A sodium aerosol detection system and detection method in open air

Abstract

A system and method for detecting sodium aerosols in open air utilizes an energy conversion unit to convert battery-stored electrical energy into high-voltage DC. A nanosecond pulse generation unit converts the high-voltage DC into repetitive high-voltage nanosecond pulses. A gas extraction device in an open-air discharge device delivers the gas to be tested into the gap between coaxial metal rod electrodes. The repetitive high-voltage nanosecond pulses act on the open-air discharge device, generating a spark discharge across the gap. This process efficiently excites sodium aerosols through collision ionization and dissociation excitation, and the sodium deexcitation process forms a characteristic sodium spectral line. A fiber collimator collects all light emitted from the discharge gap and transmits it to a spectrometer. A pulse discharge and spectrometer time synchronization unit provides two synchronized trigger signals with an adjustable time difference. The spectrometer only captures light emitted during the spark discharge, improving the signal-to-noise ratio of the spectral signal. If the sodium characteristic spectral line measured by the spectrometer exceeds a preset limit, the presence of sodium aerosols in the open air is determined.

Description

Technical Field

[0001] The present invention relates to the field of sodium aerosol detection technology, and in particular to a sodium aerosol detection system and method in open air. Background Art

[0002] A sodium-cooled fast neutron reactor (SFR) is a fast neutron breeder reactor that uses liquid sodium metal as a coolant. Liquid sodium metal has excellent properties such as low density, high thermal conductivity, and a high boiling point. It also has a small neutron absorption cross-section and good compatibility with core materials. However, sodium is a reactive metal. When pipelines or equipment are damaged, liquid sodium metal may leak into the air and burn, leading to serious fire accidents and equipment damage. Therefore, real-time monitoring and early warning of liquid sodium metal leaks are of great significance to the safe and stable operation of sodium-cooled fast neutron reactors. In the early stages of a liquid sodium metal leak, sodium aerosols will form in the air. Daily equipment operation and maintenance require operators to regularly inspect and monitor the sodium aerosol content in the air. Real-time, accurate, and portable open air sodium aerosol detection sensors are urgently needed to monitor liquid sodium metal leaks.

[0003] Existing sodium metal leak detection principles at home and abroad include distributed or single-point contact sodium leak sensing, fluctuating sodium ionization sensing, laser ionization mass spectrometry, high-energy laser dissociation, sodium fire product monitoring, and microwave plasma methods using carrier gases such as argon. Distributed or single-point contact sodium leak sensing utilizes the electrical conductivity of sodium metal. When a sodium metal leak occurs, the liquid sodium short-circuits the two stainless steel wire electrodes of the distributed or single-point contact sodium leak sensor, generating a short-circuit signal. However, in the early stages of a liquid sodium leak, only trace amounts of sodium aerosol are present in the air, and the impedance between the two stainless steel wire electrodes is still extremely high, making this method suitable only for large-scale sodium metal leaks. Fluctuating sodium ionization sensing essentially monitors ion current under a DC voltage. Ion current fluctuations reflect the sodium aerosol content in the air. However, this method requires detecting weak currents in the hundreds of picoamps, requiring high current measurement accuracy from the measuring equipment. Moreover, the weak current amplitude is affected by the thermal noise of the resistive components in the detection circuit. The characteristic of laser oscillation ionization mass spectrometry is that it only detects metallic sodium isotopes, which is helpful for distinguishing between background sodium aerosols in the air and sodium aerosols generated by leaks in pipelines. It includes steps such as sampling, laser excitation atomization, laser oscillation, and sodium ion detection based on a mass spectrometer. However, this method requires complex equipment such as lasers and time-of-flight mass spectrometers, and is not suitable for on-site inspections. The high-energy laser dissociation method uses laser pulses to dissociate the sampled gas to form a local high-temperature plasma, and the sodium aerosol content is obtained by detecting the characteristic spectral lines of metallic sodium. The output energy stability of the high-energy laser determines the detection stability. However, the stable energy output of the laser requires strict temperature and humidity conditions, which is difficult to apply to on-site inspections. The basic principle of the sodium fire product monitoring method is to atomize the sampled gas through the combustion of organic gas. Similar to the high-energy laser dissociation method, the sodium aerosol content is obtained by detecting the characteristic spectral lines of metallic sodium. However, this method requires the introduction of organic gas, which poses a fire risk. The basic principle of the microwave plasma method, which uses a carrier gas such as argon, is similar to that of high-energy laser dissociation and sodium pyrolysis product monitoring. The difference lies in the method used to generate the plasma. This method involves sampling air and introducing it into a reaction chamber along with an easily ionizable carrier gas such as argon. The gas is then atomized by a microwave power source. This method requires a carrier gas such as argon to generate a stable plasma, requiring the use of high-pressure gas cylinders and overall power consumption in the hundreds of watts.

