An atmospheric pollutant in-situ qualitative and quantitative detection system and detection method

Abstract

The application discloses an atmospheric pollutant in-situ qualitative and quantitative detection system and a detection method. The system comprises a first-stage vacuum system, a second-stage vacuum system and a third-stage vacuum system which are connected in sequence through differential holes. The first-stage vacuum system comprises an aerosol particle focusing inlet structure for forming a collimated particle beam from aerosol particles in a sample and a first-stage vacuum cavity. The second-stage vacuum system comprises a second-stage vacuum cavity and a second-stage vacuum pump. A diameter measuring module and an optical multi-cell module are arranged in the second-stage vacuum cavity. The third-stage vacuum system comprises a third-stage vacuum cavity and an aerosol particle spectrum / mass spectrum detection unit. The application can realize synchronous in-situ online qualitative and quantitative detection of aerosol particles and gaseous pollutants.

Description

Technical Field

[0001] This invention relates to the field of laser detection technology for air pollutants, specifically to an in-situ qualitative and quantitative detection system and method for atmospheric pollutants. Background Technology

[0002] Common ambient air pollutants mainly include aerosol particulate matter, volatile organic compounds (VOCs), and nitrogen oxides (NOx). X Sulfur dioxide (SO2), carbon dioxide (CO2), carbon monoxide (CO), ozone (O3), and other air pollutants typically exist in a mixed state in ambient air. When conducting analysis of the composition and content of ambient air pollutants, due to the significant differences in the physicochemical properties of aerosol particles and various gaseous pollutants, it is often necessary to equip specialized instruments and equipment for simultaneous sampling and analysis based on the type of target pollutant. This results in high manpower and material costs, and there is also the possibility of cross-interference between different types of pollutants affecting the analysis results.

[0003] Online quantitative detection of aerosol particulate matter primarily utilizes the light scattering method, based on Rayleigh scattering. Aerosol particles are focused into a beam through a nozzle or aerodynamic lens, causing them to accelerate under low pressure or vacuum conditions. The scattered light signal generated when the aerosol particles are irradiated by a laser is collected and converted into an electrical signal, allowing for the counting and statistical analysis of the aerosol particles. Commonly available commercial instruments include aerodynamic particle size analyzers and atmospheric dust monitors.

[0004] Online qualitative detection methods for aerosol particles mainly include single-particle aerosol time-of-flight mass spectrometry (TOF-MS), laser-induced breakdown spectroscopy (LAS-MS), and aerosol optical tweezers Raman spectroscopy. Single-particle aerosol TOF-MS utilizes vacuum ionization techniques such as high-energy pulsed lasers and electron bombardment to decompose aerosol particles into ions. These ions are accelerated by an accelerating electric field into a vacuum field-free flight region, ultimately reaching a microchannel plate ion detector where their vacuum flight time is recorded. Based on different ion flight times and their signal intensities, corresponding mass spectra can be obtained, allowing analysis of the aerosol particles' chemical composition. LAS-MS excites aerosol particles with a laser, forming a high-temperature plasma, from which elemental composition information is obtained. Aerosol optical tweezers Raman spectroscopy utilizes optical tweezers to confine and capture suspended aerosol particles. Combined with Raman spectroscopy, it enables high-precision manipulation and non-destructive analysis of the molecular structure characteristics of typical airborne particles such as single cells and nanoparticles.

[0005] The mainstream methods for online quantitative and qualitative detection of gaseous pollutants include optical spectroscopy, electrochemical sensor methods, chromatography-mass spectrometry, and ion mobility spectrometry. Among them, optical spectroscopy commonly uses non-dispersive infrared spectroscopy, tunable diode laser absorption spectroscopy, and online Fourier transform infrared spectroscopy. Based on the Lambert-Beer law or molecular characteristic spectral responses, it is the core technology for fixed-source CEMS and online ambient air monitoring, and has advantages such as strong anti-interference and stable continuous operation. Electrochemical sensor methods are mainly based on the oxidation / reduction reaction of gases at the contact of the sensor's working electrode. The current signal is proportional to the concentration, and it has the advantages of low cost and miniaturization, making it suitable for portable online monitoring and emergency inspection. However, it is susceptible to cross-gas interference and requires periodic calibration. Chromatography-mass spectrometry mainly uses chromatographic separation combined with mass spectrometry / dedicated detectors for qualitative and quantitative analysis. It is suitable for the analysis of complex VOCs components, and online implementation requires an automatic pre-concentration system. Proton transfer reaction mass spectrometry can quickly detect trace gases such as VOCs, odorous substances, and halogenated hydrocarbons online. It has a fast response speed and does not require chromatographic separation, but it relies on standard calibration, which limits the quantitative accuracy. It also does not respond to poorly ionized substances such as saturated alkanes.

[0006] The above-mentioned online qualitative and quantitative detection methods for aerosol particles and gaseous pollutants have the following problems: 1. The detection methods are scattered. Aerosol particles and gaseous pollutants need to be sampled and detected using different specialized instruments, which not only increases the cost of equipment purchase and maintenance, but also increases the complexity of on-site deployment and operation; 2. Cross-interference is difficult to avoid. During the detection of different types of pollutants, aerosol particles may interfere with the spectral, mass spectrometric, or electrochemical detection signals of gaseous pollutants, leading to a decrease in the accuracy of the detection results; 3. Some technologies have functional limitations. For example, the light emission method can only detect the particle size distribution of aerosol particles but cannot obtain chemical components. The electrochemical sensor method is susceptible to cross-gas interference and requires frequent calibration. Proton transfer reaction mass spectrometry does not respond to poorly ionized substances such as saturated alkanes. Online chromatography-mass spectrometry requires a pre-concentration system, resulting in a slow response speed; 4. There is a lack of integrated in-situ online detection solutions, making it impossible to simultaneously achieve real-time qualitative and quantitative analysis of aerosol particles and gaseous pollutants, which is difficult to meet the needs of monitoring complex air pollution. Summary of the Invention

[0007] One of the objectives of this invention is to provide an in-situ qualitative and quantitative detection system for atmospheric pollutants. Based on vacuum single-particle focusing injection technology, it utilizes the inertial separation mechanism between aerosol particle beams and gaseous pollutants during their inertial flight to achieve simultaneous in-situ online qualitative and quantitative detection of aerosol particles and gaseous pollutants.

