Method and apparatus for measuring the number concentration of particulate matter

Abstract

This invention provides a measurement method and apparatus that can reduce the cost of developing equipment for measuring the number concentration of fine particles using the diffusion charging method. [Solution] The method for measuring the number concentration of particulate matter involves measuring the number concentration of particulate matter in a gas by the diffusion charging method. The method for measuring the number concentration of particulate matter involves alternately introducing the gas containing particulate matter, which has been ionized by corona discharge and onto which generated ions adhere to the particulate matter, and the air that has passed through the filter 6 into the Faraday cage 11, and measuring the induced current generated to determine the number concentration.

Description

Technical Field

[0001] The present invention relates to a technique for measuring the number concentration of particulate matter contained in a gas such as exhaust gas of an automobile.

Background Art

[0002] For the measurement of the number concentration of inhalable particles (small particles that can reach the alveoli scattered in the working environment) and diesel exhaust particles, etc., a condensation particle counter (abbreviated as "CPC") or a measuring device using the diffusion charging method is used.

[0003] CPC is a method in which fine particles are passed through the saturated vapor of a water or alcohol working fluid and rapidly cooled to form a supersaturated atmosphere, and the working fluid vapor is condensed and grown around the fine particles to coarsen them into droplet particles and optically detected. It is widely used in the above-mentioned measurements (Non-Patent Document 1).

[0004] Since CPC directly measures fine particles, it has high measurement accuracy as the number concentration. However, CPC that requires a water or alcohol working fluid is not suitable for simple measurements at sites such as vehicle inspection stations.

[0005] On the other hand, the diffusion charging method charges fine particles by passing them through ions generated by corona discharge, and calculates the number concentration of fine particles by measuring the amount of charge. For example, there is known a method in which charged fine particles are introduced into a Faraday cage by the attachment of ions generated by unipolar corona discharge, and the number concentration of fine particles is obtained from the current value flowing at that time by capturing the charged particles on a filter installed inside. In this method using a filter, it is necessary to replace the filter regularly or according to the cumulative measurement time, and since pressure loss occurs in the filter, a load is imposed on the suction pump or blower, and there are problems such as an increase in the maintenance frequency of managing and replacing the pressure loss of the filter.

[0006] To solve these problems, a method has been proposed (Non-Patent Literature 2) in which the high voltage applied to the unipolar corona discharger 71 is switched on and off at regular time intervals, causing charged and uncharged particles to alternately flow into the Faraday cage 72, thereby generating induced charge and extracting it externally as a current value (Figure 8(a)).

[0007] Furthermore, a method has been proposed in which a constant high voltage is applied in a DC corona discharger 81 to induce diffusion charging, and the charged fine particles are then switched on and off at a subsequent pulse electrostatic collector 83 to create a state where charged particles are present and absent, thereby generating induced charge and extracting it externally as a current value (Non-Patent Documents 3, 4) (Figure 8(b)).

[0008] The induced charge described above arises when charged particles flow into a space (Faraday cage) covered with a conductor, generating charges opposite to the positive and negative polarity of the charged particles within the Faraday cage 72,82. This generated charge is called space charge. The amount of space charge is induced by the time change of the charge flux (amount of charge) when charged particles flow into and out of the Faraday cage 72,82. Note that the direction of the induced charge signal during inflow and outflow is opposite in terms of the time it takes for the charge in the Faraday cage 72,82 to increase and decrease. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] U.S. Patent No. 7406855 [Non-patent literature]

[0010] [Non-Patent Document 1] ISO 27891,Aerosol number concentration-Calibration of condensation particle counters,1st ed.,2015 [Non-Patent Document 2] M.Fierz,et al.,Aerosol Measurement by Induced Currents,Aerosol Science and Technology,2014,48,350-357 [Non-Patent Document 3] MASchriefl,et al.,Characterization of particle number counters based on pulsed-mode diffusion charging,Aerosol Science and Technology,2020,54,772-789 [Non-Patent Document 4] M.Knoll,et al.,Impact of pre-charged particles on steady state and pulsed modes of unipolar diffusion chargers,Aerosol Science and Technology,2021,55,512-525 [Overview of the Initiative] [Problems that the invention aims to solve]

[0011] In order to intermittently introduce charged particles into the Faraday cages 72 and 82, the technique described in non-referenced reference 2 applies a high voltage in a pulsed manner to the unipolar corona discharger 71. In the techniques described in non-referenced references 3 and 4, a pulsed electrostatic collector 83 is provided to intermittently eliminate the charged particles.

