A method, device and application of NO2 photolysis conversion based on chemiluminescence NOx measurement

Abstract

The present invention discloses a method, device and application of NO2 photolysis conversion based on chemiluminescence NOx measurement. The device includes an ultraviolet LED light source module, a high-transmittance quartz glass tube, a light-proof light shield, a heat-conducting device, a heat dissipation and temperature control device, and a polytetrafluoroethylene gas path connection device. The ultraviolet LED light source module is arranged in a horizontal direction, and can stably radiate high-flux 390nm-400nm ultraviolet light directly to the environmental sample in the high-transmittance quartz glass tube, so as to achieve efficient and specific dissociation of NO2 in the environmental sample to NO. The photolysis channel and the gas path connection device of the NO2 conversion device of the present invention are all made of inert materials, and the ultraviolet light source is precisely temperature-controlled at the same time, which has the advantages of high conversion efficiency, good specificity, simple device, small size, low power consumption, stable and reliable operation, etc., and can be applied to the precise online measurement of NO2 in the online analysis chemiluminescence method of nitrogen oxides in the ambient atmosphere.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental monitoring, and in particular to a method, device and application of NO2 photolysis conversion based on chemiluminescence NOx measurement. Background Art

[0002] Ambient atmospheric nitrogen oxides (NOx) are a general term for nitric oxide (NO) and nitrogen dioxide (NO2). The monitoring methods can be divided into NO2-based monitoring methods and NO-based monitoring methods. NO2-based monitoring methods can be further divided into wet chemical methods and optical measurement methods, while NO-based monitoring methods are mainly chemiluminescence methods. Measurement methods based on NO2, such as naphthylethylenediamine hydrochloride spectrophotometry, cavity ring-down spectroscopy, and laser-induced fluorescence, generally have problems such as high instrument prices, complex systems, cumbersome operations, and low online levels. They are not suitable for routine online monitoring of ambient atmospheric NOx. The chemiluminescence method based on NO measurement is based on the chemiluminescence reaction of NO and ozone, that is, the reaction of nitric oxide molecules with ozone will generate excited nitrogen dioxide (NO2 * ), when the excited nitrogen dioxide decays to a lower energy state, it releases photons (590nm-3000nm, spectral center 1200nm), and the photon signal intensity and NO concentration conform to the Lambert-Beer law to quantify the NO concentration. The measurement of NO2 is to reduce NO2 to NO for measurement. Chemiluminescence has the advantages of high sensitivity, few interference factors, and good specificity. It is widely used in the measurement of atmospheric NOx. The important technical problem is the efficient and specific conversion of NO2 to obtain high-precision NO2 measurement data.

[0003] At present, the main online measurement instruments for atmospheric NOx at home and abroad are all chemiluminescence monitors based on molybdenum conversion, that is, the conversion of NO2 is achieved by molybdenum catalyst under a working environment of 325℃, and the NO and NOx measurement results are obtained by switching the three-way solenoid valve between the NO and NOx channels respectively, and the NO2 measurement result is obtained by calculating the difference between NOx and NO. Studies have found that the molybdenum conversion method will not only catalytically reduce NO2 to NO, but also convert a variety of nitrogen-containing compounds in the atmosphere such as NO3, HNO3, N2O5, PAN, HONO, and some NH3, RO2NO2 and particulate nitrogen-containing compounds into NO, resulting in the widespread problem of overestimation of NO2, and the measured value is not the real NOx. Therefore, the development of a method and device that can specifically target the efficient conversion of atmospheric NO2 to NO has become a key issue in the online and accurate measurement of atmospheric NOx.

[0004] Through searching, no patent publication documents related to the patent application of the present invention have been found. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method, device and application of NO2 photolysis conversion based on chemiluminescence NOx measurement.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A NO2 photolysis conversion device for NOx measurement based on a chemiluminescence method, the device comprising an ultraviolet LED light source module, a high-transmittance quartz glass tube, a light-shielding cover, a heat-conducting device, a heat-dissipating device, a polytetrafluoroethylene gas path connecting device and a heat-dissipating temperature control device, wherein the ultraviolet LED light source module is arranged in a horizontal direction, and can release 390nm-400nm ultraviolet light, the ultraviolet LED light source module is connected to the heat-conducting device, and the heat-conducting device is also connected to the heat-dissipating device; the high-transmittance quartz glass tube is connected to the polytetrafluoroethylene gas path connecting device, and is arranged in parallel with the ultraviolet LED light source module in the light-shielding cover, and the light-shielding cover can perform light-shielding operation on the high-transmittance quartz glass tube; the light-shielding cover is also connected to the heat-conducting device and the polytetrafluoroethylene gas path connecting device, and the polytetrafluoroethylene gas path connecting device is also connected to the heat-conducting device;

[0008] The high-transmittance quartz glass tube is arranged in the horizontal direction. The high-transmittance quartz glass tube is in the shape of a hollow cylinder with horizontal openings at both ends. The openings at both ends of the high-transmittance quartz glass tube are tightly connected to the polytetrafluoroethylene gas path connecting device. One end opening of the high-transmittance quartz glass tube can be tightly connected to the ambient air sample through the polytetrafluoroethylene gas path connecting device. The ambient air sample can be input through the end opening. The hollow interior of the high-transmittance quartz glass tube can hold the ambient air sample. The other end opening of the high-transmittance quartz glass tube can output the photolyzed atmospheric sample through the polytetrafluoroethylene gas path connecting device.

[0009] The ultraviolet LED light source module is arranged directly opposite to the high-transmittance quartz glass tube, and the ultraviolet light released by the ultraviolet LED light source module can photodissociate NO2 in the ambient atmosphere sample in the high-transmittance quartz glass tube into NO;

[0010] The heat dissipation and temperature control device can perform heat dissipation and temperature control operations on the ultraviolet LED light source module through the heat dissipation device and the heat conduction device, ensuring that the temperature of the ultraviolet LED light source module is stable at 35±0.5°C.

