A monitoring method based on gas-liquid interface N2O emission flux

Abstract

The present application relates to the technical field of environmental monitoring, and particularly relates to a monitoring method based on N2O emission flux of gas-liquid interface, which collects interface gas samples by constructing a closed sampling space, obtains continuous concentration values by using an N2O sensor, extracts effective interface area based on a positive projection image, and forms a complete data chain which can be used to calculate concentration change rate and initial flux. The method obtains the concentration change rate by linear regression, and calculates the initial N2O emission flux by combining the internal volume value of the sampling space and the interface area value. At the same time, the wind speed-temperature comprehensive correction coefficient is constructed by using the filtered wind speed value and the verified temperature value, the initial flux is corrected, and the final N2O emission flux used for emission evaluation is obtained. The present application realizes the whole process high-precision monitoring of gas sampling, concentration measurement, interface area calculation and environmental correction, and is suitable for water body greenhouse gas emission research and environmental monitoring application.

Description

Technical Field

[0001] This invention relates to the field of environmental monitoring technology, and in particular to a method for monitoring N2O emission flux based on the gas-liquid interface. Background Technology

[0002] Monitoring greenhouse gas emission fluxes at the gas-liquid interface is a crucial foundational task in current environmental science and global climate change research. Among these, N2O, as a highly efficient greenhouse gas, has emission characteristics in water bodies such as rivers, lakes, reservoirs, wetlands, and artificial water bodies that directly affect the accuracy of regional carbon and nitrogen cycle assessments and greenhouse gas inventory compilation.

[0003] Existing methods for monitoring N2O emissions at the gas-liquid interface mostly employ static chamber or simplified gas chamber methods. However, in practical applications, these methods commonly suffer from problems such as insufficient sealing of the sampling space leading to gas leakage, uneven gas mixing within the sampling space causing concentration fluctuations, inaccurate measurement of the interface area leading to flux calculation errors, and insufficient correction for the effects of wind speed and temperature on the interface transport rate. Furthermore, existing methods rely heavily on a small number of discrete samples for analyzing N2O concentration changes, lacking mechanisms for calculating continuous rate of change for time-series data. Simultaneously, flux results lack a structured output consistent with standard units, timestamps, and environmental parameters, resulting in insufficient comparability and traceability. Summary of the Invention

[0004] This invention provides a monitoring method for N2O emission flux based on the gas-liquid interface, which can achieve high stability and high precision control throughout the entire process of sampling, detection, calculation and correction.

[0005] A method for monitoring N2O emission flux based on the gas-liquid interface includes the following steps: S1: Arrange a gas sampling device at the gas-liquid interface to collect interface gas samples and obtain interface gas samples. S2: Use an N2O sensor to measure the N2O concentration of the interface gas sample in real time to obtain the N2O concentration value; S3: Measure the effective area of ​​the gas-liquid interface and obtain the interface area value; S4: Calculate the initial N2O emission flux based on the N2O concentration value and the interface area value; S5: Measure the ambient wind speed and temperature at the interface to obtain wind speed and temperature values; S6: Correct the initial N2O emission flux based on the wind speed and temperature values ​​to obtain the final N2O emission flux.

[0006] Optionally, S1 includes: S11: Start the gas sampling device to put it into a working ready state; S12: Operate the gas sampling device in the ready-to-work state to cover the gas-liquid interface to be monitored, so as to form a closed sampling space. S13: Within the enclosed sampling space, an interface gas sample is collected using a gas sampling device to obtain the interface gas sample to be analyzed. S14: The interface gas sample to be analyzed is exported from the gas sampling device and transmitted to the N2O sensor.

[0007] Optionally, the gas sampling device includes a sampling chamber with a bottom opening, a buoyancy / support structure disposed on the sampling chamber to provide buoyancy or support, an annular sealing component for sealing when the sampling chamber covers the gas-liquid interface, a gas outlet disposed on the sampling chamber for exporting the interface gas sample in the enclosed sampling space, and a gas inlet for introducing external gas to balance the pressure.

[0008] Optionally, S2 includes: S21: Start and preheat the N2O sensor to bring it into a stable measurement working state; S22: The interface gas sample is continuously introduced into the detection chamber of the N2O sensor in the measurement working state, so that the N2O sensor continuously detects the N2O concentration in the interface gas sample and outputs a real-time detection signal corresponding to the concentration. S23: The signal processing unit built into or connected to the N2O sensor receives the real-time detection signal, processes and converts the real-time detection signal according to a preset calibration curve, and generates raw N2O concentration data. S24: The original N2O concentration data is smoothed and time-stamped to obtain a continuous and stable N2O concentration value for calculating the initial N2O emission flux.

[0009] Optionally, S3 includes: S31: Identify and locate the target gas-liquid interface region to be measured, which is covered by the gas sampling device; S32: Use an area measuring device to collect boundary or surface dimension data of the target gas-liquid interface region to be measured, and obtain the original dimension data of the interface; S33: Based on the original size data of the interface, the precise effective area of ​​the target gas-liquid interface region is calculated using an image analysis algorithm; S34: Record and output the calculated precise effective area as the interface area value used to calculate the initial N2O emission flux.

[0010] Optionally, S31 specifically involves: using an image acquisition device fixed above the gas sampling device to vertically capture an orthographic image containing the bottom outline of the gas sampling device, and using an image recognition algorithm to automatically identify and locate the target gas-liquid interface region to be measured covered by the gas sampling device from the orthographic image.

