Water, gas and mercury coupling online monitoring device and method

Abstract

The invention provides a water-gas mercury coupling online monitoring device and method. The water-gas mercury coupling online monitoring device comprises a water body mercury automatic online sampling unit, a gas mercury automatic online sampling unit and a mercury detector, the water body mercury automatic online sampling unit comprises a filtering membrane, a first drying pipe, a stop valve, a first mass flow controller and a first mercury enrichment pipe which are sequentially connected through a pipeline; the gas mercury automatic on-line sample injection unit comprises a peristaltic pump, a precipitation bottle, a metering pump, a water quality mercury thermal desorption pipe, a second drying pipe and a second mercury enrichment pipe which are sequentially connected through a pipeline; the mercury detector is connected to the first mercury enrichment pipe and the second mercury enrichment pipe; and an inlet of the first mercury enrichment pipe and an inlet of the water quality mercury thermal desorption pipe are connected with a carrier gas source. The invention innovatively develops the water-gas mercury coupling on-line monitoring device and method, and provides a scientific technical method and support for collaborative monitoring and evaluation of environmental water quality, gas mercury concentration and pollution conditions, accurate measurement of exchange flux of mercury on a water-gas interface and treatment of mercury pollution.

Description

Technical Field

[0001] This invention relates to the field of atmospheric environment monitoring technology, and more specifically, to a water-gas-mercury coupled online monitoring device and method. Background Technology

[0002] Mercury is a toxic and harmful heavy metal element that is liquid at room temperature and pressure and can volatilize into the atmosphere. Therefore, mercury is widely distributed in various media on the Earth's surface, including water, soil, rocks, atmosphere, and organisms, undergoing complex migration and transformation within these media. To accurately monitor and assess the mercury concentration levels and pollution status in water and atmosphere under the same monitoring environment, to clearly understand and study the distribution, migration, and transformation patterns of mercury in various media, and especially to clarify the mercury exchange mechanism at the water-air interface, it is necessary to simultaneously perform high-precision and high-temporal-resolution online measurements of mercury concentrations in both water and air, and to accurately and quantitatively measure the mercury exchange flux at the water-air interface. The mercury exchange flux is directly related to the mercury concentrations in both water and atmosphere at the water-air interface; changes in the coupling of these concentrations directly affect the mercury exchange flux at the water-air interface. Therefore, only through high-precision and high-temporal-resolution coupled online measurement and analysis of mercury concentrations at the water-air interface and in the atmosphere can the mercury exchange flux at the water-air interface be accurately and effectively calculated. This allows for precise quantification of mercury emissions from water to the atmosphere and atmospheric deposition into water, and further, more accurately estimates of the absorption and emission of atmospheric mercury by global lakes and oceans. However, due to the different sample pretreatment procedures for online measurements of gaseous mercury and water mercury, current international measurements of gaseous mercury and water mercury are conducted separately, preventing simultaneous real-time coupled online monitoring of both. The lack of high-precision and high-temporal-resolution coupled online monitoring technology for water-air mercury makes it impossible to accurately measure and study water-air mercury concentrations and the mercury exchange flux at the water-air interface. This results in significant errors in the current calculations of mercury emissions from water to the atmosphere, severely hindering our understanding of whether global water bodies are sources or sinks of mercury. Summary of the Invention

[0003] (a) Technical problems to be solved The technical problem to be solved by this invention is that existing methods cannot simultaneously measure dissolved gaseous mercury in water and actual atmospheric mercury in real time, resulting in inaccurate calculation of mercury exchange flux at the water-air interface.

