JP2003042932A - Method and instrument for measuring suspended particulate matter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a particulate size distribution of a suspended particulate matter(SPM) or a microfine particulate matter (PM2.5) in the atmosphere, over a wide particulate size range, including 10 μm or larger for particulate size, at a high resolution. SOLUTION: The atmospheric air is sucked by a pump 3 to be supplied to a filter 1, the suspended particulate matter P in the atmosphere is deposited thereby on the filter 1, the spatial intensity distribution of diffracted/scattered light provided by being irradiated with a laser beam is measured under the condition, of the filter 1 being deposited with the suspended particulate matter P brought into a transparent state by a liquid, and the particle size distribution of the suspended particulate matter P is found, based on a measured result therein. The density of the suspended particulate matter P on the filter 1 is brought to a degree, capable of adopting a laser diffraction/scattering type particle size distribution measurement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the particle size distribution of suspended particulate matter existing in the atmosphere, and more particularly, to a method for measuring the particle size distribution of suspended particulate matter with high resolution over a wide particle size range. The present invention relates to a method and apparatus for measuring suspended particulate matter that can be originally measured.

[0002]

2. Description of the Related Art Among dust particles floating 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, but black smoke, unburned fuel, and sulfur compounds emitted by diesel vehicles account for a large proportion (35% in the Kanto region are from diesel vehicles). Is said to be more harmful. The particulate matter caused by the exhaust gas from this diesel vehicle is especially called DEP. Further, particles having a particle size of 2.5 μm or less, which are smaller, are called fine particulate matter (PM2.5), and investigations and studies have become popular in Europe and America. In the case of PM2.5, it is said that the cause of the emission is a higher proportion of exhaust gas from diesel vehicles.

Suspended particulate matter (S
As a device for measuring the particle size distribution of PM and fine particulate matter (PM2.5), a device based on the cascade impactor system has been put into practical use. The measuring device based on the cascade impactor method uses an impactor method in which particles are separated from a fluid by colliding the fluid with a collecting plate to suddenly change the flow direction thereof.
Measuring the amount of trapping in each stage by connecting in series multiple impactors with varying particle size of% trapping efficiency in series and using the particle size of 50% trapping efficiency in each stage as the representative diameter of each stage. The particle size distribution in the fluid is determined from the results.

[0004]

By the way, SPM and P
In the measuring device based on the cascade impactor method used for the measurement of M2.5, there is a problem that the upper limit of the particle size measurement is limited to about 10 μm and the resolution of the particle size is trapped. Since it depends on the number of collecting plates, it is not possible to measure the particle size distribution with high resolution.

The present invention has been made in view of the above circumstances, and the particle size distribution of suspended particulate matter (SPM) and fine particulate matter (PM2.5) in the atmosphere is more than that including a particle diameter of 10 μm or more. It is an object of the present invention to provide a method and apparatus for measuring suspended particulate matter that can be measured with a high resolution in a wide particle size range.

[0006]

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 pumped. By aspirating and supplying it to the filter, airborne particulate matter in the atmosphere is attached to and collected by the filter, and for the filter to which the airborne particulate matter is attached, the filter is optically used with a liquid. In the transparent state, the spatial intensity distribution of the diffracted / scattered light obtained by irradiating the laser beam is measured, and the particle size distribution of the suspended particulate matter is obtained from the measurement result (claim 1).

The airborne particulate matter measuring apparatus of the present invention is an apparatus for measuring airborne particulate matter contained in the atmosphere using the above-described method of the present invention. A filter for adhering, a pump for sucking the air and supplying it to the filter, a holding means for holding the filter to which the suspended particulate matter adheres by the air supply in a transparent state using a liquid, and the holding thereof An irradiation optical system for irradiating the filter held by the means with laser light, and a measurement optical system for measuring the spatial intensity distribution of the diffracted / scattered light by the suspended particulate matter adhering to the filter of the laser light , Characterized in that it comprises a computing 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. Section 2).