[0011] Optionally, S4 includes: S41: Based on the N2O concentration value that changes over time, calculate the rate of change of N2O concentration per unit time using numerical differentiation or linear regression algorithms. S42: Obtain the internal volume value of the closed sampling space formed by the gas sampling device, and substitute the N2O concentration change rate value, the internal volume value and the interface area value into the emission flux calculation formula to calculate a preliminary N2O emission flux value. S43: Perform dimension unification and formatted output processing on the preliminary N2O emission flux value to obtain the initial N2O emission flux.

[0012] Optionally, S5 includes: S51: Install and calibrate the wind speed sensor and the temperature sensor at a preset reference height above the gas-liquid interface, respectively. S52: Synchronously start the wind speed measurement sensor and temperature measurement sensor to continuously measure the wind speed and temperature of the environment at the gas-liquid interface, and obtain real-time wind speed measurement data and real-time temperature measurement data respectively. S53: Perform a moving average filtering process on the real-time wind speed measurement data to obtain filtered real-time wind speed data, and perform outlier removal processing on the real-time temperature measurement data to obtain verified real-time temperature data. S54: Convert the filtered real-time wind speed data into wind speed values ​​in standard units, and convert the verified real-time temperature data into temperature values ​​in standard units to obtain wind speed and temperature values ​​for flux correction.

[0013] Optionally, S6 includes: S61: Based on the wind speed and temperature values, calculate the wind speed-temperature comprehensive correction coefficient corresponding to the current interface transmission conditions using a preset interface transmission model. S62: Multiply the wind speed-temperature comprehensive correction coefficient by the initial N2O emission flux to calculate the intermediate N2O emission flux after environmental parameter correction; S63: Perform rationality verification and data rounding on the intermediate N2O emission flux, and output the final N2O emission flux that conforms to the specifications and can be directly used for emission assessment.

[0014] Optionally, the preset interface transport model is an air-water interface gas transport model based on boundary layer theory.

[0015] The beneficial effects of this invention are: 1. This invention, through the startup, positioning, enclosed sampling space construction, gas internal circulation mixing, and filtration purification processes of the gas sampling device, achieves thorough mixing, uniform collection, and impurity-free transmission of interface gas samples, ensuring that the interface gas samples entering the N2O sensor have a stable composition and consistent physical state. Combined with preheating and stabilization control of the N2O sensor, constant flow rate delivery, calibration curve conversion, and moving average smoothing, this invention provides highly stable and repeatable N2O concentration values, effectively suppressing measurement deviations caused by sensor noise, airflow disturbances, and environmental fluctuations, providing a highly reliable input data foundation for subsequent emission flux calculations.

[0016] 2. This invention achieves high-precision extraction of the effective interface area through orthographic image acquisition, boundary pixel extraction, closed contour construction, and pixel area conversion, ensuring that the interface area value accurately reflects the actual contact range between the sampling space and the interface. By employing a linear regression-based N2O concentration change rate extraction method and a standardized flux calculation formula based on internal volume and interface area values, this invention accurately reflects the temporal emission trends of N2O at the gas-liquid interface. Furthermore, the unified unit and formatted output mechanism ensures a consistent initial N2O emission flux data structure, providing a reliable data foundation for subsequent environmental corrections and cross-time period comparisons, and ensuring high consistency and traceability throughout the entire calculation chain.

[0017] 3. This invention acquires filtered and verified wind speed and temperature values, and calculates a comprehensive wind speed-temperature correction coefficient using an air-water interface transport model based on boundary layer theory. This allows the emission flux to reflect the real-time impact of environmental wind field and temperature changes on the interface diffusion rate. After combining the comprehensive correction coefficient with the initial flux to obtain an intermediate flux, and through a reasonableness verification by comparing with historical flux ranges and a data rounding mechanism with three significant figures, the final N2O emission flux generated by this invention exhibits high environmental adaptability, reliability, and engineering usability, meeting the requirements of scientific monitoring, emission accounting, and environmental management for flux accuracy, stability, and compliance. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the method flow according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the S2 process in an embodiment of the present invention. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should also be noted that, to make the embodiments more comprehensive, the following embodiments are the best and preferred embodiments, and those skilled in the art can use other alternative methods to implement some well-known technologies; moreover, the accompanying drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0021] It should be noted that the use of terms such as "an embodiment," "an embodiment," "an exemplary embodiment," and "some embodiments" in the specification indicates that the described embodiment may include a specific feature, structure, or characteristic, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments (whether explicitly described or not) should be within the knowledge of those skilled in the art.

[0022] Generally, terms can be understood at least partly from their use in context. For example, depending at least partly on the context, the term "one or more" as used herein can be used to describe any feature, structure, or characteristic in a singular sense, or a combination of features, structures, or characteristics in a plural sense. Additionally, the term "based on" can be understood not necessarily to convey an exclusive set of factors, but rather, alternatively, depending at least partly on the context, to allow for the presence of other factors that are not necessarily explicitly described.

[0023] like Figures 1-2 As shown, a method for monitoring N2O emission flux based on the gas-liquid interface includes the following steps: S1: Deploy a gas sampling device at the gas-liquid interface to collect interfacial gas samples. The specific steps are as follows: S11: First, construct the structure of the gas sampling device. Process the sampling box with the bottom opening into a hollow structure with the top closed and the bottom open. Fix a buoyancy / support structure on the outer side of the upper end of the sampling box so that the buoyancy / support structure can provide stable support on the water surface, thereby causing the entire sampling box to be suspended above the gas-liquid interface to be monitored.