[0004] Comparison documents:

[0005] The patent document with publication number CN 110320203A and patent name “An online detection device and method for sodium aerosol in air” discloses an online detection device and method for sodium aerosol in air. The device. The device includes: a sampling and diversion device, an atomic emission spectrometer excitation source, a spectrum monitoring device, and a calibration bottle. The sampling and diversion device transports the air sample to the atomic emission spectrometer excitation source, and the atomic emission spectrometer excitation source excites the sodium aerosol in the air sample to produce an atomic emission spectrum, and the atomic emission spectrum is collected by the spectrum monitoring device. However, the patent document requires a carrier gas such as argon to generate plasma, and a high-pressure gas cylinder must be carried, and the overall power consumption is on the order of hundreds of watts. Summary of the Invention

[0006] In response to the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a sodium aerosol detection system and detection method in open air, in which a discharge device forms a high-frequency high-voltage nanosecond pulse spark discharge in the open air to achieve efficient ionization and excitation of sodium aerosol, and through the pulse discharge and the spectrometer time synchronization unit, the spectrometer only collects the spectral signal during the pulse discharge, thereby improving the signal-to-noise ratio of the spectral signal. The present invention realizes real-time detection of sodium aerosol in open air, without the need for easily ionized carrier gases such as argon and complex equipment such as high-energy lasers, and the power consumption is only about one-tenth of the existing microwave plasma method, which is conducive to on-site inspections and large-scale distributed real-time monitoring. In addition, the present invention can achieve control of sodium aerosol detection sensitivity by flexibly adjusting pulse parameters (such as pulse voltage amplitude, pulse frequency, etc.).

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0008] A sodium aerosol detection system in open air comprises a battery 1 for storing electrical energy, an electric energy conversion unit 2 connected to the battery 1 and converting the electric energy stored in the battery into a DC high voltage, a nanosecond pulse generating unit 3 connected to the electric energy conversion unit 2 and converting the DC high voltage into a high-frequency high-voltage nanosecond pulse and applying it to an open-air discharge device 4 to adjust the parameters of the high-frequency high-voltage nanosecond pulse, an open-air discharge device 4 connected to the nanosecond pulse generating unit 3, a spectrometer 5 connected to the open-air discharge device 4 to obtain the spectral characteristics of the emitted light and determine whether there is a sodium characteristic spectral line, and a spectrometer 5 connected to the nanosecond pulse generating unit 3 and the light source. The spectrometer 5 is connected to a pulse discharge and spectrometer time synchronization unit 6 that provides two synchronous trigger signals with adjustable time difference for the pulse generation unit and the spectrometer; a repetition rate high-voltage nanosecond pulse spark discharge is formed in the open air to achieve efficient ionization and excitation of sodium aerosol, and the pulse discharge and spectrometer time synchronization unit 6 only collects spectral signals within the duration of the pulse spark discharge, reducing the background noise during the pulse interval, and improves the signal-to-noise ratio of the spectral signal by accumulating multiple repetition rate high-voltage nanosecond pulse spark discharge emission spectra; if the sodium characteristic spectral line measured by the spectrometer 5 is higher than the preset limit, it is determined that sodium aerosol exists in the open air.

