CN109031468B - Synchronous measurement of N2O、CH4And CO2Vortex motion correlation method device for flux - Google Patents
Synchronous measurement of N2O、CH4And CO2Vortex motion correlation method device for flux Download PDFInfo
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Abstract
Synchronous measurement N based on single gas analyzer2O、CH4And CO2Net exchangeThe eddy current correlation method device and method of flux realize the effective software and hardware integration of the ultrasonic anemometer, the gas sampling system, the closed-circuit gas analyzer, the calibration system and the data acquisition and processor based on the principle of the eddy current correlation method2O、CH4And CO2The net exchange flux is synchronously, efficiently and accurately measured. The ultrasonic anemometer measures three-dimensional wind speed. The gas sampling system collects an air sample and delivers it to a closed-circuit gas analyzer. Closed-loop gas analyzer for detecting N contained in air sample from gas sampling system2O、CH4And CO2The concentration of (c). The calibration system calibrates the closed-circuit gas analyzer. The data acquisition and processor receives, stores and processes the three-dimensional wind speed and gas concentration data measured by the ultrasonic anemometer and the closed-circuit gas analyzer, and calculates N based on the vortex correlation method principle2O、CH4And CO2The net exchange flux of (a).
Description
Technical Field
The invention relates to the field of measurement of greenhouse gas flux, in particular to a synchronous measurement method for N based on a single gas analyzer2O、CH4And CO2Apparatus and method for vortex correlation of net exchange flux.
Background
Nitrous oxide (N)2O), methane (CH)4) And carbon dioxide (CO)2) Is a greenhouse gas strictly regulated by the global climate change frame convention of the United nations and the kyoto protocol thereof, and simultaneously, the three gases are also important components of the geochemical cycle of carbon and nitrogen biology of the land ecosystem. Establishing N between land ecosystem and atmosphere2O、CH4And CO2Net exchange flux (i.e. N emitted or absorbed per unit area to atmosphere per unit time)2O、CH4And CO2Quantity) of the gas, and the reliable quantitative technology and method thereof, which are helpful for clarifying the source and sink changes of the gas and the influence and feedback rules and mechanisms thereof on the changes of climate, environment and human activities. Development of a set of reliable, efficient and synchronous measurement N2O、CH4And CO2The net flux exchange means will greatly facilitate the development of the related research fields described above.
Static-box method and vortex correlation (eddy covariance)) The method is to measure N at present2O、CH4And CO2The main method of net exchange of flux. The principle of the static box method is that a closed box body is covered on a research object, and gas flux is calculated according to the increasing or decreasing rate of the gas concentration in the box body within a period of time, but the static box method has technical defects, so that the accuracy of flux observation data obtained by the static box method is questioned, such as: the sealed box body can change the original environmental conditions of the research object; the measured result only represents the flux of a limited observation point on the space and sometimes cannot represent the average level on the scale of the ecological system; limited gas sample concentration data often results in the inability to employ more accurate (non-linear) flux calculations, resulting in fluxes being systematically underestimated. The vortex correlation method is one of micrometeorological methods, is the most direct and accurate method for measuring the carbon-nitrogen gas flux of an ecosystem at present, can solve the problems existing in a static box method, has no interference to a measuring object, and the measuring result represents the spatial average on the scale of a land mass.
At present, the vortex motion correlation method is widely applied to the CO of the land ecosystem2Long term observation of net exchange flux, however N2O and CH4More than 95% of effective measured data of flux still come from static box method, and the most authoritative land ecosystem N provided by the special committee of climate change among governments of the united nations2O and CH4The emission list establishment method and key parameters thereof are almost based on the observation result of the static box method. The important reason for this situation is the lack of the swirl correlation method N2O and CH4The gas analysis instrument equipment with high precision and fast response (10 Hz or more) is necessary for flux observation. In recent years, with the progress of mid-infrared laser absorption spectroscopy technology, such gas analyzers are increasingly being produced commercially, however, due to CH4And N2O has low concentration in the atmosphere and can be used for measuring the flux of the vortex correlation method at present4And N2Most of O gas analyzers are based on closed-circuit type sourcesThe air sample is required to be introduced into an optical cell of the analyzer, the laser is reflected for multiple times in the optical cell, and the laser absorption intensity is increased by increasing the optical path, so that the detection precision of the analyzer is improved.