[0024] An annular sealing component is installed around the bottom opening of the sampling box to form a continuous sealing ring around the bottom edge of the sampling box.

[0025] A gas outlet is opened on the upper side wall of the sampling box, and a sealing joint for connecting the gas pipeline is installed at the gas outlet. A gas inlet is provided on the upper surface of the sampling chamber, and an air inlet valve structure with pressure regulation function is installed at the gas inlet to introduce external gas into the sampling chamber to balance the pressure when needed.

[0026] The gas outlet is connected to the inlet of the filter housing of the filter device through a gas guide pipe. The outlet of the filter device is then connected to the inlet of the vacuum pump through a gas guide pipe. The outlet of the vacuum pump is then connected to the inlet of the detection chamber of the N2O sensor through a gas guide pipe. At the same time, the micro pump built into the gas sampling device is connected to the internal space of the sampling box through an internal pipeline to form a closed internal circulation loop.

[0027] After the above structural connections are completed, a start signal is sent to the control unit of the gas sampling device according to the preset timing command or remote control command. The control unit then supplies power to the micro pump, the suction pump, and the electrically controlled valves connected to the gas outlet and gas inlet in sequence, and executes a self-test program to confirm that each component is working normally, thereby putting the gas sampling device into the working ready state.

[0028] S12: When the gas sampling device is in the working ready state, the whole device with sampling box and buoyancy / support structure is slowly placed on the surface of the water body to be monitored, so that the buoyancy / support structure is in direct contact with the water body and generates upward buoyancy support, so that the sampling box remains basically vertical under the action of gravity and balance force.

[0029] The sampling chamber is gradually lowered by a vertical adjustment mechanism so that the bottom opening of the sampling chamber approaches the gas-liquid interface area to be monitored in the vertical direction. When the annular sealing component comes into contact with the gas-liquid interface, the sampling chamber is pressed down further so that the annular sealing component fits tightly against the gas-liquid interface under the action of gravity and the pressure applied by the adjustment mechanism. The contact pressure between the annular sealing component and the gas-liquid interface is monitored by a sealing status indicator device set on the sampling chamber to see if it reaches the preset sealing pressure threshold.

[0030] When the contact pressure reaches the preset sealing pressure threshold, it is determined that the bottom opening of the sampling box has completely covered the gas-liquid interface area to be monitored, and there is no obvious air leakage gap between the annular sealing component and the gas-liquid interface. At this time, the inside of the sampling box and the gas-liquid interface form a closed sampling space that is temporarily isolated from the external environment. The entry of external gas is restricted by closing the air inlet valve structure on the gas inlet to keep the closed sampling space in a stable and sealed state.

[0031] S13: After the closed sampling space is formed, start the built-in micro pump of the gas sampling device. The micro pump draws gas from the upper part of the sampling box through the internal circulation pipeline connected to the inside of the sampling box, and sends the drawn gas back to the lower part of the sampling box. This allows the gas in the closed sampling space to flow continuously along a closed circulation path from the top to the bottom and back to the top.

[0032] During the internal circulation process, the gas flow direction is changed by the flow guiding structure set in the internal circulation pipeline, so that the gas at different locations in the closed sampling space is continuously mixed during the circulation flow, thereby eliminating the concentration gradient that may exist inside the sampling box.

[0033] The control unit continuously drives the micro pump to perform gas internal circulation mixing in the closed sampling space according to the preset circulation time parameter. When the circulation time reaches the preset circulation time parameter and the internal temperature and pressure of the sampling chamber are stable as monitored by the internal sensor, the control unit switches the internal circulation working mode to the sampling working mode.

[0034] In sampling mode, the micro-pump extracts the homogeneously mixed gas from the enclosed sampling space through a sampling branch connected to the gas outlet, and delivers the extracted gas to the gas delivery pipeline connected to the gas outlet. This portion of gas is defined as the interface gas sample, and extraction continues until the flow rate and pressure in the gas delivery pipeline stabilize. The interface gas sample obtained under stable extraction conditions is used as the interface gas sample to be analyzed, providing a stable gas source for subsequent transmission and detection.

[0035] S14: After obtaining the interface gas sample to be analyzed, the control unit starts the vacuum pump, which generates a negative pressure driving force in the gas guide line along the direction from the gas outlet to the N2O sensor detection chamber. This drives the interface gas sample to be analyzed from the gas outlet of the sampling box into the gas guide line and into the filter device installed on the gas guide line.

[0036] Inside the filtration device, the interfacial gas sample to be analyzed first passes through a particulate filter element located upstream of the filter housing. The particulate filter element intercepts suspended particulate matter in the interfacial gas sample through its dense porous filter material structure, so that the gas passing through the particulate filter element is basically free of solid particles.

[0037] Subsequently, the gas, after initial filtration by the particulate filter, continues to enter the desiccant layer located downstream of the particulate filter along the gas guiding direction. The desiccant layer, through the hygroscopic material filled inside, contacts and adsorbs water vapor in the gas, reducing the water vapor content in the interface gas sample to be analyzed, thereby reducing the interference of water vapor on the subsequent N2O concentration measurement.

