Method for testing flux and kinetic parameters of stable gaseous pollutants under cross-media conditions

Abstract

The application discloses a method for testing stable gaseous pollutant flux and kinetic parameters under cross-medium conditions, which comprises the following steps: filling the soil to be tested into a testing device to form a testing soil column, the soil filling parameters in different regions in the soil column are consistent with the original state conditions, and the water content is the mean value of the change value under the original state condition of the soil; during the testing, the stable gaseous pollutant is injected into the testing soil column from the upper part of the testing soil column, and the concentration of the gaseous pollutant is kept unchanged during the whole testing period; the soil solution at the 1 / 4, 1 / 2 and 3 / 4 depth positions is extracted through a negative pressure sampling port at different time points t1, t2, … t n during the testing, the concentration of the tracer is determined, and the stable gaseous transmission flux at the depth position is determined based on the mass balance method. The numerical equation under the stable gaseous cross-medium transmission condition is discretized based on the central difference method, and the flux of the atmosphere-soil-underground water medium and the gaseous transmission diffusion coefficient of the soil layer and the underground water layer are determined.

Description

Technical Field

[0001] This invention relates to the field of gaseous pollutant flux measurement, and more particularly to the field of stable gaseous pollutant flux measurement under cross-medium transport conditions, specifically to a method for testing the flux and kinetic parameters of stable gaseous pollutants under cross-medium conditions. Background Technology

[0002] Under the conditions of cross-media transport of gaseous pollutants, there are two difficult problems to solve in measuring their flux: (1) A boundary needs to be formed to form the conditions for measuring flux. However, the boundary will cause changes in the cross-media transport conditions. Due to the changes in the cross-media transport conditions, the measured flux cannot truly reflect the actual flux. (2) Under the conditions of cross-media transport, the transport conditions of gaseous pollutants are significantly different under different media conditions, which causes the main factors affecting the transport flux (gas gradient and transport conditions) to change continuously. Both in-situ or simulated measurements need to consider the impact on cross-media transport flux. Summary of the Invention

[0003] To overcome the shortcomings of the prior art, this invention provides a method for testing the flux of stable gaseous pollutants under cross-medium transport conditions. This invention can determine the flux across the atmosphere-soil-groundwater media and the gas transport diffusion coefficients of the soil layer and groundwater layer by measuring the stable gas flux at different depths and discretizing the numerical equation of stable gas transport under cross-medium transport conditions based on the central difference method.

[0004] According to one aspect of the present invention, a method for testing the flux and kinetic parameters of stable gaseous pollutants under cross-medium conditions is provided, comprising:

[0005] S1. The soil to be tested is filled into the testing device to form a test soil column with a height of not less than 1.0m. The soil filling parameters in different areas of the soil column are consistent with the original conditions, and the moisture content is the average value of the change value under the original soil conditions. The soil moisture content is controlled by a tracer solution. Multiple negative pressure sampling ports are set outside the testing device. The soil solution is collected by vacuum to measure the concentration change of the tracer. The lower boundary water chamber is located below the test soil column.

[0006] S2. Stable gaseous pollutants are injected into the upper boundary of the test soil column. During the entire test, the concentration of gaseous pollutants is kept constant by the gas chamber concentration control device. During the test, under the action of the concentration gradient, the gaseous pollutants will flow from top to bottom in the soil column.