To realize synchronous measurement N based on vortex correlation method principle2O、CH4And CO2The most efficient method is to select an analyzer which can detect the concentrations of the three gases simultaneously, and the analyzer meeting the requirement in the market at present is only in a closed circuit mode. The use of closed-circuit gas analyzers, meaning that a large-volume gas pump needs to be deployed to pump air into the analyzer, involves how to properly configure and combine the various instrument hardware to integrate into a system setup, and involves a number of key technical issues that directly affect flux results, including: how to design a gas sampling system suitable for field conditions and regulate and control reasonable sampling flow, how to accurately correct time difference between wind speed and gas concentration data, how to accurately calculate gas flux according to obtained three-dimensional wind speed and gas concentration data and the like, and no related patent reports that N is synchronously measured based on vortex correlation method principle2O、CH4And CO2The flux device, and even less the related patent, proposes a specific solution to the above technical problem.
Disclosure of Invention
Technical problem to be solved
The invention aims to provide a synchronous measurement method for N based on a single gas analyzer2O、CH4And CO2The vortex related method and device of net exchange flux solves at least one of the above technical problems.
(II) technical scheme
The invention provides a synchronous measurement method for N based on a single gas analyzer2O、CH4And CO2A net exchange flux whirl correlation method apparatus comprising:
the ultrasonic anemometer is used for measuring three-dimensional wind speed, namely wind speed components in three directions of a Cartesian coordinate system;
the gas sampling system is used for collecting an air sample and conveying the air sample to the closed-circuit gas analyzer;
closed loop gas analyzer for detecting N contained in air sample from gas sampling system2O、 CH4And CO2The concentration of (c);
the calibration system is used for calibrating the closed-circuit gas analyzer;
a data acquisition and processor for receiving, storing and processing three dimensional wind speed measured by the ultrasonic anemometer and N measured by the closed circuit gas analyzer2O、CH4And CO2Concentration data and based on the vortex correlation principle, calculating N2O、CH4And CO2The net exchange flux of (a).
In some embodiments of the invention, the data acquisition and processor calculates N2O、CH4And CO2The net exchange flux of (a) means in particular: average value of flux was calculated in half an hour
Wherein the unit of F is mu g m-2h-1W' is the instantaneous pulsation value of the vertical wind speed from the average of half an hour, in m s-1C' is N2O、CH4And CO2Instantaneous pulsation value of concentration deviating from average value of half an hour in nmol-1；
Means half-hour average value of w 'c', p is air density, and the value is 1.29kg m-3(ii) a M is the molar mass of air and is 0.029kg mol-1(ii) a 3600 means 3600 seconds for 1 h; a represents 1mol of N2O、CH4And CO2Mass of molecule in g mol-1。
In some embodiments of the invention, the gas sampling system comprises:
a sampling head as an inlet for air to enter the gas sampling system;
one end of the sampling gas path is connected with the sampling head, and the other end of the sampling gas path is connected with the closed-circuit gas analyzer and is used for transmitting the air;
the three-way joint is used for connecting the sampling gas circuit and the calibration gas circuit;
the filter is connected with the three-way joint, has the filter aperture of 0.45 mu m and is used for filtering particles in the air;
the needle valve is positioned at the air inlet of the closed-circuit gas analyzer, is connected with the filter and is used for adjusting the flow of the sampling gas circuit;
one end of the ball valve is connected with the air outlet of the closed-circuit gas analyzer and is used for controlling the actual pumping force of the air pump and manually closing the air pump when the air pump is closed so as to prevent dust in the air pump from being sucked back into the closed-circuit gas analyzer;
one end of the steel wire PVC pipe is connected with the air pump and is used for circulating the air;
the air pump is connected with the other end of the ball valve through the steel wire PVC pipe, provides power for pumping air and discharges the air.
