A highly sensitive aerosol single particle detection device using laser-induced breakdown spectroscopy

Abstract

The present invention provides a highly sensitive laser-induced breakdown spectroscopy (LIBS) aerosol single-particle detection device, belonging to the field of aerosol detection. The device comprises an aerosol sampling unit, a laser excitation unit, a spectrum acquisition unit, and a control unit. The aerosol sampling unit collects aerosol and forms an aerosol single-particle beam, generating a plasma under the pulsed laser ablation generated by the laser excitation unit. The spectrum acquisition unit is used to efficiently collect and collimate the optical signal emitted by the plasma, with a first acquisition component and a second acquisition component efficiently collecting the optical signal. The control unit is connected to the laser excitation unit and the spectrum acquisition unit, and is used to control the testing process and collect and analyze electrical signals to determine the type and content of the element to be detected in the aerosol single particle, thereby achieving online detection of the aerosol single particle. This invention greatly enhances the ability of LIBS to detect weak optical signals, achieving highly sensitive LIBS aerosol single-particle detection.

Description

Technical Field

[0001] The present invention belongs to the field of aerosol detection, and more specifically, relates to a highly sensitive aerosol single particle detection device using laser-induced breakdown spectroscopy. Background Art

[0002] Aerosols are gaseous dispersions composed of solid or liquid particles suspended in a gaseous medium. Aerosols are ubiquitous in daily life, and their sources can be categorized into two types: natural and anthropogenic. PM2.5, which has garnered considerable public attention in recent years, refers to particulate matter with an aerodynamic diameter of 2.5 microns or less. As a result of growing public awareness of aerosols, a growing number of research reports have demonstrated that the harmful effects of aerosol particulate pollution have far exceeded initial expectations, directly and indirectly impacting human production and daily life. Therefore, the development of reliable aerosol analysis techniques is of great significance.

[0003] Existing aerosol analysis technologies can be divided into two categories: offline analysis and online analysis. Offline analysis involves separating aerosol particles from the atmosphere to make samples, which are then taken to the laboratory for chemical analysis. Offline analysis technology has high analytical accuracy and is mature, but during the sampling process, the physical or chemical properties of the sample will change, resulting in the measurement results not reflecting the original characteristics of the particles and making it impossible to achieve accurate measurement. Online analysis has the advantages of being in situ and not requiring sample pretreatment, and its results directly reflect the intrinsic properties of the particles, so real-time online analysis is the future development prospect of aerosol analysis technology. Existing aerosol online analysis technologies (such as online organic carbon element analyzers, online ion chromatography, and aerosol time-of-flight mass spectrometry) have problems such as low precision and limited analysis elements, making it difficult to meet the needs of complex detection scenarios. Therefore, there is an urgent need for an aerosol online analysis technology that is high-precision, fast, and capable of full-element analysis. Laser-induced breakdown spectroscopy (LIBS) is a chemical analysis technique that enables rapid elemental detection. It works by focusing a high-energy pulsed laser onto the sample surface to excite a plasma. The wavelength and intensity of the plasma radiation are then used to derive the elemental identity and concentration of the sample. LIBS, due to its characteristics of requiring no sample preparation, rapid, in-situ, and comprehensive elemental analysis, is suitable for rapid, on-site aerosol detection.

[0004] Academics classify LIBS aerosol detection into two categories: aerosol population analysis and single-particle analysis. Population analysis involves studying the average chemical composition of all particles within a plasma, with more than one particle present within the plasma sampling region. However, the characteristics of the target particles are easily masked by high-concentration background particles, and differences in chemical properties between particles cannot be distinguished. In contrast, single-particle analysis has particle-level resolution and analyzes only one aerosol particle at a time. However, in LIBS aerosol single-particle detection, due to the small mass of the material contained in a single aerosol particle and the low emission intensity of the elemental characteristic spectral lines, the detection limit of conventional LIBS methods cannot meet the requirements of single-particle detection, resulting in the detection results not reflecting the actual situation.