[0008] The technical solution adopted to achieve the above-mentioned objectives of the present invention is as follows:

[0009] An in-situ qualitative and quantitative detection system for atmospheric pollutants includes a first-stage vacuum system, a second-stage vacuum system, and a third-stage vacuum system connected sequentially through differential orifices;

[0010] The first-stage vacuum system includes an aerosol particle focusing and injection structure for forming a collimated particle beam from aerosol particles in a sample and a first-stage vacuum chamber, wherein the aerosol particle focusing and injection structure is located upstream of the first-stage vacuum chamber.

[0011] The second-stage vacuum system includes a second-stage vacuum chamber and a second-stage vacuum pump. The second-stage vacuum chamber houses a diameter measuring module and an optical multi-pass cell module. The diameter measuring module includes an ellipsoidal mirror and a photomultiplier tube. The optical multi-pass cell module includes an optical multi-pass cell cavity connected to the second-stage vacuum pump. The optical multi-pass cell cavity has a laser inlet, a gaseous contaminant inlet, and a laser output port. The laser output port is connected to a photodetector. The second-stage vacuum system is also equipped with an optical path module, which includes a tunable continuous laser, a focusing lens, a first beam splitter, a reflecting mirror, and a second beam splitter. The continuous laser emitted by the tunable continuous laser is focused into a laser beam of the target width by the focusing lens and then passes through the... The first beam splitter divides the laser beam into a transmission direction laser and a reflection direction laser. The transmission direction laser enters the laser entrance of the optical multi-pass cell cavity. The reflection direction laser is emitted to the second beam splitter after the optical path is corrected by the reflector. The second beam splitter splits the laser beam into two co-directional diameter measuring lasers. When the collimated particle beam formed by aerosol particles in the sample passes through the diameter measuring laser, the particle scattering light generated is collected and focused by the ellipsoidal mirror into the photomultiplier tube and converted into a photoelectric signal. The gaseous pollutants in the sample enter the optical multi-pass cell cavity through the gaseous pollutant inlet under the action of the second-stage vacuum pump. The photodetector measures the laser photoelectric signal output from the laser output port of the optical multi-pass cell cavity.

[0012] The third-stage vacuum system includes a third-stage vacuum chamber and an aerosol particle spectral / mass spectrometry detection unit, used to detect the spectral / mass spectrometry information of aerosol particles in the collimated particle beam entering the third-stage vacuum system from the second-stage vacuum system;

[0013] It also includes a data acquisition and control module, which is connected to the tunable continuous laser, the photomultiplier tube, the photodetector, and the aerosol particle spectroscopy / mass spectrometry detection unit. The data acquisition and control module acquires and continuously controls the laser wavelength of the tunable continuous laser; acquires the photoelectric signal output by the photomultiplier tube and obtains the flight velocity and aerodynamic particle size information of each aerosol particle based on the two diameter-measuring laser beams, which is used to predict the time for each aerosol particle to reach the laser desorption / ionization region of the aerosol particle spectroscopy / mass spectrometry detection unit in the third-stage vacuum system; acquires the laser photoelectric signal of the photodetector, and combines it with the laser wavelength information fed back by the tunable continuous laser to obtain the laser intensity attenuation rate distribution data of the characteristic bands of gaseous pollutants in the sample, thereby obtaining the corresponding laser absorption spectrum information of the gaseous pollutants.

[0014] The first-stage vacuum system, second-stage vacuum system, and third-stage vacuum system of this invention are, respectively, a low-vacuum system, a high-vacuum system, and an ultra-high-vacuum system. The first-stage vacuum system uses vacuum single-particle focusing injection technology to focus aerosol particles into a collimated particle beam. In the second-stage vacuum system, after the collimated particle beam formed by the aerosol particles is inertially separated from the gaseous pollutants, the in-situ online qualitative and quantitative integrated detection and analysis of aerosol particles and gaseous pollutants in the air is achieved through an aerosol particle spectroscopy / mass spectrometry detection unit and an optical multi-pass cell module. The optical path module is designed based on the optical path layout of a tunable continuous laser and a dual-beam diameter measurement method. A single laser can complete dual-beam diameter measurement of aerosol particles and detection of gaseous pollutant components using optical multi-pass cell laser absorption spectroscopy. Simultaneously, the aerosol particle spectroscopy / mass spectrometry detection unit performs laser ionization mass spectrometry detection of aerosol particles, making in-situ online detection of aerosol particles and gaseous pollutants feasible.