[0004] (II) Technical Solution To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a water-gas-mercury coupled online monitoring device, comprising an automatic online mercury injection unit for water, an automatic online mercury injection unit for gas, and a mercury detector; the automatic online mercury injection unit for water includes a filter membrane, a first drying tube, a shut-off valve, a first mass flow controller, and a first mercury enrichment tube connected in sequence via pipelines; the automatic online mercury injection unit for gas includes a peristaltic pump, a sedimentation bottle, a metering pump, a water quality mercury thermal desorption tube, a second drying tube, and a second mercury enrichment tube connected in sequence via pipelines; the mercury detector is connected to the outlet of the first mercury enrichment tube and the outlet of the second mercury enrichment tube; wherein, the inlet of the first mercury enrichment tube and the inlet of the water quality mercury thermal desorption tube are connected to a carrier gas source. The above technical solution, by integrating two injection units and one detector, ensures the temporal consistency and comparability of the data.

[0005] Preferably, the water mercury thermal desorption tube includes a first tube body, quartz wool, a first heating wire, and a water mercury decomposition agent. Quartz wool is filled at both ends of the first tube body, and the water mercury decomposition agent is placed between the quartz wool ends. The first heating wire is located outside the first tube body. This technical solution ensures complete thermal desorption of mercury in the water sample. The quartz wool prevents sample boiling and decomposition agent loss, and the first heating wire maintains a high temperature of 800-1000°C, converting mercury into gaseous elemental mercury. This improves the accuracy and reproducibility of water mercury measurement and reduces the risk of underestimation due to incomplete desorption.

[0006] Preferably, the water-based mercury pyrolysis agent includes at least one of modified activated carbon, silicon carbide, and high-temperature resistant ceramics.

[0007] Preferably, the first mercury enrichment tube includes a second tube body, a second heating wire, and a mercury adsorbent. The mercury adsorbent is placed inside the second tube body, and the second heating wire is disposed outside the second tube body. This structure is specifically designed for the enrichment of mercury in gaseous samples. The mercury adsorbent (such as a gold-based material) has a high adsorption capacity, and the second heating wire enables thermal desorption at 500-800°C, improving the sensitivity of gaseous mercury detection. The enrichment process purifies the sample, removes interfering substances, and ensures detection of mercury up to 10 ng / m³. 3 The following is an accurate measurement of ultra-trace atmospheric mercury.

[0008] Preferably, the second mercury enrichment tube includes a third tube body, a third heating wire, and a mercury adsorbent, wherein the mercury adsorbent is placed inside the third tube body, and the third heating wire is provided outside the third tube body.

[0009] Preferably, the mercury adsorbent is gold metal or gold-plated quartz sand particles. Gold-based adsorbents exhibit high selectivity and adsorption capacity for mercury, while gold-plated quartz sand particles increase the specific surface area, optimize adsorption-desorption kinetics, improve enrichment efficiency, and reduce mercury loss. The inertness of gold materials ensures long-term stability, reduces maintenance frequency, and thus saves monitoring costs.

[0010] Preferably, the sedimentation bottle, the first drying tube, the water quality mercury thermal desorption tube, the second drying tube, the second mercury enrichment tube, and the pipes are all made of Teflon.

[0011] Preferably, it further includes a second mass flow controller, which is located on the output pipeline of the carrier gas source.

[0012] Preferably, the first and second drying tubes are filled with soda lime. Soda lime, as a desiccant, effectively removes moisture and acidic gases (such as CO2) from the sample, avoiding interference from moisture and acidic substances on mercury detection (such as corrosion of the tubing or impact on the sensor), and improving the signal-to-noise ratio of the detection signal.