[0005] In response to the problem that traditional LIBS cannot obtain effective spectral signals of aerosol single particles, some scholars have proposed that the use of an orthogonal dual-pulse structure can obtain a higher signal-to-noise ratio, enhance the spectral signal, and also improve the single-particle sampling rate (Windom BC, Diwakar PK, Hahn D W. Dual-pulse Laser Induced Breakdown Spectroscopy for analysis of gaseous and aerosol systems: Plasma-analyte interactions[J]. Spectrochimica Acta Part B Atomic Spectroscopy, 2006, 61(7): 788-796.). However, this method requires the use of two pulsed lasers, which adds additional instruments, resulting in a complex device, a large system, and high device cost. At the same time, the laser pulse delay between the two lasers needs to be optimized, which increases the difficulty of the experiment. In addition, some researchers have proposed that the spatial position of the particle in the plasma and the size of the acquisition space of the detection system will affect the acquisition efficiency (Lithgow GA, Buckley SG. Effects of focal volume and spatial inhomogeneity onuncertainty in single-aerosol Laser-induced breakdown spectroscopy measurements [J]. Applied Physics Letters, 2005, 87 (1): 011501-011501-3.), the authors believe that the reason why the side-axis acquisition has a stronger signal but greater volatility than the coaxial acquisition is that the area of ​​plasma collected by the side-axis structure is smaller than the coaxial structure, and the probability of particles appearing in this area is lower, so the volatility is large. However, as long as the particle appears in this area, as many spectral lines emitted by the particle as possible can be collected, so the signal will be stronger. In general, scholars have carried out a lot of research on how to obtain effective spectral signals of single aerosol particles from the perspective of LIBS excitation and acquisition, but there are few reports on the optimization of the acquisition system.

[0006] In summary, in current LIBS aerosol single-particle detection, a unified, effective, and cost-effective solution to the problem of low luminescence intensity due to low single-particle content has yet to be found. Most studies attempt to address this issue through laser excitation, but few address the optimization of the acquisition device. A typical LIBS aerosol acquisition device primarily consists of a collection lens, optical fiber, spectrometer, and detector. However, when applied to single-particle detection, this conventional setup often struggles with signal detection. This is primarily due to two factors: First, due to limitations in lens size, optical fiber numerical aperture, and spectrometer f-number, the acquisition system's light collection efficiency is low, resulting in a weak light signal transmitted to the detector surface. Second, the detector's low sensitivity makes it unsuitable for detecting weak signals. Some researchers have used intensified charge-coupled devices (ICCDs) as detectors to enhance the detection capabilities of LIBS systems, but their high cost hinders the widespread adoption of LIBS in various applications. Therefore, developing a highly sensitive acquisition device would be beneficial in addressing the difficulty in detecting single-particle signals in LIBS aerosols. Summary of the Invention

[0007] In view of the defects of the prior art, the purpose of the present invention is to provide a highly sensitive laser-induced breakdown spectroscopy aerosol single particle detection device, aiming to solve the problems of low sensitivity and difficulty in detecting signals in existing detection devices.

[0008] To achieve the above objectives, the present invention provides a highly sensitive aerosol single particle detection device using laser-induced breakdown spectroscopy. The detection device comprises an aerosol sampling unit, a laser excitation unit, a spectrum acquisition unit, and a control unit, wherein:

[0009] The aerosol sampling unit and the laser excitation unit are arranged perpendicular to each other, and the aerosol sampling unit is used to collect aerosol and form an aerosol single particle beam;

[0010] The laser excitation unit is used to generate pulsed laser to ablate the aerosol single particle beam generated by the aerosol injection unit and generate plasma;

[0011] The spectrum acquisition unit includes a parabolic mirror, a dichroic mirror, a first acquisition assembly, and a second acquisition assembly. The parabolic mirror is arranged at the intersection of the aerosol sampling unit and the laser excitation unit, and is used to collimate the light emitted by the plasma. The dichroic mirror is arranged in the propagation direction of the collimated light, with its mirror surface forming a 45° angle with the collimated light, and is used to separate the characteristic spectrum line of the element to be measured in the collimated light, so as to divide the collimated light into reflected light and transmitted light, and respectively send the collimated light into the first acquisition assembly and the second acquisition assembly. The first acquisition assembly includes a first narrowband filter, a first focusing lens, and a first photomultiplier tube, which are arranged in sequence along the propagation direction of the reflected light, and are used to transmit the light beam of the characteristic spectrum line of a certain element to be measured and convert it into an electrical signal. The second acquisition assembly includes a second narrowband filter, a second focusing lens, and a second photomultiplier tube, which are arranged in sequence along the propagation direction of the transmitted light, and are used to transmit the light beam of the characteristic spectrum line of another element to be measured and convert it into an electrical signal.

