JP3758603B2 - Device for collecting suspended particulate matter in the atmosphere - Google Patents

Description

BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for collecting suspended particulate matter existing in the atmosphere, and is suitable for use in measuring the particle size distribution of suspended particulate matter using, for example, a laser diffraction / scattering particle size distribution measuring apparatus. It relates to a collection device.
[Prior art]
Of the dust suspended in the atmosphere, those having a particle size of 10 μm or less are called suspended particulate matter (SPM). This suspended particulate matter includes rolled-up soil, etc., but black smoke, unburned fuel, sulfur compounds, etc., emitted by diesel cars account for a lot (35% is from diesel cars in Kanto). Is said to be more harmful. Particulate matter caused by exhaust gas from this diesel vehicle is particularly referred to as DEP. In addition, those having a smaller particle diameter of 2.5 μm or less are referred to as microparticulate substances (PM2.5), and research and research are actively conducted in the West. In the case of this PM2.5, it is said that the ratio of exhaust gas from diesel vehicles becomes higher.
The shape of such suspended particulate matter (SPM) or microparticulate matter (PM2.5) in the atmosphere is examined with a microscope, or chemical analysis is performed to identify chemical substances contained therein. However, it is necessary to collect these particulate substances from the atmosphere, and conventionally, a method of collecting these particulate substances from the atmosphere using a filter has been adopted.
In addition, as a device for measuring the particle size distribution of suspended particulate matter (SPM) and fine particulate matter (PM2.5) in the atmosphere as described above, a device based on the cascade impactor method has been put into practical use. This measuring device based on the cascade impactor system uses an impactor method in which particles are separated from the fluid by causing the fluid to collide with the collecting plate and abruptly changing the flow direction. The impactors with different diameters are connected in series in multiple stages, and the particle diameter of 50% collection efficiency at each stage is used as the representative diameter of each stage. The particle size distribution is obtained.
[Problems to be solved by the invention]
By the way, it is very difficult to extract SPM and PM2.5 with a microscope or to collect them with a filter so as to be used for various chemical analysis instruments. In doing so, the suspended particulate matter adhering to the filter is observed, but in that case, there is a problem that the image of the particle becomes unclear in the background filter image, and is difficult to observe. In addition, even when the collected suspended particulate matter is used in various chemical analysis instruments, it is difficult to extract the suspended particulate matter alone from the filter. In this case, for example, in an X-ray fluorescence spectrometer, it is difficult to irradiate only the particles with X-rays, and there is a problem that the analysis becomes substantially impossible.
In addition, in the conventional method of collecting by attaching to a filter, there is also a problem that it is difficult to store the collected suspended particulate matter without changing the initial state.
Furthermore, in the conventional measuring apparatus based on the cascade impactor system used for measuring the particle size distribution of suspended particulate matter, there is a problem that the upper limit value of the particle size is limited to about 10 μm in principle. In addition, since the resolution of the particle size is determined by the number of collecting plates, there is a disadvantage that it is not possible to measure the particle size distribution with high resolution.
As an effective method for measuring the particle size distribution of suspended particulate matter, there is a method using a laser diffraction / scattering particle size distribution measuring apparatus. This laser diffraction / scattering particle size distribution measuring device measures the spatial intensity distribution of diffracted / scattered light obtained by irradiating laser beams to a group of particles in a dispersed flight state. By utilizing the diffraction theory of Fraunhofer, the particle size distribution of the group of particles to be measured is obtained from the measurement result of the spatial intensity distribution of the diffracted / scattered light. The particle size distribution can be determined. However, in order to obtain the particle size distribution of suspended particulate matter using this laser diffraction / scattering type particle size distribution measuring device, it is necessary to collect suspended particulate matter that is the group of particles to be measured and to make it dispersed. The conventional method of collecting suspended particulate matter using a filter has a problem that it is extremely difficult to separate the suspended particulate matter from the filter and disperse it in a liquid medium or the like.