[0007] S3. During the test, at different times t1, t2, ... t n, through the negative pressure sampling port simultaneously extracts 1 / 4, 1 / 2 and 3 / 4 depth position soil solution, and after collecting the solution, immediately replenish the same volume of soil solution, keep the soil moisture content unchanged, at the same time, in the lower boundary water chamber, extract water sample, after extracting the water sample, immediately replenish the same volume of water body, keep the water volume in the lower boundary water chamber unchanged;

[0008] S4, end the test under the condition that the mass of the tracer substance reacted with the water body in the lower boundary water chamber per unit time is unchanged, measure the extracted soil solution and the water sample in the lower boundary water chamber;

[0009] S5, construct the numerical equation of stable gaseous pollutants under the cross-medium condition, discretize the numerical equation under the cross-medium transmission condition by using the central difference method, solve the discretized numerical equation based on the upper and lower boundary conditions, the stable gaseous pollutant fluxes at the 1 / 4, 1 / 2 and 3 / 4 depth positions of the soil layer, and the set concentration and flux of the upper and lower boundaries, to obtain the transmission kinetic parameters of the soil water and groundwater layer and the stable gaseous pollutant flux across the soil-groundwater boundary. As a further technical solution, the soil column in step S1 is divided into an inner ring part and an outer ring part at the 1 / 4, 1 / 2 and 3 / 4 depth positions of the soil layer, and the filling method and moisture content of the soil to be tested in the inner ring part and the outer ring part are consistent.

[0010] As a further technical solution, the gaseous pollutant in step S2 is nitrous oxide (N2O), the inner ring part controls the soil moisture content by using deionized water, and the outer ring part controls the moisture content by using a mixed solution prepared by 0.05 mol / L stannous chloride (SnCl2) and 0.01 mol / L β-glycerophosphate disodium, and the change of the tracer substance in the outer ring is determined to determine the stable gaseous flux at the position based on the mass balance principle.

[0011] As a further technical solution, in step S5, the method for determining the flux across the atmosphere-soil-groundwater medium and the gas transmission diffusion coefficient of the soil layer and the groundwater layer based on the discretization of the numerical equation under the cross-medium transmission condition by using the central difference method is as follows:

[0012] Under the test conditions, for any equilibrium zone of the atmosphere, soil and groundwater, the diffusion equation of the stable gaseous pollutant is expressed as follows:

[0013] (1);

[0014] Wherein, c is the concentration of the stable gaseous pollutant, which is a function of time t and depth position z, D s is the kinetic parameter under the stable gaseous cross-medium transmission condition;

[0015] After expanding by central difference method, we have

[0016] (2);

[0017] Based on the mass balance principle, we have

[0018] (3);

[0019] wherein

[0020] ;

[0021] ;

[0022] ;

[0023] ;

[0024] wherein the superscript j represents the testing time, j+1 / 2 represents the arithmetic mean value at the j time point and the j+1 time point (for example ), Δt and Δz are the step length in the time direction and the space direction respectively; q i and q i+1 are the fluxes of the steady-state gas entering from above the equilibrium zone and flowing out from below the equilibrium zone respectively, ;

[0025] i=0, 1, 2, 3, 4, 5 are the measured cross-section positions, 0 is located at the soil-air chamber interface, 1, 2, 3 are respectively the soil layer 1 / 4, 1 / 2 and 3 / 4 depth positions, 4 is the soil-groundwater interface cross-section, and 5 is the groundwater-water chamber interface.

[0026] As a further technical solution, the method for solving each variable of the functional relationship of the fluxes of each layer with respect to the upper and lower boundaries and the average concentration in the equilibrium zone is:

[0027] 1) Under the condition of atmospheric-soil-groundwater cross-media transport, the soil layer 0-1 / 4, 1 / 4-1 / 2, 1 / 2-3 / 4 and 3 / 4-surface water upper boundary 4 depth intervals and the groundwater layer 5 equilibrium zones, equation (3) can be written for each equilibrium zone;

[0028] 2) Based on the N2O flux measurement results at the 1 / 4, 1 / 2 and 3 / 4 depth positions of the soil layer, six fluxes are determined, for the adjacent two layers, the input flux of the upper layer is the input flux of the lower layer, based on the upper and lower boundary setting conditions, the upper and lower boundary concentrations and fluxes are determined, based on the five equations, the remaining variables, including the average concentration in each equilibrium zone and the fluxes of other layers, are solved;

[0029] 3) Based on the variables of the five equations solved in step 2), compare the solutions for the average concentration and flux of each layer to determine the D with the smallest equilibrium difference. s By using the concentration function, the diffusion kinetic coefficients of the stable gas in each layer are obtained, and the transport flux across the soil-groundwater boundary is determined.

