JP3961244B2 - Method and apparatus for measuring suspended particulate matter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for measuring the particle size distribution of airborne particulate matter present in the atmosphere, and more particularly, to measure the particle size distribution of airborne particulate matter over a wide particle size range with high resolution. The present invention relates to a method and apparatus for measuring suspended particulate matter.
[0002]
[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.
[0003]
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 system 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.
[0004]
[Problems to be solved by the invention]
By the way, in the measuring device based on the cascade impactor method used for the measurement of SPM and PM2.5, there is a problem that the upper limit value of the particle size is limited to about 10 μm in principle, and the particle size In other words, the particle size distribution cannot be measured with high resolution.
[0005]
The present invention has been made in view of such a situation, and the particle size distribution of the suspended particulate matter (SPM) and the fine particulate matter (PM2.5) in the atmosphere is wider than the particle size including 10 μm or more. An object of the present invention is to provide a measurement method and apparatus for suspended particulate matter that can be measured with high resolution in a range.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the method for measuring suspended particulate matter of the present invention is a method for measuring suspended particulate matter contained in the atmosphere, wherein the atmosphere is sucked by a pump and supplied to a filter. In addition to collecting and collecting suspended particulate matter in the atmosphere on the filter, laser light is absorbed in the filter so that the suspended particulate matter adheres to the filter and optically transparent. It is characterized by measuring the spatial intensity distribution of the diffracted / scattered light obtained by irradiating and determining the particle size distribution of the suspended particulate matter from the measurement result (claim 1).
[0007]
Moreover, the suspended particulate matter measuring device of the present invention is a device for measuring suspended particulate matter contained in the atmosphere using the above-described method of the present invention, in order to attach the suspended particulate matter in the atmosphere. A filter for sucking the atmosphere and supplying it to the filter, a holding means for holding the liquid soaked in a filter to which suspended particulate matter has adhered by the supply of the atmosphere and holding it transparent, and the holding means Irradiation optical system for irradiating laser light to the held filter, measurement optical system for measuring spatial intensity distribution of diffracted / scattered light due to suspended particulate matter adhering to the laser light filter, and It is characterized by comprising a calculation means for calculating the particle size distribution of the suspended particulate matter adhering to the filter from the measured spatial intensity distribution of the diffracted / scattered light. .
[0008]
Here, the pump referred to in each of the above claims refers to an air machine capable of sucking and feeding the atmosphere and specifically a compressor or a blower.
[0009]
In the present invention, the filter for adhering the suspended particulate matter and the liquid for optically transparentizing the filter are preferably a membrane filter and an immersion oil having a refractive index substantially equal to that of the membrane filter. Can be adopted.
[0010]
The present invention utilizes the particle size distribution measurement based on the laser diffraction / scattering method capable of measuring the particle size distribution with high resolution in a wide particle size range for measuring the particle size distribution of suspended particulate matter in the atmosphere. At the same time, in order to obtain sufficient intensity of diffracted / scattered light at the time of laser beam irradiation, the suspended particulate matter is not directly irradiated to the suspended particulate matter in the atmosphere. A substance is efficiently collected and attached by a filter, and an intended purpose is achieved by irradiating a laser beam in a state where the filter is optically transparent using a liquid.
[0011]
In other words, a laser diffraction / scattering particle size distribution analyzer generally measures the spatial intensity distribution of diffracted / scattered light obtained by irradiating a group of particles in a dispersed state with laser light, and the light intensity. Using the fact that the distribution conforms to Mie's scattering theory or Fraunhofer's diffraction theory, the particle size of the particle group to be measured is calculated from the measurement result of the spatial intensity distribution of the diffracted / scattered light by calculation based on Mie's scattering theory or Fraunhofer's diffraction theory. Find the distribution. According to the laser diffraction / scattering type particle size distribution measuring apparatus, the particle size distribution can be obtained with high resolution in a wide particle size range by dispersing the particles to be measured in the medium in an appropriate concentration range. That is, if the concentration is too low, the spatial intensity distribution of the diffracted / scattered light cannot be measured accurately, and if the concentration is too high, multiple scattering or the like occurs and the accurate spatial intensity distribution cannot be measured.
[0012]
Here, even if it is intended to measure the diffraction / scattered light by directly irradiating the suspended particulate matter in the atmosphere with laser light, the concentration distribution of the suspended particulate matter in the atmosphere is too low. Sufficient diffracted / scattered light cannot be obtained.
[0013]
Therefore, in the present invention, the air is sucked with a pump and supplied to the filter, so that the suspended particulate matter contained in the atmosphere is attached to the filter and collected, and the suspended particulate matter is attached. The diffracted / scattered light is measured by irradiating the filter with a laser beam in an optically transparent state using a liquid. By setting the density of suspended particulate matter adhering to the filter to a range that allows accurate measurement of the spatial intensity distribution of laser diffraction / scattered light, wide particles equivalent to normal laser diffraction / scattering type particle size distribution measurement In the diameter range, that is, in a wide particle diameter range from the submicron order to over 10 μm, the particle size distribution of the suspended particulate matter can be obtained with high resolution.
