values of the polarization ratio and dissymmetry factor were calculated for various size distributions assuming a logarithmic normal distribution. The experiments were performed with linoleic acid, triphenylphosphate (TPP), and stearic acid aerosols, and the estimated values of geometric mean size and standard deviation were confirmed with the values obtained from electronmicroscopic observations.

Morphological and dynamic characterization of Pb fume particles undergoing Brownian coagulation

Morphological changes of Pb fume particles undergoing Brownian coagulation in a flowing system were studied using computer image processing of two-dimensional electron micrographs to measure radii of gyration and perimeters. From these two parameters; (1) fractal dimensions were calculated considering the aggregates as multifractal; changes in fractal dimension were related to the degree of agglomeration; (2) volume equivalent diameters were calculated based on a new relationship between volume and projected area for fractal aggregates, presented in Appendix A. The validity of this equation was confirmed for aggregates composed of small numbers of primary particles (n < 30); and (3) dynamic shape factors were calculated and comparison was made with a new relationship between shape factor and volume equivalent diameter presented in Appendix B.

A method of determining aerosol particle size distribution applying Boltzmann's law

Abstract An experimental evaluation was conducted on a method for determination of submicron aerosol particle size distribution. The method utilizes prediction curves based on Boltzmanns charge distribution law and measurements of particle number concentration related to the electrical mobility. The measurements of metallic fumes showed fair agreement with the prediction curves of size distribution. The curves were derived from direct electron microscopic observation of the fumes. For lead fume, the measurement falls within a range of ± 10 per cent of the prediction curve.

Occlusion of retinal vessels using targeted delivery of a platelet aggregating agent.

Local laser targeted delivery of a platelet aggregating agent to occlude retinal and choroidal vessels was evaluated in rabbits and rats. Liposomes containing adenosine diphosphate (ADP) were administered intravenously and an argon laser was used to lyse the liposomes in main retinal arteries. Control vessels were treated with the same energy of laser without administering ADP. Fluorescein angiography performed 2 weeks later showed that all the control vessels were perfused. Ninety percent of the ADP-treated arteries showed complete or partial occlusion. Successful occlusion increased with the laser energy and decreased with increasing vessel diameter. Histopathology showed that occlusion was achieved in retinal as well as choroidal vessels. The inner retina remained relatively unaffected at the treatment site but the outer retina was thermally damaged. These preliminary results suggest that targeted delivery of a platelet aggregating agent holds promise for occluding vessels in the fundus.