[0012] In other words, the technology described in non-cited reference 2 uses a pulsed high-voltage device for corona discharge, and the technologies described in non-cited references 3 and 4 use a pulsed voltage generator in the electrostatic collector. In all of the particulate matter number concentration measurement methods described in these documents, a pulse drive device is required in addition to a steady-state voltage generator, and since the pulse drive device operates under high voltage of several kV (several tens to 100 mW), there is a problem that the overall equipment cost is high.

[0013] The present invention has been made in view of the above-mentioned problems, and aims to provide a measurement method and a measuring apparatus that can reduce the cost of equipment for measuring the number concentration of fine particles by the diffusion charging method. [Means for solving the problem]

[0014] The present invention provides a method for measuring the number concentration of fine particles in a gas by the diffusion charging method. The method involves alternately introducing a gas into a Faraday cage, where ions generated by ionization of the gas by corona discharge are introduced, and air that has passed through a filter is introduced. The number concentration is then determined by measuring the induced current generated.

[0015] Preferably, ions that do not adhere to the fine particles are removed from the ionized gas, which is ionized by corona discharge.

[0016] Another method for measuring the number concentration of particulate matter according to the present invention involves ionizing air that has passed through a first filter by corona discharge to generate ions, and then combining it with a gas containing particulate matter to cause the generated ions to adhere to the particulate matter. Subsequently, the combined gas, which is the mixture of air and the gas containing particulate matter, The number concentration is determined by alternately introducing air that has passed through a second filter (different from the first filter) into a Faraday cage and measuring the induced current generated.

[0017] Preferably, ions that do not adhere to particulate matter are removed from the combined gas.

[0018] The particulate matter number concentration measuring device according to the present invention is a device that measures the number concentration of particulate matter in a gas by the diffusion charging method.

[0019] The particulate matter number concentration measuring device comprises a corona discharge unit that ionizes gas containing particulate matter by corona discharge, an ion trap that removes ions generated in the corona discharge unit that do not adhere to the particulate matter, a filter through which air passes, an induction current detector, an ammeter, and a control / calculation unit equipped with a memory device.

[0020] The control and arithmetic unit alternately causes the gas passing through the ion trap and the air passing through the filter to flow into the induction current detector, and calculates the number concentration of fine particles in the gas by using the calibration data stored in the storage device based on the value of the induction current generated in the induction current detector.

[0021] Preferably, it has an automatic three-way valve, and the automatic three-way valve alternately causes the gas passing through the ion trap and the air passing through the filter to flow into the induction current detector.

[0022] Any of the other fine particle number concentration measuring devices according to the present invention includes a first filter and a second filter through which air passes, a corona discharge unit that ionizes the air passing through the first filter by corona discharge, an ion trap that removes ions that do not adhere to fine particles from the combined gas in which the air containing the ions generated in the corona discharge unit is combined with the gas containing fine particles, an induction current detector, an ammeter, and a control and arithmetic unit having a storage device.

[0023] The control and arithmetic unit alternately causes the combined gas passing through the ion trap and the air passing through the second filter to flow into the induction current detector, calculates the number concentration of fine particles in the combined gas by using the calibration data stored in the storage device based on the value of the induction current generated in the induction current detector, and calculates the number concentration of fine particles in the gas in consideration of the ratio of the gas containing fine particles in the combined gas.

[0024] Preferably, it has an automatic three-way valve, and the automatic three-way valve alternately causes the combined gas passing through the ion trap and the air passing through the second filter to flow into the induction current detector.

[0025] The ion trap included in the fine particle number concentration measuring device functions by applying a voltage between a pair of separated electrodes.