In some embodiments of the present invention, the sampling head is funnel-shaped and is directed downward to prevent rainwater from entering the sampling gas path.
In some embodiments of the present invention, the sampling gas circuit is made of teflon; and/or
And a heating belt is arranged on the outer side of the sampling gas circuit and is wrapped with a waterproof heat-insulating material.
In some embodiments of the present invention, the calibration system comprises a calibration gas unit, a calibration gas circuit and a solenoid valve, wherein,
the standard gas unit is connected with an inlet of the electromagnetic valve and used for outputting standard gas;
the calibration gas circuit is connected with an outlet of the electromagnetic valve and used for transmitting the calibration gas;
the turn-off and turn-on of the electromagnetic valve respectively correspond to the operation of the gas sampling system and the operation of the calibration system.
In some embodiments of the invention, the reynolds coefficient Re of the air movement in the sampling air path is v × d/γ, and is used to determine whether the flow state is turbulent,
wherein v is the flow rate of air in the sampling gas circuit, and the unit is m s-1；
d is the diameter of the sampling gas circuit, and the unit is m;
gamma is the kinematic viscosity of air and has a value of 1.5X 10-5m2s-1。
In some embodiments of the invention, the flow rate of the marker gas is greater than the flow rate of the air.
In some embodiments of the invention, the data acquisition and processor is further configured to correct the three dimensional wind speed and N according to maximum covariance or co-timing differentials2O、CH4And CO2Data time difference of concentration.
The embodiment of the invention also provides a synchronous measurement method for N based on the single gas analyzer2O、CH4And CO2Method for net exchange flux for simultaneous measurement of N based on a single gas analyzer as described in any of the above2O、CH4And CO2Vortex related method of net exchange flux.
(III) advantageous effects
The invention is based on the synchronous measurement of N of a single gas analyzer2O、CH4And CO2Compared with the prior art, the device and the method of the flux vortex motion related method have at least the following advantages:
1. according to the principle of the vortex correlation method, a stable and reliable device based on a single gas analyzer is constructed, so that N on land ecosystem plot scale is realized2O、CH4And CO2The undisturbed high-frequency continuous synchronous measurement of the net exchange flux of the three gases solves the technical defects of a static box method in the traditional method, and can provide an advanced technical method and long-term high-frequency high-quality measurement data for the research in the fields of greenhouse gas emission reduction, biogeochemical circulation and the like.
2. The invention reasonably designs a closed-circuit gas sampling system, provides an operation method for reasonably regulating and controlling gas sampling flow, and provides an operation method for efficiently and accurately regulating and controlling gas sampling flowCalculating closed vortex correlation method N2O、CH4And CO2The flux method (especially the scheme for correcting the time difference of the wind speed and the gas concentration data) solves the key technical problem existing in the field of measuring the gas flux by the closed vortex motion related method, simultaneously ensures that the measuring device has stronger universality, and can realize automatic and continuous operation with the minimum maintenance cost under the field unattended condition.
Drawings
FIG. 1 shows a single gas analyzer based synchronous measurement of N in accordance with an embodiment of the present invention2O、CH4And CO2Schematic structure diagram of vortex motion related method device for net exchange flux.
FIG. 2 is a diagram of a single gas analyzer based synchronous measurement of N in accordance with an embodiment of the present invention2O、 CH4And CO2Schematic structure diagram of vortex motion related method device for net exchange flux.
FIG. 3 is a schematic diagram of a data processing flow of the data acquisition and processor of the present invention.
