Online photoionization detector system for measuring volatile organic compounds

Abstract

The utility model relates to the technical field of organic matter detection, in particular to an online photoionization detector system for measuring volatile organic compounds, which comprises a gas circuit module, an ionization module, a signal amplification module, a data storage module and a power supply module. The gas path module is used for collecting and guiding gas and realizing real-time monitoring of gas flow, gas path temperature and humidity; the ionization module can efficiently ionize to-be-detected gas, an ionization chamber in the ionization module can efficiently capture gas ions and electrons, interference of environmental condition changes on signals is reduced, and generated current signals and the concentration of the to-be-detected gas are in a linear relation; the signal amplification module amplifies the generated current and converts the current into a voltage signal, and the amplification efficiency can reach 109 times; the data storage module records and stores the voltage signal to realize online data visualization; the power supply module provides working voltage for the detector system. The system is high in integration degree, strong in stability and high in sensitivity, and the detection limit is superior to 0.5 ppbv.

Description

Technical Field

[0001] The utility model relates to the technical field of organic matter detection, in particular to an online photoionization detector system for measuring volatile organic compounds. Background Art

[0002] Volatile Organic Compounds (VOCs) generally refer to organic compounds with a boiling point below 250°C under normal pressure or that can be emitted into the air in the form of gas molecules. In the atmosphere, VOCs can come from processes such as fossil fuel combustion, transportation, solvent processes, cleaning products, and plant emissions. VOCs are important precursors to the formation of atmospheric ozone and play an important role in the formation of air pollution. VOCs can also participate in the formation of atmospheric particulate matter, which can form secondary aerosols through photochemical oxidation and other pathways. Secondary aerosols can reduce urban visibility and have an important impact on the earth's radiation balance by absorbing and scattering solar radiation and changing the microphysical properties of clouds. Therefore, accurate detection of VOCs is particularly important for the control and prevention of atmospheric pollutants.

[0003] At present, there are many instruments used for VOCs detection, such as flame ionization detector, mass spectrometer, Fourier infrared analyzer, thermal infrared imager, etc. Gas chromatography-mass spectrometry is often regarded as the gold standard for analyzing atmospheric VOCs due to its high sensitivity, good reproducibility, and stable performance. However, the widespread application of this technology is limited by many factors such as purchase cost, operation complexity, and analysis time. In addition, the weight and volume of the instrument itself also greatly reduce its portability, limiting its large-scale deployment in field observations. In comparison, the photoionization detector (PID) has the advantages of low cost and high portability, and can be used for large-scale environmental online monitoring. At present, commercial PIDs are mostly used for high-concentration (tens of ppbv to ppmv) VOCs monitoring, such as gas leaks; the concentration of most VOCs in urban atmospheric environment is in the ppbv to sub-ppbv range, resulting in the problem that the detection limit of commercial PID cannot meet the demand. At the same time, commercial PIDs often have poor stability and are prone to detection baseline drift during use.

[0004] Therefore, there is an urgent need to develop a VOCs detection system that is low-cost, small in size, sensitive and stable. Utility Model Content

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide an online photoionization detector system for measuring volatile organic compounds, aiming to solve the problems of low sensitivity, insufficient detection limit, and poor stability of the existing photoionization detectors.

[0006] The technical solution of the utility model is as follows:

[0007] An on-line photoionization detector system for measuring volatile organic compounds, comprising:

[0008] The gas circuit module includes a gas flow sensor, a temperature and humidity sensor, and an air pump which are sequentially connected through an air pipe;

[0009] An ionization module is connected to one end of the gas flow sensor through an air pipe;

[0010] A signal amplification module, electrically connected to the ionization module;

[0011] A data storage module, electrically connected to the signal amplification module, the gas flow sensor and the temperature and humidity sensor respectively;

[0012] The power supply module includes a total power supply for supplying power to the gas circuit module and the data storage module, a radio frequency excitation power supply for supplying power to the ionization module, and positive and negative power supplies for supplying power to the signal amplification module.

[0013] In the online photoionization detector system for measuring volatile organic compounds, the ionization module is connected to an end of the gas flow sensor that is away from the temperature and humidity sensor.

[0014] The online photoionization detector system for measuring volatile organic compounds, wherein the ionization module includes an ionization chamber, an electrode rod, a polytetrafluoroethylene film and a photoionization lamp; the electrode rod is arranged inside the ionization chamber, the photoionization lamp is placed at the bottom of the ionization chamber, and the polytetrafluoroethylene film is arranged on the top of the photoionization lamp.

