Method for testing stable gaseous pollutant flux and kinetic parameters under cross-medium condition

Abstract

The invention discloses a method for testing flux and kinetic parameters of stable gaseous pollutants under a cross-medium condition, which comprises the following steps of: filling soil to be tested into a testing device to prepare a testing soil column, enabling soil filling parameters in different areas in the soil column to be consistent with undisturbed conditions, enabling the moisture content to be a mean value of change values of the soil under the undisturbed condition, and enabling the moisture content to be equal to the mean value of change values of the soil under the undisturbed condition during testing; stable gaseous pollutants are injected into the test soil column from the position above the test soil column, and the concentration of the gaseous pollutants is controlled to be kept unchanged in the whole test period; during testing, soil solutions at 1 / 4, 1 / 2 and 3 / 4 depth positions are extracted through negative pressure sampling ports at different moments t1, t2,... tn, the concentration of tracer substances is measured, and the stable-state gaseous transmission flux of the depth positions is determined based on a mass balance method. And discretizing the numerical equation under the steady-state gas cross-medium transmission condition based on a central difference method, and determining the flux of a cross-atmosphere-soil-underground water medium and gas transmission diffusion coefficients of a soil layer and an underground water layer.

Description

Technical Field

[0001] The present invention relates to the field of gaseous pollutant flux measurement, and in particular to the field of stable gaseous pollutant flux measurement under cross-medium transmission conditions, specifically to a method for testing stable gaseous pollutant flux and kinetic parameters under cross-medium conditions. Background Art

[0002] There are two difficult problems in measuring the flux of gaseous pollutants under cross-medium transmission conditions: (1) a boundary needs to be formed to form the conditions for measuring the flux. However, the boundary will cause changes in the cross-medium transmission conditions. Due to the changes in the cross-medium transmission conditions, the measured flux cannot truly reflect the actual flux. (2) Under cross-medium transmission conditions, the transmission conditions of gaseous pollutants under different medium conditions are significantly different, resulting in the main factors affecting the transmission flux (gas gradient and transmission conditions) constantly changing. Both in-situ or simulated measurements need to consider the impact on the cross-medium transmission flux. Summary of the invention

[0003] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a method for testing the flux of stable gaseous pollutants under cross-media transmission conditions. The present invention can measure the stable gas flux at different depths and discretize the stable gas transport numerical equation under cross-media transmission conditions based on the central difference method to determine the flux across the atmosphere-soil-groundwater medium and the gas transmission diffusion coefficient of the soil layer and the groundwater layer.

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

[0005] S1. The soil to be tested is filled into the test device to form a test soil column. The height of the soil column is 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 of the change value of the soil under the original condition. The soil moisture content is controlled by the tracer substance solution. A plurality of negative pressure sampling ports are set outside the test device to collect the soil solution by vacuum to measure the concentration change of the tracer substance. The lower boundary water chamber is 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 period, the concentration of the gaseous pollutants is controlled to remain constant through the gas chamber concentration control device. During the test period, 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, extract soil solutions at 1 / 4, 1 / 2 and 3 / 4 depth positions through the negative pressure sampling port at the same time, and immediately add the same volume of soil solution after collecting the solution to keep the soil moisture content unchanged. At the same time, extract water samples in the lower boundary water chamber. After extracting the water samples, immediately add the same volume of water to keep the water volume in the lower boundary water chamber unchanged;

[0008] S4. When the mass of the tracer substance reacting per unit time between the gaseous pollutants and the water in the lower boundary water chamber remains unchanged, the test is terminated, and the extracted soil solution and the water sample in the lower boundary water chamber are measured;

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

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

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

[0013] (1);

[0014] Where c is the concentration of stable gaseous pollutants, which is a function of time t and depth position z, D s To stabilize the kinetic parameters of gas under cross-medium transmission conditions;

[0015] After expansion using the central difference method, we get:

[0016] (2);