[0011] Furthermore, the UV LED light source module can stably release 390nm-400nm UV light in the temperature range of 0-50°C, the maximum photochemical flux can reach 15000-18000mW, and the maximum NO2 photolysis conversion rate constant can reach 30s. -1 ;

[0012] Alternatively, the volume of the photolysis conversion device is 60mm*100mm*80mm, and the maximum operating power consumption is 240W;

[0013] Alternatively, the horizontal ends of the high-transmittance quartz glass tube are cut into smooth surfaces and are cylindrical in shape with an inner diameter of 15 mm, an outer diameter of 18 mm, and a length of 60 mm.

[0014] Further, the ultraviolet LED light source module includes an ultraviolet LED light source, a light source mounting plate, highly transparent quartz glass, a positive power source and a negative power source, a plurality of ultraviolet LED light sources are evenly spaced and arranged on the light source mounting plate, the ultraviolet LED light source includes a light-emitting end and a mounting end, the light source mounting plate and the light-emitting ends of the plurality of ultraviolet LED light sources are all arranged facing the highly transparent quartz glass tube, and the mounting end of the ultraviolet LED light source is connected to the light source mounting plate;

[0015] The highly transparent quartz glass is connected to the light source mounting plate, and the light emitting end of the ultraviolet LED light source is in contact with the inner surface of the highly transparent quartz glass;

[0016] The positive electrode of the power supply and the negative electrode of the power supply are connected on the light source installation plate, and the ultraviolet LED light source is connected to the positive electrode of the power supply and the negative electrode of the power supply, and the positive electrode of the power supply and the negative electrode of the power supply provide power for the ultraviolet LED light source;

[0017] Alternatively, the light-shielding light shield comprises a light shield body, a glass tube installation channel, a guide groove, a screw hole, a screw and a screw hole, the light shield body is integrally formed with a glass tube installation channel and a guide groove, a high-transmittance quartz glass tube can be installed in the glass tube installation channel, and the light shield body is installed together with the ultraviolet LED light source module through the guide groove;

[0018] The photomask body is connected to the heat conduction device through screw holes and screws, and the photomask body is tightly connected to the polytetrafluoroethylene gas path connection device through screw holes and screws;

[0019] Alternatively, the heat-conducting device includes a heat-conducting copper plate, and the heat dissipation and temperature control device includes a high-speed adjustable fan.

[0020] Furthermore, the ultraviolet LED light source is an ultraviolet LED light source chip, the ultraviolet LED light source chip is 8 parallel 20 series 160 390nm-400nm ultraviolet LED light source chips, the light source mounting plate is a gold-plated copper plate, and the ultraviolet LED light source chip is welded on the gold-plated copper plate by a chip-on-board packaging method;

[0021] Alternatively, the material of the light mask body is brass;

[0022] Alternatively, the heat conduction device further comprises a temperature sensor and a temperature controller which are connected to each other. The temperature sensor is connected to the center of the heat conduction copper plate, and the temperature sensor is also connected to the heat dissipation temperature control device. The information of the temperature sensor is read by the temperature controller and the heat dissipation temperature control device is adjusted to control the temperature of the ultraviolet LED light source module to be stable at 35±0.5°C.

[0023] Alternatively, heat dissipation copper fins are connected and arranged on the outer surface of the mask body.

[0024] Furthermore, the positive electrode and the negative electrode of the power supply are powered by a constant current source, with a maximum supply current of 10A and a voltage of 24V;

[0025] Alternatively, the UV LED light source module has a total length of 56 mm and a width of 28 mm;

[0026] Alternatively, six fixing holes are arranged at intervals on the light source mounting plate, and the light source mounting plate is mounted together with the heat conducting device through the fixing holes and screws;

[0027] Alternatively, the temperature sensor information is read by the temperature controller and the air volume of the high-speed adjustable fan is adjusted by PWM mode to control the temperature of the ultraviolet LED light source module to be stable at 35±0.5°C;

[0028] Alternatively, the number of the screw holes is 4.

[0029] Furthermore, the device also includes a high thermal conductivity silicone grease layer, the high thermal conductivity silicone grease layer is connected between the ultraviolet LED light source module and the heat conduction device, and the high thermal conductivity silicone grease layer is also connected between the heat conduction device and the heat dissipation device;

[0030] Alternatively, the device further comprises a gas path pressing connection fixing screw, and the high-transmittance quartz glass tube is connected to the polytetrafluoroethylene gas path connecting device by the gas path pressing connection fixing screw and the pressure-sealed connection.

[0031] Furthermore, a high thermal conductivity silicone grease layer is coated between the ultraviolet LED light source module and the heat conducting device, and a high thermal conductivity silicone grease layer is coated between the heat conducting device and the heat dissipation device.

[0032] The heat conduction device is a heat conduction copper plate, the heat dissipation device is a copper tube radiator, the upper surface of the heat conduction copper plate is provided with a light source module threaded hole, and the ultraviolet LED light source module is connected to the upper surface of the heat conduction copper plate through the light source module threaded hole and screws;

[0033] Alternatively, a small hole is provided in the middle of the heat-conducting copper plate, in which a temperature sensor can be placed, and the air volume blown by the fan through the copper tube radiator is automatically controlled by pulse width control to control the temperature of the ultraviolet LED light source module to be stable within the range of 35°C±0.5°C, and a temperature protection program is provided at the same time, when the temperature of the light source exceeds 50°C, the power supply of the light source will be automatically disconnected;

[0034] Alternatively, a 1 / 4NPT threaded interface is provided at the center of one side of the polytetrafluoroethylene gas path connecting device, which can be connected to the sample gas path through an NPT ferrule joint and a 1 / 4NPT threaded interface, and a plurality of through holes are evenly spaced along the circumferential direction on the other side of the polytetrafluoroethylene gas path connecting device, several of which can be connected to the screw holes on the light-shielding cover by screws, and the remaining through holes are connected to the screw holes on the heat-conducting device by screws.