[0015] The online photoionization detector system for measuring volatile organic compounds, wherein the ionization chamber includes a first air inlet, a first air outlet, and a baffle disposed inside the ionization chamber and located between the first air inlet and the first air outlet; the electrode rod is located on one side of the baffle close to the bottom of the ionization chamber.

[0016] In the online photoionization detector system for measuring volatile organic compounds, the first air inlet, the first air outlet and the baffle are all made of polytetrafluoroethylene.

[0017] In the online photoionization detector system for measuring volatile organic compounds, the signal amplification module is a transimpedance amplifier, which is used to amplify the current signal of the ionization module and convert it into a voltage signal.

[0018] The online photoionization detector system for measuring volatile organic compounds, wherein the data storage module includes a microcomputer controller and a Node-RED platform stored in the microcomputer controller; the data storage module is used to read the voltage signal output by the signal amplification module in real time online.

[0019] The online photoionization detector system for measuring volatile organic compounds, wherein the gas path module, the ionization module, the signal amplification module, the data storage module and the power module are all fixed on a circuit board; the circuit board is arranged in a shielding box; the shielding box includes a second air inlet, a second air outlet and a heat sink, the second air inlet is connected to the ionization module through an air pipe, and the second air outlet is connected to the air pump through an air pipe.

[0020] The online photoionization detector system for measuring volatile organic compounds, wherein the total power supply is a positive 5V power supply; the radio frequency excitation power supply is a positive 24V radio frequency excitation power supply; and the positive and negative power supplies are positive and negative 5V power supplies.

[0021] A detection method based on an online photoionization detector system for measuring volatile organic compounds comprises the steps of:

[0022] The gas is introduced into the ionization module through an air pump, and the gas flow rate, temperature and humidity of the gas are monitored and recorded in real time using a gas flow sensor and a temperature and humidity sensor;

[0023] The gas generates a current signal after being photoionized and ionized in the ionization module;

[0024] Amplifying the current signal and converting it into a voltage signal using a signal amplification module;

[0025] The voltage signal is read and stored in real time by a data storage module, and visualized through a Node-RED platform to achieve online detection of volatile organic compounds.

[0026] Beneficial effects: The utility model provides an online photoionization detector system for measuring volatile organic compounds, and the online photoionization detector system includes a gas path module, an ionization module, a signal amplification module, a data storage module, and a power supply module. The gas to be measured is guided by the gas path module, accurately and quantitatively input into the ionization module, and efficiently ionized by the ionization module to produce gas ions and electrons. The optimized ionization module reduces the interference of environmental conditions on the detection signal, and can efficiently capture the gas ions and electrons produced by ionization. The current signal generated by this process is positively correlated linearly with the concentration of the gas to be measured. The current signal is converted into a voltage signal by the signal amplification module, and the amplification efficiency can reach 10 9times, which can realize quantitative analysis of analytes. The data storage module records and stores voltage signals and can realize online data visualization; the power module provides stable, low-noise positive and negative working voltages for the detection system. The above five modules are integrated on a self-designed circuit board, making the detection equipment highly integrated and stable. The online photoionization detection system involved in the utility model has high sensitivity and a detection limit better than 0.50ppbv. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a structural schematic diagram of an online photoionization detector system for measuring volatile organic compounds according to the utility model;

[0028] Figure 2 It is a structural schematic diagram of the ionization chamber;

[0029] Figure 3 Design circuit boards and circuit layouts;

[0030] Figure 4 is a linear graph of the response of the photoionization detector in Example 1 to an exemplary volatile organic gas (benzene) of different concentrations;

[0031] Figure 5 This is a flow chart in the Node-RED platform;

[0032] Figure 6 A schematic diagram for viewing data information in real time for visiting a website;

[0033] Explanation of the reference numerals: ionization chamber 10 , first air inlet 101 , first air outlet 102 , baffle 103 , electrode rod 20 , polytetrafluoroethylene film 30 , photoionization lamp 40 , radio frequency excitation power supply 50 , second air inlet 60 , second air outlet 70 , heat sink 80 . DETAILED DESCRIPTION

[0034] The utility model provides an online photoionization detector system for measuring volatile organic compounds. In order to make the purpose, technical solution and effect of the utility model clearer and more specific, the utility model is further described in detail below. It should be understood that the specific embodiments described here are only used to explain the utility model, and are not used to limit the utility model.

[0035] Those skilled in the art will understand that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as the general understanding of ordinary technicians in the field to which the utility model belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and if no specific definition is given, they will not be interpreted with idealized or overly formal meanings.