The present invention has been made in view of such circumstances, and can efficiently collect suspended particulate matter in the atmosphere, and can store the collected suspended particulate matter as it is. It is easy and can be observed very easily with a microscope, or individual particles can be easily taken out for analysis by an analytical instrument, etc., and further easy to measure with a laser diffraction / scattering particle size distribution analyzer The purpose is to provide a collection device that can be used for
[Means for Solving the Problems]
In order to achieve the above object, the airborne particulate matter trapping device of the present invention is a device for collecting airborne particulate matter in the air, and includes a collecting container and the inside of the collecting container. And a discharge electrode which is disposed in a collection container and generates monopolar ions to charge floating particulate matter in the container, and a potential difference is given to the discharge electrode. It has a dust collection electrode that attracts and collects suspended particulate matter charged in the collection container, and this dust collection electrode has a transparent member with a recess formed on the surface and a transparent coated at least on the bottom surface of the recess It is characterized by being comprised by the electrode film.
In the present invention, suspended particulate matter in the atmosphere is charged, and the charged suspended particulate matter is provided with a concave portion on the surface of a transparent member such as a glass plate or a transparent plastic plate, and a transparent electrode is provided on the bottom surface of the concave portion. The intended purpose is achieved by collecting the coated dust collecting electrode using a potential difference.
That is, in the configuration of the present invention, when the atmosphere is sucked into the collection container by a pump and the unipolar ions are generated by the discharge electrode disposed in the collection container, the suspended particulates contained in the atmosphere Material is charged. This charged floating particulate matter moves toward the dust collecting electrode where a potential difference is given to the discharge electrode in the collecting container, and is collected on the dust collecting electrode. As the dust collecting electrode, a concave part is formed on the surface of the transparent member, and at least the bottom surface of the concave part is coated with the transparent electrode film, so that the charged suspended particulate matter is captured on the transparent electrode film in the concave part. Be collected.
Since the suspended particulate matter is collected in the recess, the collected suspended particulate matter can be easily preserved in the original attached state by, for example, covering the recessed portion with a lid. Moreover, since the dust collecting electrode is a transparent member, it can be easily observed with a microscope while attached to the dust collecting electrode, and furthermore, suspended particulate matter can be easily taken out. It is easy to use for analysis or for particle size distribution measurement by a laser diffraction / scattering type particle size distribution measuring apparatus.
When measuring the particle size distribution of suspended particulate matter using a laser diffraction / scattering type particle size distribution measuring device, prior to measuring the spatial intensity distribution of diffracted / scattered light by the collected suspended particulate matter, The standard particles dispersed in can be sealed in the concave portion of the dust collecting electrode, and the apparatus can be adjusted, and the difference in the particle size distribution measurement result due to the shape of the dust collecting electrode can be eliminated.
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing a configuration of an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view showing a detailed structure of the dust collecting electrode 4.
A collection container 1 having an openable / closable lid 1 is formed with an air inlet 1b and a communication port 1c communicating with a suction port of a pump (collecting compressor) 2. The lid 1a is closed. By driving the pump 2 in this state, the atmosphere is sucked into the collection container 1 through the inlet 1b.
In the collection container 1, a discharge electrode 3 is provided at the upper part thereof, and a dust collection electrode 4 is disposed at the lower part thereof so as to face the discharge electrode 3. A high voltage from the high-voltage power supply 5 is applied to the discharge electrode 3, whereby the air in the vicinity of the discharge electrode 3 is ionized and unipolar ions are generated.
On the other hand, as shown in FIG. 2, the dust collecting electrode 4 has a structure in which a concave portion 41a is formed on one surface of a transparent glass plate 4a and a transparent electrode film 4b is formed on a bottom surface 41b of the concave portion 41a. . In the collection container 1, the surface on the formation side of the recess 41 a is disposed so as to face the discharge electrode 3 and face upward, and the transparent electrode film 4 b is connected to the ground potential 6. As a material of the transparent electrode film 4b, a known conductive material such as ITO or SnO ₂ can be used. Further, instead of the glass plate 4a, a transparent plastic such as an acrylic resin plate can be used. Further, the plate of the dust collecting electrode may be formed with a recess by bonding one flat plate and another plate with holes cut out.