[0012] The control unit is connected to the laser excitation unit and the spectrum acquisition unit, and is used to control the test process and collect electrical signals for analysis to obtain the type and content of the element to be tested in the aerosol single particle, thereby realizing online detection of the aerosol single particle.

[0013] As a further preference, the aerosol sampling unit includes an aerosol collector, an aerosol transport element, a pneumatic connecting element, a capillary and an exhaust pump, wherein: the aerosol collector is connected to the capillary through the aerosol transport element and the pneumatic connecting element in sequence to collect aerosols in the air and transport them into the capillary; the capillary is inserted into the interior of the parabolic mirror from the top to form an aerosol single particle beam; the exhaust pump is inserted into the interior of the parabolic mirror from the bottom to recover waste gas.

[0014] As a further preferred embodiment, the laser excitation unit includes a pulse laser and a laser focusing lens connected in sequence along the laser propagation direction, the pulse laser is used to emit pulse laser, and the optical axis of the laser focusing lens is collinear with the pulse laser, and is used to focus the pulse laser on a single aerosol particle beam to ablate it and generate plasma.

[0015] As a further preferred embodiment, the control unit includes a timing generator, a data acquisition card and a computer. The timing generator is respectively connected to the pulse laser, the first photomultiplier tube, the second photomultiplier tube and the data acquisition card to trigger their operation; the data acquisition card is connected to the first photomultiplier tube and the second photomultiplier tube to collect the electrical signals output by them; the computer is connected to the data acquisition card to read and analyze the electrical signals to obtain the type and content of the element to be measured in the single aerosol particle.

[0016] As a further preference, the laser focusing lens is an aspheric plano-convex lens coated with a laser anti-reflection film.

[0017] As a further preference, the parabolic mirror is a parabolic mirror coated with a UV-enhanced aluminum film.

[0018] As a further preference, the dichroic mirror is a long-wave pass dichroic mirror, and its operating wavelength range is from ultraviolet to near-infrared.

[0019] As a further preference, the first narrowband filter and the second narrowband filter are filters with narrow half-width at half maximum, and are installed in a filter wheel to achieve switching of the narrowband filters.

[0020] In general, the above technical solutions conceived by the present invention have the following advantages compared with the prior art:

[0021] Beneficial effects:

[0022] 1. The highly sensitive laser-induced breakdown spectroscopy (LIBS) aerosol single-particle detection device provided by the present invention efficiently collects and collimates light emitted by the plasma into parallel light using a parabolic mirror. The device then separates the characteristic spectral lines of the element being measured using a dichroic mirror and a narrow-band filter. Finally, a highly sensitive photomultiplier tube efficiently collects the light signal, reflecting the properties of the aerosol particles and the differences in chemical properties between the particles. Reflective optical systems can achieve a wider collection angle than transmissive optical systems, while photomultiplier tubes are single-point detectors with no collection angle restrictions and a large photosensitive surface, allowing them to receive a greater amount of light energy and achieving higher sensitivity. This significantly enhances LIBS's ability to detect weak light signals, enabling highly sensitive LIBS aerosol particle detection.

[0023] 2. Furthermore, the present invention optimizes the structure of the aerosol injection unit, utilizing a capillary tube to generate a stable aerosol single-particle beam. This significantly reduces abnormal fluctuations in the detection signal and significantly improves the stability of the monitoring device. Compared with complex sheath gas devices, it also has the advantage of a simpler structure.