[0015] The present invention also has the following preferred designs:

[0016] The aerosol particle focusing and injection structure of the present invention includes an inlet, a critical orifice, a buffer chamber, an injection focusing lens group, and an accelerating nozzle connected in sequence. The sample enters the first-stage vacuum system through the inlet. The critical orifice is used to limit the flow rate of the sample gas and maintain a suitable vacuum injection pressure downstream. The orifice diameter can be 0.05 mm to 0.35 mm to provide a suitable vacuum pressure to the downstream injection focusing lens group. The buffer chamber is used to buffer the aerosol particles and airflow downstream of the critical orifice, avoiding particle transport collision losses caused by inertial expansion of aerosol particles under the supersonic accelerated airflow of the critical orifice. The injection focusing lens group is composed of multiple orifice plate structures with a certain spacing. When aerosol particles pass through the orifice plate structure, the airflow upstream of the orifice plate contracts and accelerates, and the aerosol particles... Under the drag of the airflow, the particles contract, converge, and accelerate forward due to inertia. Based on the inertial difference between gas molecules and aerosol particles, the aerosol particles form a collimated particle beam with a certain beam width after passing through multiple orifice plate structures. The diameter of the collimated particle beam is usually controlled within 1 mm. As a feasible implementation, the thickness of the orifice plate can be set to 0.5 mm to 1.0 mm, the spacing between the orifice plates can be 20 mm to 100 mm, the orifice diameter can be 2 mm to 6 mm, and the number of orifice plates can be 3 to 7. The accelerating nozzle is located downstream of the sample introduction focusing lens group and is used to control the collimated particle beam transmitted upstream to further accelerate forward. At the same time, it is used to transition the vacuum pressure between the sample introduction focusing lens group and the downstream first-stage vacuum chamber. The nozzle orifice diameter of the accelerating nozzle can be 2 mm to 4 mm.

[0017] The first-stage vacuum chamber of the present invention is connected to a first-stage vacuum pump.

[0018] The differential aperture of the present invention is used to isolate the vacuum environment between adjacent first-stage vacuum systems, second-stage vacuum systems and third-stage vacuum systems, and the diameter of the two differential apertures can be set to 1 mm.

[0019] The focusing lens of the optical path module described in this invention controls the diameter of the laser beam to about 0.5 mm.

[0020] The third-stage vacuum cavity of this invention is equipped with an accelerating electrode, a positive ion reflecting electrode, a negative ion reflecting electrode, a positive ion detector, and a negative ion detector. A pulsed ionizing laser is disposed outside the third-stage vacuum cavity. The positive ion detector and the negative ion detector are connected to the data acquisition and control module. These devices constitute an aerosol particle spectral / mass spectrometry detection unit. A collimated particle beam leaves the second-stage vacuum cavity and enters the accelerating electrode of the third-stage vacuum cavity. The region where the accelerating electrode is located serves as the laser desorption / ionization region. The pulsed ionizing laser emits high-energy ionizing laser light to irradiate the aerosol particles passing through the accelerating electrode. The electric field of the accelerating electrode... In this process, the positive and negative ions generated by the desorption and ionization of aerosol particles fly in opposite directions in an accelerating electric field. In the third-stage vacuum chamber, they are repelled by the electric fields of the positive and negative ion reflecting electrodes, changing their flight direction. They then fly to the positive and negative ion detectors, respectively. The ion flight time and ion signal intensity acquired by the positive and negative ion detectors are transmitted to the data acquisition and control module. Since there is a corresponding relationship between the flight times of ions with different mass-to-charge ratios under the same electric field, the mass spectrum information of the aerosol particles can be obtained. The chemical composition information of the aerosol particles can be obtained by analyzing the mass spectrum.

[0021] The third-stage vacuum chamber of this invention is connected to a third-stage vacuum pump.

[0022] The second objective of this invention is to provide a detection method using the above-mentioned in-situ qualitative and quantitative detection system for air pollutants, comprising the following steps:

[0023] S100: The sample enters the first-stage vacuum system. The aerosol particles in the sample are accelerated by the aerosol particle focusing and injection structure to form a collimated particle beam. The collimated particle beam and gaseous pollutants in the sample enter the second-stage vacuum system through the differential orifice.

[0024] S200: The collimated particle beam continues to move forward due to inertia in the second-stage vacuum system and enters the diameter measurement module. When the aerosol particles in the collimated particle beam pass through the diameter measurement laser, the scattered light generated by the particles is collected and focused by the ellipsoidal mirror into the photomultiplier tube and converted into a photoelectric signal. The particle flight time of each aerosol particle passing through the two laser beams can be measured by the two diameter measurement laser beams, and then the corresponding particle flight speed and aerodynamic particle size information can be calculated. The particle flight speed is used to predict the time for the aerosol particles to reach the laser desorption ionization region in the third-stage vacuum system.

[0025] Gaseous contaminants in the sample diffuse through the second-stage vacuum system and are drawn into the optical multi-pass cell cavity. The gaseous contaminants undergo inertial separation from the collimated particle beam and, after passing through a laser beam path with multiple reflections within the optical multi-pass cell cavity, the laser photoelectric signal output by the optical multi-pass cell module is measured by a photodetector, thereby obtaining the laser absorption spectrum of the gaseous contaminants. Specifically,

[0026] In the process from aerosol particle diameter measurement to laser desorption / ionization mass spectrometry detection, gaseous pollutants in the sample are separated from the collimated particle beam and diffuse into the second-stage vacuum chamber under the action of the second-stage vacuum pump. Then, they enter the optical multi-pass cell chamber through the gaseous pollutant inlet. After being absorbed by laser irradiation, they are discharged to the external environment by the second-stage vacuum pump. After being absorbed by the gaseous pollutants, the laser in the optical multi-pass cell chamber is output from the laser output port to the photodetector. The photodetector converts the received laser intensity signal into an electrical signal. Combined with the laser wavelength information fed back by the tunable continuous laser, it is synchronously transmitted to the data acquisition and control module to obtain the laser intensity attenuation rate distribution data of the characteristic band of the gaseous pollutants. Thus, the corresponding laser absorption spectrum information of the gaseous pollutants is obtained, and the molecular composition and content information of the gaseous pollutants are obtained.

[0027] S300: The collimated particle beam enters the third-stage vacuum system through the differential aperture. Based on the flight velocity of individual aerosol particles measured in the second-stage vacuum system, the trigger time of the pulsed ionization laser corresponding to each aerosol particle is obtained. The corresponding aerosol particles are irradiated by the pulsed ionization laser emitted by the pulsed ionization laser of the aerosol particle spectral / mass spectrometry detection unit, and the spectral / mass spectrometry information of the aerosol particles is obtained, thereby analyzing the chemical composition information of individual aerosol particles.

