Aerosol measurement device and method based on photoacoustic technology

Abstract

The present invention relates to the field of aerosol measurement technology, and specifically provides an aerosol measurement device and method based on photoacoustic technology, wherein the device comprises a laser emitting unit for generating lasers of four different wavebands; a coupling unit for coupling the lasers of four different wavebands into a mixed laser beam; a photoacoustic cell, wherein the mixed laser beam is incident on the photoacoustic cell, wherein a main resonant cavity is arranged in the photoacoustic cell, and a plurality of enhanced resonant cavities connected to the main resonant cavity through a connecting hole are arranged outside the main resonant cavity, the resonant frequency of the main resonant cavity is the same as the resonant frequency of the enhanced resonant cavity, and a microphone is arranged in each enhanced resonant cavity to pick up a photoacoustic signal, and the laser beam is injected into the main resonant cavity from one end and emitted from the other end of the main resonant cavity; and a data processing unit for processing the photoacoustic signal and inverting the concentration of the sample to be measured. The present invention can improve the sensitivity of the aerosol measurement device.

Description

Technical Field

[0001] The present invention relates to the technical field of aerosol measurement, and in particular to an aerosol measurement device and method based on photoacoustic technology. Background Art

[0002] Carbonaceous aerosols include black carbon and organic carbon. Black carbon mainly comes from the burning of fossil fuels and biomass and the release of natural combustion processes. Black carbon can reduce atmospheric visibility, heat the air and aggravate global warming. Its greenhouse effect is second only to carbon dioxide and methane. Organic carbon mainly comes from the burning of biomass, the release of organisms and atmospheric chemical reactions. Due to changes in the environment such as temperature and humidity, organic carbon in the atmosphere will continue to be oxidized and condensed into nuclei, forming photochemical smog, which affects people's health and safety. In addition, organic carbon can be adsorbed on black carbon, changing the optical absorption characteristics of black carbon aerosols and affecting the climate effect assessment of carbonaceous aerosols.

[0003] The current aerosol measurement device passes a laser into a resonant cavity containing a sample to be measured, and generates a photoacoustic signal in the resonant cavity. The absorption coefficient of the sample to be measured is obtained by analyzing the photoacoustic signal. However, the current device has some shortcomings. The photoacoustic signal intensity generated by the resonant cavity is low. Although the photoacoustic signal is amplified when analyzing the signal, the amplification method is achieved by amplifying the current, and its basic signal intensity is low. The signal details after amplification are insufficient, which makes the sensitivity of the measurement device low. Therefore, the present application proposes an aerosol measurement device and method based on photoacoustic technology. Summary of the invention

[0004] The purpose of the present invention is to provide an aerosol measurement device and method based on photoacoustic technology to solve the problem of low sensitivity of current aerosol measurement devices.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] An aerosol measuring device based on photoacoustic technology, characterized in that the measuring device comprises:

[0007] A laser emission unit, used to generate lasers of four different wavelength bands;

[0008] A coupling unit, wherein the coupling unit couples four laser beams of different wavelength bands into a mixed laser beam;

[0009] A photoacoustic cell, wherein the mixed laser is incident on the photoacoustic cell, wherein a main resonant cavity is arranged in the photoacoustic cell, and a plurality of enhanced resonant cavities are arranged outside the main resonant cavity and connected to the main resonant cavity through a connecting hole, the resonant frequency of the main resonant cavity is the same as the resonant frequency of the enhanced resonant cavity, and a microphone is arranged in each enhanced resonant cavity to pick up the photoacoustic signal, and the laser is incident from one end of the main resonant cavity and emitted from the other end of the main resonant cavity;

[0010] The data processing unit is used to process the photoacoustic signal and invert the concentration of the sample to be tested.

[0011] Furthermore, the photoacoustic cell further comprises:

[0012] A body, wherein the main resonance cavity is a through-hole structure arranged at the center of the body, the enhanced resonance cavity is a through-hole structure, and the axes of the main resonance cavity and the enhanced resonance cavity are parallel;

[0013] Window sheets, located at both ends of the body, used to block the ends of the main resonance cavity and the enhanced resonance cavity to close the body, and the window sheets are transparent;

[0014] A microphone is sealed and connected to the body, and is communicated with the enhanced resonance cavity to pick up the photoacoustic signal in the enhanced resonance cavity.

[0015] Furthermore, the main resonance cavity is a cylindrical resonance cavity, and the enhanced resonance cavity is a rectangular resonance cavity.

[0016] Furthermore, the plurality of enhanced resonance cavities are evenly distributed around the axis of the main resonance cavity in the circumferential direction.

[0017] Furthermore, buffer cavities are provided on both sides of the main resonance cavity, and both ends of the enhanced resonance cavity are connected to the buffer cavities.