[0013] Secondly, the present invention also provides a method for online monitoring of water-gas-mercury coupling, implemented using the aforementioned online monitoring device for water-gas-mercury coupling, the method comprising the following steps: S1. Close the shut-off valve, start the peristaltic pump, and extract a water sample from the water source to be tested. The water sample is settled and overflowed in a sedimentation bottle, and then a preset volume of water sample is extracted by a metering pump and injected into the water quality mercury thermal desorption tube. All the mercury in the water sample in the water quality mercury thermal desorption tube is thermally desorbed into gaseous elemental mercury. After the gaseous elemental mercury is dried by the second drying tube, it is enriched in the second mercury enrichment tube. The mercury enriched in the second mercury enrichment tube is thermally desorbed and carried into the mercury detector for analysis and determination of mercury concentration, so as to obtain the dissolved gaseous mercury concentration in the water source to be tested. S2. Open the shut-off valve and start the air pump in the mercury detector. The gas sample is filtered through the filter membrane to remove large particles, then dried through the first drying tube, and the flow rate is precisely controlled by the first mass flow controller to enrich the mercury in the gas sample into the first mercury enrichment tube. The mercury enriched in the first mercury enrichment tube is thermally desorbed and carried into the mercury detector for analysis and determination of mercury concentration to obtain the actual atmospheric mercury concentration of the water source to be tested. S3. Repeat steps S1 and S2 a preset number of times; S4. Using Henry's Law, convert the dissolved gaseous mercury concentration in the water into a gas-phase equilibrium concentration, then calculate the effective concentration difference ΔC between the gas-phase equilibrium concentration and the actual atmospheric mercury concentration, according to formula F. Hg The mercury exchange flux F at the water-air interface is calculated as k×ΔC. Hg , where k is the diffusion efficiency of mercury at the gas-liquid interface.

[0014] (III) Beneficial Effects The above-described technical solution of the present invention has at least the following advantages: The water-gas-mercury coupled online monitoring device and method provided by this invention achieves, for the first time, high-precision and high-temporal-resolution coupled online measurement of mercury concentrations in water and gas. This provides a scientific and technical method and support for accurately monitoring and assessing environmental water quality and gaseous mercury concentration levels and pollution status, accurately measuring mercury exchange flux at the water-gas interface, and controlling mercury pollution. It also greatly reduces the cost of environmental mercury monitoring. Therefore, this invention has good economic and social benefits and broad application prospects. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the structure of the water-gas-mercury coupling online monitoring device provided in an embodiment of the present invention.

[0017] Figure 2 This is a graph showing the measurement results obtained using the water-gas-mercury coupling online monitoring method provided in an embodiment of the present invention.

[0018] The labels for the attached figures are as follows: 1. Automatic online mercury sampling unit for water; 2. Automatic online mercury sampling unit for gas; 3. Mercury detector; 4. Second mass flow controller; 11. Filter membrane; 12. First drying tube; 13. Shut-off valve; 14. First mass flow controller; 15. First mercury enrichment tube; 16. First three-way valve; 21. Peristaltic pump; 22. Sedimentation bottle; 23. Metering pump; 24. Water mercury thermal desorption tube; 25. Second drying tube; 26. Second mercury enrichment tube; 27. Second three-way valve; 31. Second three-way solenoid valve; 41. First three-way solenoid valve; 151. Second tube body; 152. Second heating wire; 153. Mercury adsorbent; 221. Inlet pipe; 222. Outlet pipe; 223. Overflow port; 241. First tube body; 242. Quartz wool; 243. First heating wire; 244. Water mercury decomposition agent; 261. Third tube body; 262. Third heating wire. Detailed Implementation

[0019] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0020] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be located directly on or indirectly on the other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to the other component.