[0038] During the continuous operation of the air pump, by adjusting the speed of the air pump and the cross-sectional size of the air guide pipe, the filtered interface gas sample enters the detection chamber of the N2O sensor through the air guide pipe at a basically constant volumetric flow rate, and forms a stable flow state in the detection chamber.

[0039] As the pump continuously draws gas from the enclosed sampling space, the internal pressure gradually decreases. A pressure sensor at the gas inlet monitors the internal pressure of the sampling chamber in real time. When the internal pressure is detected to be lower than the preset lower pressure limit, the control unit opens the inlet valve at the gas inlet, allowing external gas to be introduced into the sampling chamber at a controlled flow rate. This balances the pressure difference between the inside and outside of the sampling chamber, preventing structural deformation due to excessive pressure difference. Simultaneously, it ensures a stable gas flow field within the enclosed sampling space, thus reliably providing the N2O sensor with a continuous and stable sample of the interface gas to be analyzed.

[0040] S2: Use an N2O sensor to measure the N2O concentration of the interface gas sample in real time to obtain the N2O concentration value. The specific steps are as follows: S21: According to the preset measurement cycle, at the beginning of the measurement cycle, the upper-level monitoring system sends a start command to the control unit of the N2O sensor.

[0041] After receiving the start command, the control unit first turns on the power supply to the heating unit inside the N2O sensor, so that the heating unit continuously supplies heat to the detection chamber and the sensitive detection element connected to the detection chamber.

[0042] Meanwhile, the control unit reads the real-time temperature signal output by the temperature sensor arranged near the detection chamber, compares the temperature signal with the pre-stored working temperature setting value, calculates the heating power adjustment amount based on the temperature deviation, and continuously adjusts the output power of the heating unit through pulse width modulation or multi-level power switching, so that the gas temperature in the detection chamber approaches the working temperature setting value along a smooth trajectory.

[0043] During the temperature rise phase, the control unit records the temperature change curve at fixed time intervals. When the temperature is detected to be within the allowable deviation range of the set value and remains stable in multiple consecutive samplings, the control unit continues to maintain closed-loop temperature control and locks the temperature in the detection chamber near the working temperature set value. After the duration reaches the preset stability judgment time, the current state is marked as a stable measurement working state, and subsequent steps are allowed to introduce interface gas samples into the detection chamber for continuous detection.

[0044] S22: After the N2O sensor has entered a stable measurement working state, reliably connect the outlet of the gas guide pipe to the inlet of the mass flow controller, and connect the outlet of the mass flow controller to the inlet nozzle of the N2O sensor detection chamber to form a single gas path from the interface gas sample to the detection chamber.

[0045] The control unit sends the target flow rate setpoint to the mass flow controller and simultaneously collects the real-time flow signal fed back by the flow sensing component inside the mass flow controller. Based on the deviation between the real-time flow signal and the target flow rate setpoint, the control unit adjusts the opening of the regulating valve inside the mass flow controller so that the interface gas sample is delivered to the inlet of the detection gas chamber at a constant flow rate in the gas delivery pipeline.

[0046] During this process, the control unit monitors the pressure changes on the inlet side and the detection chamber to ensure that the detection chamber maintains a stable pressure state close to atmospheric pressure, preventing unstable output of the sensitive detection element due to pressure fluctuations.

[0047] After the interface gas sample enters the detection chamber at a stable flow rate, the sensitive detection element in the detection chamber continuously identifies the N2O component and converts the signal of the interface gas sample flowing through the detection area. The change in N2O concentration is reflected in real time as an analog or digital electrical signal, and the real-time detection signal is output to the signal processing unit through the signal interface to provide continuous raw input for subsequent concentration calculation.

[0048] S23: The signal processing unit is connected to the output port of the N2O sensor. After the arrival of the real-time detection signal, the analog-to-digital conversion module first samples the real-time detection signal at a fixed sampling frequency and converts the analog real-time detection signal into a discrete digital signal sequence.

[0049] Subsequently, the signal processing unit calls the calibration curve parameters pre-saved in the storage unit. The calibration curve consists of the detection signal values ​​and corresponding N2O concentration values ​​obtained when multiple sets of N2O standard gases of known concentration are introduced into the detection chamber. The functional relationship between the real-time detection signal and the N2O concentration is obtained through a fitting algorithm.

[0050] At each sampling moment, the signal processing unit substitutes the digital quantity corresponding to the current real-time detection signal into the function relationship to calculate the N2O concentration value corresponding to the current moment, and stores the value in the original data buffer to form a concentration sequence arranged in chronological order.

[0051] The calibration curve is expressed in linear function form as follows: ; in, , Indicates the first At each sampling time, the N2O concentration value corresponding to the interface gas sample measured by the N2O sensor is the single data point of the "raw N2O concentration data" in S23. Indicates the first The corrected detection signal value is obtained by performing zero-point correction on the real-time detection signal output by the N2O sensor at each sampling time. Indicates the first At each sampling moment, the digital quantity corresponding to the real-time detection signal output by the N2O sensor after detecting the interface gas sample. This indicates the digital value corresponding to the zero-point baseline signal output by the N2O sensor during the zero-point calibration process, when a standard gas without N2O is introduced into the detection chamber. This represents the intercept coefficient of the calibration curve obtained through fitting during the calibration process. This represents the slope coefficient of the calibration curve obtained through fitting during the calibration process.