Here, the pump referred to in each of the above claims refers to an air machine capable of sucking air and sending it by pressure, and more specifically, it is a compressor or a blower.

Further, in the present invention, the filter to which the suspended particulate matter is attached and the liquid for optically making the filter transparent are a membrane filter and an immersion oil having a refractive index substantially equal to that of the membrane filter. Can be suitably adopted.

The present invention uses a particle size distribution measurement based on a laser diffraction / scattering method capable of measuring a particle size distribution with a high resolution in a wide particle size range, and a particle size distribution measurement of suspended particulate matter in the atmosphere. In addition to irradiating directly to the suspended particulate matter in the atmosphere with laser light in order to obtain diffracted / scattered light of sufficient intensity when irradiating with laser light, Achieving the intended purpose by efficiently collecting and adhering suspended particulate matter with a filter and irradiating laser light in a state where the filter is optically transparent using a liquid Is.

That is, in the laser diffraction / scattering type particle size distribution measuring apparatus, generally, the spatial intensity distribution of the diffracted / scattered light obtained by irradiating the measured particle group in the dispersed state with laser light is measured. By utilizing that the light intensity distribution is based on Mie's scattering theory or Fraunhofer's diffraction theory, the measured particles can be calculated from the measurement results of the spatial intensity distribution of diffracted / scattered light by Mie's scattering theory or Fraunhofer's diffraction theory. Determine the particle size distribution of the group. According to this 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 measured particle group 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 accurately measured, and if the concentration is too high, multiple scattering occurs and the spatial intensity distribution cannot be accurately measured.

Here, even if an attempt is made to measure the diffracted / scattered light by directly irradiating the suspended particulate matter in the atmosphere with a laser beam, the particle size distribution is considered because the concentration of the suspended particulate matter in the atmosphere is too low. It is not possible to obtain enough diffracted and scattered light to obtain

Therefore, in the present invention, the atmospheric air is sucked by the 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 collected. Diffracted / scattered light is measured by irradiating laser light on a filter to which a substance is attached and making it optically transparent with a liquid. By setting the density of suspended particulate matter adhering to the filter to a range that allows accurate measurement of the laser diffraction / scattered light spatial intensity distribution,
Wide particle diameter range equivalent to that of ordinary laser diffraction / scattering particle size distribution measurement, that is, from submicron order to 10 μm
It is possible to obtain the particle size distribution of suspended particulate matter with a high resolution in a wide particle size range exceeding the above.

Further, in the present invention, since the air is sucked by the pump and supplied to the filter, the suspended particulate matter contained in the air is adhered to and collected by the filter. The amount of atmospheric air supplied to the filter can be easily grasped by the driving time and its driving time, and by selecting the filter appropriately, suspended particulate matter in the atmospheric air supplied from the pump can be collected with almost no leakage. Therefore, it is possible to easily determine the amount of suspended particulate matter existing in the atmosphere for each particle size.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an embodiment of the present invention, and is a diagram in which a schematic diagram showing an optical configuration and a mechanical configuration and a block diagram showing an electrical configuration are shown together.

The filter 1 is a membrane filter having a submicron pore size in this example, and is held inside a filter holding member 2 comprising a base 21 and a lid 22 which is detachable from the base 21. The inside of the filter holding member 2 is partitioned vertically. The base 21 and the lid 22 of the filter holding member 2 have large diameter portions 21a and 22a for holding the filter 1 and a small diameter opening portion 2 respectively.
It has a funnel-like shape with 1b and 22b, the opening 21b of the base 21 communicates with the suction port of the pump (compression compressor) 3, and the opening 22b of the lid 22 has It is open to the atmosphere and forms an inlet for the atmosphere.

In the above structure, when the pump 3 is driven, the atmosphere is sucked into the inside of the filter holding member 2 through the opening 22b, and after passing through the filter 1, the opening 21 is opened.
It is sucked into the suction port of the pump 3 via b. At this time,
The suspended particulate matter P existing in the atmosphere is almost entirely adhered and collected when passing through the filter 1 using a membrane filter having a pore size of submicron order.