[0035] Furthermore, high-density thermal conductive silicone grease is applied between the thermal conductive copper plate and the ultraviolet LED light source module, which can quickly introduce the heat of the light source into the thermal conductive copper plate; the lower surface of the thermal conductive copper plate is fitted together with a copper tube radiator and fixed together by screws, and the fitting part is applied with high-density thermal conductive silicone grease, which can quickly transfer the heat of the thermal conductive copper plate to the copper tube radiator, and quickly introduce the heat of the light source of the ultraviolet LED light source module into the copper tube radiator, and the heat in the copper tube radiator is finally released through a heat dissipation and temperature control device such as a high-speed speed regulating fan.

[0036] Application of the device as described above in NO2 photolysis conversion.

[0037] A method for photolysis and conversion of NO2 based on chemiluminescence NOx measurement using the device as described above, the method comprising the following steps:

[0038] The atmospheric sample enters the hollow interior of the high-transmittance quartz glass tube through the sampling pump and the polytetrafluoroethylene gas path connection device. The ultraviolet light released by the ultraviolet LED light source module can photolyze the NO2 in the ambient atmospheric sample in the high-transmittance quartz glass tube into NO. Through the photolysis conversion device of the present invention, the NO2 in the atmospheric sample is efficiently and specifically converted into NO and enters the reaction chamber to react with excess ozone, and a chemiluminescent reaction occurs. The relationship between the fluorescence intensity of the reaction radiation and the NO concentration conforms to the Lambert-Beer law, thereby accurately obtaining the NOx concentration in the atmospheric sample. When the ultraviolet LED light source module is turned off, the NO concentration in the ambient atmospheric sample is measured, and the NO2 concentration can be obtained by subtracting the NO concentration from the NOx concentration.

[0039] The central radiation wavelength of the UV LED light source module is 395nm, and the radiation wavelength range is 390nm-400nm, which can ensure the specific conversion of NO2 in the atmospheric sample without converting other nitrogen-containing components in the atmospheric sample; the maximum photochemical flux reaches 15000-18000mW, and the maximum photolysis conversion rate constant of NO2 reaches 30s -1 ; When the sampling gas flow rate is 1L / min, the residence time of the sample gas in the high-transmittance quartz glass tube is 0.64s, which can ensure the efficient quantitative conversion of NO2 in the atmospheric sample, and the conversion efficiency is stable at 98.5±1.0%;

[0040] The heat dissipation and temperature control device can dissipate heat and control the temperature of the ultraviolet LED light source module through the heat conduction device, ensuring that the temperature of the ultraviolet LED light source module is stable at 35±0.5℃, which can ensure the stability of the radiation wavelength and protect the long-term stable operation of the ultraviolet LED light source module.

[0041] The advantages and positive effects achieved by the present invention are:

[0042] 1. The NO2 conversion device of the present invention has the advantages of high conversion efficiency, good specificity, simple device, small size, low power consumption, stable and reliable operation, etc., and can realize the conversion of ambient atmospheric NO by chemiluminescence method. x Precise online measurement.

[0043] 2. The chip-on-board packaged ultraviolet LED light source module of the device of the present invention has narrow-band light source characteristics and high radiation flux characteristics. It can not only specifically perform photolysis conversion on NO2 to avoid interference from other nitrogen-containing components, but also achieve a conversion efficiency of about 98.5%.

[0044] 3. The device of the present invention has an ultraviolet LED light source module connected to a copper tube radiator through a thermally conductive copper sheet, and the temperature is controlled by PWM. The heat dissipation device is simple, the temperature control method is accurate, the heat dissipation energy consumption is low, and the operation is stable. It can ensure that the light source works continuously and stably, meeting the requirements of online continuous observation, and there is no consumables.

[0045] 4. The photolysis channel of the device of the present invention is made of highly transparent quartz, and the connecting device is made of polytetrafluoroethylene. The material has low adsorption and good tolerance, and can minimize the interference between pipelines and walls. At the same time, it is isolated from the light source, avoiding the problem of changes in conversion efficiency caused by surface contamination of the light source.

[0046] 5. The light shielding and heat dissipation cover of the device of the present invention is made of brass material and heat dissipation fins, which can be beneficial to the dissipation of the radiant heat of the light source and reduce the influence of the thermal effect of the quartz tube wall on the NO2 conversion.

[0047] 6. The photolysis channel and gas connection device of the NO2 conversion device of the present invention are all made of inert materials. The present invention can also set a light source protection program. By setting a temperature switch, the light source is automatically locked when it is over-temperature, and the ultraviolet light source is accurately temperature-controlled, thereby improving the operating stability and safety and reliability of the photolysis conversion device. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A schematic diagram of the structure connection of the photolysis conversion device in the present invention;

[0049] Figure 2 for Figure 1 A structural connection diagram of a mid-ultraviolet LED light source module;

[0050] Figure 3 for Figure 1 A schematic diagram of a structural connection of a light shielding hood;

[0051] Figure 4 This is a comparison chart of the NO2 measured by the molybdenum conversion or photolysis conversion device based on the chemiluminescence method in Beijing in winter / summer in the present invention. DETAILED DESCRIPTION

[0052] The present invention will be further described below in conjunction with the embodiments. The following embodiments are descriptive rather than restrictive, and the protection scope of the present invention cannot be limited by the following embodiments.

[0053] The various experimental operations involved in the specific embodiments are all routine techniques in the art. For parts not specially annotated in this document, ordinary technicians in the art can implement them by referring to various commonly used reference books, scientific and technological literature or related instructions, manuals, etc. before the filing date of this invention.