[0036] like Figure 1 As shown, the utility model provides an online photoionization detector system for measuring volatile organic compounds, comprising:

[0037] The gas circuit module includes a gas flow sensor, a temperature and humidity sensor, and an air pump which are sequentially connected through an air pipe;

[0038] An ionization module is connected to one end of the gas flow sensor through an air pipe;

[0039] A signal amplification module, electrically connected to the ionization module;

[0040] A data storage module, electrically connected to the signal amplification module, the gas flow sensor and the temperature and humidity sensor respectively;

[0041] The power module includes a main power supply for supplying power to the gas circuit module and the data storage module, a radio frequency excitation power supply 50 for supplying power to the ionization module, and positive and negative power supplies for supplying power to the signal amplification module.

[0042] In this embodiment, the gas is introduced into the ionization module through an air pump, and the gas flow rate, temperature, and humidity of the gas are monitored and recorded in real time using a gas flow sensor and a temperature and humidity sensor; then the gas to be measured will generate a nA-level current signal after ionization in the ionization module, and the current signal is directly proportional to the concentration of the gas to be measured; the current signal is converted and amplified into a voltage signal by the signal amplification module, and finally the voltage signal is recorded by the data recording module and the concentration of the gas to be measured is displayed in real time. The ionized gas ions will recombine and pass through the gas flow sensor and the temperature and humidity sensor (RHT) in turn, and finally be discharged. It has been verified that the detection limit of the online photoionization detector system for measuring volatile organic compounds is better than 0.50ppbv, which has the advantage of a low detection limit and can realize the detection of trace volatile organic compounds; at the same time, the detection system has the advantages of convenience and stability.

[0043] In some embodiments, the ionization module is connected to an end of the gas flow sensor away from the temperature and humidity sensor. The gas flow sensor is arranged between the ionization module and the temperature and humidity sensor to control the air intake flow of the ionization module.

[0044] Specifically, the gas flows out of the ionization module and enters the gas flow sensor, which records the instantaneous gas flow and transmits the data to the microcomputer controller in real time for subsequent data analysis.

[0045] In some embodiments, Figure 2 As shown, the ionization module includes an ionization chamber 10, an electrode rod 20, a polytetrafluoroethylene film 30 and a photoionization lamp 40; the electrode rod is arranged inside the ionization chamber, the photoionization lamp is arranged at the bottom of the ionization chamber, and the polytetrafluoroethylene film is arranged on the top of the photoionization lamp. The ionization chamber provides a cavity for ionizing gas and captures gas ions and electrons generated by ionization through the electrode rod, while the photoionization lamp generates ultraviolet light for ionizing gas, and the polytetrafluoroethylene film is used to reduce the influence of air humidity on the ionization effect.

[0046] Specifically, the photoionization lamp is located at the bottom of the ionization chamber, and the electrode rod is placed close to the photoionization lamp and within the irradiation range of the photoionization lamp, so that after the gas is ionized, it is quickly captured by the electrode rod to generate an electrical signal.

[0047] In some embodiments, the ionization chamber 10 is in the shape of a cuboid but not limited to a cylindrical inner wall; the cylindrical inner wall is convenient for connection with the photoionization lamp and the rectangular outer wall is convenient for close connection with the gas path.

[0048] In other embodiments, the ionization chamber may also be in other shapes, for example, both the inner wall and the outer wall are cylindrical.

[0049] In some embodiments, the volume of the ionization chamber is 2000-2500mm 3 between.

[0050] In one embodiment, the gas flow rate is set to 1 L / min, and the gas residence time in the ionization chamber is 0.12-0.15 s, which can improve the detection time resolution.

[0051] In some embodiments, the ionization chamber 10 includes a first air inlet 101, a first air outlet 102, and a baffle 103 disposed inside the ionization chamber and located between the first air inlet 101 and the first air outlet 102; the electrode rod 20 is located on one side of the baffle 103 close to the bottom of the ionization chamber 10.

[0052] Furthermore, the baffle 103 separates the upper half of the ionization chamber 10 into two parts. After the gas enters the cavity of the ionization chamber 10, the baffle causes the gas to move downward and enter the irradiation area of ​​the photoionization lamp to be ionized. After the gas is ionized, it is immediately captured by the electrode under the baffle to generate an electrical signal. This process can promote gas flow mixing, reduce the dead volume of the ionization chamber, and improve the gas ionization efficiency.