[0028] S400: By collecting the number distribution of aerosol particles in each particle size range, the average spectrum / mass spectrum of aerosol particles, and the average laser absorption spectrum of gaseous pollutants in each time period, the physicochemical information such as the number concentration of aerosol particles, the particle size distribution of aerosol particles, the chemical composition of aerosol particles, the concentration of gaseous pollutants, and the chemical composition of gaseous pollutants in the sample in each time period can be statistically analyzed.

[0029] The present invention has the following beneficial effects:

[0030] 1. The first-stage vacuum system of this invention uses vacuum single-particle focusing injection technology to focus aerosol particles into a collimated particle beam. In the second-stage vacuum system, the collimated particle beam formed by aerosol particles is inertially separated from gaseous pollutants. The in-situ online qualitative and quantitative integrated detection and analysis of aerosol particles and gaseous pollutants in the air is realized through the aerosol particle spectroscopy / mass spectrometry detection unit and the optical multi-pass cell module, respectively. This overcomes the problems of redundancy, cross-contamination interference, and low efficiency of composite analysis of detected substances in traditional air pollutant detection instruments.

[0031] 2. The optical path module design of this invention is based on the optical path layout of a tunable continuous laser and the method of dual-beam diameter measurement. The optical path module can complete dual-beam diameter measurement of aerosol particles and detection of gaseous pollutant components by optical multi-pass cell laser absorption spectroscopy using a single laser. At the same time, an aerosol particle spectroscopy / mass spectrometry detection unit is used to perform laser ionization mass spectrometry detection of aerosol particles. This makes in-situ online detection of aerosol particles and gaseous pollutants feasible, improves the utilization rate of laser detection, and reduces the hardware and space costs of laser detection. Attached Figure Description

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0033] Figure 1 This is a schematic diagram illustrating the principle of an in-situ qualitative and quantitative detection system for air pollutants according to the present invention.

[0034] Figure 2 This is a schematic diagram of the structural connection of an in-situ qualitative and quantitative detection system for air pollutants according to an embodiment of the present invention;

[0035] Figure 3 This is a flowchart of an in-situ qualitative and quantitative detection method for air pollutants according to the present invention;

[0036] Figure 4 This is a timing control principle diagram of the data acquisition control module in an embodiment of the present invention.

[0037] Explanation of reference numerals in the attached figures:

[0038] 100: Aerosol particle focusing and injection structure; 101: Inlet; 102: Critical orifice; 103: Buffer chamber; 104: Injection focusing lens group; 105: Accelerating nozzle; 106: First-stage vacuum chamber; 107: First-stage vacuum pump; 108: First differential orifice; 201: Second-stage vacuum chamber; 202: Ellipsoidal mirror; 203: Photomultiplier tube; 204: Tunable continuous laser; 205: Focusing lens; 206: First beam splitter; 207: Reflector; 208: Second beam splitter; 209: Laser entrance port; 210: Optical multi-pass cell cavity; 211: Gaseous pollutant inlet; 212: Laser output port; 213: Photodetector; 214: Second-stage vacuum pump; 215: Second differential aperture; 300: Aerosol particle spectroscopy / mass spectrometry detection unit; 301: Third-stage vacuum cavity; 302: Accelerating electrode; 303 304: Pulsed ionizing laser; 305: Positive ion reflecting electrode; 306: Positive ion detector; 307: Negative ion detector; 308: Third-stage vacuum pump; 400: Data acquisition and control module; 401: Photoelectric signal of aerosol particle scattered light; 402: Pulsed ionizing laser trigger level signal; 403: Positive ion detector trigger acquisition level signal; 404: Negative ion detector trigger acquisition level signal; 405: Gaseous pollutant laser absorption spectrum trigger acquisition level signal; 4011: Flight time of aerosol particles between two diameter-measuring laser beams; 4012: Pulsed ionizing laser trigger time; 4021: Ion detector acquisition trigger time; 4031: Positive ion detector acquisition time; 4041: Negative ion detector acquisition time; 4051: Gaseous pollutant laser absorption spectrum acquisition time; 500: Computer. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the present invention more apparent, exemplary embodiments according to the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are merely a part of the embodiments of the present invention, and not all of the embodiments of the present invention. It should be understood that the present invention is not limited to the exemplary embodiments described herein. Based on the embodiments of the present invention described herein, all other embodiments obtained by those skilled in the art without inventive effort should fall within the protection scope of the present invention.

[0040] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0041] Example:

[0042] An in-situ qualitative and quantitative detection system for air pollutants, such as Figure 1 and Figure 2 As shown, it includes a first-stage vacuum system, a second-stage vacuum system, and a third-stage vacuum system connected in sequence through differential orifices;

[0043] The first-stage vacuum system includes an aerosol particle focusing and injection structure 100 for forming a collimated particle beam from aerosol particles in a sample and a first-stage vacuum chamber 106, wherein the aerosol particle focusing and injection structure 100 is disposed upstream of the first-stage vacuum chamber 106.