[0018] Furthermore, a photoelectric detector and a second reflector are fixedly connected in the buffer cavity, and the second reflector reflects scattered light and focuses it on the photoelectric detector. The photoacoustic cell also includes:

[0019] A reference cavity located at the end of the buffer cavity, the reference cavity is cylindrical with openings at both ends, the inner size of the reference cavity is the same as the size of the buffer cavity, the reference cavity is closed by a window sheet, the reference cavity is filled with zero air, a photoelectric detector and a second reflector are arranged in the reference cavity, the arrangement of the photoelectric detector and the second reflector in the reference cavity is the same as that of the photoelectric detector and the second reflector in the buffer cavity, the mixed laser passes through the reference cavity and then enters the buffer cavity, and the zero air is a mixed gas of 78% nitrogen and 22% oxygen;

[0020] When measuring the scattering characteristics of particles in the sample to be tested, the signal value of the photoelectric detector in the buffer cavity minus the signal value of the photoelectric detector in the control cavity is used as the measurement value of the particles.

[0021] The present invention also discloses an aerosol measurement method based on photoacoustic technology, which is implemented based on the above-mentioned aerosol measurement device and is used to measure black carbon, organic carbon and nitrogen dioxide. The method comprises the following steps: step A, a laser emitting unit generates four beams with a wavelength of , , as well as The coupling unit couples the four laser beams into a mixed laser beam, and the modulation frequencies of the four laser beams are different, wherein organic carbon and nitrogen dioxide have a wavelength of The absorption coefficient of the laser is zero;

[0022] Step B, passing the mixed laser into a photoacoustic cell containing a sample to be tested, and picking up the photoacoustic signal in the photoacoustic cell, wherein the modulation frequency of the four laser beams is within the frequency response range of the acoustic resonance cavity in the photoacoustic cell; Step C, processing the photoacoustic signal by a data processing unit, and obtaining the black carbon, organic carbon and nitrogen dioxide at a wavelength of , , as well as Total absorption coefficient under laser as well as ;

[0023] Step D: According to the law that the absorption coefficients of black carbon, organic carbon and nitrogen dioxide vary with the laser wavelength, the absorption coefficients of black carbon at , , as well as The relationship between the laser absorption coefficient and the organic carbon , , The relationship between the laser absorption coefficient and nitrogen dioxide , , The relationship between the absorption coefficient of the laser; step E, combining the calculations in step C and step D to obtain a group of equations about the absorption coefficients of black carbon, organic carbon and nitrogen dioxide, solving them to obtain the absorption coefficients of black carbon, organic carbon and nitrogen dioxide under lasers of various wavelengths, and inverting the concentrations of black carbon, organic carbon and nitrogen dioxide according to the relationship between the absorption coefficients of black carbon, organic carbon and nitrogen dioxide and their concentrations.

[0024] Preferably, as well as As shown in formula (4), formula (5), formula (6) and formula (7):

[0025] ;Formula (4)

[0026] ;Formula (5)

[0027] ;Formula (6)

[0028] ;Formula (7)

[0029] In the formula, They are nitrogen dioxide, black carbon and organic carbon at wavelengths of Absorption coefficient under laser; They are nitrogen dioxide, black carbon and organic carbon at wavelengths of Absorption coefficient under laser; They are nitrogen dioxide, black carbon and organic carbon at wavelengths of Absorption coefficient under laser; They are nitrogen dioxide, black carbon and organic carbon at wavelengths of The absorption coefficient under the laser is ;

[0030] In step D, formula (10) to formula (16) are obtained:

[0031] ;Formula (10)

[0032] ;Formula (11)

[0033] ;Formula (12)

[0034] ;Formula (13)

[0035] ;Formula (14)

[0036] ;Formula (15)

[0037] ;Formula (16)

[0038] Where A and B are the absorption Ångström coefficients of black carbon and organic carbon, respectively, A=1, ; and are constants, and It can be calculated using the standard absorption cross section of nitrogen dioxide;

[0039] In step E, substitute formula (10) to formula (16) into formula (4) to formula (6) to obtain the matrix formula (17):

[0040] ; Matrix formula (17)

[0041] Solve the matrix formula (17) and combine Calculated to obtain , And B, the concentrations of black carbon, organic carbon and nitrogen dioxide are inverted according to the relationship between their absorption coefficients and concentrations.

[0042] In summary, the present invention has the following beneficial effects compared with the prior art:

[0043] The aerosol measuring device based on photoacoustic technology disclosed in the embodiment of the present invention performs secondary amplification on the photoacoustic signal generated by the main resonance cavity at the physical level by setting an enhanced resonance cavity, and improves the details of the amplified photoacoustic signal, thereby improving the sensitivity of the aerosol measuring device. At the same time, four microphones are set in four enhanced resonance cavities to improve the signal-to-noise ratio of the signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic diagram of the structure of an aerosol measurement device based on photoacoustic technology disclosed in Example 1 of the present invention.