The filter 1 to which an appropriate amount of the suspended particulate matter P is attached is taken out from the filter holding member 2 and impregnated with immersion oil having the same refractive index as the filter 1, whereby the filter 1 is made transparent. It

The filter 1 to which the suspended particulate matter P is attached and which is made transparent is, for example, two transparent glass plates 41.
Filter holder 4 comprising a and 41b and its supporting member 42
In the state of being held by 0, the laser diffraction / scattering type particle size distribution measuring device 50 is used to measure the diffracted / scattered light. That is, the filter 1 in which the suspended particulate matter P is attached and which is made transparent by the immersion of the immersion oil is
A laser diffraction / scattering particle size distribution in which a glass plate 41a, 41b is sandwiched between two glass plates 41a and 41b, and the whole is supported by a support tool 42 along a vertical direction and is irradiated with laser light from a horizontal direction. It is arranged at the measurement position of the measuring device 50.

Laser diffraction / scattering type particle size distribution measuring device 50
Is an irradiation optical system 51 for irradiating the filter 1 held by the filter holder 40 along the vertical direction with laser light along a horizontal optical axis, and the irradiation optical system 51.
Measuring optical system 52 for measuring the spatial intensity distribution of the diffracted / scattered light of the laser light from the device, a data sampling circuit 53 for sampling the output of the measured optical system 52, and a diffracted / scattered sampled by 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 light.

The irradiation optical system 51 is composed of a laser light source 51a, a condenser lens 51b, a spatial filter 51c, and a collimator lens 51d, and the laser light output from the laser light source 51a is held by the filter holder 40 as a parallel light beam. At the same time, the transparent filter 1 is irradiated.
The laser light applied to the filter 1 is diffracted and scattered by the suspended particulate matter P attached to the transparentized filter 1. The spatial intensity distribution of the diffracted / scattered light is measured by the measurement optical system 52.

The measurement optical system 52 includes a condenser lens 52a and a ring detector 52b arranged on the optical axis of the irradiation optical system 51 with the filter 1 interposed therebetween, and a front wide-angle scattered light sensor group 52c arranged outside thereof. And a side / back scattered light sensor group 52d arranged on the side and the rear of the filter 1 (on the side of the irradiation optical system 51). The ring detector 52b is an optical sensor array in which optical sensors having ring-shaped, ½ ring-shaped, or ¼ ring-shaped light-receiving surfaces having different radii are concentrically arranged, and are condensed by a condenser lens 52a. It is possible to detect the intensity distribution of the diffracted / scattered light within the predetermined front angle. Therefore, the measurement optical system 52 including these sensor groups
Thus, the spatial intensity distribution of the diffracted / scattered light by the suspended particulate matter P attached to the filter 1 is measured in a wide range from the front minute angle to the rear side.

The light intensity detection signal for each diffraction / scattering angle by the above measurement optical system 52 is a data sampling circuit 53 having respective amplifiers and AD converters.
Is amplified, digitized, and taken into the computer 54 as spatial intensity distribution data of diffracted / scattered light.

The computer 54 uses the spatial intensity distribution of the diffracted / scattered light to calculate the laser light by a calculation method based on Mie's scattering theory and Fraunhofer's diffraction theory, which are known in the laser diffraction / scattering type particle size distribution measurement. The particle size distribution of the suspended particulate matter P, which is the causative particle that was diffracted and scattered, is calculated.

In the above structure, the total amount of the air supplied to the filter 1 can be grasped from the flow rate of the pump 3 per unit time and its driving time, and the total amount of the air supplied to the filter 1 can be set appropriately. By doing so, the density of the suspended particulate matter P adhering to the filter 1 can be set to such an extent that the measurement optical system 52 can sufficiently measure the spatial intensity distribution of the diffracted / scattered light.

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 a high resolution in a wide particle size range from the submicron order to over 10 μm.