[0044] The second-stage vacuum system includes a second-stage vacuum chamber 201 and a second-stage vacuum pump 214. The second-stage vacuum chamber 201 contains a diameter measuring module and an optical multi-pass cell module. The diameter measuring module includes an ellipsoidal mirror 202 and a photomultiplier tube 203. The optical multi-pass cell module includes an optical multi-pass cell cavity 210 connected to the second-stage vacuum pump 214. The optical multi-pass cell cavity 210 has a laser inlet 209, a gaseous contaminant inlet 211, and a laser outlet 212. The laser outlet 212 is connected to a photodetector 213. The second-stage vacuum system is equipped with an optical path module, which includes a tunable continuous laser 204, a focusing lens 205, a first beam splitter 206, a reflector 207, and a second beam splitter 208. The continuous laser emitted by the tunable continuous laser 204 is focused by the focusing lens 209. 5. After being focused into a laser beam of the target width, the laser beam is split into a transmission laser and a reflection laser by the first beam splitter 206. The transmission laser enters the laser entrance 209 of the optical multi-pass cell cavity 210. The reflection laser is emitted to the second beam splitter 208 after the optical path is corrected by the reflector 207. The second beam splitter 208 splits the laser beam into two unidirectional diameter-measuring lasers. When the collimated particle beam formed by aerosol particles in the sample passes through the diameter-measuring laser, the particle scattering light generated is collected by the ellipsoidal mirror 202 and converged into the photomultiplier tube 203, which converts it into a photoelectric signal. The gaseous pollutants in the sample enter the optical multi-pass cell cavity 210 through the gaseous pollutant inlet 211 under the action of the second-stage vacuum pump 214. The photodetector 213 measures the laser photoelectric signal output from the laser output port 212 of the optical multi-pass cell cavity 210.

[0045] The third-stage vacuum system includes a third-stage vacuum chamber 301 and an aerosol particle spectral / mass spectrometry detection unit 300, which is used to detect the spectral / mass spectrometry information of aerosol particles in the collimated particle beam entering the third-stage vacuum system from the second-stage vacuum system.

[0046] It also includes a data acquisition and control module 400 connected to a computer 500. The data acquisition and control module 400 is connected to a tunable continuous laser 204, a photomultiplier tube 203, a photodetector 213, and an aerosol particle spectroscopy / mass spectrometry detection unit 300. The data acquisition and control module 400 acquires and continuously controls the laser wavelength of the tunable continuous laser 204, acquires the photoelectric signal output by the photomultiplier tube 203, and obtains the flight speed and aerodynamic particle size information of each aerosol particle based on the two diameter-measuring lasers. This information is used to predict the time it takes for each aerosol particle to reach the laser desorption / ionization region of the aerosol particle spectroscopy / mass spectrometry detection unit 300 in the third-stage vacuum system. The laser photoelectric signal of the photodetector 213 is acquired, and combined with the laser wavelength information fed back by the tunable continuous laser 204, the laser intensity attenuation rate distribution data of the characteristic bands of gaseous pollutants in the sample is obtained, thereby obtaining the corresponding laser absorption spectrum information of the gaseous pollutants.

[0047] In one embodiment, such as Figure 2 As shown, the aerosol particle focusing and injection structure 100 includes an inlet 101, a critical orifice 102, a buffer chamber 103, an injection focusing lens group 104, and an accelerating nozzle 105 connected in sequence. The sample enters the first-stage vacuum system through the inlet 101. The critical orifice 102 is used to limit the flow rate of the sample gas and maintain a suitable vacuum injection pressure downstream. The orifice diameter of the critical orifice 102 can be 0.05 mm to 0.35 mm to provide a suitable vacuum pressure to the downstream injection focusing lens group 104. The buffer chamber 103 is used to buffer the aerosol particles and airflow downstream of the critical orifice 102 to avoid inertial expansion of aerosol particles under the supersonic accelerating airflow of the critical orifice 102, which would cause particle transport collision loss. The injection focusing lens group 104 is composed of multiple orifice plate structures with a certain spacing. When aerosol particles pass through the orifice plate structure, the orifice... The upstream airflow contracts and accelerates. Under the drag force of the airflow, the aerosol particles contract, converge, and accelerate forward due to inertia. Based on the inertial difference between gas molecules and aerosol particles, the aerosol particles form a collimated particle beam with a certain beam width after passing through multiple orifice plate structures. The diameter of the collimated particle beam is usually controlled within 1 mm. The thickness of the orifice plate can be set to 0.5 mm to 1.0 mm, the orifice plate spacing can be 20 mm to 100 mm, the orifice plate diameter can be 2 mm to 6 mm, and the number of orifice plates can be 3 to 7. The accelerating nozzle 105 is located downstream of the sample introduction focusing lens group 104. It is used to control the collimated particle beam transmitted upstream to further accelerate forward and to transition the vacuum pressure between the sample introduction focusing lens group 104 and the downstream first-stage vacuum chamber 106. The nozzle orifice diameter of the accelerating nozzle 105 can be 2 mm to 4 mm.

[0048] In one embodiment, a first-stage vacuum chamber 106 is connected to a first-stage vacuum pump 107 for controlling the vacuum level inside the first-stage vacuum chamber 106.

[0049] Differential orifices are used to isolate the vacuum environment between adjacent first-stage vacuum systems, second-stage vacuum systems, and third-stage vacuum systems. In one embodiment, a first differential orifice 108 is provided between the first-stage vacuum chamber 106 and the second-stage vacuum chamber 201, and a second differential orifice 215 is provided between the second-stage vacuum chamber 201 and the third-stage vacuum chamber 301. The diameter of the two differential orifices can be set to 1 mm.

[0050] In one embodiment, the focusing lens 205 of the optical path module controls the diameter of the laser beam to about 0.5 mm.