[0021] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate that the device or element must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating relative importance or the number of technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. The specific implementation of this invention will be described in more detail below with reference to specific embodiments: like Figure 1 As shown, this embodiment of the invention provides a water-gas-mercury coupling online monitoring device, including an automatic online mercury injection unit 1 for water, an automatic online mercury injection unit 2 for gas, and a mercury detector 3. The automatic online mercury injection unit 1 for water includes a filter membrane 11, a first drying tube 12, a shut-off valve 13, a first mass flow controller 14, and a first mercury enrichment tube 15 connected in sequence through pipes. The automatic online mercury injection unit 2 for gas includes a peristaltic pump 21, a sedimentation bottle 22, a metering pump 23, a water mercury thermal desorption tube 24, a second drying tube 25, and a second mercury enrichment tube 26 connected in sequence through pipes. The mercury detector 3 is connected to the outlet of the first mercury enrichment tube 15 and the outlet of the second mercury enrichment tube 26. The inlet of the first mercury enrichment tube 15 and the inlet of the water mercury thermal desorption tube 24 are connected to a carrier gas source. Specifically, it also includes a first three-way valve 16, a second three-way valve 27, a first three-way solenoid valve 41, and a second three-way solenoid valve 31. The three ports of the first three-way valve 16 are respectively connected to the pipeline outlet of the first mass flow controller 14, the pipeline inlet of the first mercury enrichment pipe 15, and the output pipeline of the carrier gas source. The three ports of the second three-way valve 27 are respectively connected to the pipeline outlet of the metering pump, the pipeline inlet of the water quality mercury thermal desorption pipe 24, and the output pipeline of the carrier gas source. The three ports of the first three-way solenoid valve 41 are respectively connected to the output pipeline of the carrier gas source, one port of the first three-way valve 16, and one port of the second three-way valve 27. The three ports of the second three-way solenoid valve 31 are respectively connected to the pipeline outlet of the first mercury enrichment pipe 15, the pipeline outlet of the second mercury enrichment pipe 26, and the pipeline inlet of the mercury detector 3.

[0023] In one embodiment, the water-based mercury thermal desorption tube 24 includes a first tube body 241, quartz wool 242, a first heating wire 243, and a water-based mercury decomposition agent 244. The two ends of the first tube body 241 are respectively filled with quartz wool 242, and the water-based mercury decomposition agent 244 is placed between the two ends of the quartz wool 242. The first heating wire 243 is provided outside the first tube body 241.

[0024] In one embodiment, the water-based mercury pyrolysis agent 244 comprises at least one of modified activated carbon, silicon carbide, and high-temperature resistant ceramics.

[0025] In one embodiment, the first mercury enrichment tube 15 includes a second tube body 151, a second heating wire 152, and a mercury adsorbent 153. The mercury adsorbent 153 is placed inside the second tube body 151, and the second heating wire 152 is provided outside the second tube body 151.

[0026] In one embodiment, the second mercury enrichment tube 26 includes a third tube body 261, a third heating wire 262, and a mercury adsorbent 153. The mercury adsorbent is placed inside the third tube body 261, and the third heating wire 262 is provided outside the third tube body 261.

[0027] In one embodiment, the mercury adsorbent 153 is gold metal or gold-plated quartz sand particles.

[0028] In one embodiment, the precipitation bottle 22, the first drying tube 12, the water quality mercury thermal desorption tube 24, the second drying tube 25, the second mercury enrichment tube 26, and the pipelines are all made of Teflon. Furthermore, the first three-way valve 16, the second three-way valve 27, the first three-way solenoid valve 41, and the second three-way solenoid valve 31 are all preferably made of Teflon to prevent the pipelines from adsorbing mercury from the sample.

[0029] In one embodiment, a second mass flow controller 4 is also included, which is located on the output pipeline of the carrier gas source.

[0030] In one embodiment, the first drying tube 12 and the second drying tube 25 are filled with soda lime.