[0052] To reduce the impact of zero-point offset caused by long-term operation, the signal processing unit performs a zero-point calibration process before the start of the measurement cycle. The output signal when no N2O standard gas passes through the detection chamber is used as the zero-point baseline. The subsequent real-time detection signal is then baseline-corrected, and a calibration curve conversion is performed to obtain the original N2O concentration data with the error corrected. This ensures that the concentration data calculated later has a reliable and accurate measurement reference.

[0053] S24: After obtaining the raw N2O concentration data that changes over time, the signal processing unit constructs a moving average filtering algorithm according to the preset sliding window length.

[0054] The specific implementation method is as follows: taking the original N2O concentration data at the current moment as the center, read the original N2O concentration data of several sampling moments before and after the current moment from the original data buffer, take the arithmetic mean of this set of data as the filtered N2O concentration value at the current moment, and move the sliding window sequentially to cover all sampling moments in the entire measurement cycle, thereby obtaining a smoothed N2O concentration time series.

[0055] During this process, the signal processing unit calls the system clock module to read the current precise time information for each N2O concentration value obtained after the moving average filtering process, and appends the time information to the corresponding concentration value data structure in the form of a timestamp, so that each concentration value has a unique time stamp.

[0056] Subsequently, the signal processing unit stores the smoothed and time-stamped N2O concentration values ​​into the output data buffer according to the timestamp order, forming a continuous and stable N2O concentration value sequence for calculating the initial N2O emission flux, providing complete and reliable input data for subsequent emission flux calculation based on the gas-liquid interface area and concentration change law.

[0057] S3: Measure the effective area of ​​the gas-liquid interface to obtain the interface area value. The specific steps are as follows: S31: Fix the image acquisition device above the gas sampling device, so that the optical axis of the image acquisition device is perpendicular to the target gas-liquid interface area to be measured, and the field of view of the image acquisition device covers the area where the bottom opening of the sampling box is located.

[0058] A collection command is sent to the image acquisition device, which then acquires an orthographic image containing the bottom outline of the gas sampling device, and sends the orthographic image to the central processing unit.

[0059] The central processing unit calls the image recognition algorithm to perform grayscale boundary detection and contour extraction operations on the orthographic projection image. The detected contour points are connected into a closed contour according to the image coordinate order, and the area inside the closed contour is determined as the target gas-liquid interface area to be measured, which is covered by the gas sampling device, thereby completing the identification and positioning of the target gas-liquid interface area.

[0060] S32: Input the obtained orthographic image into the area measurement device, and call the boundary extraction algorithm to perform pixel-level scanning on the closed contour of the corresponding target gas-liquid interface region in the orthographic image.

[0061] During the scanning process, the image coordinates of each pixel that meets the boundary pixel determination condition are recorded one by one, so that all boundary pixels form a boundary pixel coordinate set.

[0062] The set of boundary pixel coordinates is stored as the original size data of the interface, and the total number of boundary pixels is recorded, so that the original size data of the interface is completely represented as the boundary data of the target gas-liquid interface region in pixel coordinates.

[0063] S33: Call the image analysis algorithm, import the stored set of boundary pixel coordinates into the image analysis module, construct the closed boundary contour according to the pixel coordinate order, and perform a pixel-by-pixel filling operation on all pixels inside the closed contour so that all internal pixels form a rasterized region.

[0064] The number of all internal pixels within the rasterized region is counted, and the ratio coefficient between the pre-calibrated image pixel size and the actual physical size is read from the storage unit. The number of internal pixels is multiplied by the area unit corresponding to the image pixel size to calculate the result, so that the calculation result corresponds to the accurate effective area of ​​the target gas-liquid interface region at the actual physical scale, thereby obtaining the calculated accurate effective area value.

[0065] Image analysis algorithms are represented as follows: ; in, This represents the precise effective area of ​​the target gas-liquid interface region calculated using an image analysis algorithm. This represents the set of all image pixels within the closed contour formed by the set of boundary pixel coordinates obtained by S32. In this invention, this set is obtained by the image analysis module after performing a pixel-by-pixel fill operation, and is used to represent the complete pixel coverage of the actual target gas-liquid interface region to be measured on the image plane. This represents the pixel coordinates of each pixel within the closed contour in the orthographic projection image coordinate system, used to uniquely identify an internal pixel. This represents the area corresponding to a single pixel at the actual physical scale. It is an area expression of the ratio between the image pixel size and the actual physical size. This value is obtained by device calibration and is retrieved from the storage unit by the central processing unit in S33. S34: Write the obtained accurate effective area value to the local storage unit for storage, and read the current time value from the system clock module, and append the time value as a timestamp to the storage data structure of the accurate effective area.

[0066] Simultaneously, the precise effective area is sent to the central processing unit via the data transmission module, so that the central processing unit saves the precise effective area as the interface area value used to calculate the initial N2O emission flux, and ensures that each area value corresponds to the N2O concentration measurement cycle, thereby ensuring that the initial N2O emission flux calculated subsequently has a clear area basis and time correlation.

[0067] S4: Calculate the initial N2O emission flux based on the N2O concentration and interfacial area values. The specific steps are as follows: S41: Input the N2O concentration values ​​obtained in S24, which vary with the time series, into the data fitting module of the central processing unit in chronological order. Pair all N2O concentration values ​​with their corresponding timestamps to ensure that each N2O concentration value has a unique time series position. Call the linear regression algorithm to perform a least squares fitting operation on all data points, constructing the following form: A linear function is derived that best fits all N2O concentration data points in the least squares sense. After calculation, the slope parameter is extracted from the fitted linear equation. , slope parameter This value represents the rate of change in N2O concentration per unit time and is stored as input data for subsequent calculations of preliminary N2O emission flux values.