[0051] In one embodiment, an accelerating electrode 302, a positive ion reflecting electrode 304, a negative ion reflecting electrode 305, a positive ion detector 306, and a negative ion detector 307 are disposed within the third-stage vacuum cavity 301. A pulsed ionization laser 303 is disposed outside the third-stage vacuum cavity 301. The positive ion detector 306 and the negative ion detector 307 are connected to a data acquisition and control module 400. The above devices constitute an aerosol particle spectroscopy / mass spectrometry detection unit 300. The collimated particle beam leaves the second-stage vacuum cavity 201 and enters the accelerating electrode 302 of the third-stage vacuum cavity 301. The region where the accelerating electrode 302 is located serves as the laser desorption / ionization region. The pulsed ionization laser 303 emits high-energy ionization laser light to irradiate the aerosol particle beam passing through the accelerating electrode 302. Under the electric field of accelerating electrode 302, the positive and negative ions generated by the desorption and ionization of aerosol particles fly in opposite directions in the accelerating electric field. In the third-stage vacuum chamber 301, they are changed in flight direction by the electric repulsion of positive ion reflecting electrode 304 and negative ion reflecting electrode 305, respectively. Then they fly to positive ion detector 306 and negative ion detector 307, respectively. The ion flight time and ion signal intensity acquired by positive ion detector 306 and negative ion detector 307 are transmitted to data acquisition and control module 400. Since there is a corresponding relationship between the flight time of ions with different mass-to-charge ratios under the same electric field, the mass spectrum information of aerosol particles can be obtained. The chemical composition information of aerosol particles can be obtained by analyzing the mass spectrum.

[0052] In one embodiment, the third-stage vacuum chamber 301 is connected to a third-stage vacuum pump 308 for controlling the vacuum level within the third-stage vacuum chamber 301.

[0053] The first-stage vacuum system, second-stage vacuum system, and third-stage vacuum system of this invention are, respectively, a low-vacuum system, a high-vacuum system, and an ultra-high-vacuum system. The first-stage vacuum system uses vacuum single-particle focusing injection technology to focus aerosol particles into a collimated particle beam. In the second-stage vacuum system, after the collimated particle beam formed by the aerosol particles is inertially separated from the gaseous pollutants, the in-situ online qualitative and quantitative integrated detection and analysis of aerosol particles and gaseous pollutants in the air is achieved through the aerosol particle spectroscopy / mass spectrometry detection unit 300 and the optical multi-pass cell module, respectively. The optical path module is designed based on the optical path layout of a tunable continuous laser and the dual-beam diameter measurement method. A single laser can complete the dual-beam diameter measurement of aerosol particles and the detection of gaseous pollutant components by optical multi-pass cell laser absorption spectroscopy. Simultaneously, the aerosol particle spectroscopy / mass spectrometry detection unit 300 performs laser ionization mass spectrometry detection of aerosol particles, making in-situ online detection of aerosol particles and gaseous pollutants feasible.

[0054] like Figure 3 As shown, the detection method using the above-mentioned in-situ qualitative and quantitative detection system for air pollutants includes the following steps:

[0055] S100: The sample enters the first-stage vacuum system. The aerosol particles in the sample are accelerated by the aerosol particle focusing and injection structure 100 to form a collimated particle beam. The collimated particle beam and gaseous pollutants in the sample enter the second-stage vacuum system through the differential orifice.

[0056] S200: The collimated particle beam continues to move forward under inertial force in the second-stage vacuum system and enters the diameter measurement module. When the aerosol particles in the collimated particle beam pass through the diameter measurement laser, the scattered light generated by the particles is collected and focused by the ellipsoidal mirror 202 and converted into a photoelectric signal in the photomultiplier tube 203. The particle flight time of each aerosol particle passing through the two diameter measurement lasers can be measured, and then the corresponding particle flight speed and aerodynamic particle size information can be calculated. The particle flight speed is used to predict the time when the aerosol particle reaches the laser desorption ionization region in the third-stage vacuum system. This time is the pulse ionization laser trigger time corresponding to the aerosol particle.

[0057] Gaseous contaminants in the sample diffuse through the second-stage vacuum system and are drawn into the optical multi-pass cell cavity. The gaseous contaminants undergo inertial separation from the collimated particle beam and, after passing through a laser beam path with multiple reflections within the optical multi-pass cell cavity 210, the laser photoelectric signal output by the optical multi-pass cell module is measured by the photodetector 213, thereby obtaining the laser absorption spectrum of the gaseous contaminants. Specifically,

[0058] In the process from aerosol particle diameter measurement to laser desorption / ionization mass spectrometry detection, gaseous pollutants in the sample are separated from the collimated particle beam and diffuse into the second-stage vacuum chamber 201 under the action of the second-stage vacuum pump 214. Then, they enter the optical multi-pass cell chamber 210 through the gaseous pollutant inlet 211. After being absorbed by laser irradiation, they are discharged to the external environment by the second-stage vacuum pump 214. After being absorbed by the gaseous pollutants, the laser in the optical multi-pass cell chamber 210 is output from the laser output port 212 to the photodetector 213. The photodetector 213 converts the received laser intensity signal into an electrical signal. Combined with the laser wavelength information fed back by the tunable continuous laser 204, the signal is synchronously transmitted to the data acquisition and control module 400 to obtain the laser intensity attenuation rate distribution data of the characteristic band of the gaseous pollutants. Thus, the corresponding laser absorption spectrum information of the gaseous pollutants is obtained, and the molecular composition and content information of the gaseous pollutants are obtained.

[0059] S300: The collimated particle beam enters the third-stage vacuum system through the differential aperture. Based on the flight velocity of individual aerosol particles measured in the second-stage vacuum system, the trigger time of the pulsed ionization laser corresponding to each aerosol particle is obtained. The pulsed ionization laser 303 of the aerosol particle spectral / mass spectrometry detection unit 300 emits a high-energy pulsed laser to irradiate the corresponding aerosol particles, thereby obtaining the spectral / mass spectrometry information of the aerosol particles and analyzing the chemical composition information of individual aerosol particles.

[0060] S400: By collecting the number distribution of aerosol particles in each particle size range, the average spectrum / mass spectrum of aerosol particles, and the average laser absorption spectrum of gaseous pollutants in each time period, the physicochemical information such as the number concentration of aerosol particles, the particle size distribution of aerosol particles, the chemical composition of aerosol particles, the concentration of gaseous pollutants, and the chemical composition of gaseous pollutants in the sample in each time period can be statistically analyzed.