Further, 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 to emit laser light. After irradiating, measuring the spatial intensity distribution of the diffracted / scattered light to obtain the particle size distribution and discarding the filter 1, or at the same time, a new filter 1 is set on the filter holding member 2 and the filter 1 is set in the same manner as above. If the operation of supplying the atmosphere to the filter 1 to attach the suspended particulate matter P to make it transparent and then measuring the spatial intensity distribution of the diffracted / scattered light next time is repeated at regular intervals, Moreover, it is possible to monitor the state of the suspended particulate matter P in the atmosphere.

Further, the filter 1 is used in each measurement operation.
Assuming that the total amount of the atmosphere supplied to the air is constant, the absolute intensity of the diffracted / scattered light obtained in each measurement is correlated with the concentration of the suspended particulate matter P in the atmosphere. It is possible to monitor the time-dependent change in the concentration of the suspended particulate matter P.

Furthermore, if calibration is performed using standard particles of which the number adhered to the filter 1 per unit area is known, the total amount of the atmosphere supplied to the filter 1 during the actual measurement and the filter 1 From the spatial intensity distribution of the diffracted / scattered light obtained by irradiating the laser beam on the above, 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 It can also be calculated.

The structure of the filter holding member 2 that holds the filter 1 when the air is supplied to the filter 1 to attach the suspended particulate matter P is limited to that used in the above-described embodiments. Any structure having an arbitrary structure can be used as long as it can guide the sucked air to the filter 1 completely.

Further, in the above-described embodiments, the example in which the membrane filter is used as the filter 1 and the immersion oil is used to make the filter 1 transparent is shown, but the present invention is not limited to this. Any filter can be used as long as it can adhere particles of submicron order to more than 10 μm and can be made transparent with an appropriate liquid.

[0032]

As described above, according to the present invention, the air is supplied to the filter by the pump, and the suspended particulate matter contained in the atmosphere is adhered to the filter. By irradiating laser light with the filter that has adhered to it made transparent by the liquid, the spatial intensity distribution of the diffracted / scattered light by the suspended particulate matter adhering to the filter is measured, and the laser diffraction /
Since the particle size distribution of suspended particulate matter is obtained based on the principle of scattering type particle size distribution measurement, it is possible to significantly improve the particle size resolution compared to the conventional particle size distribution measurement using a cascade impactor. It has become possible to measure the particle size distribution in the particle size range of 10 μm or more.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, in which a schematic diagram showing an optical configuration and a mechanical configuration and a block diagram showing an electrical configuration are shown together.

[Explanation of symbols]

1 filter 2 Filter holding member 21 Base 22 Lid 21a, 22a Large diameter part 21b, 22b openings 3 pumps 40 filter holder 41a, 41b glass plate 42 Support material 50 Laser Diffraction / Scattering Particle Size Analyzer 51 Irradiation optical system 52 Measurement optical system 53 Data sampling circuit 54 Computer P Suspended particulate matter

Claims (2)

[Claims] 1. A method for measuring airborne particulate matter contained in the atmosphere, wherein air is sucked by a pump and supplied to a filter so that airborne airborne particulate matter is adhered to the filter and trapped. Measure the spatial intensity distribution of the diffracted / scattered light obtained by irradiating laser light on the filter to which the suspended particulate matter adheres, while the filter is optically transparent using a liquid Then, the particle size distribution of the suspended particulate matter is obtained from the measurement result, and the suspended particulate matter is measured. 2. An apparatus for measuring suspended particulate matter contained in the atmosphere, comprising: a filter for adhering suspended particulate matter in the atmosphere; and a pump for sucking the atmosphere and supplying it to the filter. Holding means for holding the filter to which the suspended particulate matter is attached by the supply of the air in a transparent state using a liquid, and an irradiation optical system for irradiating the filter held by the holding means with a laser beam, A measurement optical system that measures the spatial intensity distribution of the diffracted / scattered light by the suspended particulate matter attached to the laser light filter,
An apparatus for measuring suspended particulate matter, comprising an arithmetic means for calculating a particle size distribution of suspended particulate matter adhering to a filter from the measured spatial intensity distribution of diffracted / scattered light.