[0014]
Also, in the present invention, air is sucked with a pump and supplied to the filter, so that the suspended particulate matter contained in the air is attached to the filter and collected. The amount of air supplied to the filter over time can be easily grasped, and by selecting the filter appropriately, airborne particulate matter supplied from the pump can be collected almost without leakage. Therefore, it is possible to easily determine the amount of suspended particulate matter existing in a certain amount of air for each particle diameter.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an embodiment of the present invention, and is a diagram illustrating a schematic diagram showing an optical configuration and a mechanical configuration, and a block diagram showing an electrical configuration.
[0016]
The filter 1 is a membrane filter having a submicron pore diameter in this example, and is held inside a filter holding member 2 including a base body 21 and a lid 22 that is detachably attached to the base body 21. The inside of the holding member 2 is partitioned up and down. The base 21 and the lid 22 of the filter holding member 2 have a funnel-like shape including large diameter portions 21 a and 22 a for holding the filter 1 and small diameter openings 21 b and 22 b, respectively. The part 21b communicates with the suction port of the pump (collecting compressor) 3, and the opening 22b of the lid 22 is opened to the atmosphere to form an air inlet.
[0017]
In the above configuration, when the pump 3 is driven, the air is sucked into the filter holding member 2 through the opening 22b, and after passing through the filter 1, is sucked into the suction port of the pump 3 through the opening 21b. . At this time, when the suspended particulate matter P existing in the atmosphere passes through the filter 1 using a membrane filter having a pore size of submicron order, almost the entire amount adheres and is collected.
[0018]
The filter 1 to which an appropriate amount of suspended particulate matter P adheres is taken out from the filter holding member 2 and impregnated with immersion oil having the same refractive index as that of the filter 1, thereby making the filter 1 transparent.
[0019]
The filter 1 to which the suspended particulate matter P adheres and is made transparent is held by a filter holder 40 including, for example, two transparent glass plates 41a and 41b and a support member 42, and laser diffraction is performed. -It is used for the measurement of the diffraction / scattered light of the scattering type particle size distribution measuring apparatus 50. That is, the filter 1 to which the suspended particulate matter P adheres and is made transparent by the immersion of immersion oil is sandwiched between the two glass plates 41a and 41b, and the whole is along the vertical direction. As described above, the laser beam is supported by the support tool 42 and disposed at the measurement position of the laser diffraction / scattering particle size distribution measuring apparatus 50 that is irradiated with laser light from the horizontal direction.
[0020]
The laser diffraction / scattering particle size distribution measuring apparatus 50 includes an irradiation optical system 51 that irradiates a laser beam along a horizontal optical axis to the filter 1 held by the filter holder 40 along the vertical direction, Sampled by a measurement optical system 52 that measures the spatial intensity distribution of the diffracted / scattered light of the laser light from the irradiation optical system 51, a data sampling circuit 53 that samples the output of the measurement optical system 52, and the data sampling circuit 53. The computer 54 is mainly configured to calculate the particle size distribution of the suspended particulate matter P adhering to the filter 1 using the spatial intensity distribution data of the diffracted / scattered light.
[0021]
The irradiation optical system 51 includes a laser light source 51a, a condenser lens 51b, a spatial filter 51c, and a collimator lens 51d. The laser light output from the laser light source 51a is held in the filter holder 40 as a parallel light beam, and is transparent. The irradiated filter 1 is irradiated. The laser light applied to the filter 1 is diffracted and scattered by the suspended particulate matter P adhering to the transparent filter 1. The spatial intensity distribution of the diffracted / scattered light is measured by the measurement optical system 52.
[0022]
The measurement optical system 52 includes a condensing lens 52a and a ring detector 52b disposed on the optical axis of the irradiation optical system 51 with the filter 1 interposed therebetween, a front wide angle scattered light sensor group 52c disposed on the outer side, a filter The side / backscattered light sensor group 52d is disposed on the side 1 and rear (irradiation optical system 51 side). The ring detector 52b is a photosensor array in which photosensors having ring-shaped, half-ring, or quarter-ring-shaped light receiving surfaces with different radii are arranged concentrically, and is condensed by a condenser lens 52a. The intensity distribution of the diffracted / scattered light within a predetermined forward angle can be detected. Therefore, the spatial intensity distribution of the diffracted / scattered light by the suspended particulate matter P adhering to the filter 1 is measured in a wide range from the front minute angle to the rear by the measurement optical system 52 including these sensor groups. .
[0023]
The light intensity detection signal for each diffraction / scattering angle by the measurement optical system 52 is amplified by the data sampling circuit 53 having the respective amplifiers and AD converters, digitized, and then diffracted / diffracted. It is taken into the computer 54 as spatial intensity distribution data of the scattered light.
[0024]
The computer 54 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 P that is the cause particle that has been scattered is calculated.