[0054] A NO2 photolysis conversion device based on chemiluminescence NOx measurement, such as Figure 1 As shown, the device includes an ultraviolet LED light source module 1, a high-transmittance quartz glass tube 2, a light-shielding light shield 3, a heat-conducting device 4, a heat dissipating device 5, a polytetrafluoroethylene gas path connecting device and a heat dissipation temperature control device 9. The ultraviolet LED light source module is arranged in a horizontal direction, and the ultraviolet LED light source module can release 390nm-400nm ultraviolet light. The ultraviolet LED light source module is connected to the heat-conducting device, and the heat-conducting device is also connected to the heat dissipating device; the high-transmittance quartz glass tube is connected to the polytetrafluoroethylene gas path connecting device, and is arranged in parallel with the ultraviolet LED light source module in the light-shielding light shield, and the light-shielding light shield can perform light-shielding operation on the high-transmittance quartz glass tube; the light-shielding light shield is also connected to the heat-conducting device and the polytetrafluoroethylene gas path connecting device, and the polytetrafluoroethylene gas path connecting device is also connected to the heat-conducting device;

[0055] The high-transmittance quartz glass tube is arranged in the horizontal direction. The high-transmittance quartz glass tube is in the shape of a hollow cylinder with two horizontal openings. The openings at both ends of the high-transmittance quartz glass tube are tightly connected to the polytetrafluoroethylene gas path connecting device. One end opening of the high-transmittance quartz glass tube can be tightly connected to the ambient air sample through the polytetrafluoroethylene gas path connecting device 6. The ambient air sample can be input through the end opening. The hollow interior of the high-transmittance quartz glass tube can hold the ambient air sample. The other end opening of the high-transmittance quartz glass tube can output the photolyzed atmospheric sample through the polytetrafluoroethylene gas path connecting device 8.

[0056] The ultraviolet LED light source module is arranged directly opposite to the high-transmittance quartz glass tube, and the ultraviolet light released by the ultraviolet LED light source module can photodissociate NO2 in the ambient atmosphere sample in the high-transmittance quartz glass tube into NO;

[0057] The heat dissipation and temperature control device can dissipate heat and control the temperature of the ultraviolet LED light source module through the heat dissipation device and the heat conduction device, ensuring that the temperature of the ultraviolet LED light source module is stable at 35±0.5°C, thereby ensuring a stable radiation process of the light source.

[0058] The photolysis conversion device includes an ultraviolet LED light source module, a high-transmittance quartz glass tube, a light-shielding cover, a heat conducting device, a heat dissipating device, a polytetrafluoroethylene gas path connecting device, and a heat dissipation temperature control device. When in use, the ambient air sample enters the hollow interior of the high-transmittance quartz glass tube through the polytetrafluoroethylene gas path connecting device, and the ultraviolet light released by the ultraviolet LED light source module can photodissociate the NO2 in the ambient air sample in the high-transmittance quartz glass tube into NO. The heat dissipation temperature control device can perform heat dissipation and temperature control operations on the ultraviolet LED light source module through the heat dissipating device and the heat conducting device, ensuring that the temperature of the ultraviolet LED light source module is stable at 35±0.5℃, ensuring the stable radiation process of the light source. Since the photolysis channel of the device of the present invention adopts a high-transmittance quartz glass tube, and the connecting device adopts polytetrafluoroethylene material, the material has low adsorption, good tolerance, can minimize the interference of pipelines and walls, and is isolated from the light source, avoiding the problem of changes in conversion efficiency caused by surface contamination of the light source.

[0059] The radiation wavelength range of the ultraviolet LED light source module of this device is 390nm-400nm. In this band, ultraviolet light has a large absorption cross section and quantum yield for NO2, and can quickly dissociate NO2 into NO. At the same time, it is separated from the typical absorption cross sections of other substances including peroxyacetyl nitrate (PANs), HONO, NO3 and other nitrogen-containing compounds, and will not convert other gaseous nitrogen-containing compounds in the atmosphere such as NO3, HNO3, PAN, HONO, NH3, RO2NO2 and particulate nitrogen-containing compounds into NO, which effectively solves the common problem of existing molybdenum converters that convert most nitrogen-containing substances in the atmosphere into NO, resulting in overestimation of NOx measurements. The array LED light source module can stably release 390nm-400nm ultraviolet light in the temperature range of 0-50℃, and the maximum photochemical flux can reach 15000-18000mW, and the maximum photolysis conversion rate constant of NO2 can reach 30s -1 .

[0060] In the present invention, the light source and the gas path are isolated by a high-transmittance quartz glass tube, thereby preventing the light source from being contaminated by gas path samples and ensuring the long-term stable photolysis conversion efficiency of NO2 to NO.

[0061] Preferably, the UV LED light source module can stably release 390nm-400nm UV light in the temperature range of 0-50°C, the maximum photochemical flux can reach 15000-18000mW, and the maximum NO2 photolysis conversion rate constant can reach 30s -1 ;

[0062] Preferably, the volume of the photolysis conversion device is 60mm*100mm*80mm, the normal operating power consumption is 120W, there is no need to replace consumables during operation, and it can operate stably and autonomously for a long time.

[0063] In this embodiment, in order to improve the thermal conductivity efficiency, the device also includes a high thermal conductivity silicone grease layer (not numbered in the figure), a high thermal conductivity silicone grease layer is connected between the ultraviolet LED light source module and the thermal conduction device, and a high thermal conductivity silicone grease layer is also connected between the thermal conduction device and the heat dissipation device.

[0064] Preferably, a high thermal conductivity silicone grease layer is coated between the ultraviolet LED light source module and the heat conducting device, and a high thermal conductivity silicone grease layer is coated between the heat conducting device and the heat dissipation device.

[0065] Specifically, the heat conduction device is a heat conduction copper plate, the heat dissipation device is a copper tube radiator, a light source module threaded hole (not shown in the figure) is provided on the upper surface of the heat conduction copper plate, and the ultraviolet LED light source module is connected to the upper surface of the heat conduction copper plate through the light source module threaded hole and screws;

[0066] A high-density thermal conductive silicone grease is applied between the thermal conductive copper plate and the ultraviolet LED light source module, which can quickly transfer the heat of the light source to the thermal conductive copper plate. The lower surface of the thermal conductive copper plate is fitted together with a copper tube radiator and fixed together by screws. The fitting part is coated with a high-density thermal conductive silicone grease, which can quickly transfer the heat of the thermal conductive copper plate to the copper tube radiator, and then quickly transfer the heat of the light source of the ultraviolet LED light source module to the copper tube radiator. The heat in the copper tube radiator is finally released through a heat dissipation temperature control device such as a high-speed speed regulating fan.