[ description of symbols ]
1-ultrasonic anemometer
2-gas sampling system
21-sampling head 22-sampling gas circuit
23-three way connection 24-filter
25-needle valve 26-steel wire PVC pipe
27-air pump 28-ball valve
3-closed circuit gas analyzer
4-calibration system
41-calibration gas circuit 42-calibration gas unit
43-solenoid valve
5-data acquisition and processor
Detailed Description
In the prior art, no related technology can achieve the following technical effects: reasonably designs a closed-circuit gas sampling system, determines and regulates reasonable sampling flow and efficiently and accurately calculates nitrous oxide (N)2O), methane (CH)4) And oxidation ofCarbon (CO)2) Net exchange of flux. In view of the above, the present application provides a stable and reliable apparatus for measuring gas flux based on the principles of the swirl correlation method according to the three-dimensional wind speed and N2O、CH4And CO2Can efficiently and accurately calculate N2O、CH4And CO2The net exchange flux of (a).
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings.
The embodiment of the invention provides a synchronous measurement method for N based on a single gas analyzer2O、CH4And CO2A vortex related method device for net exchange flux, fig. 1 is a schematic structural diagram of an embodiment of the present invention, as shown in fig. 1, the device includes:
the ultrasonic anemometer 1 is used for measuring three-dimensional wind speed, namely wind speed components in three directions of a Cartesian coordinate system;
the gas sampling system 2 is used for collecting an air sample and conveying the air sample to the closed-circuit gas analyzer 3;
a closed-loop gas analyzer 3 for detecting N contained in the air sample from the gas sampling system 22O、CH4And CO2The concentration of (c);
a calibration system 4 for calibrating the closed-circuit gas analyzer 3;
a data acquisition and processor 5 for receiving, storing and processing the three-dimensional wind speed measured by the ultrasonic anemometer 1 and the N measured by the closed-circuit gas analyzer 32O、CH4And CO2Concentration data and based on the vortex correlation principle, calculating N2O、CH4And CO2The net exchange flux of (a).
In fig. 1, thick line arrows indicate gas lines, and thin line arrows indicate data transmission lines. In the embodiment of the invention, each main integrated component can adopt mainstream brand equipment sold in the international market as long as the performance of each component is kept stable. For example, the ultrasonic anemometer 1 may be a CSAT3 model available from Campbell Scientific Inc. of America, a WMPro model available from Gill Instruments Inc. of UK, etc., the closed-loop gas analyzer 3 may be a single gas analyzer, a QC-TILDAS-DUAL model available from Aerodyne Research Inc. of America, etc., and the data acquisition and processor 5 may be a CR3000 model available from Campbell Scientific Inc. of America, etc.
It should also be noted that the programs internal to the data acquisition and processor 5 (i.e., the data processing software), the gas sampling system 2, and the calibration system 4 were primarily designed by the inventors.
Referring to fig. 2, the piping arrows indicate the gas flow direction, and the dotted lines indicate data lines or power lines. The ultrasonic anemometer 1 is horizontally arranged on the observation bracket and is used for measuring wind speed components in three directions of a Cartesian coordinate system, and a signal output line of the ultrasonic anemometer is connected with the data acquisition and processor 5 and stores three-dimensional wind speed of 10Hz for example.
The gas sampling system 2 consists of a sampling head 21, a sampling gas path 22, a three-way joint 23, a filter 24, a needle valve 25, a ball valve 28, a steel wire PVC pipe 26 and an air pump 27, and the detailed configuration and design scheme are as follows:
the sampling gas path 22 may be a ptfe tube having a total length of 15m and an inner diameter of 1/4 inches, and is selected because of its high chemical stability and low adsorption to gas molecules. In other embodiments, the length and the inner diameter of the sampling gas path 22 may vary according to actual conditions, and the length may be as short as possible without affecting the measurement, and may reach 50m at the maximum, and the inner diameter of the sampling gas path 22 may range from 1/8 inches to 3/8 inches.