[0045] Figure 2 This is a schematic diagram of the structure of the photoacoustic cell in the aerosol measurement device based on photoacoustic technology disclosed in Example 1 of the present invention.

[0046] Figure 3 for Figure 2 main view.

[0047] Figure 4 for Figure 3 Sectional view of AA.

[0048] Figure 5 for Figure 3 Cross-sectional view of BB.

[0049] Figure 6 for Figure 3 The disclosed photoacoustic cell does not include a schematic diagram of the structure of a window piece.

[0050] Figure 7 This is a schematic diagram of the structure of the photoacoustic cell in the aerosol measurement device based on photoacoustic technology disclosed in Example 2 of the present invention.

[0051] Figure 8 for Figure 7 main view.

[0052] Fig. 9 for Figure 8 Cross-sectional view of CC.

[0053] Fig.10 Schematic diagram of the modulation frequency distribution of four lasers.

[0054] Fig.11 This is a step diagram of the aerosol measurement method based on photoacoustic technology disclosed in Example 3 of the present invention.

[0055] Reference numerals:

[0056] 1. The first laser; 2. The second laser; 3. The third laser; 4. The fourth laser; 5. The first reflector; 6. The first optical filter; 7. The second optical filter; 8. The third optical filter; 9. The photoacoustic cell; 910. The main body; 911. The main resonance cavity; 912. The enhanced resonance cavity; 913. The buffer cavity; 920. The window; 921. The plug bracket; 930. The microphone; 940. The photodetector; 950. The second reflector; 960. The control cavity; 10. The preamplifier; 11. The phase-locked amplifier; 12. The data acquisition card; 13. The industrial computer; 14. The signal generator. DETAILED DESCRIPTION

[0057] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0058] Example 1

[0059] like Figure 1 As shown, the present invention discloses an aerosol measuring device based on photoacoustic technology, the measuring device includes a laser emitting unit, a coupling unit, a photoacoustic cell 9 and a data processing unit, the laser emitting unit generates lasers of four different bands, the coupling unit couples the lasers of four different bands into a mixed laser beam, the mixed laser is incident on the photoacoustic cell 9, a microphone 930 is arranged in the photoacoustic cell 9 to pick up the photoacoustic signal, and the data processing unit is used to process the photoacoustic signal and invert the concentrations of black carbon, organic carbon and nitrogen dioxide.

[0060] In this embodiment, the laser is a semiconductor laser in the prior art, which generates lasers of different wavelengths by modulation. The four groups of lasers are recorded as a first laser 1, a second laser 2, a third laser 3 and a fourth laser 4. The first laser 1, the second laser 2, the third laser 3 and the fourth laser 4 are intensity modulated by the signal frequency generated by the signal generator 14. In this embodiment, the first laser 1 generates a 405nm laser, the second laser 2 generates a 450nm laser, the third laser 3 generates a 660nm laser, and the fourth laser generates an 800nm ​​laser.

[0061] like Fig.10 As shown, the signal generator 14 controls the modulation frequencies of the first laser 1, the second laser 2, the third laser 3 and the fourth laser 4 to be near the resonance frequency of the photoacoustic pool 9, and the modulation frequencies of the lasers differ by 20 Hz, that is, the modulation frequencies of the four lasers are within the frequency response range of the acoustic resonance cavity in the photoacoustic pool 9.

[0062] The coupling unit includes a first reflector 5, a first optical filter 6, a second optical filter 7 and a third optical filter 8. The laser generated by the first laser 1 is reflected by the first reflector 5 and then incident on the first optical filter 6. The laser generated by the second laser 2 is reflected by the first optical filter 6 to the second optical filter 7. The laser generated by the third laser 3 is reflected by the second optical filter 7 to the third optical filter 8. The laser generated by the third laser 4 is reflected by the third optical filter 8 to the photoacoustic pool 9. The laser generated by the first laser 1 passes through the first optical filter 5, the second optical filter 7 and the third optical filter 8. The laser generated by the second laser 2 passes through the second optical filter 7 and the third optical filter 8. The laser generated by the third laser 3 passes through the third optical filter 8. The lasers generated by the four lasers are coupled into mixed lasers.