[0067] Preferably, a small hole is opened in the middle of the heat-conducting copper plate, and a temperature sensor can be placed in the small hole. The air volume blown by the fan through the copper tube radiator can be automatically controlled by pulse width modulation (PWM) to control the temperature of the ultraviolet LED light source module to be stable within the range of 35℃±0.5℃, so as to meet the requirements of stable operation of the light source. At the same time, a temperature protection program can be set. When the temperature of the light source exceeds 50℃, the power supply of the light source will be automatically disconnected, thereby ensuring the stable operation and safety of the light source.

[0068] In this embodiment, the horizontal ends of the high-transmittance quartz glass tube are cut into smooth surfaces and are cylindrical in shape with an inner diameter of 15 mm, an outer diameter of 18 mm, and a length of 60 mm.

[0069] In this embodiment, if Figure 2 As shown, the ultraviolet LED light source module includes an ultraviolet LED light source 101, a light source mounting plate 102, a highly transparent quartz glass 103, a positive power supply electrode 104, and a negative power supply electrode 105. A plurality of ultraviolet LED light sources are evenly and spaced apart on the light source mounting plate. The ultraviolet LED light source includes a light-emitting end and a mounting end (not numbered in the figure). The light source mounting plate and the light-emitting ends of the plurality of ultraviolet LED light sources are all arranged facing the highly transparent quartz glass tube, and the mounting end of the ultraviolet LED light source is connected to the light source mounting plate;

[0070] The highly transparent quartz glass is connected to the lamp source mounting plate, and the light-emitting end of the ultraviolet LED lamp source is in contact with the inner surface of the highly transparent quartz glass (for example, the light-emitting end of the ultraviolet LED lamp source is bonded to the inner surface of the highly transparent quartz glass). The light-emitting end of the LED lamp source is in contact with the inner surface of the highly transparent quartz glass, which can effectively protect the lamp source;

[0071] The positive pole and the negative pole of the power supply are connected on the light source installation plate, and the ultraviolet LED light source is connected with the positive pole and the negative pole of the power supply, and the positive pole and the negative pole of the power supply supply power to the ultraviolet LED light source.

[0072] Preferably, the ultraviolet LED light source is an ultraviolet LED light source chip, for example, a chip with model EP458S20P, the ultraviolet LED light source chip is 8 in parallel and 20 in series with 160 390nm-400nm ultraviolet LED light source chips, the light source mounting plate is a gold-plated copper plate, and the ultraviolet LED light source chip is welded on the gold-plated copper plate by chip-on-board packaging.

[0073] Preferably, the positive electrode and the negative electrode of the power supply are powered by a constant current source, with a maximum supply current of 10A and a voltage of 24V.

[0074] Preferably, the ultraviolet LED light source module has a total length of 56 mm and a width of 28 mm.

[0075] Preferably, six fixing holes 106 are arranged at intervals on the light source mounting plate, and the light source mounting plate is mounted together with the heat conducting device through the fixing holes and screws.

[0076] In this embodiment, the heat conduction device includes a heat-conducting copper plate 401, and the heat dissipation and temperature control device includes a high-speed adjustable fan.

[0077] Preferably, the heat conducting device also includes a temperature sensor 402 and a temperature controller (not shown in the figure) connected to each other. The temperature sensor is connected to the center of the heat conducting copper plate, and the temperature sensor is also connected to the heat dissipation temperature control device. The information of the temperature sensor is read by the temperature controller and the heat dissipation temperature control device is adjusted to control the temperature of the ultraviolet LED light source module to be stable at 35±0.5℃, thereby ensuring the stable radiation process of the light source.

[0078] Preferably, the temperature sensor information is read by the temperature controller and the air volume of the high-speed adjustable fan is adjusted through PWM mode to control the temperature of the ultraviolet LED light source module to be stable at 35±0.5°C.

[0079] In this embodiment, if Figure 3 As shown, the light-shielding light shield includes a light shield body 301, a glass tube installation channel 302, a guide groove 303, a screw hole 304, a screw (not shown in the figure) and a screw hole 305. The glass tube installation channel and the guide groove are integrally formed on the light shield body. A high-transmittance quartz glass tube can be installed in the glass tube installation channel. The light shield body is installed together with the ultraviolet LED light source module through the guide groove.

[0080] The photomask body is connected to the heat conduction device through screw holes and screws, and the photomask body is tightly connected to the polytetrafluoroethylene gas path connection device through screw holes and screws.

[0081] Preferably, the light shield body is made of brass, which can cooperate well with the ultraviolet LED light source module and can protect the high-transmittance quartz glass tube.

[0082] Preferably, a heat dissipation copper fin (not shown in the figure) is connected to the outer surface of the mask body. Since the light source radiates heat, most of the radiated heat is absorbed by the mask, and a heat dissipation copper fin is connected to the outer surface of the mask body to improve the efficiency of the dissipation of the radiant heat from the light source, reduce the thermal effect interference of the sample on the inner wall of the high-transmittance quartz glass tube, and thus reduce the impact on the efficient and specific conversion of NO2.

[0083] Preferably, the number of the screw holes is 4.

[0084] In this embodiment, the device further comprises a gas path press-fit connection fixing screw 7, and the high-light-transmittance quartz glass tube is connected to the polytetrafluoroethylene gas path connection device by press-fitting and sealing through the gas path press-fit connection fixing screw. Based on the press-fit sealing characteristics of the polytetrafluoroethylene material, by tightening the gas path press-fit connection fixing screw, the two ends of the high-light-transmittance quartz glass tube can be press-fit sealed with the polytetrafluoroethylene gas path connection device, respectively, with a simple structure and good sealing effect.