[0061] Figure 4 This is a timing control principle diagram of the data acquisition and control module 400. In the photoelectric signal 401 of aerosol particle scattered light acquired by the photomultiplier tube 203, the time between two peaks is the flight time 4011 of the aerosol particle between the two diameter-measuring laser beams. Based on the distance between the two diameter-measuring laser beams, the flight velocity of the aerosol particle can be calculated, which is used to predict the time it takes for the particle to reach a specific position in the aerosol particle spectral / mass spectrometry detection unit 300. In this embodiment, this time is called the pulsed ionization laser trigger time 4012, corresponding to... Figure 2The pulsed ionization laser trigger time 4012 is the time it takes for an aerosol particle to travel from the diameter-measuring laser to the center of the accelerating electrode 302. Knowing the pulsed ionization laser trigger time 4012, it can be combined with other aerosol particle qualitative detection methods such as laser ionization mass spectrometry, thermal ionization mass spectrometry, laser-induced breakdown spectroscopy, laser Raman spectroscopy, laser-induced fluorescence spectroscopy, and laser photoacoustic spectroscopy to simultaneously and qualitatively detect the chemical composition information of each aerosol particle. Figure 2 and Figure 4 As shown, in one embodiment, a pulsed ionization laser 303 is triggered by a pulsed ionization laser trigger level signal 402. After a certain ion detector acquisition trigger time 4021, a positive ion detector acquisition level signal 403 and a negative ion detector acquisition level signal 404 are triggered to trigger positive ion detector 306 and negative ion detector 307, respectively. Positive and negative ion signals generated by the desorption and ionization of aerosol particles are collected at the corresponding positive ion detector acquisition time 4031 and negative ion detector acquisition time 4041. During laser diameter measurement, a photodetector 213 is triggered by a gaseous pollutant laser absorption spectrum trigger acquisition level signal 405. Laser intensity attenuation rate distribution data of the characteristic band of gaseous pollutants are collected at the corresponding gaseous pollutant laser absorption spectrum acquisition time 4051.

[0062] In some embodiments, the aerosol focusing and injection structure 100 is used to focus and accelerate aerosol particles into a collimated particle beam. It can employ existing technologies such as aerodynamic lenses, sheath gas-assisted accelerating nozzles, and capillaries. The optical multi-pass cell module extends the optical path through multiple reflection optical paths, detecting the gas component content by measuring the laser attenuation intensity distribution after absorption by a specific wavelength laser. It can be a built-in module of a tunable laser absorption spectrometer such as an Aerodyne N2O trace gas monitor, a Mesa Photonics Herriott cell module, or a Los Gatos Research UGGA-24EP (Ultraportable GHG). The photodetector 213 can be a Japanese Hamamatsu G12180-010C or a US Thorlabs PDA10D2. The aerosol particle spectrometer can be a Thermo Fisher Scientific ARL iSpark direct-reading spectrometer or an Alcatel-Lucent Calibus 3S. PLUS handheld laser-induced breakdown spectrometer, marine optical laser-induced laser spectrometer LIBS-MX2500+, etc.; aerosol particle mass spectrometers can be the Aerodyne AMS aerosol mass spectrometer (USA) or the domestic Hexin SPAMS single-particle aerosol time-of-flight mass spectrometer, etc.

[0063] The above embodiments of the present invention are not intended to limit the scope of protection of the present invention. The implementation of the present invention is not limited thereto. All other modifications, substitutions or alterations made to the above structure of the present invention based on the above content of the present invention, in accordance with ordinary technical knowledge and common practice in the field, without departing from the basic technical idea of ​​the present invention, shall fall within the scope of protection of the present invention.

Claims

1. An in-situ qualitative and quantitative detection system for air pollutants, characterized in that: It includes a first-stage vacuum system, a second-stage vacuum system, and a third-stage vacuum system connected sequentially via differential apertures; The first-stage vacuum system includes an aerosol particle focusing and injection structure for forming a collimated particle beam from aerosol particles in a sample and a first-stage vacuum chamber, wherein the aerosol particle focusing and injection structure is located upstream of the first-stage vacuum chamber. The second-stage vacuum system includes a second-stage vacuum chamber and a second-stage vacuum pump. The second-stage vacuum chamber houses a diameter measuring module and an optical multi-pass cell module. The diameter measuring module includes an ellipsoidal mirror and a photomultiplier tube. The optical multi-pass cell module includes an optical multi-pass cell cavity connected to the second-stage vacuum pump. The optical multi-pass cell cavity has a laser inlet, a gaseous contaminant inlet, and a laser output port. The laser output port is connected to a photodetector. The second-stage vacuum system is also equipped with an optical path module, which includes a tunable continuous laser, a focusing lens, a first beam splitter, a reflecting mirror, and a second beam splitter. The continuous laser emitted by the tunable continuous laser is focused into a laser beam of the target width by the focusing lens and then passes through the... The first beam splitter divides the laser beam into a transmission direction laser and a reflection direction laser. The transmission direction laser enters the laser entrance of the optical multi-pass cell cavity. The reflection direction laser is emitted to the second beam splitter after the optical path is corrected by the reflector. The second beam splitter splits the laser beam into two co-directional diameter measuring lasers. When the collimated particle beam formed by aerosol particles in the sample passes through the diameter measuring laser, the particle scattering light generated is collected and focused by the ellipsoidal mirror into the photomultiplier tube and converted into a photoelectric signal. The gaseous pollutants in the sample enter the optical multi-pass cell cavity through the gaseous pollutant inlet under the action of the second-stage vacuum pump. The photodetector measures the laser photoelectric signal output from the laser output port of the optical multi-pass cell cavity. The third-stage vacuum system includes a third-stage vacuum chamber and an aerosol particle spectral / mass spectrometry detection unit, used to detect the spectral / mass spectrometry information of aerosol particles in the collimated particle beam entering the third-stage vacuum system from the second-stage vacuum system; It also includes a data acquisition and control module, which is connected to the tunable continuous laser, the photomultiplier tube, the photodetector and the aerosol particle spectroscopy / mass spectrometry detection unit. The data acquisition and control module acquires and continuously controls the laser wavelength of the tunable continuous laser. The photoelectric signal output from the photomultiplier tube is collected, and the flight velocity and aerodynamic particle size information of each aerosol particle are obtained based on the two diameter-measuring laser beams. This information is used to predict the time it takes for each aerosol particle to reach the laser desorption / ionization region of the aerosol particle spectral / mass spectrometry detection unit in the third-stage vacuum system. The laser photoelectric signal from the photodetector is collected, and combined with the laser wavelength information fed back by the tunable continuous laser, the laser intensity attenuation rate distribution data of the characteristic band of gaseous pollutants in the sample is obtained, thereby obtaining the corresponding laser absorption spectrum information of the gaseous pollutants.