[0053] Specifically, when using the online photoionization detector system for measuring volatile organic compounds to detect low concentrations of VOCs, first set the air pump's air flow rate to quantitatively extract gas, and the gas enters the cavity of the ionization chamber 10 from the first air inlet 101. The gas flows to the area where ultraviolet light is generated by the photoionization lamp and is then ionized. The generated gas ions and electrons are captured by the electrode rod 20 to generate a current signal, and the gas ions generated by the ionization will reunite and flow out from the first air outlet 102.

[0054] In other embodiments, the first gas inlet 101 and the first gas outlet 102 may be located at the lower left and upper right of the ionization chamber, respectively. In this case, the gas can be ionized faster without a baffle, thereby generating a signal.

[0055] In some embodiments, the first air inlet 101, the first air outlet 102 and the baffle 103 are all made of polytetrafluoroethylene; further, the ionization chamber body is also made of polytetrafluoroethylene material. The ionization chamber body and the first air inlet and the first air outlet are made of polytetrafluoroethylene material, which can make the ionization chamber have a good insulation effect.

[0056] In some embodiments, one end of the electrode rod 20 is in the shape of a flat rectangle, so that it has a larger specific surface area and can fully capture gas ions. Combined with the design of the ionization chamber, experiments have verified that the detection limit of the photoionization detector system can be better than 0.50 ppbv, which can detect trace volatile organic compounds. For example, if the electrode rod is 20 mm long, the shape of one end of the electrode rod is changed to a flat rectangle by mechanical pressure, so that its surface area can be increased from the original 200 mm 2 Increased to 520mm 2 , which fully improves the electron capture efficiency of the electrode rod.

[0057] In some embodiments, the material of the electrode rod 20 may be, but is not limited to, brass. The electrode rod forms an electric field in the ionization chamber cavity under the action of the additional voltage, and the gas ions and electrons generated by ionization move to the negative electrode and the positive electrode of the electrode rod respectively under the action of the electric field, thereby forming a current. In this embodiment, the additional voltage provided to the electrode rod can be adjusted, and the ability of the electrode to capture ions and electrons can be adjusted by increasing or decreasing the intensity of the additional voltage, thereby affecting the signal response intensity.

[0058] In some embodiments, the photoionization lamp 40 can be a photoionization lamp with different ionization energies. The higher the ionization energy, the more types of gas molecules can be ionized.

[0059] In some embodiments, in order to ensure that the ionization module has a better sealing effect, polytetrafluoroethylene tape and a sealing ring are used to seal the ionization module.

[0060] In some embodiments, the signal amplification module is a transimpedance amplifier, which is used to amplify the current signal of the ionization module and convert it into a voltage signal. Since the current signal generated by the electrode rod 20 capturing gas ions and electrons is in the nA order of magnitude, a transimpedance amplifier (with an amplification efficiency of 10 9 times) to amplify it and convert it into a voltage signal to facilitate subsequent data collection.

[0061] In some embodiments, the data storage module includes a microcomputer controller and a Node-RED platform stored in the microcomputer controller; the data storage module is used to read the voltage signal output by the signal amplification module in real time online.

[0062] Specifically, by writing code on the Node-RED platform, the client can realize the function of real-time visualization of data. This design can improve the practicality of the detection system. The code example is as follows:

[0063]

[0064]

[0065] In some embodiments, the gas circuit module, the ionization module, the signal amplification module, the data storage module and the power supply module are all fixed on a circuit board; the circuit board is arranged in a shielding box; the shielding box includes a second air inlet 60, a second air outlet 70 and a heat sink 80; the second air inlet is connected to the ionization module through an air pipe, and the second air outlet is connected to the air pump through an air pipe.

[0066] Specifically, the first air inlet of the ionization module is connected to the second air inlet, the first air outlet is connected to the gas flow sensor, and the second air outlet is connected to the air pump.

[0067] In some embodiments, the modules in the online photoionization detector system for measuring volatile organic compounds are connected and fixed on the circuit board and placed in a shielding box to obtain a 20×15×10 cm 3 The detector has a volume of only 0.003m 3 , which makes it highly portable. The detector can be used outdoors rather than limited to laboratories, or it can be carried on mobile vehicles and unmanned aerial vehicles for coordinated observation of atmospheric pollutants.

[0068] In some embodiments, the heat sink 70 is, but is not limited to, a fan, and is used to cool the system.

[0069] In some embodiments, the total power supply is a positive 5V power supply; the RF excitation power supply 50 is a positive 24V RF excitation power supply; and the positive and negative power supplies are positive and negative 5V power supplies.