[0031] This invention also provides a method for online monitoring of water-gas-mercury coupling, implemented using a water-gas-mercury coupling online monitoring device, and the method includes the following steps: S1. Close the shut-off valve 13, start the peristaltic pump 21, and extract water samples from the water source to be tested. The water samples are settled and overflowed through the sedimentation bottle 22, and then metered by the metering pump 23 to extract a preset volume of water samples and inject them into the water quality mercury thermal desorption tube 24. All the mercury in the water sample in the water quality mercury thermal desorption tube 24 is thermally desorbed into gaseous elemental mercury. The gaseous elemental mercury is dried by the second drying tube 25 and enriched in the second mercury enrichment tube 26. The mercury enriched in the second mercury enrichment tube 26 is thermally desorbed and carried into the mercury detector 3 for analysis and determination of mercury concentration, thereby obtaining the dissolved gaseous mercury concentration in the water source to be tested; specifically, first First, the measurement of mercury in the water body is started by the automatic online sampling unit 1. The water sample from the water source to be tested is injected into the sedimentation bottle 22 through the inlet pipe 221 by the peristaltic pump. When the water level exceeds the overflow port 223, the water will be discharged from the overflow port 223, thus keeping the water sample in the sedimentation bottle 22 fresh. Then, the metering pump 23 draws a certain amount (1-100 ml) of water sample through the outlet pipe 222 of the sedimentation bottle 22 and injects it into the water quality mercury thermal desorption tube 24. The two ends of the water quality mercury thermal desorption tube 24 are filled with quartz wool 242, and the middle of the two ends of the quartz wool 242 is filled with water quality mercury decomposition agent 244 (modified activated carbon, etc.). (Silicon carbide or high-temperature resistant ceramic), quartz wool 242 can prevent water sample from boiling over and water mercury decomposition agent 244 from slipping out of water mercury thermal desorption tube 24, and the first heating wire 243 maintains a high temperature of 800-1000 degrees Celsius, thereby thermally desorbing all the mercury in the water sample into gaseous elemental mercury (zero-valent mercury). At the same time, the first three-way solenoid valve 41 is opened to one end of the second three-way valve 27, and the end of the first three-way valve 16 is kept closed, so that after the carrier gas passes through the first mass flow controller 14 to precisely control the flow rate, it can carry the gaseous elemental mercury released from the water mercury thermal desorption tube 24 into the second drying tube 25, the second The second drying tube 25 is filled with soda lime to remove water vapor and acidic gas impurities. Then, a carrier gas carries gaseous elemental mercury into the second mercury enrichment tube 26, which is filled with a mercury adsorbent (pure gold or gold-plated quartz sand particles). This further enriches and purifies the gaseous elemental mercury from the high-temperature thermal desorption of the water. The mercury is then heated to 500-800 degrees Celsius by the third heating wire 262, causing the mercury in the enrichment tube to be released and carried by the carrier gas into the mercury detector 3 for analysis and measurement of mercury concentration. At this time, the second three-way solenoid valve 31 opens one end of the second mercury enrichment tube 26 and closes the end leading to the first mercury enrichment tube 15. The mercury concentration (Cw) of the water sample can then be calculated based on the volume of water sample (Vw) injected into the water mercury thermal desorption tube by the metering pump and the mass of mercury (Mw) measured by the mercury detector 3. The calculation formula is as follows: Cw = Mw / Vw.