In the above configuration, when a high voltage is applied to the discharge electrode 3 while driving the pump 2, the unipolar ions generated by ionizing the surrounding air are collected on the dust collection electrode 4 side by the potential difference with the transparent electrode film 4b. In the process, it is brought into contact with the suspended particulate matter P in the atmosphere sucked into the collection container 1 and charged. The charged suspended particulate matter P is also collected in a state of being randomly dispersed on the transparent electrode film 4b, that is, on the bottom surface 41b of the concave portion 41a of the dust collecting electrode 4 due to the potential difference between the discharge electrode 3 and the transparent electrode film 4b. It will be done. Even if a large amount of charged floating particulate matter P is collected, the transparent electrode film 4b is installed, so that the suspended particulate matter P is maintained while maintaining high efficiency without lowering the collection efficiency. Can be collected.
Since the suspended particulate matter P collected as described above is attached to the transparent electrode film 4b in the concave portion 41a of the dust collecting electrode 4, individual particles can be easily taken out and subjected to various analyzes. It can be easily used for analysis using an instrument or the like. Further, since the dust collecting electrode 4 is transparent, it can be directly used for observation with a microscope to obtain a clear particle image. Further, as shown in a cross-sectional view in FIG. 3, a lid 42 covering the recess 41 a is prepared, and the suspended particulate matter P is collected, and then the lid 42 is covered with the lid 41 a by the lid 42. The particulate matter P can be stored without contact.
In addition, the suspended particulate matter P collected as described above can be obtained easily and with high resolution over a wide particle size range by using the following laser diffraction / scattering particle size distribution measuring device. Distribution can be measured.
FIG. 4 is a diagram showing an apparatus configuration example for measuring the particle size distribution, and is a diagram showing a schematic diagram showing an optical configuration and a block diagram showing an electrical configuration.
The laser diffraction / scattering particle size distribution measuring apparatus 20 includes an irradiation optical system 21 that irradiates a laser beam parallel to a group of particles to be measured, and measurement optics that measures the spatial intensity distribution of diffracted / scattered light by the group of particles to be measured. Using the system 22, the data sampling circuit 23 that samples the output of the measurement optical system 22, and the spatial intensity distribution data of the diffracted / scattered light sampled by the data sampling circuit 23, the particle size distribution of the group of particles to be measured is determined. The computer 24 to be calculated is mainly configured.
The suspended particulate matter P collected in the concave portion 41a of the dust collecting electrode 4 by the collecting device shown in FIG. 1 remains attached to the transparent electrode film 4b in the concave portion 41a, and the irradiation optics. Between the system 21 and the measurement optical system 22, it is arranged upright so as to be orthogonal to the optical axis.
The irradiation optical system 21 includes a laser light source 21a, a condensing lens 22b, a spatial filter 22c, and a collimating lens 23d. The laser light output from the laser light source 21a is attached to the transparent electrode film 4b of the dust collecting electrode 4 as a parallel light beam. The suspended particulate matter P is irradiated. The laser light applied to the dust collection electrode 4 is diffracted and scattered by the suspended particulate matter P adhering to the transparent electrode film 4b. The spatial intensity distribution of the diffracted / scattered light is measured by the measurement optical system 22.
The measurement optical system 22 is disposed on the side and back of the dust collecting electrode 4 (on the irradiation optical system 21 side), and the front wide-angle scattered light sensor group 22c disposed on the outside of the condenser lens 22a and the ring detector 22b. The side / backscattered light sensor group 22d is configured. The ring detector 22b is a photosensor array in which photosensors having ring-shaped, ½-ring or ¼-ring-shaped light receiving surfaces with different radii are arranged concentrically, and condensed by a condenser lens 22a. The spatial intensity distribution of the diffracted / scattered light within the predetermined forward angle can be detected. Therefore, the spatial intensity distribution of the diffracted / scattered light by the suspended particulate matter P that is randomly dispersed and attached to the transparent electrode film 4b by the measurement optical system 22 composed of these sensor groups is changed from the front minute angle to the rear. Measured over a wide range.
The light intensity detection signal for each diffraction / scattering angle by the measurement optical system 22 is amplified by the data sampling circuit 23 having the respective amplifiers and AD converters, digitized, It is taken into the computer 24 as spatial intensity distribution data of scattered light.
The computer 24 uses the spatial intensity distribution of the diffracted / scattered light to diffract the laser light by a calculation method based on Mie's scattering theory and Fraunhofer's diffraction theory known in laser diffraction / scattering type particle size distribution measurement. The particle size distribution of the suspended particulate matter that is the cause particle that has been scattered is calculated.