[0024] 3. In addition, the present invention optimizes the control unit, uses a timing generator to set the time interval between the moment when the pulse laser emits the pulse laser and the moment when the first and second photomultiplier tubes collect the spectrum, as well as the acquisition gate width, and uses a data acquisition card and a computer to collect and analyze data in real time, thereby achieving real-time online detection of single aerosol particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of a highly sensitive aerosol single particle detection device using laser-induced breakdown spectroscopy provided by an embodiment of the present invention;

[0026] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0027] 1-Laser excitation unit, 2-Timing generator, 3-Pulsed laser, 4-Computer, 5-Laser focusing lens, 6-Aerosol collector, 7-Aerosol injection unit, 8-Parabolic mirror, 9-Suction pump, 10-Aerosol transport element, 11-Pneumatic adapter element, 12-Capillary, 13-Spectral acquisition unit, 14-First photomultiplier tube, 15-First focusing lens, 16-First narrow-band filter, 17-Dichroic mirror, 18-Second focusing lens, 19-Second narrow-band filter, 20-Data acquisition card, 21-Second photomultiplier tube, 22-Control unit. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] like Figure 1 As shown, the present invention provides a highly sensitive laser-induced breakdown spectroscopy aerosol single particle detection device, which includes an aerosol sampling unit 7, a laser excitation unit 1, a spectrum acquisition unit 13 and a control unit 22, wherein:

[0030] The aerosol sampling unit 7 and the laser excitation unit 1 are arranged perpendicular to each other. The aerosol sampling unit 7 is used to sample the aerosol in the atmospheric environment in real time and form an aerosol single particle beam;

[0031] The laser excitation unit 1 is used to generate pulsed laser light to ablate the aerosol single particle beam generated by the aerosol sampling unit 7 and generate plasma. The laser excitation unit 1 includes a pulsed laser 3 and a laser focusing lens 5 connected in sequence along the laser propagation direction. The pulsed laser 3 is used to emit pulsed laser light. The optical axis of the laser focusing lens 5 is collinear with the pulsed laser light. The center of the pulsed laser beam coincides with the center of the mirror surface of the laser focusing lens 5. The laser excitation unit 1 is used to focus the high-energy pulsed laser light emitted by the pulsed laser 3 on the aerosol single particle beam to ablate it and generate plasma.

[0032] The spectrum acquisition unit 13 includes a parabolic mirror 8, a dichroic mirror 17, a first acquisition component and a second acquisition component. The parabolic mirror 8 is set at the intersection of the aerosol sampling unit 7 and the laser excitation unit 1, and is used to collimate the light emitted by the plasma. The focus of the parabolic mirror 8 coincides with the center of the plasma excited by the pulse laser 3. A through hole is opened on its surface, and the central axis of the through hole passes through the focus of the parabolic mirror 8 and is orthogonal to the optical axis of the parabolic mirror 8; the dichroic mirror 17 is set in the propagation direction of the collimated light, and its mirror surface forms a 45° angle with the collimated light, which is used to separate the characteristic spectral lines of the element to be measured in the collimated light, and the light beam of the wavelength segment. The reflected light is reflected by the dichroic mirror 17 and propagates in a direction at a 90° angle to the incident direction and is sent to the first collection component. The long-wavelength light beam passes through the dichroic mirror 17 to form transmitted light and is sent to the second collection component. The first collection component includes a first narrow-band filter 16, a first focusing lens 15 and a first photomultiplier tube 14 arranged in sequence along the propagation direction of the reflected light, which is used to transmit the light beam of the characteristic spectrum line of a certain element to be measured and convert it into an electrical signal. The surface of the first narrow-band filter 16 is perpendicular to the short-wavelength light beam reflected by the dichroic mirror 17, and its optical axis coincides with the central axis of the short-wavelength light beam reflected by the dichroic mirror 17. Its transmission wavelength is in the short wavelength range. The optical axis of the first focusing lens 15 coincides with the optical axis of the first narrow-band filter 16, and is used to focus the reflected light transmitted by the first narrow-band filter 16. The first photomultiplier tube 14 is located after the first focusing lens 15, with its photosensitive surface facing the focused light beam, and its photosensitive surface center aligned with the focused light beam center, and is used to collect the light beam focused by the first focusing lens 15. The second collection component includes a second narrow-band filter 19, a second focusing lens 18, and a second photomultiplier tube 21, which are sequentially arranged along the propagation direction of the transmitted light, and are used to transmit the light beam of the characteristic spectrum of another element to be measured and convert it into The second narrowband filter 19 is an electrical signal. The surface of the second narrowband filter 19 is perpendicular to the long-wavelength light beam transmitted by the dichroic mirror 17. The optical axis of the second narrowband filter 19 coincides with the central axis of the long-wavelength light beam transmitted by the dichroic mirror 17. The transmission wavelength is within the long-wavelength range and is used to transmit the light beam of the characteristic spectrum line of another element to be measured. The optical axis of the second focusing lens 18 coincides with the optical axis of the second narrowband filter 19 and is used to focus the collimated light beam transmitted by the second narrowband filter 19. The second photomultiplier tube 21 is located after the second focusing lens 18. Its photosensitive surface is opposite to the focused light beam, and the center of its photosensitive surface is aligned with the center of the focused light beam. It is used to collect the light beam focused by the second focusing lens 18.