[0026] Preferably, the detection range of the ammeter is 10 -10 ~10 -15 amperes.

Advantages of the Invention

[0027] According to the present invention, it is possible to provide a measurement method and a measuring apparatus that can reduce the cost of equipment development in measuring the number concentration of fine particles by the diffusion charging method. [Brief explanation of the drawing]

[0028] [Figure 1] Figure 1 is a schematic diagram of a device for measuring the number concentration of fine particles using the diffusion charging method. [Figure 2] Figure 2 is a schematic cross-sectional view of the induced current detector 4. [Figure 3] Figure 3 is a schematic diagram of the temporal change in the current detected by the induction current detector in the number concentration measuring device. [Figure 4] Figure 4 shows the change in current over time when the gas flowing into the induction current detector contains charged particles and when it does not. [Figure 5] Figure 5 shows the amplitude of the induced current value when the number concentration of charged particles is changed. [Figure 6] Figure 6 shows the relationship between the flow rate of the gas containing charged particles flowing into the induced current detector and the amplitude of the induced current. [Figure 7] Figure 7 is a schematic diagram of another particle number concentration measuring device. [Figure 8] Figure 8 is a schematic diagram of a particle number concentration measuring device used in the conventional diffusion charging method. [Modes for carrying out the invention]

[0029] Figure 1 is a schematic diagram of the particle number concentration measuring device 1 (hereinafter sometimes abbreviated as "particle number concentration measuring device 1") using the diffusion charging method, and Figure 2 is a schematic cross-sectional view of the induced current detector 4.

[0030] The number concentration measuring device 1 consists of a DC corona discharge unit 2, an ion trap 3, an induced current detector 4, a three-way solenoid valve 5, a filter 6, an ammeter 15, and a control / calculation device, etc.

[0031] The DC corona discharge section 2 is a known corona discharge device composed of spaced needle-shaped electrodes and plate-shaped electrodes made of a porous plate or wire mesh through which generated ions can pass. A gas containing suspended particulate matter (aerosols) (hereinafter referred to as "fine particles") to be measured in number concentration, such as exhaust gas from a diesel engine, is fed into the DC corona discharge section 2. Hereinafter, "gas to be measured in number concentration" may be abbreviated as "exhaust gas," but this does not mean that the gas measured by the fine particle number concentration measuring device 1 is limited to exhaust gas.

[0032] The term "fine particles" is used in fields such as physics, chemistry, and biology, and its particle size range is not standardized across scientific disciplines. In this document, "fine particles" refers to "particles of a size that can be measured by the diffusion charging method."

[0033] The DC corona discharge section 2 is equipped with a needle-shaped electrode and a plate-shaped electrode facing it. A high voltage of several kV to more than 10 kV is applied to the needle-shaped electrode to generate a corona discharge between it and the plate-shaped electrode. This generates ion molecules themselves through the ionization of the gas. The ions generated in the DC corona discharge section 2 adhere to the surface of fine particles in the gas, causing the particles to become charged.

[0034] The ion trap 3 applies a voltage between a pair of separated electrodes, and uses electrostatic force to settle and remove only excess ions that do not adhere to the fine particles (hereinafter sometimes referred to as "free ions"), thereby eliminating the influence of free ions on the induced current.

[0035] Referring to Figure 2, the induced current detector 4 consists of a Faraday cage 11, an outer cylinder 12, and a pair of inner insulating parts 13, 13 and outer insulating parts 14, 14, respectively. The Faraday cage 11 is cylindrical in shape. The shape of the Faraday cage 11 may also be rectangular. The outer cylinder 12 is a cylinder with both ends closed, having an inner diameter larger than the outer diameter of the Faraday cage 11. The outer cylinder 12 has circular holes on both end faces that are approximately equal to the inner diameter of the Faraday cage 11. Both the Faraday cage 11 and the outer cylinder 12 are made of stainless steel, but other metals with good conductivity may also be used. Wire mesh may be provided at the inlet and outlet of the Faraday cage 11 to prevent the formation of an electric field inside the Faraday cage 11.