[0009] The nanosecond pulse generating unit 3 adjusts the sodium aerosol detection sensitivity by changing the repetition rate and high voltage nanosecond pulse parameters.

[0010] The open air discharge device 4 includes a housing 12, a pair of coaxial metal rod electrodes 7 fixed to the top and bottom surfaces of the housing 12 by a metal electrode fixing device 8, and a gap is left between the ends of the pair of coaxial metal rod electrodes 7 inserted into the housing 12; a gas extraction device 9 installed on one side of the housing 12 to extract gas from the environment to be measured, and a gas exhaust port 10 installed on the other side of the housing 12 opposite to the gas extraction device 9; a light collimator 11 installed on the front of the housing 12, and the light collimator 11 is used to collect light generated by spark discharge formed by applying a repetitive nanosecond pulse voltage to the gap between the coaxial metal rod electrodes 7 and transmit the optical signal to the spectrometer 5 via an optical fiber.

[0011] The pair of coaxial metal electrodes 7 are made of a metal material with a high melting point and ablation resistance, and the electrode atomic emission spectrum cannot have a spectral peak in the characteristic spectrum range of metallic sodium to avoid interfering with the characteristic spectrum detection of metallic sodium.

[0012] The distance between the ends of a pair of coaxial metal electrodes 7 is adjusted within the range of 1 mm to 10 mm.

[0013] The optical fiber collimator 11 adopts an aspheric convex lens and ensures that the optical fiber end face is located at the focus of the convex lens, thereby improving the efficiency of the emitted light feeding into the optical fiber.

[0014] The housing 12 is a plastic cubic housing, and a pair of device brackets 13 are connected to the bottom.

[0015] The spectrometer 5 is a portable fiber optic spectrometer with a non-cross-symmetric Czerny-Turner structure and needs to have an external synchronous trigger function.

[0016] The method for detecting a sodium aerosol in open air comprises the following steps:

[0017] Step 1: The power conversion unit 2 converts the low-voltage DC voltage stored in the battery 1 into the DC high voltage required by the nanosecond pulse generation unit 3;

[0018] Step 2: The nanosecond pulse generating unit 3 converts the DC high voltage into a high-frequency high-voltage nanosecond pulse. The nanosecond pulse generating unit 3 adjusts the sodium aerosol detection sensitivity by changing the parameters of the high-frequency high-voltage nanosecond pulse.

[0019] Step 3: The repetitive high-voltage nanosecond pulse acts on the discharge device 4 in the open air, and a repetitive high-voltage nanosecond pulse spark discharge is formed in the discharge gap of the coaxial metal rod electrode 7;

[0020] Step 4: High-voltage nanosecond pulse spark discharge at a high frequency excites sodium aerosol in the open air to produce sodium characteristic spectral lines;

[0021] Step 5: The pulse discharge and spectrometer time synchronization unit 6 provides two synchronous trigger signals with an adjustable time difference, which are transmitted to the nanosecond pulse generation unit 3 and the spectrometer 5 respectively; the time difference between the two synchronous trigger signals is adjusted so that the acquisition range of the spectrometer 5 completely covers the duration of the spark discharge, reducing the background noise during the pulse interval, and improving the signal-to-noise ratio of the spectral signal by accumulating multiple repetition-rate high-voltage nanosecond pulse spark discharge emission spectra; the measurement results of the spectrometer 5 are transmitted to the computer software via a data line for subsequent processing and judgment; if the sodium characteristic spectral line is higher than the preset limit, it is determined that sodium aerosol is present in the open air.