The sampling head 21 is located at the end of the sampling air path 22, and is funnel-shaped and oriented downward to prevent rainwater from entering the pipeline and is installed on one side of the sensing head of the ultrasonic anemometer 1. The other end of the sampling gas path 22 is connected with the gas inlet of the closed-circuit gas analyzer 3, and a filter 24 with the aperture of 0.45 μm is arranged 20cm away from the front end of the connection part, so that particles in the air sample can be effectively filtered out, and the optical mirror surface in the closed-circuit gas analyzer 3 is prevented from being polluted. A needle valve 25 is installed at the air inlet of the closed-circuit gas analyzer 3 and used for adjusting the flow of the sampling air path 22. The whole sampling gas circuit 22 is wound with a heating tape and wrapped with a waterproof heat-insulating material, so that the temperature of the sampling gas circuit 22 is slightly higher than the ambient temperature, and the purpose is to prevent water vapor in the air from condensing on the inner wall when passing through the sampling gas circuit 22.
It should be noted that the selection criteria of the length and the inner diameter of the sampling gas path 22 are to ensure that the movement state of the air sample in the sampling gas path 22 is turbulent flow, and the determination criterion is that the reynolds coefficient is greater than 3500.
This is because the closed-loop vortex correlation method measures the gas flux, and requires that the motion state of the air vortex in the sampling gas path 22 is turbulent, otherwise the measured flux is seriously underestimated. Typically, the fluid has a Reynolds number greater than 3500, which can be considered turbulent, and the Reynolds number can be calculated according to the following equation:
Re＝v×d/γ
in the formula:
re is a Reynolds coefficient and is dimensionless;
v is the flow rate of air in the sampling gas path 22, and has a unit of m s-1；
d is the diameter of the sampling gas path 22, and the unit is m;
mu is the kinematic viscosity of air, and the value is 1.5X 10-5m2s-1。
The hardware configuration and specific operating method required to achieve turbulent flow of the motion state of the air within sampling gas path 22 are listed below: first, the minimum sampling flow rate satisfying the turbulent flow condition is calculated according to the formula, in the present invention, the inner diameter of the sampling gas path 22 is 1/4 inches (6.35mm), and the flow rate needs to reach 8.3m s-1The above; second, the maximum potential suction force of the air pump 27 is required to be set to 600L min-1As mentioned above, the invention can meet the requirement by selecting XDS35i type vortex air pump from Edwards company of UK, or selecting TriScroll-600 type air pump from Varian company of America; thirdly, the ball valve 28 at the air outlet of the analyzer is opened to the maximum state to provide enough power, then the needle valve 25 at the air inlet of the analyzer is adjusted to adjust the flow rate, the actual flow rate is ensured to be larger than the calculated minimum flow rate, and during the specific operation, a flow rate meter can be connected at the sampling head 21 for measurement; fourth, the sampling flow rate will gradually decrease as the filter 24 becomes dirtyThe filter membrane is replaced periodically according to the change of the actual flow rate.
The gas outlet of the closed-circuit gas analyzer 3 is connected with a ball valve 28 with the inner diameter of 1 inch, the other end of the ball valve 28 is connected with a steel wire PVC pipe 26 with the length of 2m and the inner diameter of 1 inch, and the material is selected to prevent the PVC pipe from deforming under the condition of air exhaust and negative pressure. The tail end of the steel wire PVC pipe 26 is connected with a large-flow air pump 27, air enters the light cell of the closed-circuit gas analyzer 3 through the sampling head 21, the three-way joint 23, the sampling gas path 22, the filter 24 and the needle valve 25 in sequence under the pumping action of the air pump 27, and N is completed2O、CH4And CO2The air is finally discharged through the air outlet of the air pump 27. The function of the ball valve 28 is to control the actual pumping force of the air pump 27 and to manually close the air pump 27 when it is closed, preventing dust inside the air pump from being sucked back into the closed-circuit gas analyzer 3.