[0017] Based on the mass balance principle, we get:

[0018] (3);

[0019] in:

[0020] ;

[0021] ;

[0022] ;

[0023] ;

[0024] In the formula, the superscript j represents the test time, and j+1 / 2 represents the arithmetic mean of time j and time j+1 (for example ), Δt and Δz are the step lengths in time and space respectively; q i and q i+1 The steady-state gas fluxes entering and exiting the equilibrium zone from above and below, 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 the 1 / 4, 1 / 2 and 3 / 4 depths of the soil layer respectively, 4 is the soil-groundwater interface section, and 5 is the interface between groundwater and water chamber.

[0026] As a further technical solution, the method for solving the various variables of the functional relationship between the flux of each layer about the upper and lower boundaries and the average concentration in the equilibrium zone is:

[0027] 1) Under the conditions of cross-medium transmission of atmosphere, soil and groundwater, there are four depth intervals of soil layer 0-1 / 4, 1 / 4-1 / 2, 1 / 2-3 / 4 and 3 / 4-upper boundary of surface water and five equilibrium zones of groundwater layer. 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 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 setting conditions, four variables, the upper and lower boundary concentrations and fluxes, were determined. Based on the five equations, the remaining variables, including the average concentration in each equilibrium zone and the fluxes of other layers, were solved;

[0029] 3) Based on the variables of the five equations solved in step 2), compare the average concentration and flux of each layer to determine the D with the smallest equilibrium difference. s The diffusion kinetic coefficients of the stable gases in each layer are obtained as a function of concentration, 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-media conditions is provided, comprising:

[0031] The test shell is used to fill the soil to be tested to form a test soil column;

[0032] An upper boundary air chamber disposed above the measuring soil column for injecting stable gaseous pollutants;

[0033] The lower boundary water chamber is arranged below the measuring soil column, and is used to obtain a 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, corresponding to the 1 / 4, 1 / 2 and 3 / 4 depth positions of the soil layer, the test shell is divided into an inner circle part and an outer circle part; and the inner circle part and the outer circle part are separated by a waterproof and airtight material.

[0035] As a further technical solution, the negative pressure sampling ports at the outer circle corresponding to the 1 / 4, 1 / 2 and 3 / 4 depth positions in the soil layer are all connected to negative pressure cavities, and the negative pressure cavities are also connected to a vacuum pump and a solution collector respectively.

[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 effect of the present invention is that due to the nonlinear process of the boundary under the cross-medium transmission conditions of stable gas, it is impossible to construct a numerical equation. Therefore, the traditional inversion-based method cannot invert the process and parameters of cross-medium gaseous transmission. This invention utilizes the measurement method and the central difference approximation method to solve the core problem that restricts the cross-medium transmission process and parameter analysis. It is a brand-new method. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief introduction is given below to the drawings used in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

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

[0040] Figure 2 The N2O concentration process measured at the test points of the method for testing the flux and kinetic parameters of stable gaseous pollutants under cross-media conditions provided by an embodiment of the present invention.

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

[0042] In the figure: 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 DESCRIPTION

[0043] The terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions, for example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to the steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0044] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In addition, the technical features in the various embodiments or single embodiments provided by the present invention are arbitrarily combined with each other to form a new technical solution. This combination is not restricted by the sequence of steps and / or the structural composition mode, but must be based on the ability of ordinary technicians in this field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that this combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0045] See also Figure 1-3 The embodiment of the present invention provides a method for testing the flux and kinetic parameters of stable gaseous pollutants under cross-media conditions, comprising the following steps:

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

[0047] S1. The soil to be tested is filled into the test device to form a test soil column. The soil filling method in different areas of the soil column is consistent with the original condition (according to the results of the on-site investigation, the soil column height is set to 3:1, and the thickness of the simulated soil layer and groundwater layer in the soil column is 0.8m and 0.2m respectively. The diameters of the inner and outer circles in the 0-20cm area of ​​the soil column layer are 60cm and 50cm respectively, the diameters of the inner and outer circles in the 20-40cm area are 50cm and 40cm respectively, and the diameters of the inner and outer circles in the 40-60cm area are 40cm and 30cm respectively. Below the soil layer, the diameter of the groundwater and the water chamber is 30cm. Sampling is taken from the site, and the soil column is filled. According to the determination The soil bulk density and moisture content of each depth are determined by controlling the soil moisture content to 0.24cm3 / cm3. The soil weight and moisture content are determined by the outer ring of the soil layer 0-20cm, 20-40cm, and 40-60cm, and the outer ring is connected by a flange. The moisture content is the average of the change value of the original state of the soil, and the soil moisture content is controlled by the tracer solution. Multiple negative pressure sampling ports are set outside the test device, and the soil solution is collected by vacuum for measurement (porous ceramic plates are set on the outer ring of the soil layer 0-20cm, 20-40cm, and 40-60cm. Under vacuum extraction, the outer ring solution enters the soil solution collector.), and the lower boundary water chamber 8 is below the test soil column.

[0048] The soil column in step S1 is at the 1 / 4, 1 / 2 and 3 / 4 depth positions of the soil layer, and the test device is divided into an inner circle part and an outer circle part. The filling method and moisture content of the soil to be tested in the inner circle part and the outer circle part are consistent.

[0049] Before the test, prepare a mixed solution of 0.05 mol / L stannous chloride and 0.01 mol β-glycerophosphate disodium. When installing the measuring soil column, the height of the soil column can be determined according to the depth ratio of the measured soil-groundwater profile. Figure 1As shown, the height of the soil column is not less than 1.0m; after determining the height of the measuring soil column, the soil of the corresponding depth can be evenly filled from bottom to top in the measuring soil column, and the soil moisture content in the inner circle part 9 is controlled by deionized water, while the soil moisture content in the outer circle part 10 is controlled by the configured stannous chloride and β-glycerophosphate disodium mixed solution. The tracer substance is stannous chloride, and by measuring the change of the tracer substance in the outer circle part 10, that is, the concentration change of stannous chloride, the stable gaseous flux at the location is determined based on the mass balance principle.

[0050] Since stable gaseous pollutants do not undergo physical, chemical, or biological processes during the transmission process between the atmosphere, soil, and groundwater, the mass of the pollutants does not change significantly, with a mass change of less than 5%. The test principle is that N2O reacts chemically with SnCl2, and the reaction equation is:

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

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

[0053] S2. Stable gaseous pollutants are injected into the upper boundary of the test soil column, and during the entire test period, the concentration of the gaseous pollutants is controlled to remain constant by the gas chamber concentration control device 6. During the test period, under the action of the concentration gradient, the gaseous pollutants will flow from top to bottom in the soil column. The gaseous pollutants are nitrous oxide (N2O).

[0054] There is an upper boundary air chamber 1 above the test device, and the gaseous pollutants are filled in the upper boundary air chamber 1. The air chamber concentration control device 6 is arranged above the upper boundary air chamber 1 to control the N2O concentration in the upper boundary air chamber 1 to remain unchanged.

[0055] S3. During the test, at different times t1, t2, ... tn, soil solutions at the depths of 1 / 4, 1 / 2 and 3 / 4 of the soil column are extracted simultaneously through multiple negative pressure sampling ports. The test starts at time 0, and soil solutions are extracted 2hr, 6hr, 12hr, 16hr, 18hr, 22hr, 28hr, 30hr, 38hr and 46hr after the start. After the solution is extracted, the same volume of soil water is immediately added to keep the soil moisture content unchanged. At the same time, water samples are extracted from the lower boundary water chamber 8. After the water samples are extracted, the same volume of water is immediately added to keep the volume of the water in the lower boundary water chamber unchanged. The soil solution added to the soil layer and the water in the lower boundary water chamber 8 are both deionized water.