[0033] The control unit 22 is connected to the laser excitation unit 1 and the spectrum acquisition unit 13, and is used to control the test process and collect electrical signals for analysis to obtain the type and content of the element to be tested in the aerosol single particle, thereby realizing online detection of the aerosol single particle.

[0034] Furthermore, the aerosol sampling unit 7 includes an aerosol collector 6, an aerosol transport element 10, a pneumatic connecting element 11, a capillary 12 and an air pump 9, wherein: the aerosol collector 6 is connected to the capillary 12 through the aerosol transport element 10 and the pneumatic connecting element 11 in sequence to collect aerosols in the air and transport them to the capillary 12; the capillary 12 is inserted into the interior of the parabolic mirror 8 through a through hole from the top to form an aerosol single particle beam; the air pump 9 is inserted into the interior of the parabolic mirror 8 through a through hole from the bottom to recover exhaust gas.

[0035] Furthermore, the control unit 22 includes a timing generator 2, a data acquisition card 20 and a computer 4. The timing generator 2 is connected to the pulse laser 3, the first photomultiplier tube 14, the second photomultiplier tube 21 and the data acquisition card 20 respectively to trigger their operation, specifically including triggering the pulse laser 3 to generate high-energy pulses, triggering the first photomultiplier tube 14 and the second photomultiplier tube 21 to collect spectra, controlling the time interval between the moment when the pulse laser 3 outputs laser and the moment when the first photomultiplier tube 14 and the second photomultiplier tube 21 collect spectra, and controlling the collection gate width of the first photomultiplier tube 14 and the second photomultiplier tube 21; the data acquisition card 20 is connected to the first photomultiplier tube 14 and the second photomultiplier tube 21 for manually collecting the electrical signals output by them; the computer 4 is connected to the data acquisition card 20 to read and analyze the electrical signals, and derive the type and content of the element to be measured in the single aerosol particle through the intensity information of the characteristic spectral line.

[0036] Furthermore, the pulse laser is a high-energy Nd:YAG nanosecond pulse Q-switched laser; the laser focusing lens 5 is an aspheric plano-convex lens coated with a laser anti-reflection film; the parabolic mirror 8 is a parabolic mirror coated with a UV-enhanced aluminum film; the dichroic mirror 17 is a long-wave pass dichroic mirror with an operating wavelength range from ultraviolet to near-infrared; the first narrow-band filter 16 and the second narrow-band filter 19 are narrow half-width filters and are installed in the filter wheel to realize the switching of narrow-band filters.

[0037] Before using the laser-induced breakdown spectroscopy aerosol single particle high-sensitivity detection device provided by the present invention, it is necessary to check whether the aerosol sampling unit 7 is damaged or blocked, whether the aerosol particle beam is a single particle beam; whether the pulse laser 3, the first photomultiplier tube 14, the second photomultiplier tube 21, the timing generator 2, the data acquisition card 20 and the computer 4 are working properly; and whether the laser focusing lens 5, the parabolic mirror 8, the dichroic mirror 17, the first narrow-band filter 16, the second narrow-band filter 19, the first focusing lens 15 and the second focusing lens 18 are intact and undamaged.