The data acquisition and processor 5 is connected with the closed-circuit gas analyzer 3 through an RS232 data transmission line for storing N besides three-dimensional wind speed data2O、CH4And CO2Concentration data of (2), concentration unit is nmol mol-1(relative to dry air). The data acquisition and processor 5 stores a self-defined software program inside, performs preprocessing on the original 10Hz data, as shown in fig. 3, and includes the steps of removing abnormal values, correcting three-dimensional wind speed coordinate axes, correcting time difference of wind speed and concentration data, calculating instantaneous pulsation values, and the like, and calculates gas flux according to the following formula, and usually calculates the average value of flux in half an hour.
In the formula:
f is N2O、CH4And CO2Average flux in units of μ g m for half an hour-2h-1；
w' is vertical wind speed deviationInstantaneous pulsation value of half-hour average, in m s-1；
c' is N2O、CH4And CO2Instantaneous pulsation value of concentration deviating from average value of half an hour in nmol-1；
Rho is the air density, and the value is 1.29kg m-3；
M is the molar mass of air and is 0.029kg mol-1；
3600 means 3600 seconds for an hour;
a represents 1mol of N2O、CH4And CO2Mass of molecule in g mol-1。
Then, for N2O、CH4And CO2The correction of the low-frequency and high-frequency parts of the turbulent flow is carried out successively for half an hour of average flux, because the high-frequency change of the gas concentration can be attenuated by the tube wall of the sampling gas path 22, the flux of the gas can be underestimated by artificially defining the average time taking half an hour as the calculated flux, and other factors, and the purpose is to make the corrected flux closer to the true value.
In order to calibrate the closed-circuit gas analyzer and make the gas concentration measurement result accurate, the device also comprises a calibration system 4 which is composed of a calibration gas unit 42, an electromagnetic valve 43 and a calibration gas circuit 41. The calibration gas path 41 is a polytetrafluoroethylene tube with the length of 15m and the inner diameter of 1/8 inches, one end of the calibration gas path is connected to the sampling gas path 22 through a three-way joint 23, the joint is 20cm away from the sampling head, the other end of the calibration gas path 41 is connected with the gas outlet of the electromagnetic valve 43, and the gas inlet of the electromagnetic valve 43 is connected with the calibration gas unit 42. The power supply line of the solenoid valve 43 is connected to the circuit board of the closed circuit gas analyzer 3 to supply power thereto. When the air sample is normally collected, the solenoid valve 43 is closed. When the closed-circuit gas analyzer 3 needs to be calibrated, the electromagnetic valve 43 is opened, the standard gas starts from the standard gas unit 42 and enters the closed-circuit gas analyzer 3 through the electromagnetic valve 43, the calibration gas path 41, the three-way joint 23, the sampling gas path 22, the filter 24 and the needle valve 25 in sequence, and the detection result is used for calibrating the measurement result of the air sample. The flow rate of the standard gas in the calibration gas path 41 is slightly larger than the flow rate of the air sample during sampling, so as to ensure that the gas entering the analyzer is pure standard gas.
In calculating N2O、CH4And CO2Before flux, a key preprocessing step is required to be carried out on the original 10Hz data, namely, the time difference between the wind speed and the gas concentration data is corrected, and the flux calculation is carried out by adopting uncorrected or uncorrected inaccurate data, so that the result can be seriously deviated from the true value. The reason for the time difference is that the air sample needs to be transported in the sampling gas path 22 for a certain time to reach the closed-circuit gas analyzer 3 to complete the gas concentration detection, so that the recorded concentration data always lags behind the wind speed data. Factors affecting the time difference include the length and inner diameter of the sampling air path 22, the suction force of the air pump 27, the permeability of the filtering membrane, the change of the relative humidity of the air, etc., and the time difference between the wind speed and the gas concentration data is not a constant value but varies with time and environmental conditions.