[0085] In the present invention, the light source and the gas path are isolated by a high-transmittance quartz glass tube, thereby preventing the light source from being contaminated by the gas path sample and ensuring the stable radiation intensity of the light source.

[0086] Specifically, a 1 / 4NPT threaded interface (not numbered in the figure) is provided at the center of one side of the polytetrafluoroethylene gas path connecting device, which can be connected to the sample gas path through an NPT ferrule joint and a 1 / 4NPT threaded interface. A plurality of (for example, 5) through holes (not numbered in the figure) are evenly spaced and arranged along the circumferential direction on the other side of the polytetrafluoroethylene gas path connecting device, wherein several through holes can be connected to the screw holes on the light-shielding cover by screws, and the remaining through holes are connected to the screw holes (not numbered in the figure) on the heat-conducting device by screws, so as to realize the connection of the high-transmittance quartz glass tube.

[0087] A method for photolysis and conversion of NO2 based on chemiluminescence NOx measurement using the device as described above, the method comprising the following steps:

[0088] The atmospheric sample enters the hollow interior of the high-transmittance quartz glass tube through the sampling pump and the polytetrafluoroethylene gas path connection device. The ultraviolet light released by the ultraviolet LED light source module can photodissociate the NO2 in the ambient atmospheric sample in the high-transmittance quartz glass tube into NO;

[0089] The central radiation wavelength of the UV LED light source module is 395nm, and the radiation wavelength range is 390nm-400nm, which can ensure the specific conversion of NO2 in the atmospheric sample without converting other nitrogen-containing components in the atmospheric sample; the maximum photochemical flux reaches 15000-18000mW, and the maximum photolysis conversion rate constant of NO2 reaches 30s-1 ; When the sampling gas flow rate is 1L / min, the residence time of the sample gas in the high-transmittance quartz glass tube is 0.64s, which can ensure the efficient quantitative conversion of NO2 in the atmospheric sample, and the conversion efficiency is stable at 98.5±1%;

[0090] The heat dissipation and temperature control device can dissipate heat and control the temperature of the ultraviolet LED light source module through the heat conduction device, ensuring that the temperature of the ultraviolet LED light source module is stable at 35±0.5℃, which can ensure the stability of the radiation wavelength and protect the long-term stable operation of the ultraviolet LED light source module.

[0091] After the photolysis conversion device of the present invention, NO2 in the atmospheric sample is efficiently and specifically converted into NO molecules and enters the reaction chamber to react with excess ozone, resulting in a chemiluminescent reaction. The fluorescence radiated by the reaction and the NO concentration conform to the Lambert-Beer law, thereby accurately obtaining the NOx concentration in the atmospheric sample. When the ultraviolet LED light source module is turned off, the NO concentration in the ambient atmospheric sample is measured. The NO2 concentration can be obtained by subtracting the NO concentration from the NOx concentration. Figure 4 As shown in the figure, the actual measurement data of NO2 in the summer and winter of 2017 obtained by the photolysis conversion device and the molybdenum conversion device of the present invention through the chemiluminescence analyzer at Peking University can be seen: the two instruments have a good correlation, R 2 =0.994. At the same time, the NO2 concentration measured by the molybdenum conversion method in summer (NO2-Mo) was 3.51±3.14ppb (30.8±44.5%) higher than the NO2 concentration measured by the photolysis conversion method (NO2-PL), and in winter it was 6.18±4.41ppb (25.5±17.6%) higher.

[0092] The conversion rate of NO2 has nothing to do with its initial concentration, but is only related to the residence time of the sample in the photolysis converter, the photochemical flux of the light source, the molecular absorption cross section and quantum yield, and the oxidant in the sample. Compared with increasing the residence time, increasing the photolysis rate constant j can more significantly improve the conversion rate of NO2. The longer the residence time, the higher the conversion efficiency of NO2, but it also increases the probability of NO reacting with oxidants such as O3 in the sample, as well as the probability of thermal decomposition or heterogeneous decomposition of NO2 or other nitrogen-containing compounds. Therefore, appropriately shortening the residence time can improve the selectivity of photolysis for NO2. The present invention uses an array LED light source module to provide an ultra-large photochemical flux for the photolysis of NO2 in the sample gas, meeting the high conversion efficiency requirements (the conversion efficiency can reach 98.5%); a 390nm-400nm LED narrowband light source is selected to achieve the specific conversion of NO2. In addition, due to the extremely fast photolysis conversion reaction rate, a method based on chemiluminescence NO developed by the present invention x The NO2 photolysis conversion method and device for measurement can also meet the requirements of high-frequency monitoring of NOx.

[0093] The high-transparency quartz tube is cut into smooth surfaces at both ends and is cylindrical in shape with an inner diameter of 15 mm, an outer diameter of 18 mm, and a length of 60 mm. x The measurement requires a sample flow rate of 1L / min, and the residence time of the sample gas in the high-transparency quartz tube is about 0.64s. The sample is irradiated by the light source in the high-transparency quartz tube, and the ultraviolet radiation time in the range of 390nm-400nm is about 0.64s, which can not only meet the requirements of high-efficiency conversion of NO2, but also significantly reduce the influence of oxidants and wall effects in the sample on the NO2 measurement results, making it possible for ultra-high-efficiency conversion of NO2.

[0094] The working principle of the device of the present invention can be as follows:

[0095] The principle of photolysis conversion is that NO2 will be dissociated into NO and O under light with a wavelength less than 424nm. 3 P) atom (see R1).

[0096] NO2+hν(λ<424nm)→NO+O( 3 P)(R1)

[0097] The conversion efficiency of NO2 can be calculated using Equation 1.