[0056] S4. When the mass of the gaseous pollutants reacting with the water in the lower boundary water chamber 8 per unit time remains unchanged, the test is terminated, and the extracted soil solution and the water sample in the lower boundary water chamber are measured.

[0057] S5. Construct numerical equations for stable gaseous pollutants under cross-media conditions, and use the central difference method to discretize the numerical equations for stable gaseous pollutants under cross-media transmission conditions. 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 concentrations and fluxes of the upper and lower boundaries, solve the variables in the discrete numerical equations to obtain the transmission kinetic parameters of the soil water and groundwater layers and the stable gaseous pollutant fluxes across the atmosphere-soil-groundwater boundary.

[0058] Under cross-medium transmission conditions, such as air-soil-groundwater, the transmission process is diffusion transmission, and the soil-groundwater flux is a function of the concentration gradient and concentration, and is not a fixed value. Therefore, the numerical equation under cross-medium transmission conditions can be discretized based on the central difference method to determine the flux across the atmosphere-soil-groundwater medium and the gas transmission diffusion coefficient of soil layer 2 and groundwater layer 7. The specific calculation method is as follows:

[0059] The central difference method is used to discretize the numerical equation under the condition of cross-medium transmission, and the functional relationship between the flux of each layer about the upper and lower boundaries and the average concentration in the equilibrium zone is obtained;

[0060] Under the test conditions, for any equilibrium zone of the atmosphere, soil and groundwater, the stable gaseous pollutants are expressed by the diffusion equation as follows:

[0061] (1);

[0062] Where c is the concentration of stable gaseous pollutants, c is expressed as a function of time t and depth position z, D s It is the kinetic parameter under the condition of stable gas transmission across the medium.

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

[0064] (2);

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

[0066] (3);

[0067] in:

[0068] ;

[0069] ;

[0070]

[0071] ;

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

[0073] 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 the 1 / 4, 1 / 2 and 3 / 4 depths of the soil layer respectively, 4 is the soil-groundwater interface section, and 5 is the interface between groundwater and water chamber.

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

[0075] 1) Under the conditions of atmosphere-soil-groundwater cross-medium transmission, there are four depth intervals of soil layer 0-1 / 4, 1 / 4-1 / 2, 1 / 2-3 / 4 and 3 / 4-upper boundary of surface water and five equilibrium zones of groundwater layer. Each equilibrium zone can be written as equation (3), where each equation includes three variables: flux at the upper and lower boundaries, and average concentration in the equilibrium zone, including 15 variables.

[0076] 2) For two adjacent equilibrium zones, the output flux of the previous equilibrium zone is the input flux of the next equilibrium zone, that is, according to the N2O flux measurement results at the 1 / 4, 1 / 2 and 3 / 4 depth positions of the soil layer, 6 fluxes can be determined. For two adjacent layers, the input flux of the upper layer is the input flux of the lower layer. According to the upper and lower boundary control conditions, the four variables of upper and lower boundary concentrations and fluxes can be determined. According to the 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) In the soil layer and groundwater layer, Ds is set as a function of concentration, and the variable boundary flux and concentration in the five intervals are solved. The average concentration and flux solution results of each layer are compared, and it is considered that the D with the smallest equilibrium difference is sis a function of the concentration, i.e., the diffusion kinetic coefficient of the stable gas in each layer, and the transport flux across the soil-groundwater boundary is determined.

[0078] In an acidic environment, add ammonium ferric sulfate with a molar mass of 0.05 mol / L. Ammonium ferric sulfate reacts with SnCl2 to reduce trivalent iron to divalent iron. Using sodium diphenylamine sulfonate as an indicator, add potassium dichromate standard titration solution to quantify divalent iron and calculate the concentration of stannous chloride. According to the concentration of stannous chloride, determine the mass of N2O, and the converted control concentration is 6.4g / m 3 , the density of N2O is 1.9775kg / m³.