[0063] As a preferred implementation in this embodiment, Figures 2 to 6 As shown, the photoacoustic cell 9 comprises:

[0064] A body 910, wherein a main resonance cavity 911 with a through-hole structure is disposed at the center of the body 910, and a plurality of through-hole-shaped enhanced resonance cavities 912 evenly distributed around the axis of the main resonance cavity 911 are disposed on the outer side of the main resonance cavity 911, wherein the resonance frequency of the main resonance cavity 911 is the same as the resonance frequency of the enhanced resonance cavity 912, and the main resonance cavity 911 and the enhanced resonance cavity 912 are connected through a connecting hole, and buffer cavities 913 are disposed on both sides of the main resonance cavity 911, and air inlets and air outlets are respectively disposed on the buffer cavities 913 located on both sides;

[0065] The window piece 920 is used to block the two ends of the main body 910 to close the main body 910;

[0066] A microphone 930 , wherein the microphone 930 is sealed and connected to the body 910 , and the microphone 930 is communicated with the enhanced resonance cavity 912 to pick up the photoacoustic signal in the enhanced resonance cavity 912 , and each enhanced resonance cavity 912 is provided with a microphone 930 ;

[0067] Specifically, in this embodiment, the body 910 is in a square block shape, the main resonance cavity 911 is coaxially arranged with the body 910, four enhanced resonance cavities 912 are arranged, the main resonance cavity 911 is a cylindrical resonance cavity, the enhanced resonance cavity 912 is a rectangular resonance cavity, the length of the enhanced resonance cavity 912 is the same as the length of the main resonance cavity 911, the enhanced resonance cavity 912 is connected to the buffer cavity 913, the main resonance cavity 911 adopts a first-order longitudinal vibration mode, and its resonance frequency Calculated by formula (1):

[0068] ;Formula (1)

[0069] Wherein, L is the length of the main resonance cavity 911, ΔL=16R / 3π is the correction coefficient, R is the radius of the main resonance cavity; c is the speed of sound in air at a standard atmospheric pressure and 15°C, which is approximately 340 m / s;

[0070] The first-order longitudinal frequency of the enhanced resonance cavity 912 Calculated by formula (2):

[0071] ;Formula (2)

[0072] To enhance the length of the resonance cavity 912; in this embodiment, the main resonance cavity 911 amplifies the acoustic signal and generates a standing wave. To achieve secondary amplification of the photoacoustic signal, the resonance frequency of the main resonance cavity 911 is the same as the resonance frequency of the enhanced resonance cavity 912. The acoustic signal amplified by the main resonance cavity 911 needs to enter the enhanced resonance cavity 912 for acoustic amplification again. Formulas (1) and (2) determine the resonance frequencies of the main resonance cavity 911 and the enhanced resonance cavity 912. The resonance frequency bandwidths of the two resonance cavities are both several hundred Hz, and their resonance frequencies partially overlap. Therefore, the main resonance cavity 911 and the enhanced resonance cavity 912 can achieve secondary resonance of the acoustic signal.

[0073] It should be noted that, in this embodiment, the enhanced resonance cavity 912 may not only be rectangular, but may also be cylindrical, hemispherical, or the like.

[0074] The buffer cavity 913 is used to reduce environmental noise interference. The length of the buffer cavity 913 is half the length of the main resonance cavity 911, and the diameter of the buffer cavity 913 is twice the length of the main resonance cavity 911. The buffer cavity 913 can effectively eliminate the sound signal and environmental noise generated by the thermal effect of the optical window sheet 920;

[0075] The air inlet and the air outlet are used to connect to the charging device to charge the sample to be tested. After the charging of the sample to be tested is completed, the photoacoustic cell 9 is closed by closing the valves located at the air inlet and the air outlet.

[0076] In this embodiment, the window sheet 920 is a calcium fluoride window sheet, and a plug bracket 921 is fixed to the outside of the window sheet 920 by gluing, and the plug bracket 921 is connected to the end of the body 910 by screws, and a sealing gasket is also provided between the plug bracket 921 and the body 910, and the plug bracket 912 is a square, annular metal sheet;

[0077] A countersunk hole structure communicating with the enhanced resonance cavity 912 is provided on the side wall of the body 910 , and the microphone 930 is sealed and connected to the countersunk hole structure by gluing.

[0078] The microphone 930 sends the collected signal to the data processing unit through a wire.

[0079] In this embodiment, the data processing unit includes a preamplifier 10, a phase-locked amplifier 11, a data acquisition card 12 and an industrial computer 13. The preamplifier 10 is electrically connected to the microphone 930 through a wire. The preamplifier 10 is used to amplify the signal of the microphone 930. The phase-locked amplifier 11 is electrically connected to the signal generator 14 through a wire. The phase-locked amplifier 11 extracts the photoacoustic signal by acquiring the modulation signal of the signal generator 14. The data acquisition card 12 acquires the photoacoustic signal through the phase-locked amplifier 11. The industrial computer 13 analyzes the photoacoustic signal and extracts the absorption coefficient. The industrial computer 13 is a computer. The method for extracting the absorption coefficient by the industrial computer 13 is the prior art.