[0032] S2. Open the shut-off valve 13 and start the air pump in the mercury detector 3. The gas sample is filtered by the filter membrane 11 to remove large particles, and then dried by the first drying tube 12. The flow rate is precisely controlled by the first mass flow controller 14 to enrich the mercury in the gas sample into the first mercury enrichment tube 15. The mercury enriched in the first mercury enrichment tube 15 is thermally desorbed and carried into the mercury detector 3 for analysis and determination of mercury concentration to obtain the actual atmospheric mercury concentration of the water source to be tested. Specifically, after the measurement of the mercury concentration in the water body is completed (step S1), the program automatically controls the second three-way solenoid valve 31 to close one end of the guide to the second mercury enrichment tube 26 and open one end of the first mercury enrichment tube 15. The first three-way solenoid valve 41 is closed to stop the supply of carrier gas, and the shut-off valve 13 is opened. The built-in vacuum pump of the mercury detector 3 is activated to extract a gas sample. The gas sample is filtered through the filter membrane 11 to remove large particles, and then passes through the first drying tube 12 to remove water vapor and other acidic gaseous impurities. The flow rate is precisely controlled by the first mass flow controller 14 (0.5-2.5 liters / minute), enriching the gaseous mercury onto the mercury adsorbent in the first mercury enrichment tube 15. After enrichment for a certain period of time (5-60 minutes), the built-in vacuum pump of the mercury detector 3 is turned off, the shut-off valve 13 is closed, the first three-way solenoid valve 41 is guided to one end of the first three-way valve 16 to open, and the second heating wire 152 starts heating to 500-800 degrees Celsius, thermally desorbing all the mercury enriched in the first mercury enrichment tube 15 into gaseous elemental mercury, which is then carried into the mercury detector 3 by the carrier gas to determine the mercury content. Then, based on the gas flow rate (Va) measured by the first mass flow controller 14, the enrichment time of the gas sample (Ta), and the mercury mass (Ma) measured by the mercury detector 3, the mercury concentration (Ca) of the gas sample can be calculated using the following formula: Ca = Ma / VaTa S3. Repeat steps S1 and S2 a preset number of times. Specifically, after the measurement of the gaseous mercury concentration is completed (step S2), the program automatically controls the second three-way solenoid valve 31 to close one end of the guide tube 15 of the first mercury enrichment tube and open one end of the second mercury enrichment tube 26. The shut-off valve 13 is closed. The device of the present invention automatically runs step S1 to perform automatic online measurement of the mercury concentration in the water. After the water mercury concentration measurement is completed, step S2 is automatically run to perform automatic online measurement of the gaseous mercury concentration. In this way, the coupled online monitoring of water mercury and gaseous mercury concentrations is automatically alternated. The measurement time of water mercury and gaseous mercury concentrations can be set autonomously according to the mercury concentration levels of both and the monitoring environment requirements, generally 10-60 minutes. The entire measurement process is controlled by an automatic control program to ensure accurate and effective measurement of water mercury and gaseous mercury concentrations. The specific algorithm and steps of the automatic control program are conventional technical means well known to those skilled in the art, and will not be described in detail in this application.

[0033] S4. Using Henry's Law, convert the dissolved gaseous mercury concentration in the water to the gas phase equilibrium concentration, then calculate the effective concentration difference ΔC between the gas phase equilibrium concentration and the actual atmospheric mercury concentration, according to formula F. Hg The mercury exchange flux F at the water-air interface is calculated as k×ΔC. Hg Where k is the diffusion efficiency of mercury at the gas-liquid interface (controlled by wind speed, water temperature, and salinity). The water-gas-mercury coupled online monitoring method provided in this embodiment can accurately estimate the amount of mercury emitted from water into the atmosphere and the amount of mercury deposited from the atmosphere into water. However, existing technologies can only measure atmospheric mercury online and cannot achieve simultaneous coupled measurement of mercury concentrations in water and the atmosphere. Therefore, this invention effectively solves this technical problem, which can greatly promote research on environmental mercury migration, transformation, and pollution control, and provide effective measurement technologies and methods.

[0034] The water-gas-mercury coupled online monitoring device provided in this invention has been successfully applied to online monitoring of water-gas-mercury concentrations in field environments. Preliminary monitoring results are as follows: Figure 2 As shown, it can achieve accurate real-time online measurement of ultra-trace mercury concentrations in water below 1 nanogram per liter (ng / L), and for concentrations above 10 nanograms per cubic meter (ng / m³)... 3 The device can also accurately measure ultra-trace atmospheric mercury concentrations in real time online, indicating that the device of the present invention can be applied to high-precision, high-temporal-resolution coupled online monitoring of mercury concentrations in water and the atmosphere. Furthermore, through the technical method of the present invention, coupled online measurement of mercury exchange flux at the water-air interface under the same monitoring environmental conditions can be achieved, thereby enabling the study of the coupling relationship between the two.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A water-gas-mercury coupling online monitoring device, characterized in that, The device comprises: a water mercury automatic online sampling unit, comprising a filter membrane, a first drying tube, a stop valve, a first mass flow controller and a first mercury enrichment tube connected in sequence through pipelines; a gas mercury automatic online sampling unit, comprising a peristaltic pump, a sedimentation bottle, a metering pump, a water mercury thermal desorption tube, a second drying tube and a second mercury enrichment tube connected in sequence through pipelines; a mercury detector connected to the outlet of the first mercury enrichment tube and the outlet of the second mercury enrichment tube. The inlet of the first mercury enrichment tube and the inlet of the water mercury thermal desorption tube are connected to a carrier gas source.