2. The in-situ qualitative and quantitative detection system for air pollutants according to claim 1, characterized in that: The aerosol particle focusing and injection structure includes an injection port, a critical orifice, a buffer chamber, an injection focusing lens group, and an accelerating nozzle connected in sequence. The injection focusing lens group is composed of multiple orifice plate structures with a certain spacing.

3. The in-situ qualitative and quantitative detection system for air pollutants according to claim 2, characterized in that: The diameter of the critical hole is 0.05 mm to 0.35 mm.

4. The in-situ qualitative and quantitative detection system for air pollutants according to claim 2, characterized in that: The thickness of the aperture plate of the sample focusing lens group is 0.5mm to 1.0mm, the aperture plate spacing is 20mm to 100mm, the aperture plate diameter is 2mm to 6mm, and the number of aperture plates is 3 to 7.

5. The in-situ qualitative and quantitative detection system for air pollutants according to claim 2, characterized in that: The nozzle orifice diameter of the acceleration nozzle can be 2mm to 4mm.

6. The in-situ qualitative and quantitative detection system for air pollutants according to claim 1, characterized in that: The first-stage vacuum system is connected to a first-stage vacuum pump, and the third-stage vacuum system is connected to a third-stage vacuum pump. The differential orifice, which is used to isolate the vacuum environment between adjacent first-stage, second-stage, and third-stage vacuum systems, has a diameter of 1 mm.

7. The in-situ qualitative and quantitative detection system for air pollutants according to claim 1, characterized in that: The third-stage vacuum chamber is equipped with an accelerating electrode, a positive ion reflecting electrode, a negative ion reflecting electrode, a positive ion detector, and a negative ion detector. A pulsed ionization laser is installed outside the third-stage vacuum chamber. The positive ion detector and the negative ion detector are connected to the data acquisition and control module. The pulsed ionizing laser emits high-energy ionizing laser light to irradiate aerosol particles passing through the accelerating electrode. Under the action of the electric field of the accelerating electrode, the positive and negative ions generated by the desorption and ionization of the aerosol particles fly in opposite directions in the accelerating electric field. In the third-stage vacuum cavity, they change their flight direction due to the electric repulsion of the positive and negative ion reflecting electrodes, respectively, and then fly to the positive ion detector and the negative ion detector, respectively. The ion flight time and ion signal intensity acquired by the positive and negative ion detectors are transmitted to the data acquisition and control module.

8. A detection method using the in-situ qualitative and quantitative detection system for air pollutants as described in any one of claims 1 to 7, characterized in that, Including the following steps: S100: The sample enters the first-stage vacuum system. The aerosol particles in the sample are accelerated by the aerosol particle focusing and injection structure to form a collimated particle beam. The collimated particle beam and gaseous pollutants in the sample enter the second-stage vacuum system through the differential orifice. S200: The collimated particle beam continues to move forward due to inertia in the second-stage vacuum system and enters the diameter measurement module. When the aerosol particles in the collimated particle beam pass through the diameter measurement laser, the scattered light generated by the particles is collected and focused by the ellipsoidal mirror into the photomultiplier tube and converted into a photoelectric signal. The particle flight time of each aerosol particle passing through the two laser beams can be measured by the two diameter measurement laser beams, and then the corresponding particle flight speed and aerodynamic particle size information can be calculated. The particle flight speed is used to predict the time for the aerosol particles to reach the laser desorption ionization region in the third-stage vacuum system. The gaseous pollutants in the sample diffuse in the second-stage vacuum system and are drawn into the optical multi-pass cell cavity. The gaseous pollutants are inertially separated from the collimated particle beam and pass through the laser light path that has been reflected multiple times in the optical multi-pass cell cavity. The laser photoelectric signal output by the optical multi-pass cell module is measured by the photodetector, and then the laser absorption spectrum of the gaseous pollutants is obtained. S300: The collimated particle beam enters the third-stage vacuum system through the differential aperture. Based on the flight velocity of individual aerosol particles measured in the second-stage vacuum system, the trigger time of the pulsed ionization laser corresponding to each aerosol particle is obtained. The corresponding aerosol particles are irradiated by the pulsed ionization laser emitted by the pulsed ionization laser of the aerosol particle spectral / mass spectrometry detection unit, and the spectral / mass spectrometry information of the aerosol particles is obtained, thereby analyzing the chemical composition information of individual aerosol particles. S400: By collecting the number distribution of aerosol particles in each particle size range, the average spectrum / mass spectrum of aerosol particles, and the average laser absorption spectrum of gaseous pollutants in each time period, statistical analysis is performed to obtain the number concentration of aerosol particles, the particle size distribution of aerosol particles, the chemical composition of aerosol particles, the concentration of gaseous pollutants, and the chemical composition of gaseous pollutants in the samples in each time period.

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