The invention provides different suggested methods aiming at different situations, which are used for correcting the time difference between the wind speed and the gas concentration data and listing the advantages, disadvantages and applicable conditions:
firstly, a maximum covariance method is preferably selected, that is, a time range is selected, firstly, the real time difference is ensured within the time range, for example, 0-10 s, then, the time series of the wind speed and the gas concentration are sequentially staggered by taking the concentration measurement frequency as a unit (usually, 0.1s), and the covariance of two data sequences is calculated once every time the time is staggered until the staggered moment of the maximum covariance is found, that is, the real time difference between the two data sequences is obtained. The method has the advantages of being based on the turbulence theory and reliable in result, but has the defect that the method is only suitable for the situation that the signal-to-noise ratio of concentration measurement is high, namely the flux of the actual gas is higher than the detection limit of instrument measurement.
Secondly, when maximum covariance is not applicable, a fixed time difference method may be used, i.e. the time for the air sample to travel from the sampling port to the analyzer is estimated by dividing the internal volume of the sampling gas path 22 by the average sampling flow rate, and assuming that the time difference between the wind speed and the gas concentration data at all times is the same value. This method has the advantage of simple data processing, but has the disadvantage of neglecting the effect of flow rate variations and gas on humidity variations, which can lead to a certain underestimation of the gas flux. The fixed time difference method is a simple and effective method for measuring environments with clean air and low relative humidity.
In the actual field measurement process, the closed-circuit gas analyzer is suggested to be placed in an environment with stable temperature and humidity, and the most common scheme is to configure an instrument box or a simple experimental room with a temperature and humidity control device (such as an air conditioner) for the analyzer and place the analyzer in the instrument box, so that the laser working temperature inside the gas analyzer can be ensured to be stable, and the signal drift of concentration signals caused by overlarge environmental temperature change is avoided. The closed-circuit gas analyzer requires stable alternating current power supply during operation, and if conditions allow, an uninterruptible power supply is preferably arranged, so that damage to the analyzer caused by power failure or unstable power supply voltage is reduced. In addition, the instrument box or laboratory should be positioned to avoid being in the prevailing wind direction to reduce interference with wind speed measurements.
In addition, the embodiment of the invention also provides a synchronous measurement method for N based on a single gas analyzer2O、 CH4And CO2A net exchange flux method applied to the synchronous measurement of N based on the single gas analyzer2O、CH4And CO2The net exchange flux vortex motion correlation method device constructs a stable and reliable device which can realize N on land ecosystem plot scale2O、CH4And CO2Undisturbed high-frequency continuous synchronous measurement of net exchange fluxes of the three gases.
Unless otherwise indicated, the numerical parameters set forth in the specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the present invention. In particular, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Generally, the expression is meant to encompass variations of ± 10% in some embodiments, 5% in some embodiments, 1% in some embodiments, 0.5% in some embodiments by the specified amount.
Furthermore, "comprising" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. Synchronous measurement N based on single gas analyzer2O、CH4And CO2A net exchange flux whirl correlation method apparatus comprising:
the ultrasonic anemometer is used for measuring three-dimensional wind speed, namely wind speed components in three directions of a Cartesian coordinate system;
a gas sampling system for collecting an air sample and delivering it to a closed circuit gas analyzer, the gas sampling system comprising:
a sampling head as an inlet for air to enter the gas sampling system;
one end of the sampling gas path is connected with the sampling head, and the other end of the sampling gas path is connected with the closed-circuit gas analyzer and is used for transmitting the air;
the filter is connected with the three-way joint, has the filter aperture of 0.45 mu m and is used for filtering particles in the air;
a heating belt is arranged outside the sampling gas circuit;
closed loop gas analyzer for detecting N contained in air sample from gas sampling system2O、CH4And CO2The concentration of (c);