[0030] According to another aspect of the present invention, a device for testing the flux and kinetic parameters of stable gaseous pollutants under cross-medium conditions is provided, comprising:

[0031] The test housing is used to fill the soil to be tested, forming a test soil column;

[0032] The upper boundary air chamber, located above the soil column, is used to inject stable gaseous pollutants.

[0033] The lower boundary water chamber, located below the soil column, is used to obtain the water sample solution after the gaseous pollutants diffuse from the soil layer to the groundwater layer and react with stannous chloride.

[0034] As a further technical solution, the test shell is divided into an inner ring and an outer ring at depths of 1 / 4, 1 / 2 and 3 / 4 of the soil layer; and the inner ring and the outer ring are separated by a waterproof and airproof material.

[0035] As a further technical solution, the outer ring portion is connected to negative pressure cavities at the negative pressure sampling ports at depths of 1 / 4, 1 / 2 and 3 / 4 in the soil layer, and a vacuum pump and a solution collector are respectively connected to the negative pressure cavities.

[0036] As a further technical solution, a 120-mesh gauze is provided at the entrance of the lower boundary water chamber.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows: due to the nonlinear process at the boundary of stable gas under cross-medium transport conditions, it is impossible to construct numerical equations. Therefore, traditional inversion-based methods cannot perform process and parameter inversion for cross-medium gas transport. The present invention solves this core problem that restricts the analysis of cross-medium transport processes and parameters by using measurement methods and central difference approximation methods, which is a completely new method. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of a device for testing the flux and kinetic parameters of stable gaseous pollutants under cross-medium conditions, provided in an embodiment of the present invention.

[0040] Figure 2 The N2O concentration process measured at the test point of the method for testing the flux and kinetic parameters of stable gaseous pollutants under cross-medium conditions provided in the embodiments of the present invention.

[0041] Figure 3 The method for testing the flux and kinetic parameters of stable gaseous pollutants under cross-media conditions provided in this embodiment of the invention is a process for determining the flux at the soil-groundwater interface based on the results.

[0042] In the diagram: 1. Upper boundary air chamber; 2. Soil layer; 3. Negative pressure cavity; 4. Vacuum pump; 5. Solution collector; 6. Air chamber concentration control device; 7. Groundwater layer; 8. Lower boundary water chamber. Detailed Implementation

[0043] The terms “comprising” and “having”, and any variations thereof, in the specification, claims, and accompanying drawings of this invention are intended to cover a non-exclusive inclusion, such as a process, method, system, product, or apparatus that includes a series of steps or units, not necessarily limited to those explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In addition, the technical features of the various embodiments or individual embodiments provided by the present invention can be arbitrarily combined to form new technical solutions. Such combinations are not bound by the order of steps and / or structural composition patterns, but must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0045] Please see Figures 1-3 This invention provides a method for testing the flux and kinetic parameters of stable gaseous pollutants under cross-medium conditions, comprising the following steps:

[0046] The test site was located in Wansheng Town, Dongpo District, Meishan City, Sichuan Province. According to profile survey data from Wansheng Town, Dongpo District, Meishan City, Sichuan Province in 2024, the soil thickness was 2.4m, below which was shallow groundwater. The average soil moisture content was 0.24m. 3 / m 3 The soil bulk density is 1.37 g / cm³. 3 .