[0022] To quantitatively obtain the sodium aerosol content in open air, it is necessary to first obtain the calibration coefficient of the detection device based on a standard sodium aerosol sample. Since the spectral intensity and sodium aerosol content are directly proportional, the sodium aerosol content in open air can be calculated based on the spectral intensity.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1) It adopts high-frequency high-voltage nanosecond pulse spark discharge in open air and atmospheric pressure environment discharge, without the use of argon and other easily ionized carrier gases in traditional microwave plasma methods. The detection device does not contain complex energy-consuming devices such as vacuum pumps, the device structure is simplified, and the power consumption of the equipment is significantly reduced, which facilitates on-site inspection and large-scale distributed real-time monitoring;

[0025] 2) The use of high-frequency high-voltage nanosecond pulse spark discharge has high electron density and gas temperature, and the ionization efficiency is higher than that of traditional DC and AC discharges, which improves the sodium aerosol excitation efficiency and is conducive to increasing the sodium aerosol detection efficiency and signal-to-noise ratio;

[0026] 3) The sensitivity of sodium aerosol detection can be controlled by adjusting pulse parameters (such as pulse voltage amplitude, pulse frequency, etc.);

[0027] 4) The pulse discharge and spectrometer time synchronization device is used to collect the spectral signal only during the pulse discharge period, thereby improving the signal-to-noise ratio of the effective signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the sodium aerosol detection system in open air of the present invention.

[0029] Figure 2 Schematic diagram of the discharge device in open air.

[0030] Figure 3 The figure shows the detection flow chart of the sodium aerosol detection method in open air based on repetitive nanosecond pulse discharge.

[0031] Figure 4a and Figure 4b These are the detection effect diagrams of the sodium aerosol detection method in open air based on repetitive nanosecond pulse discharge without simulated NaCl fog and with simulated NaCl fog. DETAILED DESCRIPTION

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

[0033] like Figure 1 As shown, the present invention provides a sodium aerosol detection system in open air, comprising: a battery 1, an electric energy conversion unit 2, a nanosecond pulse generation unit 3, an open air discharge device 4, a spectrometer 5, and a pulse discharge and spectrometer time synchronization unit 6. The functions of each component are as follows:

[0034] Battery 2: stores electrical energy and provides electrical energy to the power conversion unit 2;

[0035] Power conversion unit 2: converts the power stored in battery 1 into DC high voltage and inputs it into nanosecond pulse generation unit 3;

[0036] Nanosecond pulse generating unit 3: converts the DC high voltage input from the power conversion unit 2 into high-frequency high-voltage nanosecond pulses, and applies them to the discharge device 4 in open air to adjust the parameters of the high-frequency high-voltage nanosecond pulses;

[0037] Open air discharge device 4: Figure 2As shown, the open-air discharge device 4 comprises a pair of coaxial metal rod electrodes 7, secured to the top and bottom surfaces of a plastic cubic housing 12 by metal electrode fixtures 8. A gas extraction device 9 is mounted on the side of the plastic cubic housing 12 to extract gas from the environment to be measured. The gas passes through the gap between the coaxial metal rod electrodes 7 and is discharged through a gas outlet 10 mounted on the side of the plastic cubic housing 12, opposite the gas extraction device 9. A repetitive nanosecond pulse voltage is applied across the gap between the coaxial metal rod electrodes 7 to generate a spark discharge. The light generated by the discharge is collected by a fiber collimator 11 mounted on the front of the plastic cubic housing 12. The light collimator 11 transmits the optical signal via optical fiber to the spectrometer 5. A pair of device brackets 13 are connected to the bottom of the plastic cubic housing 12.

[0038] Spectrometer 5: obtains the spectral characteristics of the discharge emission light in the discharge device 4 in open air and determines whether there is a sodium characteristic spectral line;

[0039] The discharge and spectrometer time synchronization unit 6 provides two synchronous trigger signals with adjustable time difference for the nanosecond pulse generation unit 3 and the spectrometer 5 .