[0036] The Faraday cage 11 is connected to an external ammeter 15 of the induction current detector 4. The ammeter 15 is 10 -10 ~10 -15 A device capable of detecting weak currents in the ampere range (pA to fA) is used. The current value detected by the ammeter 15 is digitally converted by the control and calculation device and used to calculate the number concentration of particulate matter. Hereafter, "number concentration of particulate matter" may be abbreviated as "number concentration".

[0037] The internal insulating portion 13 is for integrating the Faraday cage 11 within the outer cylinder portion 12 while electrically insulating it from the outer cylinder portion 12. The pair of internal insulating portions 13, 13 fix the vicinity of the (axial) ends of different Faraday cages 11 within the outer cylinder portion 12 so that they do not come into contact with the vicinity of the ends of the outer cylinder portion 12, while the Faraday cage 11 is housed within the outer cylinder portion 12. A through hole approximately equal to the inner diameter of the Faraday cage 11 is provided in the center of the internal insulating portion 13, and the inside of the internal insulating portion 13 communicates with the circular hole in the outer cylinder portion 12.

[0038] The outer insulating portion 14 is for electrically insulating the flow channel material connected to the induced current detector 4 from the outer cylinder portion 12. The pair of outer insulating portions 14, 14 are circular flange-shaped, and each connects the outer cylinder portion 12 to the flow channel material on the outer surface of a different end of the outer cylinder portion 12.

[0039] For the inner insulating portion 13 and the outer insulating portion 14, for example, acetal homopolymer resin (trade name "Delrin", registered trademark) is used.

[0040] In the induced current detector 4, the outer surface of the Faraday cage 11 and the inner surface of the outer cylinder portion 12 are separated, creating a space between them. The outer cylinder portion 12 functions to block the influence of external electric fields, etc.

[0041] The three-way solenoid valve 5 is used to alternately introduce exhaust gas containing particulate matter that has passed through the ion trap 3 and particulate matter-free gas (atmosphere) that has passed through the filter 6 to the induction current detector 4. It is desirable to use a fast-response type three-way solenoid valve 5 (response time in milliseconds).

[0042] A grounded metal or antistatic tube is used in the flow path of the exhaust gas containing charged particles downstream of the DC corona discharge section 2.

[0043] Filter 6 removes particulate matter and other particles from the air taken in from the surroundings. Filter 6 uses either a HEPA filter or a ULPA filter.

[0044] The control and calculation unit digitizes the analog output of the current value measured by the ammeter 15 connected to the Faraday cage 11, and calculates the particulate matter concentration in the exhaust gas that has passed through the Faraday cage 11 from the digital data. The control and calculation unit consists of interfaces such as an A / D converter, a D / A converter, a display device and an input device, internal and external storage devices, and a calculation unit (CPU).

[0045] Although not shown in the diagram, the flow rate of the exhaust gas flowing into the DC corona discharge section 2 is measured by a flow meter, and the measured value is sent to the control and calculation unit.

[0046] Figure 3 is a schematic diagram of the temporal change in the current detected by the induced current detector 4 in the number concentration measuring device 1. In Figure 3, I is the induced current value. A characteristic of this induced current is that its polarity is opposite when charged particles flow into and out of the induced current detector 4. Furthermore, since the signal intensity is the difference between the maximum and minimum values ​​(for the two induced current values ​​I with opposite polarities), fluctuations in the base voltage when the signal is zero (when charged particles do not flow into the Faraday cage 11) do not pose a major problem in the measurement of the number concentration and can be ignored.

[0047] It is known that the induced current value I is proportional to the average charge amount Ac of the fine particles, the flow rate Q of the gas containing charged particles passing through the Faraday cage, and the number concentration N of the gaseous fine particles (Non-patent documents 3, 4, see equation (1) below).

[0048] I=e×N×Q×Ac (1) In equation (1), e is the elementary charge.

[0049] The number concentration measuring device 1 measures the number concentration of particulate matter in a gas using the relationship shown in equation (1).

[0050] Figure 4 shows the temporal change in current when the gas flowing into the induction current detector 4 contains charged particles (a) and when it does not (b).