[0047] S1. The soil to be tested is filled into the testing device to form a soil column. The soil filling method in different areas of the soil column is consistent with the original conditions (based on the field investigation results, the soil column height is set at 3:1, and the thicknesses of the simulated soil layer and groundwater layer in the soil column are 0.8m and 0.2m, respectively). The diameters of the inner and outer rings in the 0-20cm region of the soil column are 60cm and 50cm, respectively; in the 20-40cm region, the inner and outer rings are 50cm and 40cm, respectively; in the 40-60cm region, the inner and outer rings are 40cm and 30cm, respectively. Below the soil layer, the diameter of the groundwater and the water chamber is 30cm. Samples are taken from the field, filled into the soil column, and measured... The soil bulk density and controlled moisture content of 0.24 cm³ / cm³ were used to determine the soil weight and moisture content at each depth. Soil was uniformly filled from bottom to top, with the outer rings of soil layers 0-20cm, 20-40cm, and 40-60cm connected by flanges. The moisture content was the average of the variation values ​​under undisturbed soil conditions. A tracer solution was used to control the soil moisture content. Multiple negative pressure sampling ports were installed externally on the testing device to collect soil solution under vacuum for measurement. (Porous ceramic plates were installed on the outer rings of soil layers 0-20cm, 20-40cm, and 40-60cm; under vacuum, the solution in the outer rings entered the soil solution collector.) The lower boundary water chamber 8 was located below the test soil column.

[0048] In step S1, the soil column is located at the depths of 1 / 4, 1 / 2, and 3 / 4 of the soil layer. The testing device is divided into an inner circle and an outer circle. The filling method and moisture content of the soil to be tested are the same in both the inner and outer circles.

[0049] Before testing, a mixed solution of 0.05 mol / L stannous chloride and 0.01 mol β-glycerophosphate disodium solution is prepared. When installing the soil column, the height of the soil column can be determined based on the measured depth ratio of the soil-groundwater profile. The soil column is then tested as follows: Figure 1As shown, the height of the soil column is not less than 1.0m. After determining the height of the soil column, soil of the corresponding depth is uniformly filled into the soil column from bottom to top. The soil moisture content in the inner ring 9 is controlled by deionized water, while the soil moisture content in the outer ring 10 is controlled by a mixed solution of stannous chloride and β-glycerophosphate. The tracer is stannous chloride. By measuring the change in the tracer in the outer ring 10, i.e., the change in the concentration of stannous chloride, the stable gaseous flux at the location is determined based on the principle of mass balance.

[0050] Because stable gaseous pollutants do not undergo physical, chemical, or biological processes during their propagation through different media such as atmosphere, soil, and groundwater, their mass does not change significantly (mass change is less than 5%). The testing principle is based on the chemical reaction between N₂O and SnCl₂, and the reaction equation is as follows:

[0051] SnCl2+N2O+(x+1)H2O=SnO2xH2O↓+N2+2HCl

[0052] Based on this chemical reaction process, the mass of N2O passing through the cross section during the two test periods can be determined by measuring the concentration change of SnCl2 in the soil solution or the lower boundary water chamber 8, as well as the flux, i.e. the mass of gaseous pollutants per unit time and per unit area. The role of β-glycerophosphate disodium is to catalyze this reaction process.

[0053] S2. A stable gaseous pollutant is injected into the upper boundary of the test soil column. Throughout the test, the concentration of the gaseous pollutant is kept constant by the gas chamber concentration control device 6. During the test, under the influence of the concentration gradient, the gaseous pollutant will flow from top to bottom in the soil column. The gaseous pollutant is nitrous oxide (N2O).

[0054] The testing device has an upper boundary gas chamber 1, which is filled with gaseous pollutants. A gas chamber concentration control device 6 is located above the upper boundary gas chamber 1 to control the N2O concentration in the upper boundary gas chamber 1 to remain constant.

[0055] S3. During the test, soil solution was simultaneously extracted from depths of 1 / 4, 1 / 2, ..., 3 / 4 of the soil column at different times t1, t2, ..., tn through multiple negative pressure sampling ports. The test started at time 0, and soil solution was extracted at 2, 6, 12, 16, 18, 22, 28, 30, 38, and 46 hours after the start. Immediately after extraction, the same volume of soil moisture was added to maintain a constant soil moisture content. Simultaneously, water samples were extracted from the lower boundary water chamber 8. After extraction, the same volume of water was immediately added to maintain a constant water volume in the lower boundary water chamber. Both the soil solution added to the soil layer and the water in the lower boundary water chamber 8 were deionized water.