[0070] In some embodiments, the air tubes are all Teflon tubes.

[0071] In addition, the utility model also provides a detection method based on an online photoionization detector system for measuring volatile organic compounds, comprising the steps of:

[0072] Step S10: introducing gas into the ionization module through an air pump, and using a gas flow sensor and a temperature and humidity sensor to monitor and record the gas flow, temperature, and humidity of the gas in real time;

[0073] Step S20: the gas generates a current signal after being photoionized in the ionization module;

[0074] Step S30: using a signal amplification module to amplify the current signal and convert it into a voltage signal;

[0075] Step S40: using the data storage module to read and store the voltage signal in real time, and visualize it through the Node-RED platform to achieve online detection of volatile organic compounds.

[0076] In this embodiment, the online photoionization detector system for measuring volatile organic compounds is used to detect organic compounds, which has the advantages of low detection limit, good stability and real-time online data reading function. The detection system improves the response intensity of the instrument to the substance by reducing the volume of the ionization chamber and increasing the surface area of ​​the electrode rod, and the experimentally measured detection limit of the detector is better than 0.50ppbv, so that the detection method has a low detection limit; all modules and parts in the detection system are fixed in a shielding box to reduce the influence of human factors or external electric fields on the signal circuit, making the test data more stable; finally, through a microcomputer and Node-RED platform, the function of real-time visualization of data on the client terminal is realized. Therefore, the use of the photoionization detector system to realize the online detection of volatile organic compounds has the advantages of convenience, stability, low detection limit, and real-time visualization of data.

[0077] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments, and are only used to illustrate the utility model but not to limit the utility model. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0078] Example 1

[0079] This embodiment provides an online photoionization detector system (hereinafter referred to as a photoionization detector) for measuring volatile organic compounds, such as Figure 1 As shown, it includes a gas path module, an ionization module, a signal amplification module, a data storage module, and a power supply module.

[0080] The gas circuit module includes a gas flow sensor, a temperature and humidity sensor and an air pump which are connected in sequence through a Teflon tube; the ionization module is connected to the air inlet of the shielding box and one end of the gas flow sensor; the ionization module and the gas flow sensor are bidirectionally connected through the Teflon tube.

[0081] The ionization module includes an ionization chamber, an electrode rod and a photoionization lamp (10.6eV); wherein the ionization chamber is composed of a first air inlet, a first air outlet, a baffle and other parts. The first air inlet and the first air outlet are respectively located at the upper left and upper right of the ionization chamber, the baffle is located in the upper middle of the ionization chamber, the electrode rod is made of brass and is located in the lower middle of the ionization chamber, such as Figure 2 shown.

[0082] The signal amplification module includes a transimpedance amplifier, which can amplify the current signal by 10 9 times.

[0083] The data storage module includes a hardware microcomputer controller and a software Node-RED. The shielding box includes a second air inlet, a second air outlet and a heat sink.

[0084] The power supply module includes a positive 24V RF excitation power supply, a positive and negative 5V power supply, and a positive 5V power supply. The positive 24V RF excitation power supply is used to excite the photoionization lamp 40 so that it can ionize volatile organic compounds. The positive and negative 5V power supplies are used to power the signal amplification module, and the positive 5V power supply is used to power the microcomputer controller in the data storage module.

[0085] The circuit board is designed and manufactured independently and is used to fix the above five modules. Figure 3(The left picture is the circuit board design, and the right picture is the circuit layout). The power connection and signal output connection of each module are represented by thick and thin lines in the figure. The thick lines are power connection lines, which are distributed on the front and back of the circuit board to prevent cross-connection between lines. The signal output connection lines are represented by thin lines.

[0086] Figure 4 This is the linear relationship of the response of the PID in this embodiment to VOCs (e.g., benzene) at different concentrations. The detection limit is calculated by the following formula:

[0087]

[0088] Where σ is the standard deviation of the instrument baseline response data, and k is the slope of the instrument response fitting curve for different concentrations of analytes.

[0089] The plot calculation shows that the trend line fitting degree of PID concentration-response R 2 The detection limit of PID is 0.3ppbv. Based on the current importance of monitoring low-concentration volatile organic gases, the PID in this embodiment meets and satisfies current needs.

[0090] Online data reading functions such as Figure 5 As shown, the file with recorded data is obtained through the '[Get] / PID' node, 'http(200)' is used to confirm whether the data request is successful, the 'Get Data' node is used to obtain the required data in the file, the 'Debug' node is used to display whether the process is output correctly, and the 'PID' node and the 'Flow Rate' node are used to draw a line chart to display the data changes. Finally, the data information can be viewed in real time by accessing the URL, such as Figure 6 shown.