[0068] S42: Read the fixed internal volume value pre-calculated and stored from the storage unit based on the known geometric parameters of the gas sampling device, and simultaneously input the N2O concentration change rate value obtained in S41, the internal volume value, and the interface area value obtained in S34 into the flux calculation module of the central processing unit. The flux calculation module calculates the emission flux according to the following formula: ; Perform the calculation, where, This represents the preliminary N2O emission flux value. This represents the rate of change in N2O concentration. Indicates the internal volume value. This represents the interface area value. The central processing unit performs term-by-term multiplication and division operations on the formula to obtain the preliminary N2O emission flux value, and writes this value into the internal buffer, awaiting subsequent unit conversion and formatting processing.

[0069] S43: Call the unit conversion module to convert all units of the preliminary N2O emission flux values ​​obtained in S42 to milligrams per square meter per hour, so that the emission flux results have a unified dimension consistent with environmental monitoring standards.

[0070] After the conversion is complete, the data formatting module is invoked to read the current system clock time. This time is appended as a timestamp to the emission flux value, and the emission flux value is encapsulated into a standardized data record containing the timestamp, unit of measurement, and emission flux value. Finally, this standardized data record is stored in the local storage unit and sent to the central processing unit via the data transmission module, serving as the initial N2O emission flux for subsequent use in S6 for environmental correction.

[0071] S5: Measure the ambient wind speed and temperature at the interface to obtain the wind speed and temperature values. The specific steps are as follows: S51: Select a fixed position between 10 cm and 100 cm from the gas-liquid interface as the preset reference height, and set a mounting bracket at this reference height to fix the wind speed measurement sensor and the temperature measurement sensor.

[0072] Use a graduated ruler to measure vertically upwards from the liquid surface where the gas-liquid interface is located. Adjust the height of the mounting bracket so that the mounting position on the bracket is consistent with the preset reference height. Then, use fasteners to firmly fix the mounting bracket to the support structure.

[0073] The wind speed sensor is fixedly mounted on a mounting bracket at this reference height, with the measuring probe of the wind speed sensor facing the prevailing wind direction and the measuring probe fully exposed to the gas environment.

[0074] The temperature measurement sensor is also fixedly mounted on a mounting bracket at the reference height, so that the sensitive element of the temperature measurement sensor is located in the gas region above the gas-liquid interface and avoids direct obstruction by the sampling box.

[0075] Connect the wind speed sensor and temperature sensor to the data acquisition unit via signal lines and turn on the power. Perform zero-point calibration and range calibration on the wind speed sensor. Record the output signal of the wind speed sensor in a windless state and set this output as the zero wind speed baseline. Then, compare the output signal with a standard wind field with known wind speed and adjust the calibration coefficient of the wind speed sensor to make its output consistent with the standard wind speed.

[0076] Temperature calibration of the temperature measurement sensor involves placing it in a constant temperature environment with a known temperature, recording the sensor's output value, comparing it with the standard temperature of that constant temperature environment, and correcting the calibration coefficient of the temperature measurement sensor based on the difference to ensure that the sensor's output matches the standard temperature. This completes the installation and calibration of both the wind speed and temperature measurement sensors.

[0077] S52: After the installation and calibration of the wind speed and temperature measurement sensors are completed, the central processing unit sends a synchronous start command to the data acquisition unit, sets a common measurement start time and a fixed sampling time interval, so that the data acquisition unit sends start sampling signals to the wind speed and temperature measurement sensors at the predetermined start time.

[0078] After receiving the start sampling signal, the wind speed measurement sensor continuously measures the wind speed at the gas-liquid interface according to the set sampling time interval, and converts the wind speed signal obtained from each measurement into a digital quantity, which is then stored as real-time wind speed measurement data with a timestamp through the data acquisition unit.

[0079] After receiving the start sampling signal, the temperature measurement sensor continuously measures the temperature of the environment at the gas-liquid interface at the same sampling time interval, and converts the temperature signal obtained from each measurement into a digital quantity, which is then stored as real-time temperature measurement data with a timestamp through the data acquisition unit.

[0080] The central processing unit pairs real-time wind speed measurement data and real-time temperature measurement data according to timestamp order, so that the wind speed and temperature data at the same moment are synchronized in time, providing continuous real-time wind speed measurement data and real-time temperature measurement data for subsequent flux correction.

[0081] S53: Input the real-time wind speed measurement data arranged in chronological order into the wind speed data processing module, set the time window length of the moving average filtering process to 10 minutes, so that at any current moment, the wind speed data processing module selects all real-time wind speed measurement data within the time range of 10 minutes before that moment as a sliding window, calculates the arithmetic mean of all real-time wind speed measurement data within the sliding window, and uses it as the filtered real-time wind speed data corresponding to the current moment.

[0082] The sliding window is moved point by point along the time axis, and the above calculation process is repeated for every moment within the entire measurement period to form a filtered real-time wind speed data sequence covering the entire measurement cycle. The real-time temperature measurement data arranged in chronological order is input into the temperature data processing module, and outlier removal is performed on the real-time temperature measurement data using the Laida criterion.