[0025]
In the above configuration, the total amount of air supplied to the filter 1 can be grasped from the flow rate per unit time of the pump 3 and its driving time, and the total amount of air supplied to the filter 1 can be set appropriately. The density of the suspended particulate matter P adhering to the filter 1 can be set to such an extent that the spatial intensity distribution of the diffracted / scattered light can be sufficiently measured by the measurement optical system 52.
[0026]
According to the measurement of the particle size distribution by the laser diffraction / scattering type particle size distribution measuring device 50, the particle size distribution can be measured with high resolution in a wide particle size range from submicron order to over 10 μm.
[0027]
In addition, as described above, a predetermined amount of air is supplied to the filter 1 to attach the suspended particulate matter P to the filter 1, and the attached filter 1 is made transparent with immersion oil or the like and irradiated with laser light. After measuring the spatial intensity distribution of the diffracted / scattered light to determine the particle size distribution and discarding the filter 1, or simultaneously, setting a new filter 1 on the filter holding member 2 and applying the filter 1 to the filter 1 in the same manner as described above. If the operation of supplying atmospheric air, attaching suspended particulate matter P, making it transparent and measuring the spatial intensity distribution of the next diffracted / scattered light at regular intervals is repeated, In addition, the state of the suspended particulate matter P can be monitored.
[0028]
Furthermore, if the total amount of air supplied to the filter 1 in each measurement operation is constant, the absolute intensity of diffracted / scattered light obtained in each measurement correlates with the concentration of suspended particulate matter P in the atmosphere. The change with time of the concentration of the suspended particulate matter P in the atmosphere can be monitored from the change in the absolute intensity.
[0029]
Furthermore, if calibration is performed using standard particles with a known number of particles adhering to the unit area of the filter 1, the total amount of air supplied to the filter 1 at the time of actual measurement and the laser light applied to the filter 1. The relationship between the particle size distribution of the suspended particulate matter P contained in the unit volume of the atmosphere and the number of particles of each particle size from the spatial intensity distribution of the diffracted / scattered light obtained by irradiating You can also.
[0030]
Note that the structure of the filter holding member 2 that holds the filter 1 when supplying the air to the filter 1 to attach the suspended particulate matter P is not limited to that used in the above embodiment, Any structure can be used as long as the sucked air can be completely guided to the filter 1.
[0031]
Moreover, in the above embodiment, while using a membrane filter as the filter 1 and an example in which immersion oil is used to make the filter 1 transparent, the present invention is not limited to this. Any filter can be used as long as it can attach particles exceeding 10 μm from the submicron order and can be made transparent with an appropriate liquid.
[0032]
【The invention's effect】
As described above, according to the present invention, the air is supplied to the filter by the pump, the suspended particulate matter contained in the atmosphere is attached to the filter, and the filter to which the suspended particulate matter is attached is provided. By irradiating laser light in a transparent state with a liquid, the spatial intensity distribution of diffracted / scattered light due to suspended particulate matter adhering to the filter is measured, and the laser diffraction / scattering particle size distribution measurement is performed from the measurement results. Since the particle size distribution of the suspended particulate matter is obtained based on the principle of the particle size, it is possible to greatly improve the particle size resolution as compared with the measurement of the particle size distribution by the conventional cascade impactor, and at the same time, the particle size of 10 μm or more. A range of particle size distributions can now be measured.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an embodiment of the present invention, and is a diagram illustrating a schematic diagram showing an optical configuration and a mechanical configuration, and a block diagram showing an electrical configuration.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Filter 2 Filter holding member 21 Base body 22 Cover body 21a, 22a Large diameter part 21b, 22b Opening part 3 Pump 40 Filter holder 41a, 41b Glass plate 42 Support material 50 Laser diffraction and scattering type particle size distribution measuring apparatus 51 Irradiation optical system 52 Measurement Optical System 53 Data Sampling Circuit 54 Computer P Suspended Particulate Matter

Claims (2)

  A method for measuring suspended particulate matter contained in the atmosphere, by sucking the atmosphere with a pump and supplying it to a filter, thereby attaching the suspended particulate matter in the atmosphere to the filter and collecting it. Measure the spatial intensity distribution of the diffracted / scattered light obtained by irradiating the filter with a liquid particle so that the filter is infiltrated with liquid and optically transparent. A method for measuring suspended particulate matter, comprising obtaining a particle size distribution of suspended particulate matter from the result.   A device for measuring suspended particulate matter contained in the atmosphere, a filter for adhering suspended particulate matter in the atmosphere, a pump for sucking the atmosphere and supplying it to the filter, and floating by supplying the atmosphere A holding means for infiltrating a liquid into a filter to which particulate matter is adhered and holding the filter in a transparent state, an irradiation optical system for irradiating the filter held by the holding means with laser light, and the laser light Measurement optical system for measuring the spatial intensity distribution of diffracted / scattered light due to suspended particulate matter adhering to the filter, and suspended particulate matter adhering to the filter from the measured spatial intensity distribution of diffracted / scattered light An apparatus for measuring suspended particulate matter, comprising a computing means for calculating the particle size distribution of the particles.

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