[0051] Figure 4 shows the results obtained by introducing 35 nm ammonium sulfate particles, which were classified by a differential mobility analyzer (DMA), into the particle number concentration measuring device 1.

[0052] In Figure 4, the frequency of the induced current (vertical axis) indicates the opening and closing period of the three-way solenoid valve 5. The opening and closing (ON / OFF) period of the three-way solenoid valve 5 is 0.5 Hz (assuming an ON / OFF duty cycle of 50:50 (1 second ON - 1 second OFF)), and a current change with a 2-second period is clearly observed in the induced current. When uncharged particles are continuously introduced into the induced current detector 4 (b), only the noise signal from the ammeter 15 is observed, but it can be seen that an induced current waveform like that in (a) is generated by turning the three-way solenoid valve 5 ON / OFF.

[0053] Figure 5 shows the amplitude of the induced current when the number concentration of charged particles is changed. Figure 5 shows the results using the same 35 nm ammonium sulfate particles after classification as in Figure 4. The horizontal axis of Figure 5 represents the number concentration of fine particles measured by the CPC (condensed particle counter), and the vertical axis represents the amplitude of the induced current when the standard gas whose number concentration was measured by the CPC was introduced into the induced current detector 4.

[0054] Figure 5 shows that at particulate matter number concentrations of 18,000 particles / cubic cm or higher, the amplitude of the induced current exhibits linearity (proportional relationship) with respect to the particulate matter number concentration. This suggests that the particle number concentration measuring device 1 using the diffusion charging method may be usable in regions with high DEP particle concentrations (diesel exhaust particulate matter concentration), such as the exhaust gas of automobiles inspected at vehicle inspection stations.

[0055] On the other hand, although not shown in Figure 5, in the region of low particulate matter number concentrations of 10,000 particles / cubic cm or less, the signal strength deviates from a straight line due to the noise limit of the ammeter 15 (below the limit where the S / N ratio becomes difficult to process). This noise limit can be reduced to, for example, around 1,000 particles / cubic cm by improving the shielding of the current input section and reducing the noise generated by the circuit itself.

[0056] Figure 6 shows the relationship between the flow rate of the gas containing charged particles flowing into the induced current detector 4 and the amplitude of the induced current in the induced current detector 4. Figure 6 shows the results measured under conditions where the opening and closing period of the three-way solenoid valve 5 and the number concentration of charged particles were constant. Since the amplitude depends on the time change of the charge flux when charged particles flow into the induced current detector 4, it shows that the amplitude signal intensity increases as the flow rate increases.

[0057] In measuring the induced current using the ammeter 15 in the particle concentration measuring device 1, for example, exhaust gas from a diesel engine is introduced into the DC corona discharge section 2, and ions generated by the corona discharge are attached to fine particles. Next, the exhaust gas containing charged particles and free ions that do not attach to the fine particles is introduced into the ion trap 3 to remove the free ions from the exhaust gas.

[0058] In the particle concentration measuring device 1, the air from which particulate matter has been removed by the filter 6 is also used for particle concentration measurement.

[0059] The exhaust gas, from which free ions have been removed by the ion trap 3, and the air that has passed through the filter 6 are alternately sent to the induction current detector 4 by the operation of the three-way solenoid valve 5 controlled by the control and calculation unit. When charged particles enter the induction current detector 4, an induced current is generated, which is measured by the ammeter 15 and transmitted to the control and calculation unit, where the induced current value is calculated after A / D conversion.

[0060] The control and calculation unit measures the flow rate of exhaust gas flowing into the DC corona discharge section 2 using a flow meter, and the measured exhaust gas flow rate and the calculated induced current value are used to determine the particulate number concentration.

[0061] Figure 7 is a schematic diagram of another particulate matter number concentration measuring device 1B.

[0062] The particle concentration measuring device 1B includes a DC corona discharge unit 2, an ion trap 3, an induced current detector 4, a three-way solenoid valve 5, a filter 6, and a control / calculation unit, with the addition of a filter 6B. The DC corona discharge unit 2, ion trap 3, induced current detector 4, three-way solenoid valve 5, filter 6, and control / calculation unit in particle concentration measuring device 1B are the same as those in particle concentration measuring device 1. Filter 6B, like filter 6, is for removing particulate matter from the atmosphere.