[0038] The detection method is as follows: first, the aerosol sampling unit 7 is started to continuously sample aerosol particles from the atmospheric environment, and the aerosol particles are transmitted through the capillary 12 to form an aerosol single particle beam; then, the time interval between the moment when the pulse laser 3 outputs the laser and the moment when the first and second photomultiplier tubes collect the spectrum is set by the timing generator 2, and the acquisition gate width of the first photomultiplier tube 14 and the second photomultiplier tube 21 is controlled; then, the pulse laser 3 is turned on, and the timing generator 2 transmits a high-level signal to the pulse laser 3, and the pulse laser 3 outputs the laser. The high-energy laser beam generated by the pulse laser 3 is focused on the aerosol single particle beam through the laser focusing lens 5, burning The aerosol particles are eroded to generate plasma. The light radiated by the plasma is collimated, split, and filtered by the spectrum acquisition unit 13, and then irradiated onto the photosensitive surfaces of the first photomultiplier tube 14 and the second photomultiplier tube 21. The timing controller 2 triggers the first photomultiplier tube 14 and the second photomultiplier tube 21 at a fixed time to collect light signals. The data acquisition card 20 then samples the electrical signals output by the first photomultiplier tube 14 and the second photomultiplier tube 21 and outputs them to the computer 4. Finally, the computer 4 receives and stores the signals output by the data acquisition card 20, analyzes them into spectral data, and obtains the types and contents of elements contained in single aerosol particles.

[0039] In a preferred embodiment of the present invention, the parabolic mirror 8 has a focal length of 2.45 mm, an opening of 8 mm on the left side and a opening of 37.5 mm on the right side, and the inner wall is coated with a UV-enhanced aluminum film; the dichroic mirror 17 is a long-wave dichroic mirror, which has high reflectivity in the short-wave region and high transmittance in the long-wave region; the first narrowband filter 16 has a passband band located in the short-wave region of the dichroic mirror, a bandwidth of less than 1 nm, a transmittance within the bandwidth of 90%, and a bandwidth including the wavelength corresponding to the characteristic spectrum line of a certain element to be measured contained in the sample to be measured, with a diameter of 25.4 mm; the second narrowband filter 19 has a passband band located in the long-wave region of the dichroic mirror 17 The bandwidth is less than 1nm, the transmittance within the bandwidth is 90%, the bandwidth includes the wavelength corresponding to the characteristic spectrum line of another element to be measured contained in the sample to be measured, and the diameter is 25.4mm; the first focusing lens 15 is a plano-convex lens coated with an ultraviolet anti-reflection film, with a diameter of 25.4mm and a focal length of 50mm; the second focusing lens 18 is a plano-convex lens coated with an infrared anti-reflection film, with a diameter of 25.4mm and a focal length of 50mm; the photosensitive surface diameter of the first photomultiplier tube 14 is 8mm, and the gate width can be set from 100ns to infinity; the photosensitive surface diameter of the second photomultiplier tube 21 is 8mm, and the gate width can be set from 100ns to infinity.