According to the particle size distribution measurement by the laser diffraction / scattering type particle size distribution measuring device 20, the particle size distribution can be measured with high resolution in a wide particle size range from submicron order to over 10 μm. By measuring the amount of suspended particulate matter P in such a manner that sufficient diffraction / scattered light intensity can be obtained, the particle size distribution of suspended particulate matter P in the atmosphere can be measured with high accuracy in a short time. it can.
Here, in order to obtain an accurate particle size distribution as described above by the laser diffraction / scattering particle size distribution measuring apparatus 20, it is necessary to adjust the apparatus. This adjustment measures the spatial intensity distribution of the diffracted / scattered light by irradiating a laser beam with standard particles of known particle size dispersed under the same conditions as when measuring the particle group to be measured. There is a need to. The dust collecting electrode 4 in the above-described embodiment of the present invention has a structure in which the concave portion 41a is formed in the transparent member and the suspended particulate matter P, which is a group of particles to be measured, is attached to the bottom surface of the concave portion 41a and collected. Therefore, the standard particles can be dispersed in a liquid medium such as water and sealed in the recess 41a, and laser light can be irradiated. This makes it possible to make adjustments using the same collection electrode 4 that is used to collect the suspended particulate matter P and to measure the spatial intensity distribution of diffracted / scattered light. An accurate particle size distribution can be obtained by eliminating the difference in the measurement result of the resulting particle size distribution.
The coating region of the dust collecting electrode 4 by the transparent electrode film 4b may be an arbitrary region including the bottom surface 41b in addition to the bottom surface 41b of the recess 41a as described above, but only the bottom surface 41b is coated with the transparent electrode film 4b. This is preferable in that the suspended particulate matter P can be concentrated and collected in the recess 41a, and the surface density of the collected suspended particulate matter P can be increased.
【The invention's effect】
As described above, according to the present invention, the suspended particulate matter in the atmosphere is charged to form a recess on the surface of the transparent member, and is captured on the dust collecting electrode coated with the transparent electrode film on the bottom surface of the recess. Since it is collected, it can be used for observation with a microscope as it is, and a clear particle image can be obtained, and individual particles can be easily taken out for analysis, etc. Further, an appropriate lid is put on. Thus, the collected suspended particulate matter can be stored without contact.
Using a laser diffraction / scattering particle size distribution measurement device, the particle size distribution is measured by directly irradiating a dust collecting electrode that collects suspended particulate matter with laser light and measuring the diffraction / scattered light. It is possible to measure the particle size distribution with high resolution in a wider particle size range than the conventional method under extremely simple work. Since it is possible to adjust the apparatus by dispersing standard particles in a liquid medium and enclosing them, there is also an advantage that the difference due to the shape of the dust collecting electrode (sample holding member) can be eliminated.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the configuration of an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view showing a detailed structure of a dust collecting electrode 4 in the embodiment of the present invention.
FIG. 3 is an explanatory diagram of an example of a method for preserving the suspended particulate matter P collected by the dust collecting electrode 4 in the embodiment of the present invention.
FIG. 4 shows an apparatus configuration example in the case where the particle size distribution of the suspended particulate matter P collected by the dust collecting electrode 4 in the embodiment of the present invention is measured using a laser diffraction / scattering type particle size distribution measuring apparatus. In the figure, a schematic diagram showing an optical configuration and a block diagram showing an electrical configuration are shown together.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Collection container 2 Pump 3 Discharge electrode 4 Dust collection electrode 4a Glass plate 41a Recess 41b Bottom surface 4b Transparent electrode film 5 High voltage power source 6 Ground potential 20 Laser diffraction / scattering type particle size distribution measuring device 21 Irradiation optical system 22 Measurement optical system 23 Data Sampling circuit 24 computer P suspended particulate matter

Claims (1)

An apparatus for collecting suspended particulate matter in the atmosphere, which is disposed in a collection container, a pump for sucking air in the collection container, and in the collection container to generate unipolar ions and A discharge electrode for charging the suspended particulate matter in the container, and a dust collection electrode for attracting and collecting the suspended particulate matter charged in the collection container by applying a potential difference to the discharge electrode. The dust collecting electrode is composed of a transparent member having a concave portion formed on a surface thereof and a transparent electrode film coated at least on the bottom surface of the concave portion.

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