[0063] The number concentration measuring device 1B performs corona discharge in the DC corona discharge section 2 on the atmosphere (air) that has passed through the filter 6B, rather than on the gas to be measured (hereinafter referred to as "exhaust gas"). The number concentration measuring device 1B differs from the aforementioned number concentration measuring device 1 in that the exhaust gas is sent to the ion trap 3 after it has merged with the atmosphere that has passed through the DC corona discharge section 2.

[0064] In the number concentration measuring device 1B, the flow rate of the air mixed with the exhaust gas is measured by a flow meter before or after passing through the filter 6B, and the measured value is transmitted to the control / calculation device. The flow rate of the air mixed with the exhaust gas may also be measured after passing through the filter 6B.

[0065] The exhaust gas, which has passed through the DC corona discharge section 2 and is mixed with the atmosphere, has its flow rate measured by a flow meter, and the measured flow rate is transmitted to the control and calculation unit. The three-way solenoid valve 5 in the number concentration measuring device 1B switches between the combined gas of the exhaust gas and the atmosphere that has passed through filter 6B and the atmosphere that has passed through filter 6.

[0066] In the number concentration measuring device 1B, the operation of the three-way solenoid valve 5 when measuring the number concentration of particulate matter in exhaust gas, and the process of calculating the number concentration of particulate matter in the gas that has passed through the Faraday cage 11 using calibration data from the gas flow rate passing through the induction current detector 4 and the value of the induced current generated in the Faraday cage 11, are the same as those in the number concentration measuring device 1. In the number concentration measuring device 1B, the flow rate of gas containing particulate matter flowing into the Faraday cage 11 used in the particulate matter number concentration calculation process is the sum of the flow rates of exhaust gas and the air that has passed through filter 6B.

[0067] The calculated particulate matter concentration of the gas that has passed through the Faraday cage 11 is the value after it has been diluted by the air that has passed through the filter 6B. Therefore, the effect of dilution is corrected by the flow rate of the air that has passed through the filter 6B and the flow rate of the exhaust gas, and the true particulate matter concentration in the exhaust gas can be determined.

[0068] The number concentration measuring device 1,1B does not use the pulsed high-voltage device described in non-referenced reference 2 and the pulsed voltage generator in the electrostatic collector described in non-referenced references 3,4. The gas containing pulsed charged particles can be fed to the induction current detector 4 using only the three-way solenoid valve 5. Therefore, the pulsed charged particle generator (three-way solenoid valve 5, etc.) of the number concentration measuring device 1 is less expensive than the pulsed charged particle generators described in non-referenced documents 2, 3, and 4.

[0069] In the particle concentration measuring device 1,1B, a high-speed response type (response time in milliseconds) three-way solenoid valve 5 is preferable for cost reduction, and the switching period between the gas containing charged particles and the air via the filter 6 by the three-way solenoid valve 5 is set in the range of 0.1 to 1 second. The switching period of the three-way solenoid valve 5 is preferably set to 0.2 to 0.5 Hz, which provides the most stable signal.

[0070] The ON / OFF duty cycle (ratio) of the three-way solenoid valve 5 should preferably be set to, for example, 50:50.

[0071] A pneumatic three-way valve can be used instead of a three-way solenoid valve.

[0072] Filter 6 uses a HEPA filter with a collection efficiency of 99.9% or higher for MPPS (Maximum Permeable Particle Size) particles of 0.3 μm, or a ULPA filter with a collection capacity of 0.3 μm or higher, to remove particulate matter from the atmosphere to an extent that does not affect the accuracy of measuring particulate matter number concentration.