[0083] The temperature data processing module calculates the average value and standard deviation of real-time temperature measurement data within a given time period. For each real-time temperature measurement data, it calculates the deviation ratio from the average value and compares the deviation ratio with the critical value of the Laida criterion determined based on the sample size and significance level. When the deviation ratio of a real-time temperature measurement data exceeds the critical value, the real-time temperature measurement data is identified as an outlier and removed from the data sequence.

[0084] The average and standard deviation of the remaining real-time temperature measurement data are recalculated, and the Raida criterion judgment process is repeated until all real-time temperature measurement data are no longer identified as outliers. The real-time temperature measurement data after removing outliers is taken as the verified real-time temperature data.

[0085] S54: Input the filtered real-time wind speed data obtained in S53 into the unit conversion module. When the filtered real-time wind speed data is expressed in kilometers per hour, the unit conversion module multiplies each filtered real-time wind speed data by a conversion factor according to the preset unit conversion relationship, converts it into a wind speed value in meters per second, and stores the converted wind speed values ​​in chronological order as a wind speed value sequence for flux correction.

[0086] The verified real-time temperature data obtained by S53 is input into the temperature unit conversion module. When the verified real-time temperature data is expressed in degrees Celsius, the temperature unit conversion module performs an addition operation on each verified real-time temperature data with the constant 273.15 to convert it into a temperature value in Kelvin. The converted temperature values ​​are then stored in chronological order as a temperature value sequence for flux correction.

[0087] The central processing unit aligns the wind speed and temperature values ​​used for flux correction with the timestamps corresponding to the initial N2O emission flux, so that the wind speed and temperature values ​​at the same moment are associated one-to-one with the initial N2O emission flux, providing standardized input data of wind speed and temperature values ​​for environmental correction of N2O emission flux in subsequent steps.

[0088] S6: Correct the initial N2O emission flux based on wind speed and temperature values ​​to obtain the final N2O emission flux. The specific steps are as follows: S61: Input the wind speed and temperature values ​​obtained in S54 for flux correction into the interface transport parameter calculation module. In the interface transport parameter calculation module, call the air-water interface gas transport model based on boundary layer theory and perform wind speed function calculation and temperature function calculation respectively.

[0089] The interface transmission parameter calculation module first substitutes the wind speed value into the wind speed function in the interface transmission model, and then performs the wind speed correction coefficient calculation so that the wind speed correction coefficient reflects the influence of wind speed changes on the degree of interface turbulence and gas exchange rate.

[0090] Subsequently, the temperature value is substituted into the Arrhenius formula parameter expression in the interface transfer model: ;in, This represents the temperature correction factor. It is an empirical constant. A constant characterizing the activation energy of gas molecule diffusion, The gas constant is... This is the temperature value.

[0091] The interface transmission parameter calculation module calculates the temperature correction coefficient according to the above formula, so that the temperature correction coefficient reflects the effect of temperature change on the diffusion rate of gas at the gas-liquid interface.

[0092] The interface transmission parameter calculation module multiplies the wind speed correction coefficient and the temperature correction coefficient to generate a wind speed-temperature comprehensive correction coefficient, and stores this comprehensive correction coefficient as the input data for subsequent S62 in the cache area.

[0093] S62: Input the wind speed-temperature integrated correction coefficient obtained in S61 and the initial N2O emission flux obtained in S43 for environmental correction into the flux correction module of the central processing unit.

[0094] In the flux correction module, the correction calculation program is called, using the initial N2O emission flux as the baseline flux value and the wind speed-temperature comprehensive correction coefficient as the adjustment factor, and a multiplication operation is performed: ; in, This represents the intermediate N2O emission flux. This represents the initial N2O emission flux. This represents the combined wind speed and temperature correction factor.

[0095] The flux correction module generates intermediate N2O emission flux based on the calculation results and writes it into a temporary storage unit so that it can be used for subsequent rationality verification and data rounding processing.

[0096] S63: Input the intermediate N2O emission flux obtained in S62 into the data verification module. The data verification module retrieves the preset reasonable range of historical flux values ​​for the monitoring point from the storage unit, reads the upper and lower limits of the reasonable range, and compares the intermediate N2O emission flux with the upper and lower limits.

[0097] When the intermediate N2O emission flux value is within a preset reasonable range, the intermediate N2O emission flux is determined to be valid data. When the intermediate N2O emission flux value exceeds the reasonable range, it is marked as abnormal data and stored according to the abnormal data marking rules.

[0098] The intermediate N2O emission flux that is determined to be valid data is input into the data rounding module. The rounding procedure is executed in the data rounding module to retain three significant digits of the intermediate N2O emission flux and generate the rounded emission flux result.

[0099] The data rounding module outputs the rounded emission flux result as the final N2O emission flux, stores the final N2O emission flux in the local storage unit, and sends it to the central processing unit through the data transmission module so that it can be directly used for environmental emission assessment and subsequent analysis.

[0100] This invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of this invention. To provide the public with a thorough understanding of this invention, specific details are described in detail in the following preferred embodiments; however, those skilled in the art will fully understand the invention even without these details. Furthermore, to avoid unnecessary misunderstanding of the essence of this invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0101] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for monitoring N2O emission flux based on the gas-liquid interface, characterized in that, Includes the following steps: S1: Arrange a gas sampling device at the gas-liquid interface to collect interface gas samples and obtain interface gas samples. S2: Use an N2O sensor to measure the N2O concentration of the interface gas sample in real time to obtain the N2O concentration value; S3: Measure the effective area of ​​the gas-liquid interface and obtain the interface area value; S4: Calculate the initial N2O emission flux based on the N2O concentration value and the interface area value; S5: Measure the ambient wind speed and temperature at the interface to obtain wind speed and temperature values; S6: Correct the initial N2O emission flux based on the wind speed and temperature values ​​to obtain the final N2O emission flux.