[0098]

[0099] In formula 1, K = k1[Ox1] + k2[Ox2] + ... + k n [Ox n ], where j is the photolysis rate constant of NO2 under the condition of λ<424nm (s -1 ), you can use Calculation; t is the reaction time (s); Ox1, Ox2,…, Ox n are the oxidants in the air that can oxidize NO, k1, k2, ..., k n They are Ox1, Ox2, ..., Ox n The second-order rate constant (cm 3 molecules -1 s -1 ); F(λ), σ(λ,T), Φ(λ,T) are the photochemical flux (photons cm -2 s -1 ), NO2 absorption cross section (cm 2 molecule -1 ) and quantum yield (molecules photon -1 ).

[0100] As can be seen from formula 1, the conversion rate of NO2 has nothing to do with its initial concentration, but is only related to the residence time, photochemical flux, absorption cross section, quantum yield and type of oxidant in the photolysis converter. The longer the residence time, the higher the conversion efficiency of NO2, but it also increases the probability of NO reacting with oxidants such as O3, as well as the probability of thermal decomposition or heterogeneous decomposition of NO2 or other nitrogen-containing compounds, so appropriately shortening the residence time can improve the selectivity of photolysis to NO2. The residence time in the photolysis converter of the present invention is 0.64s. Compared with increasing the residence time, increasing the photolysis rate constant j can more significantly improve the conversion rate of NO2. The photolysis rate constant j depends on the photochemical flux F, which in turn depends mainly on the type of light source. Using a high-intensity light source can greatly improve the conversion rate of NO2 and the sensitivity of the instrument. The light source used in the present invention is an ultraviolet light emitting diode array LED light source module (UV-LED), and the maximum radiation intensity of the light source is 18000mW, the wavelength center is 395nm, and the wavelength range is 390-400nm. This is because the absorption cross section and quantum yield of NO2 at 395nm are relatively high, and the emission spectrum of the UV-LED light source has little overlap with the absorption spectra of other nitrogen-containing compounds such as PAN, HONO, NO3, and BrONO2, which can minimize the interference of these species on the measurement.

[0101] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A NO2 photolysis conversion device based on chemiluminescence NOx measurement, characterized in that: The device comprises an ultraviolet LED light source module, a high-transmittance quartz glass tube, a light-shielding cover, a heat-conducting device, a heat-dissipating device, a polytetrafluoroethylene gas path connecting device and a heat-dissipating temperature control device. The ultraviolet LED light source module is arranged in a horizontal direction, and can release 390nm-400nm ultraviolet light. The ultraviolet LED light source module is connected to the heat-conducting device, and the heat-conducting device is also connected to the heat-dissipating device; the high-transmittance quartz glass tube is connected to the polytetrafluoroethylene gas path connecting device, and is arranged in parallel with the ultraviolet LED light source module in the light-shielding cover, and the light-shielding cover can perform light-shielding operation on the high-transmittance quartz glass tube; the light-shielding cover is also connected to the heat-conducting device and the polytetrafluoroethylene gas path connecting device, and the polytetrafluoroethylene gas path connecting device is also connected to the heat-conducting device; The high-transmittance quartz glass tube is arranged in the horizontal direction. The high-transmittance quartz glass tube is in the shape of a hollow cylinder with horizontal openings at both ends. The openings at both ends of the high-transmittance quartz glass tube are tightly connected to the polytetrafluoroethylene gas path connecting device. One end opening of the high-transmittance quartz glass tube can be tightly connected to the ambient air sample through the polytetrafluoroethylene gas path connecting device. The ambient air sample can be input through the end opening. The hollow interior of the high-transmittance quartz glass tube can hold the ambient air sample. The other end opening of the high-transmittance quartz glass tube can output the photolyzed atmospheric sample through the polytetrafluoroethylene gas path connecting device. The ultraviolet LED light source module is arranged directly opposite to the high-transmittance quartz glass tube, and the ultraviolet light released by the ultraviolet LED light source module can photodissociate nitrogen oxides in the ambient atmosphere sample in the high-transmittance quartz glass tube into NO; The heat dissipation and temperature control device can perform heat dissipation and temperature control operations on the ultraviolet LED light source module through the heat dissipation device and the heat conduction device, ensuring that the temperature of the ultraviolet LED light source module is stable at 35±0.5°C; The ultraviolet LED light source module can stably release 390nm-400nm ultraviolet light in the temperature range of 0-50°C, the maximum photochemical flux can reach 15000-18000mW, and the maximum NO2 photolysis conversion rate constant can reach 30s -1 ; The ultraviolet LED light source module comprises an ultraviolet LED light source, a light source mounting plate, a highly transparent quartz glass, a positive power source and a negative power source. A plurality of ultraviolet LED light sources are evenly and spaced apart on the light source mounting plate. The ultraviolet LED light source comprises a light-emitting end and a mounting end. The light source mounting plate and the light-emitting ends of the plurality of ultraviolet LED light sources are all arranged facing the highly transparent quartz glass tube. The mounting end of the ultraviolet LED light source is connected to the light source mounting plate. The highly transparent quartz glass is connected to the light source mounting plate, and the light emitting end of the ultraviolet LED light source is in contact with the inner surface of the highly transparent quartz glass; The positive electrode of the power supply and the negative electrode of the power supply are connected on the light source installation plate, and the ultraviolet LED light source is connected to the positive electrode of the power supply and the negative electrode of the power supply, and the positive electrode of the power supply and the negative electrode of the power supply provide power for the ultraviolet LED light source; The light-shielding light shield comprises a light shield body, a glass tube installation channel, a guide groove, a screw hole, a screw and a screw hole. The glass tube installation channel and the guide groove are integrally formed on the light shield body. A high-transmittance quartz glass tube can be installed in the glass tube installation channel. The light shield body is installed together with the ultraviolet LED light source module through the guide groove. The photomask body is connected to the heat conduction device through screw holes and screws, and the photomask body is tightly connected to the polytetrafluoroethylene gas path connection device through screw holes and screws; The heat conduction device comprises a heat-conducting copper plate, and the heat dissipation and temperature control device comprises a high-speed speed-adjustable fan; A high thermal conductivity silicone grease layer is coated between the ultraviolet LED light source module and the heat conducting device, and a high thermal conductivity silicone grease layer is coated between the heat conducting device and the heat dissipation device; The heat conduction device is a heat conduction copper plate, the heat dissipation device is a copper tube radiator, the upper surface of the heat conduction copper plate is provided with a light source module threaded hole, and the ultraviolet LED light source module is connected to the upper surface of the heat conduction copper plate through the light source module threaded hole and screws; A small hole is provided in the middle of the heat-conducting copper plate, in which a temperature sensor can be placed, and the air volume blown by the fan through the copper tube radiator is automatically controlled by pulse width control to control the temperature of the ultraviolet LED light source module to be stable within the range of 35°C±0.5°C. At the same time, a temperature protection program is provided, and when the temperature of the light source exceeds 50°C, the power supply of the light source will be automatically disconnected; A 1 / 4NPT threaded interface is provided at the center of one side of the polytetrafluoroethylene gas path connection device, which can be connected to the sample gas path through an NPT ferrule joint and a 1 / 4NPT threaded interface. A plurality of through holes are evenly spaced and arranged along the circumferential direction on the other side of the polytetrafluoroethylene gas path connection device, wherein several through holes can be connected to the screw holes on the light-shielding cover by screws, and the remaining through holes are connected to the screw holes on the heat-conducting device by screws; A high-density thermal conductive silicone grease is applied between the thermal conductive copper plate and the ultraviolet LED light source module, which can quickly transfer the heat of the light source to the thermal conductive copper plate; the lower surface of the thermal conductive copper plate is fitted together with a copper tube radiator and fixed together by screws, and the fitting part is coated with a high-density thermal conductive silicone grease, which can quickly transfer the heat of the thermal conductive copper plate to the copper tube radiator, and quickly transfer the heat of the light source of the ultraviolet LED light source module to the copper tube radiator, and the heat in the copper tube radiator is finally released through a heat dissipation temperature control device such as a high-speed speed regulating fan; A NO2 photolysis conversion method based on chemiluminescence NOx measurement using the device comprises the following steps: The atmospheric sample enters the hollow interior of the high-transmittance quartz glass tube through the sampling pump and the polytetrafluoroethylene gas connection device. The ultraviolet light released by the ultraviolet LED light source module can photodissociate the NO2 in the ambient atmospheric sample in the high-transmittance quartz glass tube into NO and O( 3 P) atoms; Among them, the central radiation wavelength of the ultraviolet LED light source module is 395nm, the radiation wavelength range is 390nm-400nm, the maximum photochemical flux reaches 15000-18000mW, and the maximum photolysis conversion rate constant of NO2 reaches 30s -1 ; When the sampling gas flow rate is 1L / min, the residence time of the sample gas in the high-transmittance quartz glass tube is 0.64s; The heat dissipation and temperature control device can perform heat dissipation and temperature control operations on the ultraviolet LED light source module through the heat conduction device, ensuring that the temperature of the ultraviolet LED light source module is stable at 35±0.5℃.

