A new analytical system to determine the size distribution of atmospheric aerosols, which includes optical constant, was developed and applied to the measurement of the size distribution of mist and ambient aerosols. The scattered light was measured with a bistatic lidar system using an 8 wavelength laser beam as the light sources at a 179 degree scattering angle. The particle size distributions of those two types of atmospheric aerosols were estimated using the singular value decomposition (SVD) from the scattered light. The method successfully retrieved the size distribution in the case of mist for which the imaginary part of refractive index was set at 0.001 rather than 0.0 and the wavelength dependence of the real part was included. The size distribution of the mist was inverted to the log-normal distribution, and the size distribution of the ambient aerosol particle to the Junge distribution, when the real part of refractive index was fixed at 1.5 and the imaginary part at 0.001 or 0.0. This method was able to discriminate the size distributions of mist and ambient aerosols.
This study proposes a statistical leakage testing method for HEPA and ULPA filters used in cleanrooms. The method consists of two parts, scanning test and stationary re-measuring test. For scanning test, a high-speed and accurate method is proposed considering the influences of particles penetrating through the normal portion of filter and the discreteness of particle measuring. For stationary re-measuring test, a method to minimize the number of data is proposed by using Wald's theory. The validity of this method is investigated by Monte-Carlo simulation, and the influence of variance of parameters which is assumed to vary, is examined. It is concluded that the variance of probe scan speed and upstream particle concentration have a strong influence on the results of scanning test. It is also concluded that we can obtain stable and accurate result in stationary re-measuring, and it is indicated that by using this method a big hole can be readily ditected as a leakage point.
Number concentrations of airborne asbestos fibers in work space and in the atmosphere are usually measured by visual counting with PCM (Phase Contrast Microscope). Since counting process of the PCM Method requires skill and much labor, the counts obtained by this method significantly vary from facility to facility and therefore the reliability is limited. In this paper, cross-check of the counting values among seven counting facilities was performed to obtain the basic information for the improvement of reliability of counting value. Seven counting facilities, one a university laboratory which is developing AFACS (Asbestos Fibers Automatic Counting System), one local self-governing body, one foundation and four private companies were involved in this study. The aim of this cross-check is to elucidate the variation in the judgement of individual asbestos fibers among the counting facilities. The results are; (1) The ratio of the maximum counts to the minimum was about 5. (2) The maximum value of the coefficients of concurrence between two arbitrary counting facilities was 50.2%. Even if their counting values were similar, the counted asbestos fibers were different from facility to facility. (3) Visual counting facilities had a tendency to overestimate fiber diameter, which resulted in underestimation of counting value. (4) Counting value with the AFACS was the medium of those measured by six visual counting facilities.
An optical analog computing system which can discriminate shapes and/or sizes of small objects by a Multiplexed Matched Spatial Filter (MMSF) has been developed. The system discriminates the shapes and/or sizes of particles instantaneously and simultaneously. The optical analog computing system is composed of three parts; (1) catching particle images, (2) discriminating the shapes and/or sizes and (3) displaying auto-correlation signals as the spatial distributions of particles. The MMSF of holographic filter is made by a new process in which holograms are made automatically and instantaneously with a photo-conductor plastic plate processed by solvent vapor. Spatial distributions of particles are visualized according to the shape and/or size by the optical analog computing system.
Effects of internal geometry and operating conditions on the aerosol flow pattern in a differential mobility analyzer (DMA) were numerically investigated. The internal three-dimensional structure of a Cluster-DMA (Okuyama et al., J. Aerosol Res., Jpn., 13, 83 (1998)) was employed to simulate the complex flow patterns in the DMA, including the swirling flow that develops near the aerosol inlet slit. The predicted aerosol flow in the DMA was affected by the width of inlet slit and the flow rate of sheath-air. The calculated results agreed with previous experimental results obtained by the flow visualization, in which the aerosol fed into the DMA was unevenly distributed along the circumference of the inlet slit when the slit width and the flow rate were large. The calculation also suggested that the nonuniform radial distribution of the aerosol near the inlet slit also affects the entire classification region of the DMA.
To accelerate measurement of particle size distributions by a differential mobility classifier (DMA) with a condensation nuclei counter (CNC), a computer-controlled rapid stepping mode was developed as an operation method. The rod voltage of DMA was varied stepwise every 6 seconds to select particles with a given mobility. Thirty aerosol concentrations were measured within 200seconds. Our system showed a 12 second time-delay between voltage shift and aerosol concentration response. After adjustment of the time-delay, the size distribution ranging from 0.014 to 0.373 μm was determined by a stepping mode analysis (Adachi, 1990). For polystyrene latex aerosol and sodium chloride aerosol, the size distributions measured with the rapid stepping mode agreed with those measured by the ordinary stepping mode.
Ultrafine powders with diameters less than 100 nm were dispersed into air by a boiling method proposed by one of the present authors, and their size distributions were measured by the differential mobility analyzer (DMA) combined with condensation nucleus counter (CNC). The size distributions were compared with those measured by electron microscope and dynamic light scattering method. It was found that the present method can disperse ultrafine powders into their primary particles, which has been thought to be very difficult in air.
Air pollution and acid precipitation in China, especially in southwestern China, are directly related to coal utilization. Since coal with a high sulfur content is burned in combustion equipment, such as medium or small boilers and domestic stoves, the impact of pollution on both vegetation and people's health has become serious in Chongqing city. A part of our study on controlling acid rain in Chongqing area is described in this paper. The experimental results showed that the effectiveness of sulfur fixation by Ca-based materials is in the order of Ca(OH)2 >CaO>CaCO3. The optimum temperature for sulfur fixation was 800 °C because CaSO4 was a stable final product. Further, bio-briquettes were made of raw coal, biomass and slaked lime simply by compression. The bio-briquette gave a significant reduction in SO2 emission, compared to the raw coal. The measurements overall indicated that the sulfur fixation effectiveness of bio-briquette is better than that of raw coal with a reduced emission to about 85-95%. The influences of combustion conditions on sulfur fixation were also discussed in the paper. The results of this study will play an important role in reducing SO2 emission and mitigating acid precipitation in Chongqing area.
Ca and Mg contents in 41 kinds of soil samples in China were measured and the regional distributions of Ca and Mg contents in the soil are presented as contour maps in this paper. The Ca and Mg contents in the soil samples are discussed in relation to the chemical components, the acid-buffering ability (ΔCb) of the atmospheric aerosol, and the acidification of precipitation. The contents of Ca and Mg decreased gradually from the north to the south and from the west to the east. The Ca content ranged from 0.01 to 16.3% with the average of 1.54%, and Mg varied from 0.2 to 4.0% with the average of 0.78%. The acid-buffering ability of aerosol in Northern China was 375∼1,710 neq/m3, which was much higher than -92.8∼71.3 neq/m3 in Southern China. Generally, acid rain has been observed in Southern China but not in Northern china. The regional distributions of acid- buffering ability of atmospheric aerosol and the acidity of precipitation coincided with the distribution of Ca and Mg contents in the soil. These results indicated that there are strong relationships among the Ca and Mg contents in soil, the acid-buffering ability of atmospheric aerosol and the acidification of precipitation in China.