[0056] S4. The experiment ends when the mass of gaseous pollutants reacting with the water in the lower boundary water chamber 8 remains constant per unit time. The extracted soil solution and water samples from the lower boundary water chamber are then measured.

[0057] S5. Construct numerical equations for stable gaseous pollutants under cross-media conditions. Discretize the numerical equations for stable gaseous pollutants under cross-media transport conditions using the central difference method. Based on the upper and lower boundary conditions, the fluxes of stable gaseous pollutants at depths of 1 / 4, 1 / 2, and 3 / 4 of the soil layer, and the set concentrations and fluxes at the upper and lower boundaries, solve the variables in the discrete numerical equations to obtain the transport dynamics parameters of soil water and groundwater layers, as well as the fluxes of stable gaseous pollutants across the atmosphere-soil-groundwater boundary.

[0058] Because cross-medium transport conditions, such as air-soil-groundwater transport, involve diffusion, the soil-groundwater flux is a function of the concentration gradient and concentration, and not a fixed value. Therefore, the flux across the atmosphere-soil-groundwater medium, as well as the gas transport diffusion coefficients of soil layer 2 and groundwater layer 7, can be determined by discretizing the numerical equations under cross-medium transport conditions using the central difference method. The specific calculation method is as follows:

[0059] The numerical equations under cross-medium transport conditions were discretized using the central difference method to obtain the functional relationships of flux at the upper and lower boundaries and average concentration in the equilibrium zone for each layer.

[0060] Under the test conditions, for any equilibrium zone of atmosphere, soil, and groundwater, the stable gaseous pollutants can be represented by the following diffusion equation:

[0061] (1);

[0062] Where c is the concentration of stable gaseous pollutants, and c is expressed as a function of time t and depth position z, D s To determine the dynamic parameters under stable gas transmedium transport conditions.

[0063] After expansion using the central difference method, we get:

[0064] (2);

[0065] Based on the principle of mass balance, we get:

[0066] (3);

[0067] in:

[0068] ;

[0069] ;

[0070]

[0071] ;

[0072] Where the superscript j represents the test time, and j+1 / 2 represents the arithmetic mean of time j and time j+1 (e.g., ...). ), Δt and Δz are the time and space step sizes, respectively; q i and q i+1 The fluxes of steady-state gas entering from above the equilibrium region and exiting from below the equilibrium region, respectively. .

[0073] i=0, 1, 2, 3, 4, 5 are the measured cross-sectional locations. 0 is located at the soil-air chamber interface, 1, 2, 3 are the soil layer depths of 1 / 4, 1 / 2, and 3 / 4 respectively, 4 is the soil-groundwater interface, and 5 is the groundwater-water chamber interface.

[0074] Based on the stannous chloride concentration in the sample, the N2O flux at the corresponding depth was obtained. Using the N2O flux at the corresponding depth and the upper and lower boundary control conditions, the variables of the functional relationship between the flux at the upper and lower boundaries and the average concentration in the equilibrium region for each layer were solved. The solution method is as follows:

[0075] 1) Under the conditions of atmospheric-soil-groundwater cross-media transport, there are 4 depth intervals in the soil layer (0-1 / 4, 1 / 4-1 / 2, 1 / 2-3 / 4 and 3 / 4-the upper boundary of surface water) and 5 equilibrium zones in the groundwater layer. Equation (3) can be written for each equilibrium zone. Each equation includes three variables: flux at the upper and lower boundaries and average concentration in the equilibrium zone, which includes 15 variables.