[0040] The detection principle of the method of the present invention is:

[0041] The electrical energy conversion unit 2 converts the electrical energy stored in the battery 1 into high-voltage DC. The nanosecond pulse generation unit 3 converts the high-voltage DC into high-frequency, high-voltage nanosecond pulses through capacitor discharge, pulse transformer boosting, and pulse compression. The rising edge, amplitude, and pulse width of the high-voltage nanosecond pulses can be adjusted by adjusting the internal component parameters of the nanosecond pulse generation unit 3. A gas extraction device 9 in the open-air discharge device 4 delivers the gas to be measured into the gap between the coaxial metal rod electrodes 7. The high-voltage nanosecond pulses act on the open-air discharge device 4, generating a spark discharge across the gap between the coaxial metal rod electrodes 7. The spark discharge instantaneously releases energy, achieving efficient excitation of the sodium aerosol through collision ionization and dissociation excitation. The sodium deexcitation process forms characteristic sodium spectral lines. A fiber collimator 11 in the open-air discharge device 4 collects all light emitted from the discharge gap and transmits it via optical fiber to the spectrometer 5. The pulse discharge and spectrometer time synchronization unit 6 provides two synchronized trigger signals with an adjustable time difference, which are transmitted to the nanosecond pulse generator 3 and the spectrometer 5, respectively. Therefore, the spectrometer 5 only collects radiation during the duration of the spark discharge, reducing background noise between the two pulses. By accumulating the emission spectra of multiple repetition-rate, high-voltage nanosecond pulsed spark discharges, the signal-to-noise ratio of the spectral signal is improved. The measurement results of the spectrometer 5 are transmitted to the computer software via a data line. If the characteristic sodium spectral line exceeds a preset limit, the presence of sodium aerosol in the open air is determined.

[0042] like Figure 3 As shown in the figure, the process of sodium aerosol detection in open air is as follows:

[0043] Step 1: The power conversion unit 2 converts the low-voltage DC voltage of the battery 1 into the DC high voltage required by the nanosecond pulse generating unit 3. The preferred low-voltage DC voltage of the battery 1 is 12V, and the DC high voltage required by the nanosecond pulse generating unit 3 is 0-1000V.

[0044] Step 2: Nanosecond pulse generation unit 3 converts the DC high voltage into repetitive high-voltage nanosecond pulses. The pulse voltage waveform parameters (including voltage amplitude, pulse width, and pulse frequency) can be determined based on the open-air discharge device and detection sensitivity. The switching devices in nanosecond pulse generation unit 3 preferably utilize high-power, all-solid-state switching devices such as magnetic switches and fully-controlled IGBTs. The circuit topology of nanosecond pulse generation unit 3 preferably utilizes a reset-free magnetic switch pulse generation circuit and a Marx pulse generation circuit based on fully-controlled IGBTs.

[0045] Step 3: The open-air discharge device 4 comprises a coaxial metal rod electrode 7, a metal electrode fixture 8, a gas extraction device 9, a gas outlet 10, a fiber optic collimator 11, a plastic cubic housing 12, and a device support 13. The open-air discharge device 4 preferably comprises two coaxially arranged rod-to-rod metal electrodes 7 with their ends spaced a certain distance apart. The selection of the metal electrodes 7 is based on two principles: First, considering that sodium metal melts with the electrode surface during spark discharge, metal materials with high melting points and ablation resistance, such as tungsten and chromium, are preferred. Metal materials or alloys with low melting points and low ablation resistance, such as copper, iron, and aluminum, should be avoided. Second, the electrode atomic emission spectrum must not have spectral peaks within the characteristic spectral range of sodium metal to avoid interference with the detection of the characteristic sodium spectrum. The distance between the ends of the two metal electrodes 7 can be adjusted within a range of 1 mm to 10 mm. The metal electrode fixture 8 ensures the coaxiality of the two metal electrodes 7. The gas extraction device 9 uses a fan or other device to extract the ambient gas to be measured, promoting directional gas flow and reducing the physical adhesion of sodium aerosols in the air to the metal electrode surfaces. A gas outlet 10 is located opposite the gas extraction device 9 to facilitate gas flow out of the open-air discharge device 4. A fiber collimator 11 is fixed to the front of the open-air discharge device 4, and an optical fiber is mounted on the fiber collimator 11 to collect all light emitted from the discharge gap. The fiber collimator 11 preferably utilizes an aspheric convex lens, with the fiber end face positioned at the lens' focal point to improve the efficiency of feeding the emitted light into the fiber. High-frequency, high-voltage nanosecond pulses are applied to the open-air discharge device 4, forming a high-frequency, high-voltage nanosecond pulse spark discharge within the discharge gap.