[0080] Example 2

[0081] As another embodiment of the present invention, this embodiment is different from Embodiment 2 in that, Figures 7 to 9 As shown, a photodetector 940 and a second reflector 950 are fixedly connected in the buffer cavity 913. The photodetector 940 and the second reflector 950 are mirror-imaged about the axis of the buffer cavity 913. The second reflector 950 reflects the scattered light of the particles and focuses it on the photodetector 940. The photoacoustic cell 9 also includes:

[0082] A reference cavity 960 is located at both ends of the body 910. The reference cavity 960 is in the shape of a cylinder with openings at both ends. The inner size of the reference cavity 960 is the same as that of the buffer cavity 913. The reference cavity 960 is closed by a window sheet 920. The reference cavity 960 is filled with zero air (78% nitrogen and 22% oxygen). A photodetector 940 and a second reflector 950 are arranged in the reference cavity 960. The arrangement of the photodetector 940 and the second reflector 950 in the reference cavity 960 is the same as that of the photodetector 940 and the second reflector 950 in the buffer cavity 913. The mixed laser passes through the reference cavity 960 and then enters the buffer cavity 913.

[0083] In this embodiment, the photodetector 940 collects scattered light of the particles and scattered light of nitrogen to measure the scattering characteristics of the particles, thereby achieving simultaneous measurement of the absorption coefficient and scattering characteristics of the particles. The second reflector 950 is a spherical reflector with a single aperture.

[0084] The photoelectric detector 940 sends the collected signal to the data processing unit through a wire for measuring the heat dissipation characteristics of the particulate matter;

[0085] Light scattering means that the propagation direction of the incident light beam deviates from its original direction due to particulate matter, thereby dispersing and propagating in various directions. A photoelectric detector is installed in a specific direction. The photoelectric detector receives the incident light and generates a photoelectric signal. After calibration with different particle concentrations, different photoelectric signals correspond to different particle concentrations.

[0086] In this embodiment, the control cavity 960 is located at the end of the buffer cavity 913. The control cavity 960 is provided with an air filling hole for filling zero air. After filling zero air, the air filling hole is closed by a valve located on the punching hole. Since the control cavity 960 is closed inside, the sample to be tested will not enter the control cavity 960.

[0087] For ease of understanding, the photodetector 940 in the reference cavity 960 at the laser incident end is recorded as the first detector, and the photodetectors 940 from the laser incident end to the laser exit end are the first detector, the second detector, the third detector and the fourth detector in sequence, the first detector and the fourth detector are located in the reference cavity 960, and the second detector and the third detector are located in the buffer cavity 913;

[0088] When measuring the scattering characteristics of particles, a mixed laser is introduced to obtain signals from the first detector to the fourth detector. The scattering signal of the particles is obtained by differential means, that is, the signal of the first detector is subtracted from the signal of the second detector, and the signal of the fourth detector is subtracted from the signal of the third detector. The scattering characteristics of the particles can be obtained by processing the obtained difference.

[0089] It should be noted that the photodetectors 940 are provided at both ends of the photoacoustic cell 9 in order to improve the signal-to-noise ratio through a redundant design, and the signal processing method thereof is a prior art and will not be described in detail here;

[0090] In the traditional particle heat dissipation characteristic test method, the scattering characteristics of zero air are measured first, and then the scattering characteristics of the sample to be tested are measured. The scattering characteristics of the particles are obtained by subtracting the value of the second measurement from the value of the first measurement. However, in actual operation, due to changes in temperature and control current, the light intensity of the laser is not maintained at a fixed value, but fluctuates within a certain range. Since the values ​​of the laser intensity measured twice are different, the accuracy of the measurement result is low;

[0091] In this embodiment, the mixed laser first passes through the control cavity 960 containing zero air, and then passes through the buffer cavity 913 containing the sample to be tested. The measurement signals of the photodetector 940 in the control cavity 960 and the buffer cavity 913 change at the same time. When the light intensity of the mixed laser changes, the measurement signals of the photodetector 940 in the control cavity 960 and the buffer cavity 913 are still obtained under the same light intensity. Therefore, after differential calculation, the measurement signal change caused by the change in the light intensity of the mixed laser is corrected, and the light intensity change of the mixed laser no longer affects the measurement result. The value obtained by subtracting the measurement signal of the photodetector 940 in the buffer cavity 913 from the measurement signal of the photodetector 940 in the control cavity 960 is the scattering characteristic of the particle. This method can not only eliminate the measurement error caused by the change in the light intensity of the mixed laser, but also improve the measurement efficiency, that is, the scattering characteristic of the particle can be obtained through one measurement, and the process of emptying the zero air is omitted.