[0079] According to the measurement results, when the equilibrium error is the smallest at each moment, the soil layer and the groundwater layer D s ~The relationship between the test gas concentration is as follows:

[0080] Soil layer: ;

[0081] Groundwater layer: ;

[0082] Where c is the concentration of the transmitted gaseous pollutant.

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

[0084] Based on the same inventive concept as the above method embodiment, the present invention also provides a device for testing the flux and kinetic parameters of stable gaseous pollutants under cross-media conditions, including:

[0085] The test shell is used to fill the soil to be tested to form a test soil column.

[0086] Among them, 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 circle part 9 and an outer circle part 10. The filling method and moisture content of the soil in the inner circle part 9 and the outer circle part 10 are consistent, and the moisture content of the soil layer in the outer circle part 10 is ensured by a mixed solution of stannous chloride and β-glycerophosphate disodium mixed solution, and the moisture content of the soil in the inner circle part 9 is controlled by deionized water.

[0087] The upper boundary air chamber 1 arranged above the measuring soil column is used for injecting stable gaseous pollutants.

[0088] The gas chamber concentration control device 6 is arranged 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 disposed below the measuring soil column is used to obtain a water sample solution after the gaseous pollutants diffuse from the soil layer to the groundwater layer and react with stannous chloride.

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

[0091] The negative pressure sampling ports of the outer ring part 10 corresponding to the 1 / 4, 1 / 2 and 3 / 4 depth positions in the soil layer 2 are all connected to negative pressure cavities 3, and the negative pressure cavities 3 are also connected to vacuum pumps 4 and solution collectors 5 respectively. During the test, a negative pressure environment can be formed in the negative pressure cavity 3 through the vacuum pump 4, so that the soil solution in the outer ring part 10 can flow into the solution collector 5 through the negative pressure cavity 3, and there are three groups of solution collectors 5, which can be used to separately collect soil solutions corresponding to the 1 / 4, 1 / 2 and 3 / 4 depth positions of the soil layer.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions 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-media conditions, characterized in that: include: S1. The soil to be tested is loaded into the test device to form a test soil column. The soil loading parameters in different areas of the soil column are consistent with the original conditions, and the moisture content is the average of the change value of the soil under the original condition. The soil moisture content is controlled by the tracer substance solution. A plurality of negative pressure sampling ports are arranged outside the test device. The soil solution is collected by vacuum to measure the concentration change of the tracer substance. The lower boundary water chamber is located below the test soil column. S2. Stable gaseous pollutants are injected into the upper boundary of the test soil column. During the entire test period, the concentration of the gaseous pollutants is controlled to remain constant through the gas chamber concentration control device. During the test period, 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 t1, t2, ...t n , extract soil solutions at 1 / 4, 1 / 2 and 3 / 4 depth of the soil column through multiple negative pressure sampling ports at the same time, and immediately add the same volume of water after extracting the solution to keep the soil moisture content unchanged. At the same time, extract water samples in the lower boundary water chamber, and immediately add the same volume of water after extracting the water samples to keep the water volume in the lower boundary water chamber unchanged; S4. When the mass of the tracer substance reacting per unit time between the gaseous pollutant and the water in the lower boundary water chamber remains unchanged, the test is terminated, and the soil solution and the water sample in the lower boundary water chamber are measured; S5. Construct numerical equations for stable gaseous pollutants under cross-media conditions, and use the central difference method to discretize the numerical equations for steady-state gas transport under cross-media transport conditions. 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 concentrations and fluxes of the upper and lower boundaries, the discrete numerical equations are solved to obtain the transport kinetic parameters of the soil water and groundwater layers and the stable gaseous pollutant fluxes across the soil-groundwater boundary.

2. The method for testing the stable gaseous pollutant flux and kinetic parameters under cross-medium conditions according to claim 1 is characterized in that: The soil columns in step S1 are at the 1 / 4, 1 / 2 and 3 / 4 depth positions of the soil layer, and the test device is divided into an inner circle part and an outer circle part. The filling method and moisture content of the soil to be tested in the inner circle part and the outer circle part are consistent.