[0046] Step 4: Repeated-frequency high-voltage nanosecond pulse spark discharge excites sodium aerosol in open air to produce sodium characteristic spectral lines, with the strongest emission lines of sodium element (588.995 nm and 589.592 nm) being preferred.

[0047] Step 5: The pulse discharge and spectrometer time synchronization unit 6 provides two synchronous trigger signals with an adjustable time difference, which are transmitted to the nanosecond pulse generation unit 3 and the spectrometer 5, respectively. The spectrometer 5 preferably utilizes a portable fiber optic spectrometer with a non-crossed symmetrical Czerny-Turner structure and must be equipped with an external synchronous trigger function. The time difference between the two synchronous trigger signals is adjusted so that the acquisition range of the spectrometer 5 fully covers the duration of the spark discharge, reducing background noise during the pulse interval. By accumulating multiple repetition-rate high-voltage nanosecond pulse spark discharge emission spectra, the signal-to-noise ratio of the spectral signal is improved. The measurement results of the spectrometer 5 are transmitted via a data line to computer software for subsequent processing and evaluation. If the sodium characteristic spectral line exceeds a preset limit, sodium aerosol is determined to be present in the open air. To quantitatively determine the sodium aerosol content in the open air, the calibration coefficient of the detection device must first be obtained based on a standard sodium aerosol sample. Since the spectral intensity and sodium aerosol content are directly proportional, the sodium aerosol content in the open air can then be calculated based on the spectral intensity.

[0048] like Figure 4a and Figure 4b As shown, the detection effect diagram of the sodium aerosol detection method in open air based on repetitive nanosecond pulse discharge is shown in the absence and presence of simulated NaCl fog. It can be seen from the figure that when there is no simulated NaCl fog, the spectral intensity in the range of 587nm to 593nm of the discharge is generally at the noise level. When there is simulated NaCl fog, the discharge spectrum has two characteristic peaks at 588.995nm and 589.592nm, and the intensities are 8 times and 5 times higher than the noise level, respectively. This proves that the present invention can achieve the purpose of sodium aerosol detection.

Claims

1. A sodium aerosol detection system in open air, characterized by: The invention comprises a battery (1) for storing electric energy, an electric energy conversion unit (2) connected to the battery (1) and converting the electric energy stored in the battery into a direct current high voltage, a nanosecond pulse generating unit (3) connected to the electric energy conversion unit (2) and converting the direct current high voltage into a high-frequency high-voltage nanosecond pulse and applying the pulse to an open-air discharge device (4) to adjust the parameters of the high-frequency high-voltage nanosecond pulse, an open-air discharge device (4) connected to the nanosecond pulse generating unit (3), a spectrometer (5) connected to the open-air discharge device (4) for obtaining the spectral characteristics of the emitted light and judging whether a sodium characteristic spectral line exists, and a spectrometer (6) connected to the nanosecond pulse generating unit (3) and the spectrometer. The instrument (5) is connected to a pulse discharge and spectrometer time synchronization unit (6) that provides two synchronous trigger signals with adjustable time difference for the pulse generating unit and the spectrometer; a repetition rate high-voltage nanosecond pulse spark discharge is formed in the open air to achieve efficient ionization and excitation of the sodium aerosol, and the pulse discharge and spectrometer time synchronization unit (6) only collects the spectral signal within the duration of the pulse spark discharge, thereby reducing the background noise during the pulse interval, and improves the signal-to-noise ratio of the spectral signal by accumulating multiple repetition rate high-voltage nanosecond pulse spark discharge emission spectra; if the sodium characteristic spectrum line measured by the spectrometer (5) is higher than the preset limit, it is judged that there is sodium aerosol in the open air; The nanosecond pulse generating unit (3) adjusts the sodium aerosol detection sensitivity by changing the repetition rate high voltage nanosecond pulse parameters; The invention is characterized in that: the open air discharge device (4) comprises a housing (12), a pair of coaxial metal rod electrodes (7) fixed to the top and bottom surfaces of the housing (12) by a metal electrode fixing device (8), a gap being left between the ends of the pair of coaxial metal rod electrodes (7) inserted into the housing (12); a gas extraction device (9) installed on one side of the housing (12) for extracting gas from the environment to be measured, and a gas exhaust port (10) installed on the other side of the housing (12) opposite to the gas extraction device (9); a light collimator (11) installed on the front of the housing (12), the light collimator (11) being used to collect light generated by spark discharge formed by applying a repetitive nanosecond pulse voltage to the gap between the coaxial metal rod electrodes (7) and transmit the light signal to the spectrometer (5) via an optical fiber; A pair of coaxial metal rod electrodes (7) are made of a metal material with a high melting point and ablation resistance, and the electrode atomic emission spectrum cannot have a spectrum peak in the characteristic spectrum range of metallic sodium to avoid interference with the detection of the characteristic spectrum of metallic sodium.