the calibration system is used for calibrating the closed-circuit gas analyzer;
a data acquisition and processor for receiving, storing and processing three dimensional wind speed measured by the ultrasonic anemometer and N measured by the closed circuit gas analyzer2O、CH4And CO2Concentration numberBased on the theory of vortex correlation method, N is calculated2O、CH4And CO2Net exchange flux of;
wherein, the N is2O、CH4And CO2The net exchange flux of (a) means in particular: average value of flux was calculated in half an hour
Wherein the unit of F is μ gm–2h–1W' is the instantaneous pulsation value of the vertical wind speed deviating from the average value of half an hour in ms-1C' is N2O、CH4And CO2Instantaneous pulsation value of concentration deviating from average value of half an hour in nmol-1；
Means half-hour average value of w 'c', p is air density, and the value is 1.29kg m-3(ii) a M is the molar mass of air and is 0.029kg mol-1(ii) a 3600 means 3600 seconds for 1 h; a represents 1molN2O、CH4And CO2Mass of molecule in g mol-1。
2. The vortex correlation apparatus of claim 1, wherein the gas sampling system further comprises:
the three-way joint is used for connecting the sampling gas circuit and the calibration gas circuit;
the needle valve is positioned at the air inlet of the closed-circuit gas analyzer, is connected with the filter and is used for adjusting the flow of the sampling gas circuit;
one end of the ball valve is connected with the air outlet of the closed-circuit gas analyzer and is used for controlling the actual pumping force of the air pump and manually closing the air pump when the air pump is closed so as to prevent dust in the air pump from being sucked back into the closed-circuit gas analyzer;
one end of the steel wire PVC pipe is connected with the air pump and is used for circulating the air;
the air pump is connected with the other end of the ball valve through the steel wire PVC pipe, provides power for pumping air and discharges the air.
3. The vortex correlation device of claim 2, wherein the sampling head is funnel shaped and oriented downward to prevent rain water from entering the sampling air path.
4. The whirl correlation method apparatus according to claim 2, wherein the sampling gas path is made of polytetrafluoroethylene; and/or
And the outer side of the sampling gas circuit is wrapped with a waterproof heat-insulating material.
5. The whirl correlation method apparatus according to claim 1, wherein the calibration system comprises a calibration gas unit, a calibration gas circuit and a solenoid valve, wherein,
the standard gas unit is connected with an inlet of the electromagnetic valve and used for outputting standard gas;
the calibration gas circuit is connected with an outlet of the electromagnetic valve and used for transmitting the calibration gas;
the turn-off and turn-on of the electromagnetic valve respectively correspond to the operation of the gas sampling system and the operation of the calibration system.
6. The vortex correlation apparatus of claim 5, wherein the flow rate of the marker gas is greater than the flow rate of the air.
7. The whirl correlation method apparatus according to claim 1, wherein a Reynolds number Re of the air movement in the sampling gas path is Vxd/γ for determining whether the flow state is turbulent,
wherein v is the flow rate of air in the sampling gas circuit, and the unit is m s-1；
d is the diameter of the sampling gas circuit, and the unit is m;
gamma is the kinematic viscosity of air and has a value of 1.5X 10-5m2s-1；
The method for adjusting the air flow state in the sampling gas circuit comprises the following steps:
calculating the minimum air flow velocity meeting the turbulent flow state according to the formula of the Reynolds coefficient;
configuring the maximum potential draft force to 600L min–1The above air pump;
and opening the ball valve at the air outlet of the closed-circuit gas analyzer to the maximum state, and then adjusting the needle valve at the air inlet of the closed-circuit gas analyzer to adjust the flow rate, so as to ensure that the flow rate of the air sample in the sampling air path is greater than the calculated minimum air flow rate.
8. The whirl correlation method apparatus according to claim 1, wherein the data acquisition and processor is further configured to correct the three dimensional wind speed and N according to a maximum covariance method or a fixed time difference method2O、CH4And CO2Data time difference of concentration.
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| CN115629164B (en) * | 2022-12-21 | 2023-04-14 | 天津飞眼无人机科技有限公司 | Unmanned aerial vehicle carbon flux monitoring data acquisition equipment and processing method |
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| CN104316645B (en) * | 2014-10-09 | 2016-01-20 | 中国科学院地理科学与资源研究所 | Soil CO 2, CH 4and N 2o flux cooperative determining device |
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