[0076] 2) For two adjacent equilibrium zones, the flux output of the previous equilibrium zone is the input flux of the next equilibrium zone. Based on the N2O flux measurements at soil depths of 1 / 4, 1 / 2, and 3 / 4, six fluxes can be determined. For two adjacent layers, the input flux of the upper layer is the input flux of the lower layer. Based on the upper and lower boundary control conditions, four variables—upper and lower boundary concentrations and fluxes—can be determined. Then, based on five equations, the remaining variables, including the average concentration in each equilibrium zone and the fluxes of other layers, can be directly solved.

[0077] 3) Setting Ds as a function of concentration for both the soil and groundwater layers, the boundary fluxes and concentrations for the five intervals are solved. The results of the average concentration and flux for each layer are compared, and the Ds with the smallest equilibrium difference is considered the one with the smallest concentration. sThe relationship between concentration and density is given by the diffusion kinetic coefficient of the stable gas in each layer, which also determines the transport flux across the soil-groundwater boundary.

[0078] In an acidic environment, 0.05 mol / L ferric ammonium sulfate is added. The ferric ammonium sulfate reacts with tin (SnCl2) to reduce ferric iron to ferrous iron. Using sodium diphenylamine sulfonate as an indicator, the ferrous iron is quantified by titrating with potassium dichromate standard solution, and the concentration of stannous chloride is calculated. Based on the stannous chloride concentration, the mass of N2O is determined, and the calculated control concentration is 6.4 g / m³. 3 The density of N2O is 1.9775 kg / m³.

[0079] Based on the measurement results, under the condition of minimum equilibrium error at each time point, the soil layer and groundwater layer D s The relationship between the concentrations of the tested gases is as follows:

[0080] Soil layer: ;

[0081] Groundwater layer: ;

[0082] Where c represents the concentration of the gaseous pollutants being transported.

[0083] The test results of soil-groundwater boundary flux processes are as follows: Figure 3 As shown.

[0084] Based on the same inventive concept as the aforementioned method embodiments, this invention also provides a device for testing the flux and kinetic parameters of stable gaseous pollutants under cross-medium conditions, comprising:

[0085] The test housing is used to fill the soil to be tested, forming a test soil column.

[0086] The test shell cavity is filled with four soil layers 2 and one groundwater layer 7 from top to bottom, corresponding to the 1 / 4, 1 / 2 and 3 / 4 depth positions of the soil layers. The test shell is divided into an inner ring 9 and an outer ring 10. The filling method and moisture content of the soil in the inner ring 9 and the outer ring 10 are the same. The moisture content of the soil layer in the outer ring 10 is ensured by a mixed solution of stannous chloride and β-glycerophosphate disodium, and the moisture content of the soil in the inner ring 9 is controlled by deionized water.

[0087] The upper boundary air chamber 1, located above the measuring soil column, is used to inject stable gaseous pollutants.

[0088] The gas chamber concentration control device 6 is located above the upper boundary gas chamber 1 and is used to control the N2O concentration in the upper boundary gas chamber 1 to remain constant.

[0089] The lower boundary water chamber 8, located below the measuring soil column, is used to obtain the water sample solution after the gaseous pollutants diffuse from the soil layer to the groundwater layer and react with stannous chloride.

[0090] The entrance to the lower boundary water chamber 8 is equipped with 120-mesh gauze to prevent soil from the groundwater layer from entering the lower boundary water chamber 8 and to avoid affecting the movement of the test gas. Corresponding to the 1 / 4, 1 / 2, and 3 / 4 depth positions of the soil layer, the test shell is divided into an inner and outer ring section; the inner and outer ring sections are separated by an impermeable and airtight material to ensure that the vertical gas flow flux is the same, and the sampling measurement in the outer ring section 10 does not disturb the movement of the test gas in the inner ring section 9.