2. The NO2 photolysis conversion device based on chemiluminescence NOx measurement according to claim 1 is characterized in that: The volume of the photolysis conversion device is 60mm*100mm*80mm, and the maximum power consumption during operation is 240W; Alternatively, the horizontal ends of the high-transmittance quartz glass tube are cut into smooth surfaces and are cylindrical in shape with an inner diameter of 15 mm, an outer diameter of 18 mm, and a length of 60 mm.

3. The NO2 photolysis conversion device based on chemiluminescence NOx measurement according to claim 1 is characterized in that: The ultraviolet LED light source is an ultraviolet LED light source chip, which is 8 in parallel and 20 in series with 160 390nm-400nm ultraviolet LED light source chips. The light source mounting plate is a gold-plated copper plate, and the ultraviolet LED light source chip is welded on the gold-plated copper plate by a chip-on-board packaging method. Alternatively, the material of the light mask body is brass; Alternatively, the heat conduction device further comprises a temperature sensor and a temperature controller which are connected to each other. The temperature sensor is connected to the center of the heat conduction copper plate, and the temperature sensor is also connected to the heat dissipation temperature control device. The information of the temperature sensor is read by the temperature controller and the heat dissipation temperature control device is adjusted to control the temperature of the ultraviolet LED light source module to be stable at 35±0.5°C. Alternatively, heat dissipation copper fins are connected and arranged on the outer surface of the mask body.

4. The NO2 photolysis conversion device based on chemiluminescence NOx measurement according to claim 1 is characterized in that: The positive and negative electrodes of the power supply are powered by a constant current source, with a maximum supply current of 10A and a voltage of 24V; Alternatively, the UV LED light source module has a total length of 56 mm and a width of 28 mm; Alternatively, six fixing holes are arranged at intervals on the light source mounting plate, and the light source mounting plate is mounted together with the heat conducting device through the fixing holes and screws; Alternatively, the temperature sensor information is read by the temperature controller and the air volume of the high-speed adjustable fan is adjusted by PWM mode to control the temperature of the ultraviolet LED light source module to be stable at 35±0.5°C; Alternatively, the number of the screw holes is 4.

5. The NO2 photolysis conversion device based on chemiluminescence NOx measurement according to claim 1 is characterized in that: The device further comprises a high thermal conductivity silicone grease layer, wherein the high thermal conductivity silicone grease layer is connected between the ultraviolet LED light source module and the heat conducting device, and the high thermal conductivity silicone grease layer is also connected between the heat conducting device and the heat dissipation device; Alternatively, the device further comprises a gas path pressing connection fixing screw, and the high-transmittance quartz glass tube is connected to the polytetrafluoroethylene gas path connecting device by the gas path pressing connection fixing screw and the pressure-sealed connection.

6. Use of the device according to any one of claims 1 to 5 in NO2 photolysis conversion.

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