[0092] Example 3

[0093] like Fig.11 As shown, the present invention also discloses an aerosol measurement method based on photoacoustic technology, which is implemented based on the aerosol measurement device described in Example 1 or Example 2, and is used to simultaneously measure black carbon, organic carbon and nitrogen dioxide. The measurement method comprises the following steps:

[0094] Step A: Generate four beams with wavelengths of , , as well as The laser beams are coupled into a mixed laser beam, and the modulation frequencies of the four groups of laser beams are different, wherein organic carbon and nitrogen dioxide are at a wavelength of The absorption coefficient of the laser is zero;

[0095] Step B, passing the mixed laser into a photoacoustic cell containing a sample to be tested, and picking up the photoacoustic signal in the photoacoustic cell through a microphone, wherein the modulation frequency of the four laser beams is within the frequency response range of the acoustic resonance cavity in the photoacoustic cell;

[0096] Step C: Process the photoacoustic signal by a data processing unit to obtain the black carbon, organic carbon and nitrogen dioxide at a wavelength of , , as well as The total absorption coefficient of the laser as well as ,in, For black carbon at a wavelength of The absorption coefficient under laser is expressed as ;

[0097] Step D: According to the law that the absorption coefficients of black carbon, organic carbon and nitrogen dioxide vary with wavelength in the ultraviolet-visible-near infrared band, the absorption coefficient of black carbon at a wavelength of , , The absorption coefficient of the laser is The relationship between organic carbon and wavelength is , The absorption coefficient of the laser is related to the wavelength The relationship between the absorption coefficient of the laser and the absorption coefficient of nitrogen dioxide at a wavelength of , The absorption coefficient of the laser is related to the wavelength The relationship between the absorption coefficient under laser;

[0098] Step E, based on the calculation results of step C and step D, the absorption coefficients of black carbon, organic carbon and nitrogen dioxide under lasers of various wavelengths are obtained, and the concentrations of black carbon, organic carbon and nitrogen dioxide are inverted according to the relationship between the absorption coefficients and concentrations of black carbon, organic carbon and nitrogen dioxide;

[0099] Specifically, in this embodiment, , , as well as Take lasers of 405nm, 450nm, 660nm, and 800nm ​​as examples;

[0100] The relationship between the absorption coefficient and concentration of black carbon, organic carbon and nitrogen dioxide is shown in formula (3): ;Formula (3)

[0101] In the formula, is the photoacoustic signal intensity; is the power of the laser, which can be measured in the experiment; is the sensitivity of the microphone sensor, which is a known parameter; is the cell constant of the photoacoustic cell, which is related to factors such as the geometric parameters of the photoacoustic cell and characterizes the ability of the photoacoustic cell to convert photon energy into photoacoustic signals. It can be obtained by calibration using gas of known concentration; is the background noise signal, which can be measured in the experiment; is the absorption coefficient of the sample to be tested, , is the absorption coefficient per unit sample concentration, C is the sample concentration. When the sample is an aerosol, The unit is g / m 2 , C unit is g / m 3 , when the sample to be tested is a gas molecule The unit is Mm -1 / ppbv, C unit is ppbv;

[0102] Among them, the total absorption coefficient of the four laser beams is shown in formula (4), formula (5), formula (6) and formula (7):

[0103] ;Formula (4)

[0104] ;Formula (5)

[0105] ;Formula (6)

[0106] ;Formula (7)

[0107] In the formula, , , , are the total absorption coefficients of the four lasers, Nitrogen dioxide, black carbon and organic carbon Absorption coefficient under nm laser; They are the absorption coefficients of nitrogen dioxide, black carbon and organic carbon under 450nm laser; These are the absorption coefficients of nitrogen dioxide, black carbon and organic carbon under 660nm laser; are the absorption coefficients of nitrogen dioxide, black carbon and organic carbon at 800nm ​​laser, respectively. The absorption coefficients of nitrogen dioxide and organic carbon at 800nm ​​laser are zero. ;

[0108] The absorption coefficients of black carbon and organic carbon in the UV-visible-near infrared band follow the power function law as the wavelength changes, as shown in formula (8) and formula (9):

[0109] ;Formula (8)

[0110] ;Formula (9)

[0111] In the formula, is the wavelength of the laser, The value is , , as well as ; as well as is a constant, A and B are the absorption Ångström coefficients of black carbon and organic carbon, respectively, where A=1, ;

[0112] Combined with black carbon Laser absorption coefficient and the absorption coefficient of organic carbon at 660nm , the absorption coefficients of black carbon at 405nm, 450nm and 660nm lasers and the absorption coefficients of organic carbon at 405nm and 450nm lasers are obtained as described in formulas (10) to (14):

[0113] ;Formula (10)

[0114] ;Formula (11)

[0115] ;Formula (12)

[0116] ;Formula (13)

[0117] ;Formula (14);

[0118] In the formula, nm, nm, =660nm, =800nm;

[0119] The absorption coefficients of nitrogen dioxide at 405nm, 450nm and 660nm lasers are in a corresponding proportional relationship, as shown in formula (15) and formula (16):