[0073] In the embodiments described above, the individual components or overall structure, shape, dimensions, number, material, etc., of the number concentration measuring devices 1,1B and 1,1B can be appropriately modified in accordance with the spirit of the present invention. [Industrial applicability]

[0074] This invention can be used to measure the number concentration of suspended particulate matter contained in gases such as automobile exhaust gas. [Explanation of Symbols]

[0075] 1.1B Number concentration measuring device (Number concentration measuring device for fine particles) 2. DC Corona Discharge Section (Corona Discharge Section) 3 Ion trap 4. Induction Current Detector 5. Three-way solenoid valve (automatic three-way valve) 6. Filter (Second Filter) 6B filter (first filter) 11 Faraday Cage 15 Ammeter

Claims

1. A method for measuring the number concentration of particulate matter in a gas by the diffusion charging method, The gas is ionized by corona discharge, and the generated ions adhere to the fine particles. Air that has passed through the filter, The number concentration is determined by measuring the induced current generated when the particles are alternately introduced into the Faraday cage. A method for measuring the number concentration of fine particles, characterized by the following features.

2. A method for measuring the number concentration of particulate matter in a gas by the diffusion charging method, After passing air through the first filter, ionization is performed by corona discharge to generate ions, and then a gas containing the fine particles is added to the fine particles to cause the generated ions to adhere to them. The air and the gas that have merged together form a combined gas, Air that has passed through a second filter, which is different from the first filter, The number concentration is determined by alternately flowing the particles into the Faraday cage and measuring the resulting induced current. A method for measuring the number concentration of fine particles, characterized by the following features.

3. Remove ions that do not adhere to the fine particles from the gas ionized by the corona discharge. The method for measuring the number concentration of fine particles according to claim 1.

4. Remove ions from the combined gas that do not adhere to the fine particles. The method for measuring the number concentration of fine particles according to claim 2.

5. A device for measuring the number concentration of fine particles in a gas by the diffusion charging method, A corona discharge unit that ionizes the gas containing the aforementioned fine particles by corona discharge, An ion trap that removes ions generated in the corona discharge section but that do not adhere to the fine particles, A filter that allows air to pass through, Induction current detector, A control and arithmetic unit equipped with a memory device, It has, The aforementioned control and calculation device, The gas that has passed through the ion trap and the air that has passed through the filter The currents are alternately fed into the induction current detector. Based on the value of the induced current generated by the induced current detector, the memory device stores The number concentration of particulate matter in the gas is calculated using the calibration data obtained. It is configured in such a way A device for measuring the number concentration of fine particles, characterized by the following features.

6. A device for measuring the number concentration of fine particles contained in a gas by the diffusion charging method, Both consist of a first filter and a second filter that allow air to pass through, A corona discharge unit that ionizes the air that has passed through the first filter by corona discharge, An ion trap that removes ions that do not adhere to the fine particles from a combined gas formed by combining air containing ions generated in the corona discharge section with the gas containing the fine particles, Induction current detector, A control and arithmetic unit equipped with a memory device, It has, The aforementioned control and calculation device, The combined gas and the air that has passed through the second filter are alternately subjected to the induced current Let it flow into the detector, Based on the value of the induced current generated by the induced current detector, the memory device stores Using the calibration data obtained, the number concentration of particulate matter in the combined gas is calculated. The calculated particulate number concentration is used to determine which particulates are contained in the combined gas. The number concentration of particulate matter in the gas is calculated by taking into account the proportion of gas. It is configured in such a way A device for measuring the number concentration of fine particles, characterized by the following features.

7. It has an automatic three-way valve, The aforementioned automatic three-way valve The gas that has passed through the ion trap and the air that has passed through the filter are alternately The current is to flow into the aforementioned induction current detector. The particulate matter number concentration measuring device according to claim 5.

8. It has an automatic three-way valve, The aforementioned automatic three-way valve The combined gas that has passed through the ion trap and the second filter Air is alternately introduced into the induction current detector. The particulate matter number concentration measuring device according to claim 6.

9. The aforementioned ion trap functions by applying a voltage between a pair of electrodes that are far apart. The particulate matter number concentration measuring device according to claim 5 or claim 6.

10. The ammeter used to measure the induced current has a detection range of 10 －１０ ~10 －１５ Amperes The particulate matter number concentration measuring device according to claim 5 or claim 6.

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