[0091] The outer ring portion 10 has negative pressure cavities 3 connected to the negative pressure sampling ports at depths of 1 / 4, 1 / 2, and 3 / 4 of the soil layer 2. The negative pressure cavities 3 are also connected to vacuum pumps 4 and solution collectors 5. During the test, the vacuum pumps 4 can create a negative pressure environment in the negative pressure cavities 3, so that the soil solution in the outer ring portion 10 can flow through the negative pressure cavities 3 to the solution collectors 5. There are three sets of solution collectors 5, which can be used to collect the soil solution at depths of 1 / 4, 1 / 2, and 3 / 4 of the soil layer respectively.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for testing the flux and kinetic parameters of stable gaseous pollutants under cross-medium conditions, characterized in that, include: S1. The soil to be tested is filled into the test device to form a test soil column. The soil filling parameters in different areas of the soil column are consistent with the original conditions, and the water content is the average value of the change value under the original soil conditions. The soil water content is controlled by the tracer solution. Multiple negative pressure sampling ports are set outside the test device. The soil solution is collected by vacuum to measure the concentration change of the tracer. The lower boundary water chamber is at the bottom of the test soil column. S2. Stable gaseous pollutants are injected into the upper boundary of the test soil column. During the entire test, the concentration of gaseous pollutants is kept constant by the gas chamber concentration control device. During the test, under the action of the concentration gradient, the gaseous pollutants will flow from top to bottom in the soil column. S3, During the test, at different times t 1, t 2,… t n Soil solution was simultaneously extracted from the soil column at depths of 1 / 4, 1 / 2, and 3 / 4 through multiple negative pressure sampling ports. After extraction, the same volume of water was immediately added to maintain the soil moisture content. At the same time, water samples were extracted from the lower boundary water chamber. After extraction, the same volume of water was immediately added to maintain the water volume in the lower boundary water chamber. S4. The experiment ends when the mass of tracer material reacting with the gaseous pollutants in the water body of the lower boundary chamber per unit time remains unchanged, and the extracted soil solution and water sample in the lower boundary chamber are measured. S5. Construct a numerical equation for steady gaseous pollutants under cross-media conditions. Discretize the numerical equation for steady gas transport under cross-media transport conditions using the central difference method. Based on the upper and lower boundary conditions, the flux of steady gaseous pollutants at depths of 1 / 4, 1 / 2, and 3 / 4 of the soil layer, and the set concentrations and fluxes at the upper and lower boundaries, solve the discrete numerical equation to obtain the transport dynamic parameters of soil water and groundwater layers, as well as the flux of steady gaseous pollutants across the soil-groundwater boundary.

2. The method for testing the flux and kinetic parameters of stable gaseous pollutants under cross-medium conditions according to claim 1, characterized in that, In step S1, the soil column is located at depths of 1 / 4, 1 / 2, and 3 / 4 of the soil layer. The testing device is divided into an inner circle and an outer circle, and the filling method and moisture content of the soil to be tested are the same in both the inner and outer circles.

3. The method for testing the flux and kinetic parameters of stable gaseous pollutants under cross-medium conditions according to claim 2, characterized in that, The gaseous pollutant in step S2 is nitrous oxide (N2O). The soil moisture content in the inner ring is controlled by deionized water, while the moisture content in the outer ring is controlled by a mixed solution prepared from 0.05 mol / L stannous chloride and 0.01 mol / L disodium β-glycerophosphate. The tracer is stannous chloride. By measuring the change in the tracer in the outer ring, i.e. the change in the concentration of stannous chloride, the stable gaseous flux at the location is determined based on the principle of mass balance.