[0120] ;Formula (15)

[0121] ;Formula (16)

[0122] In the formula, and are all constants, among which, and It can be calculated using the standard absorption cross section of nitrogen dioxide;

[0123] Combining formula (10) to formula (16), formula (4) to formula (6) can be transformed into matrix formula (17):

[0124] ; Matrix formula (17)

[0125] In formula (7) and matrix formula (17), as well as From experimental measurements, = , A=1, the matrix formula (17) can be solved to obtain , and B, therefore, it can be concluded that nitrogen dioxide wavelength absorption coefficient and organic carbon at The absorption coefficient of the calculated nitrogen dioxide at wavelength absorption coefficient, organic carbon wavelength and the absorption coefficient of black carbon at Substituting the absorption coefficient of the wavelength into formula (3), the concentrations of nitrogen dioxide, black carbon and organic carbon can be obtained.

[0126] It should be noted that the wavelengths of the four groups of lasers can also be ultraviolet light, visible light, and near-infrared light of other values. When selecting, the absorption coefficient of any two components of black carbon, organic carbon, and nitrogen dioxide in a certain band can be zero.

[0127] It should be noted that the aerosol measurement method disclosed in this embodiment can also measure other aerosol components. When measuring other aerosol measurement components, such as measuring substances M, N and I, among the components of the aerosol, other substances in the aerosol have no absorption under the laser generated by the laser emitting unit, and only substances M, N and I have absorption under three of the wavelengths of the laser. At the same time, two of the substances have no absorption under another wavelength, such as substance M, substance N and substance I have no absorption under the wavelength. , , as well as Both absorb, substance M and substance N at wavelength Without absorption, other substances in the aerosol are , , as well as No absorption.

[0128] The aerosol measuring device based on photoacoustic technology disclosed in the embodiment of the present invention eliminates the method of using traditional filters to filter aerosols. It only needs to pass the sample to be tested once to complete the simultaneous measurement of black carbon, organic carbon and nitrogen dioxide concentrations, thereby improving the measurement efficiency of black carbon, organic carbon and nitrogen dioxide concentrations. At the same time, since the samples to be tested that are passed in at the same time are measured, the measurement errors caused by fluctuations in laser intensity and pressure fluctuations when the samples to be tested are passed in are avoided, thereby improving the measurement accuracy.

[0129] It should be noted that, in this embodiment, the particulate matter refers to the black carbon, organic carbon and nitrogen dioxide in Example 1, and also the aerosol in Example 1 and Example 2, wherein different description names are for ease of understanding. For example, in Example 3, black carbon, organic carbon and nitrogen dioxide are called particulate matter in order to understand scattering, and in Example 2, black carbon, organic carbon and nitrogen dioxide are called aerosols in order to facilitate the explanation of filtration and simplify the sentences.

[0130] In the several embodiments provided by the present invention, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0131] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0132] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of hardware plus software functional units.

[0133] Those skilled in the art can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional modules is used as an example for illustration. In actual applications, the above-mentioned functions can be assigned to different functional modules as needed, that is, the internal structure of the device is divided into different functional modules to complete all or part of the functions described above. The specific working process of the device described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

Claims

1. An aerosol measurement device based on photoacoustic technology, characterized in that: The measuring device comprises: A laser emission unit, used to generate lasers of four different wavelength bands; A coupling unit, wherein the coupling unit couples four laser beams of different wavelength bands into a mixed laser beam; A photoacoustic pool, wherein the mixed laser is incident on the photoacoustic pool, wherein a main resonance cavity is arranged in the photoacoustic pool, and a plurality of enhanced resonance cavities connected to the main resonance cavity through a connecting hole are arranged outside the main resonance cavity, the resonance frequency of the main resonance cavity is the same as the resonance frequency of the enhanced resonance cavity, and a microphone is arranged in each enhanced resonance cavity to pick up a photoacoustic signal, and the laser is injected from one end of the main resonance cavity and emitted from the other end of the main resonance cavity; wherein the photoacoustic pool further comprises a body, a window sheet and a microphone, the main resonance cavity is a through-hole structure arranged at the center of the body, the enhanced resonance cavity is a through-hole structure, the axes of the main resonance cavity and the enhanced resonance cavity are parallel, the window sheet is located at both ends of the body, and is used to block the ends of the main resonance cavity and the enhanced resonance cavity to close the body, the window sheet is transparent, the microphone is sealed and connected to the body, and the microphone is connected to the enhanced resonance cavity to pick up the photoacoustic signal in the enhanced resonance cavity; The data processing unit is used to process the photoacoustic signal and invert the concentration of the sample to be tested.