2. The open air sodium aerosol detection system according to claim 1, characterized in that: The distance between the ends of a pair of coaxial metal rod electrodes (7) is adjusted within the range of 1 mm to 10 mm.

3. The open air sodium aerosol detection system according to claim 1, characterized in that: The optical fiber collimator (11) adopts an aspheric convex lens and ensures that the optical fiber end face is located at the focus of the convex lens, thereby improving the efficiency of the emitted light feeding into the optical fiber.

4. The open air sodium aerosol detection system according to claim 1, characterized in that: The housing (12) is a plastic cubic housing, and a pair of device brackets (13) are connected to the bottom.

5. The open air sodium aerosol detection system according to claim 1, characterized in that: The spectrometer (5) is a portable optical fiber spectrometer with a non-cross symmetrical Czerny-Turner structure and needs to have an external synchronous triggering function.

6. The method for detecting sodium aerosol in open air according to any one of claims 1 to 5, characterized in that: The steps include: Step 1: The power conversion unit (2) converts the low-voltage DC voltage stored in the battery (1) into the DC high voltage required by the nanosecond pulse generation unit (3); Step 2: The nanosecond pulse generating unit (3) converts the DC high voltage into a repetition-frequency high-voltage nanosecond pulse. The nanosecond pulse generating unit (3) adjusts the sodium aerosol detection sensitivity by changing the repetition-frequency high-voltage nanosecond pulse parameters. Step 3: a high-frequency, high-voltage, nanosecond pulse is applied to the discharge device (4) in the open air, and a high-frequency, high-voltage, nanosecond pulse spark discharge is formed in the discharge gap of the coaxial metal rod electrode (7); Step 4: High-voltage nanosecond pulse spark discharge at a high frequency excites sodium aerosol in the open air to produce sodium characteristic spectral lines; Step 5: The pulse discharge and spectrometer time synchronization unit (6) provides two synchronous trigger signals with an adjustable time difference, which are transmitted to the nanosecond pulse generating unit (3) and the spectrometer (5) respectively; the time difference between the two synchronous trigger signals is adjusted so that the acquisition range of the spectrometer (5) completely covers the duration of the spark discharge, the background noise during the pulse interval is reduced, and the signal-to-noise ratio of the spectral signal is improved by accumulating multiple repetition-rate high-voltage nanosecond pulse spark discharge emission spectra; the measurement results of the spectrometer (5) are transmitted to the computer software through the data line for subsequent processing and judgment; if the sodium characteristic spectrum line is higher than the preset limit, it is judged that sodium aerosol exists in the open air.

7. The detection method according to claim 6, wherein: To quantitatively obtain the sodium aerosol content in open air, it is necessary to first obtain the calibration coefficient of the detection device based on a standard sodium aerosol sample. Since the spectral intensity and sodium aerosol content are directly proportional, the sodium aerosol content in open air can be calculated based on the spectral intensity.

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