[0091] In summary, the utility model provides an online photoionization detector system for measuring volatile organic compounds, and the online photoionization detector system includes a gas circuit module, an ionization module, a signal amplification module, a data recording module, and a power supply module. The gas circuit module includes a gas flow sensor, a temperature and humidity sensor, and an air pump connected in sequence through an air pipe; the ionization module is connected to one end of the gas flow sensor through an air pipe; the signal amplification module is electrically connected to the ionization module; the data recording module is electrically connected to the signal amplification module; the power supply module includes a radio frequency excitation power supply, a positive and negative power supply, and a positive power supply; the radio frequency excitation power supply is electrically connected to the ionization module; the positive and negative power supplies are electrically connected to the signal amplification module; the positive power supply is electrically connected to the data recording module. The utility model utilizes a power supply module to provide precise working voltage for other modules, so that the gas to be measured can be accurately and quantitatively input into the ionization module through the gas path module. After the gas to be measured is ionized in the ionization module, a current signal will be generated, and the current signal is proportional to the concentration of the gas to be measured; the current signal is converted and amplified into a voltage signal through the action of the signal amplification module, and finally the voltage signal is recorded through the data recording module and the concentration of the gas to be measured is displayed in real time; thereby, the detection system can improve the convenience and stability of the detector, and can make the gas be more fully ionized, thereby reducing the detection limit of the detection system.

[0092] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made according to the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. An online photoionization detector system for measuring volatile organic compounds, characterized in that: include: The gas circuit module includes a gas flow sensor, a temperature and humidity sensor, and an air pump which are sequentially connected through an air pipe; An ionization module is connected to one end of the gas flow sensor through an air pipe; A signal amplification module, electrically connected to the ionization module; A data storage module, electrically connected to the signal amplification module, the gas flow sensor and the temperature and humidity sensor respectively; The power supply module includes a total power supply for supplying power to the gas circuit module and the data storage module, a radio frequency excitation power supply for supplying power to the ionization module, and positive and negative power supplies for supplying power to the signal amplification module.

2. The on-line photoionization detector system for measuring volatile organic compounds according to claim 1, characterized in that: The ionization module is connected to an end of the gas flow sensor away from the temperature and humidity sensor.

3. The on-line photoionization detector system for measuring volatile organic compounds according to claim 1, characterized in that: The ionization module comprises an ionization chamber, an electrode rod, a polytetrafluoroethylene film and a photoionization lamp; the electrode rod is arranged inside the ionization chamber, the photoionization lamp is placed at the bottom of the ionization chamber, and the polytetrafluoroethylene film is arranged on the top of the photoionization lamp.

4. The on-line photoionization detector system for measuring volatile organic compounds according to claim 3, characterized in that: The ionization chamber comprises a first air inlet, a first air outlet, and a baffle plate arranged inside the ionization chamber and located between the first air inlet and the first air outlet; the electrode rod is located on one side of the baffle plate close to the bottom of the ionization chamber.

5. The on-line photoionization detector system for measuring volatile organic compounds according to claim 4, characterized in that: The first air inlet, the first air outlet and the baffle are all made of polytetrafluoroethylene.

6. The on-line photoionization detector system for measuring volatile organic compounds according to claim 1, characterized in that: The signal amplification module is a transimpedance amplifier, which is used to amplify the current signal of the ionization module and convert it into a voltage signal.

7. The on-line photoionization detector system for measuring volatile organic compounds according to claim 1, characterized in that: The data storage module includes a microcomputer controller and a Node-RED platform stored in the microcomputer controller; the data storage module is used to read the voltage signal output by the signal amplification module in real time online.

8. The on-line photoionization detector system for measuring volatile organic compounds according to claim 1, characterized in that: The air path module, the ionization module, the signal amplification module, the data storage module and the power module are all fixed on a circuit board; the circuit board is arranged in a shielding box; the shielding box includes a second air inlet, a second air outlet and a heat sink, the second air inlet is connected to the ionization module through an air pipe, and the second air outlet is connected to the air pump through an air pipe.

9. The on-line photoionization detector system for measuring volatile organic compounds according to claim 1, characterized in that: The total power supply is a positive 5V power supply; the radio frequency excitation power supply is a positive 24V radio frequency excitation power supply; and the positive and negative power supplies are positive and negative 5V power supplies.

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