2. The aerosol measurement device based on photoacoustic technology according to claim 1, characterized in that: The main resonance cavity is a cylindrical resonance cavity, and the enhanced resonance cavity is a rectangular resonance cavity.

3. The aerosol measurement device based on photoacoustic technology according to claim 1, characterized in that: The plurality of enhanced resonance cavities are evenly distributed around the axis of the main resonance cavity in the circumferential direction.

4. The aerosol measurement device based on photoacoustic technology according to any one of claims 1 to 3, characterized in that: Buffer cavities are arranged on both sides of the main resonance cavity, and both ends of the enhanced resonance cavity are communicated with the buffer cavities.

5. The aerosol measurement device based on photoacoustic technology according to claim 4, characterized in that: A photoelectric detector and a second reflector are also fixedly connected in the buffer cavity, and the second reflector reflects scattered light and focuses it on the photoelectric detector. The photoacoustic cell also includes: A reference cavity located at the end of the buffer cavity, the reference cavity is cylindrical with openings at both ends, the inner size of the reference cavity is the same as the size of the buffer cavity, the reference cavity is closed by a window sheet, the reference cavity is filled with zero air, a photoelectric detector and a second reflector are arranged in the reference cavity, the arrangement of the photoelectric detector and the second reflector in the reference cavity is the same as that of the photoelectric detector and the second reflector in the buffer cavity, the mixed laser passes through the reference cavity and then enters the buffer cavity, and the zero air is a mixed gas of 78% nitrogen and 22% oxygen; When measuring the scattering characteristics of particles in the sample to be tested, the signal value of the photoelectric detector in the buffer cavity minus the signal value of the photoelectric detector in the control cavity is used as the measurement value of the particles.

6. An aerosol measurement method based on photoacoustic technology, implemented based on the aerosol measurement device based on photoacoustic technology according to any one of claims 1 to 5, for measuring black carbon, organic carbon and nitrogen dioxide, characterized in that: The method comprises the following steps: Step A: The laser emitting unit generates four beams with wavelengths of , , as well as The coupling unit couples the four laser beams into a mixed laser beam, and the modulation frequencies of the four laser beams are different, wherein organic carbon and nitrogen dioxide have a wavelength of The absorption coefficient of the laser is zero; Step B, passing the mixed laser into a photoacoustic cell containing a sample to be tested, and picking up the photoacoustic signal in the photoacoustic cell, wherein the modulation frequency of the four laser beams is within the frequency response range of the acoustic resonance cavity in the photoacoustic cell; Step C: Process the photoacoustic signal by a data processing unit to obtain the black carbon, organic carbon and nitrogen dioxide at a wavelength of , , as well as Total absorption coefficient under laser as well as ; Step D: According to the law that the absorption coefficients of black carbon, organic carbon and nitrogen dioxide vary with the laser wavelength, the absorption coefficients of black carbon at , , as well as The relationship between the laser absorption coefficient and the organic carbon , , The relationship between the laser absorption coefficient and nitrogen dioxide , , The relationship between the absorption coefficient of the laser; Step E: Combining the calculations in step C and step D, a set of equations for the absorption coefficients of black carbon, organic carbon and nitrogen dioxide is obtained, the absorption coefficients of black carbon, organic carbon and nitrogen dioxide under lasers of various wavelengths are obtained by solving them, and the concentrations of black carbon, organic carbon and nitrogen dioxide are inverted according to the relationship between the absorption coefficients and concentrations of black carbon, organic carbon and nitrogen dioxide.

7. The aerosol measurement method based on photoacoustic technology according to claim 6, characterized in that: as well as As shown in formula (4), formula (5), formula (6) and formula (7): ;Formula (4) ;Formula (5) ;Formula (6) ;Formula (7) In the formula, They are nitrogen dioxide, black carbon and organic carbon at wavelengths of Absorption coefficient under laser; They are nitrogen dioxide, black carbon and organic carbon at wavelengths of Absorption coefficient under laser; They are nitrogen dioxide, black carbon and organic carbon at wavelengths of Absorption coefficient under laser; They are nitrogen dioxide, black carbon and organic carbon at wavelengths of The absorption coefficient under the laser is ; In step D, formula (10) to formula (16) are obtained: ; Official (10) ; Official (11) ;Formula (12) ; Official (13) ; Official (14) ; Official (15) ; Official (16) Where A and B are the absorption Ångström coefficients of black carbon and organic carbon, respectively, A=1, ; and are constants, and All can be calculated using the standard absorption cross section of nitrogen dioxide; In step E, substitute formula (10) to formula (16) into formula (4) to formula (6) to obtain the matrix formula (17): ; Matrix formula (17) Solve the matrix formula (17) and combine Calculated to obtain , And B, the concentrations of black carbon, organic carbon and nitrogen dioxide are inverted according to the relationship between their absorption coefficients and concentrations.

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