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

4. The method for testing the stable gaseous pollutant flux and kinetic parameters under cross-medium conditions according to claim 3 is characterized in that: In step S5, the method for discretizing the numerical equation under the cross-medium transmission condition based on the central difference method to determine the flux across the atmosphere-soil-groundwater medium and the gas transmission diffusion coefficient of the soil layer and the groundwater layer is as follows: Under the test conditions, for any equilibrium zone of the atmosphere, soil and groundwater, the diffusion equation of the stable gaseous pollutants is expressed as follows: （1）； Where c is the concentration of stable gaseous pollutants, c is expressed as a function of time t and depth position z, D s To stabilize the kinetic parameters of gas under cross-medium transmission conditions; After expansion using the central difference method, we get: （2）； Based on the mass balance principle, we get: （3）； in: ； ； ； ； In the formula, the superscript j represents the test time, and j+1 / 2 represents the arithmetic mean of time j and time j+1. For example, , Δt and Δz are the step lengths in time and space respectively; q i and q i+1 The steady-state gas fluxes entering and exiting the equilibrium zone from above and below, respectively, ; i=0, 1, 2, 3, 4, 5 are the measured section positions, 0 is located at the soil-upper boundary interface, 1, 2, 3 are the 1 / 4, 1 / 2 and 3 / 4 depth positions of the soil layer respectively, 4 is the soil-groundwater interface section, and 5 is the interface between groundwater and water chamber.

5. The method for testing the stable gaseous pollutant flux and kinetic parameters under cross-medium conditions according to claim 4 is characterized in that: The method for solving the various variables of the functional relationship between the flux of each layer about the upper and lower boundaries and the average concentration in the equilibrium zone is: 1) Under the conditions of cross-medium transmission of atmosphere, soil and groundwater, there are four depth intervals of soil layer 0-1 / 4, 1 / 4-1 / 2, 1 / 2-3 / 4 and 3 / 4-upper boundary of surface water and five equilibrium zones of groundwater layer. Equation (3) can be written for each equilibrium zone. 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 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 setting conditions, four variables, the upper and lower boundary concentrations and fluxes, were determined. Combined with the equations of the 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), the average concentration and flux solutions of each region are compared to obtain the concentration function relationship with the smallest equilibrium difference, that is, the diffusion kinetic coefficient of the stable gas in each layer, and the transmission flux across the soil-groundwater boundary is determined at the same time.

6. A device for testing the flux and kinetic parameters of stable gaseous pollutants under cross-media conditions, used to implement the method for testing the flux and kinetic parameters of stable gaseous pollutants under cross-media conditions as claimed in any one of claims 1 to 5, characterized in that: include: The test shell is used to fill the soil to be tested to form a test soil column; An upper boundary air chamber disposed above the measuring soil column for injecting stable gaseous pollutants; The lower boundary water chamber is arranged below the measuring soil column, and is used to obtain a water sample solution after the gaseous pollutants diffuse from the soil layer to the groundwater layer and react with stannous chloride.

7. The device for testing the stable gaseous pollutant flux and kinetic parameters under cross-medium conditions according to claim 6, characterized in that: Corresponding to the 1 / 4, 1 / 2 and 3 / 4 depth positions of the soil layer, the test shell is divided into an inner circle part and an outer circle part; and the inner circle part and the outer circle part are separated by impermeable and airtight materials.

8. The device for testing the stable gaseous pollutant flux and kinetic parameters under cross-medium conditions according to claim 7, characterized in that: The negative pressure sampling ports at the outer circle portion corresponding to the 1 / 4, 1 / 2 and 3 / 4 depth positions in the soil layer are all connected to negative pressure cavities, and the negative pressure cavities are also respectively connected to a vacuum pump and a solution collector.

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

Images