4. The method for testing the flux and kinetic parameters of stable gaseous pollutants under cross-medium conditions according to claim 3, characterized in that, In step S5, the method for determining the flux across the atmosphere-soil-groundwater medium and the gas transport diffusion coefficients of the soil and groundwater layers based on the central difference method for discretizing the numerical equations under cross-medium transport conditions is as follows: Under the test conditions, for any equilibrium zone of atmosphere, soil, and groundwater, the diffusion equation for stable gaseous pollutants is as follows: （1）； in, c To stabilize the concentration of gaseous pollutants, c Represented as time t and depth position z The function, D s To stabilize the dynamic parameters of gas transport across media; After expansion using the central difference method, we get: （2）； Based on the principle of mass balance, we get: （3）； in: ； ； ； ； In the formula, superscript j Indicates the test time. j +1 / 2 represents j Time and j The arithmetic mean at time +1, Δ t and Δ z These represent the step size in the time and space directions, respectively. q i and q i+1 The fluxes of steady-state gas entering from above the equilibrium region and exiting from below the equilibrium region, respectively. ; subscript i =0, 1, 2, 3, 4, 5 represent the measured cross-sectional locations. 0 is located at the soil-upper boundary interface; 1, 2, and 3 are the soil layer depths of 1 / 4, 1 / 2, and 3 / 4, respectively; 4 is the soil-groundwater interface; and 5 is the groundwater-water chamber interface. i +1 / 2 represents i Time and i The arithmetic mean at time +1, .

5. The method for testing the flux and kinetic parameters of stable gaseous pollutants under cross-medium conditions according to claim 4, characterized in that, The method for solving the functional relationships between the fluxes at the upper and lower boundaries and the average concentration within the equilibrium zone for each layer is as follows: 1) Under the conditions of atmospheric-soil-groundwater cross-media transport, the soil layer has four depth intervals: 0-1 / 4, 1 / 4-1 / 2, 1 / 2-3 / 4 and 3 / 4-the upper boundary of the surface water, and the groundwater layer has five equilibrium zones. Equation (3) can be written for each equilibrium zone. 2) Based on the N2O flux measurements at soil depths of 1 / 4, 1 / 2, and 3 / 4, six fluxes were determined. For two adjacent layers, the input flux of the upper layer is the input flux of the lower layer. Based on the upper and lower boundary conditions, four variables, namely upper and lower boundary concentrations and fluxes, were determined. Combined with the equations for five equilibrium zones, the remaining variables, including the average concentration in each equilibrium zone and the fluxes of other layers, were solved. 3) Based on the variables of the five equations solved in step 2), compare the solutions of average concentration and flux in each region to obtain the concentration function relationship with the smallest equilibrium difference, i.e. the diffusion kinetic coefficient of the stable gas in each layer, and at the same time determine the transport flux across the soil-groundwater boundary.

6. A testing apparatus for the flux and kinetic parameters of stable gaseous pollutants under cross-medium conditions, used to implement the testing method for the flux and kinetic parameters of stable gaseous pollutants under cross-medium conditions as described in any one of claims 1 to 5, characterized in that, include: The test housing is used to fill the soil to be tested, forming a test soil column; The upper boundary air chamber, located above the soil column, is used to inject stable gaseous pollutants. The lower boundary water chamber, located below the soil column, is used to obtain the water sample solution after the gaseous pollutants diffuse from the soil layer to the groundwater layer and react with stannous chloride.

7. The testing device for stable gaseous pollutant flux and kinetic parameters under cross-medium conditions according to claim 6, characterized in that, Corresponding to the soil layer depths of 1 / 4, 1 / 2, and 3 / 4, the test shell was divided into an inner ring and an outer ring; and the inner ring and the outer ring were separated by a waterproof and airtight material.

8. The testing device for stable gaseous pollutant flux and kinetic parameters under cross-medium conditions according to claim 7, characterized in that, The outer ring portion has negative pressure sampling ports at depths of 1 / 4, 1 / 2, and 3 / 4 in the soil layer, each connected to a negative pressure cavity. A vacuum pump and a solution collector are also connected to the negative pressure cavities.

9. The testing device for stable gaseous pollutant flux and kinetic parameters under cross-medium conditions according to claim 6, characterized in that, The entrance to the lower boundary water chamber is provided with 120-mesh gauze.

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