2. The method for monitoring N2O emission flux based on the gas-liquid interface according to claim 1, characterized in that, S1 includes: S11: Start the gas sampling device to put it into a working ready state; S12: Operate the gas sampling device in the ready-to-work state to cover the gas-liquid interface to be monitored, so as to form a closed sampling space. S13: Within the enclosed sampling space, an interface gas sample is collected using a gas sampling device to obtain the interface gas sample to be analyzed. S14: The interface gas sample to be analyzed is exported from the gas sampling device and transmitted to the N2O sensor.

3. The method for monitoring N2O emission flux based on the gas-liquid interface according to claim 2, characterized in that, The gas sampling device includes a sampling chamber with an open bottom, a buoyancy / support structure disposed on the sampling chamber to provide buoyancy or support, an annular sealing component for sealing when the sampling chamber covers the gas-liquid interface, a gas outlet disposed on the sampling chamber for exporting the interface gas sample in the enclosed sampling space, and a gas inlet for introducing external gas to balance the pressure.

4. The method for monitoring N2O emission flux based on the gas-liquid interface according to claim 3, characterized in that, S2 includes: S21: Start and preheat the N2O sensor to bring it into a stable measurement working state; S22: The interface gas sample is continuously introduced into the detection chamber of the N2O sensor in the measurement working state, so that the N2O sensor continuously detects the N2O concentration in the interface gas sample and outputs a real-time detection signal corresponding to the concentration. S23: The signal processing unit built into or connected to the N2O sensor receives the real-time detection signal, processes and converts the real-time detection signal according to a preset calibration curve, and generates raw N2O concentration data. S24: The original N2O concentration data is smoothed and time-stamped to obtain a continuous and stable N2O concentration value for calculating the initial N2O emission flux.

5. The method for monitoring N2O emission flux based on the gas-liquid interface according to claim 4, characterized in that, S3 includes: S31: Identify and locate the target gas-liquid interface region to be measured, which is covered by the gas sampling device; S32: Use an area measuring device to collect boundary or surface dimension data of the target gas-liquid interface region to be measured, and obtain the original dimension data of the interface; S33: Based on the original size data of the interface, the precise effective area of ​​the target gas-liquid interface region is calculated using an image analysis algorithm; S34: Record and output the calculated precise effective area as the interface area value used to calculate the initial N2O emission flux.

6. The method for monitoring N2O emission flux based on the gas-liquid interface according to claim 5, characterized in that, S31 specifically involves: using an image acquisition device fixed above the gas sampling device to vertically capture an orthographic image containing the bottom outline of the gas sampling device, and using an image recognition algorithm to automatically identify and locate the target gas-liquid interface region to be measured covered by the gas sampling device from the orthographic image.

7. The method for monitoring N2O emission flux based on the gas-liquid interface according to claim 5, characterized in that, S4 includes: S41: Based on the N2O concentration value that changes over time, calculate the rate of change of N2O concentration per unit time using numerical differentiation or linear regression algorithms. S42: Obtain the internal volume value of the closed sampling space formed by the gas sampling device, and substitute the N2O concentration change rate value, the internal volume value and the interface area value into the emission flux calculation formula to calculate a preliminary N2O emission flux value. S43: Perform dimension unification and formatted output processing on the preliminary N2O emission flux value to obtain the initial N2O emission flux.

8. The method for monitoring N2O emission flux based on the gas-liquid interface according to claim 7, characterized in that, S5 includes: S51: Install and calibrate the wind speed sensor and the temperature sensor at a preset reference height above the gas-liquid interface, respectively. S52: Synchronously start the wind speed measurement sensor and temperature measurement sensor to continuously measure the wind speed and temperature of the environment at the gas-liquid interface, and obtain real-time wind speed measurement data and real-time temperature measurement data respectively. S53: Perform a moving average filtering process on the real-time wind speed measurement data to obtain filtered real-time wind speed data, and perform outlier removal processing on the real-time temperature measurement data to obtain verified real-time temperature data. S54: Convert the filtered real-time wind speed data into wind speed values ​​in standard units, and convert the verified real-time temperature data into temperature values ​​in standard units to obtain wind speed and temperature values ​​for flux correction.

9. The method for monitoring N2O emission flux based on the gas-liquid interface according to claim 8, characterized in that, S6 includes: S61: Based on the wind speed and temperature values, calculate the wind speed-temperature comprehensive correction coefficient corresponding to the current interface transmission conditions using a preset interface transmission model. S62: Multiply the wind speed-temperature comprehensive correction coefficient by the initial N2O emission flux to calculate the intermediate N2O emission flux after environmental parameter correction; S63: Perform rationality verification and data rounding on the intermediate N2O emission flux, and output the final N2O emission flux that conforms to the specifications and can be directly used for emission assessment.

10. The method for monitoring N2O emission flux based on the gas-liquid interface according to claim 9, characterized in that, The preset interface transport model is an air-water interface gas transport model based on boundary layer theory.

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