[0040] It will be easily understood by those skilled in the art that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A highly sensitive aerosol single particle detection device using laser-induced breakdown spectroscopy, characterized in that: The detection device comprises an aerosol sampling unit (7), a laser excitation unit (1), a spectrum collection unit (13) and a control unit (22), wherein: The aerosol sampling unit (7) and the laser excitation unit (1) are arranged perpendicular to each other, and the aerosol sampling unit (7) is used to collect aerosol and form an aerosol single particle beam; The laser excitation unit (1) is used to generate pulsed laser to ablate the aerosol single particle beam generated by the aerosol injection unit (7) and generate plasma; The spectrum acquisition unit (13) includes a parabolic mirror (8), a dichroic mirror (17), a first acquisition component and a second acquisition component. The parabolic mirror (8) is arranged at the intersection of the aerosol sampling unit (7) and the laser excitation unit (1) and is used to collimate the light emitted by the plasma; the dichroic mirror (17) is arranged in the propagation direction of the collimated light, and its mirror surface forms an angle of 45 degrees with the collimated light, and is used to separate the characteristic spectrum line of the element to be measured in the collimated light, so as to divide the collimated light into reflected light and transmitted light and send them to the first acquisition component and the second acquisition component respectively; the first acquisition component includes a first narrowband filter (16), a first focusing lens (15) and a first photomultiplier tube (14) arranged in sequence along the propagation direction of the reflected light, and is used to pass the light beam of the characteristic spectrum line of a certain element to be measured and convert it into an electrical signal; the second acquisition component includes a second narrowband filter (19), a second focusing lens (18) and a second photomultiplier tube (21) arranged in sequence along the propagation direction of the transmitted light, and is used to pass the light beam of the characteristic spectrum line of another element to be measured and convert it into an electrical signal; The control unit (22) is connected to the laser excitation unit (1) and the spectrum acquisition unit (13) and is used to control the test process and collect electrical signals for analysis to obtain the type and content of the element to be tested in the aerosol single particle, thereby realizing online detection of the aerosol single particle.

2. The laser-induced breakdown spectroscopy aerosol single particle highly sensitive detection device according to claim 1, characterized in that: The aerosol sampling unit (7) comprises an aerosol collector (6), an aerosol transport element (10), a pneumatic connecting element (11), a capillary tube (12) and an air extraction pump (9), wherein: the aerosol collector (6) is connected to the capillary tube (12) in sequence through the aerosol transport element (10) and the pneumatic connecting element (11) to collect aerosol in the air and transport it to the capillary tube (12); the capillary tube (12) is inserted from the top into the interior of the parabolic mirror (8) to form an aerosol single particle beam; and the air extraction pump (9) is inserted from the bottom into the interior of the parabolic mirror (8) to recover waste gas.

3. The laser-induced breakdown spectroscopy aerosol single particle highly sensitive detection device according to claim 1, characterized in that: The laser excitation unit (1) comprises a pulse laser (3) and a laser focusing lens (5) connected in sequence along a laser propagation direction; the pulse laser (3) is used to emit pulse laser light; the optical axis of the laser focusing lens (5) is collinear with the pulse laser light, and is used to focus the pulse laser light on a single aerosol particle beam to ablate the aerosol particle and generate plasma.

4. The laser-induced breakdown spectroscopy aerosol single particle highly sensitive detection device according to claim 1, characterized in that: The control unit (22) comprises a timing generator (2), a data acquisition card (20) and a computer (4); the timing generator (2) is respectively connected to the pulse laser (3), the first photomultiplier tube (14), the second photomultiplier tube (21) and the data acquisition card (20) to trigger their operation; the data acquisition card (20) is connected to the first photomultiplier tube (14) and the second photomultiplier tube (21) to collect the electrical signals output by them; and the computer (4) is connected to the data acquisition card (20) to read and analyze the electrical signals to obtain the type and content of the element to be measured in the aerosol single particle.

5. The laser-induced breakdown spectroscopy aerosol single particle highly sensitive detection device according to claim 3, characterized in that: The laser focusing lens (5) is an aspheric plano-convex lens coated with a laser anti-reflection film.

6. The laser-induced breakdown spectroscopy aerosol single particle highly sensitive detection device according to any one of claims 1 to 5, characterized in that: The parabolic mirror (8) is a parabolic mirror coated with an ultraviolet-enhanced aluminum film.

7. The laser-induced breakdown spectroscopy aerosol single particle highly sensitive detection device according to any one of claims 1 to 5, characterized in that: The dichroic mirror (17) is a long-wavelength dichroic mirror, and its operating wavelength range is from ultraviolet to near-infrared.

8. The highly sensitive laser-induced breakdown spectroscopy aerosol single particle detection device according to any one of claims 1 to 5, characterized in that: The first narrowband filter (16) and the second narrowband filter (19) are filters with narrow half-width, and are installed in a filter wheel to achieve switching of the narrowband filters.

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