2. The water-gas-mercury coupling online monitoring device according to claim 1, wherein, The water mercury thermal desorption tube comprises a first tube body, quartz wool, a first heating wire and a water mercury cracking agent, both ends of the first tube body are filled with quartz wool, and the water mercury cracking agent is placed between the quartz wool at both ends, and the first tube body is externally provided with a first heating wire.

3. The water-gas-mercury coupling on-line monitoring device according to claim 2, wherein, The water mercury cracking agent comprises at least one of modified activated carbon, silicon carbide and high-temperature-resistant ceramic.

4. The water-gas mercury coupling online monitoring device of claim 1, wherein, The first mercury enrichment tube comprises a second tube body, a second heating wire and a mercury adsorbent, the second tube body is internally provided with the mercury adsorbent, and the second tube body is externally provided with the second heating wire.

5. The water vapor mercury on-line monitoring device of claim 1, wherein, The second mercury enrichment tube comprises a third tube body, a third heating wire and a mercury adsorbent, the third tube body is internally provided with the mercury adsorbent, and the third tube body is externally provided with the third heating wire.

6. The water-gas mercury coupling on-line monitoring device according to claim 4 or 5, characterized in that, The mercury adsorbent is gold metal or gold-plated quartz sand particles.

7. The water vapor mercury coupling on-line monitoring device of claim 1, wherein, The sedimentation bottle, the first drying tube, the water mercury thermal desorption tube, the second drying tube, the second mercury enrichment tube and the pipelines are all made of Teflon.

8. The water vapor mercury coupling on-line monitoring device of claim 1, wherein, A second mass flow controller is further provided on the output pipeline of the carrier gas source.

9. The water vapor mercury on-line monitoring device of claim 1, wherein, The first drying tube and the second drying tube are filled with soda lime.

10. A water-gas-mercury coupling online monitoring method, characterized in that, The device is used in the method comprising the following steps: S1, closing the stop valve, starting the peristaltic pump, extracting a water sample from a water source to be measured, precipitating the water sample in the sedimentation bottle and overflowing, metering and extracting a preset volume of the water sample by the metering pump and injecting the water sample into the water mercury thermal desorption tube, completely thermally desorbing the mercury in the water sample in the water mercury thermal desorption tube into gaseous elemental mercury, drying the gaseous elemental mercury by the second drying tube and enriching the gaseous elemental mercury in the second mercury enrichment tube, thermally desorbing and air-carrying the mercury enriched in the second mercury enrichment tube into the mercury detector to analyze and measure the mercury concentration and obtain the water dissolved gaseous mercury concentration of the water source to be measured; S2, opening the stop valve, starting the air pump in the mercury detector, filtering out large particles in the gas sample by the filter membrane, drying the gas sample by the first drying tube, accurately controlling the flow rate by the first mass flow controller, enriching the mercury in the gas sample in the first mercury enrichment tube, thermally desorbing and air-carrying the mercury enriched in the first mercury enrichment tube into the mercury detector to analyze and measure the mercury concentration and obtain the actual atmospheric mercury concentration of the water source to be measured; S3, sequentially repeating steps S1 and S2 for a preset number of times. S4, converting the water body dissolved gaseous mercury concentration into the gas phase equilibrium concentration according to Henry's law, then calculating the effective concentration difference AC between the gas phase equilibrium concentration and the actual atmospheric mercury concentration, and calculating the mercury exchange flux F at the water-gas interface according to the formula F Hg =k x AC Hg , wherein k is the diffusion efficiency of mercury at the gas-liquid interface.

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