CN115561038A - Greenhouse gas constant-pressure acquisition device and method and emission flux calculation method thereof - Google Patents

Greenhouse gas constant-pressure acquisition device and method and emission flux calculation method thereof Download PDF

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CN115561038A
CN115561038A CN202211344824.1A CN202211344824A CN115561038A CN 115561038 A CN115561038 A CN 115561038A CN 202211344824 A CN202211344824 A CN 202211344824A CN 115561038 A CN115561038 A CN 115561038A
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gas
box
greenhouse gas
greenhouse
hard box
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徐彦森
徐诗韵
陈丽涵
刘硕
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Zhejiang University of Technology ZJUT
Nanjing University of Information Science and Technology
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Nanjing University of Information Science and Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00—Sampling; Preparing specimens for investigation
    • G01N1/02—Devices for withdrawing samples
    • G01N1/22—Devices for withdrawing samples in the gaseous state
    • G01N1/24—Suction devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/76—Devices for measuring mass flow of a fluid or a fluent solid material
    • G01F1/86—Indirect mass flowmeters, e.g. measuring volume flow and density, temperature or pressure
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography

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Abstract

The invention discloses a greenhouse gas constant-pressure collecting device which comprises a hard box, wherein an opening is formed in the lower portion of the hard box, a flexible air bag is arranged in the hard box, an exhaust pipe is connected to the flexible air bag and penetrates through the hard box in a sealing mode, a gas collecting pipe is arranged on the hard box in a sealing mode, and a manual gas valve is arranged on the gas collecting pipe. The invention also discloses a greenhouse gas constant-pressure acquisition device acquisition method and a greenhouse gas emission flux calculation method based on the acquisition method. The greenhouse gas constant-pressure acquisition device and method and the greenhouse gas constant-pressure emission flux calculation method provided by the invention have the advantages of low cost and simple measurement mode, and can reduce the calculation error of greenhouse gas emission flux.

Description

Greenhouse gas constant-pressure acquisition device and method and emission flux calculation method thereof
Technical Field
The invention relates to a greenhouse gas constant-pressure acquisition device and method and an emission flux calculation method thereof, belonging to the technical field of environmental detection.
Background
Greenhouse gas emission of an ecosystem is an important source of atmospheric greenhouse gas, and particularly, a large amount of methane is emitted in anaerobic environments such as rice, wetlands and the like. The study of greenhouse gas emission rates for different ecosystem types is key to controlling greenhouse gas emissions.
At present, a static box method is mainly adopted to measure the emission rate in the research process of greenhouse gases, and the basic principle is as follows: covering the ground surface or water surface to be measured by a sealed bottomless box body with known volume and bottom area to form a closed environment, extracting gas in the collection box body at intervals, storing and transporting the collected gas, returning the collected gas to a laboratory for analysis to obtain related data, and calculating the exchange rate of the gas between the ground surface and the atmosphere on the covered surface. Consequently need gather the more gas of volume at greenhouse gas observation in-process, but the fixed static incasement portion atmospheric pressure of volume can be along with extracting observation gas many times and constantly reducing, leads to the gas that dissolves in soil hole or the water to discharge to the incasement because of the negative pressure effect with higher speed in the incasement, and this kind of change is especially obvious at the application of little volume sampling case. The assumption that the air pressure in the tank is constant during the flux calculation is also violated. To solve these problems, there are currently mainly the following approaches:
(1) The volume of the sampling box is increased to reduce the change of the air pressure in the air extraction process. However, this increases the cost of manufacturing the housing and also dilutes the greenhouse gas concentration in the housing, and excessively diluted gases can increase errors in the gas detection process.
(2) And a portable device is adopted to extract gas from the static box on site for analysis and then discharge the gas back to the interior of the box body. This method mainly requires the provision of an expensive portable greenhouse gas detection device and the equipment needs to be powered and cannot be adapted to the harsh field environment. Meanwhile, the detection capability of the detection equipment for a plurality of greenhouse gases is limited, and only 1-2 kinds of greenhouse gases can be detected by one instrument. The influence of the problems that the equipment accidentally falls into water, excessive water vapor is absorbed by an instrument, the detection precision of the equipment is influenced by high temperature and the like also exists in the field environment. Therefore, the method is less used for monitoring in the field at present.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a greenhouse gas constant-pressure acquisition device, a greenhouse gas constant-pressure acquisition method and an emission flux calculation method thereof, which have the advantages of lower cost and simple measurement mode and can reduce the calculation error of the emission flux of greenhouse gas.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
the utility model provides a greenhouse gas constant voltage collection system, includes the stereoplasm case, stereoplasm case lower part opening, be provided with flexible air pocket in the stereoplasm incasement, be connected with the blast pipe on the flexible air pocket, the blast pipe is sealed to be passed the stereoplasm case, the sealed gaseous collecting pipe that is provided with on the stereoplasm case, be provided with manual gas valve on the gaseous collecting pipe.
The hard box is in a square shape and is composed of five acrylic material plates, and the adjacent acrylic material plates are bonded through PVC glue.
The flexible air bag is a polyester odor air bag.
A greenhouse gas constant pressure acquisition method is characterized by comprising the following steps: the method comprises the following steps:
completely discharging the gas in the flexible gas bag;
shaking the hard box in the measured atmosphere to ensure that the gas in the hard box is fully exchanged with the ambient atmosphere of the measurement area;
the hard box is inserted into soil or a water body for a certain depth, so that a completely closed gas space is formed between the box body and the ground or the water surface;
respectively extracting gas samples from the gas collecting pipe at a plurality of sampling time points after the hard box is placed, wherein the total sampling volume of the gas samples is smaller than that of the flexible air bag;
storing and transporting the gas sample, and measuring the concentration of the gas sample by using a gas chromatograph.
The depth of the hard box inserted into soil or water is 5-10 cm.
The number of sampling times is four, sampling time points are 0s, ts,2ts and 3ts respectively, and t is sampling interval time.
A method for calculating the emission flux of a greenhouse gas constant-pressure acquisition device is based on the acquisition method of the greenhouse gas constant-pressure acquisition device and comprises the following steps:
respectively calculating the sum of the target greenhouse gas mass in the hard box corresponding to the four sampling points and the target greenhouse gas mass in the existing gas sample, and respectively recording the sum as m 1 ’,m 2 ’,m 3 ' and m 4 ’；
Using m 1 ’,m 2 ’,m 3 ' and m 4 Performing linear regression with the measuring time 0, t,2t and 3t, and calculating to obtain a slope delta m/delta t;
dividing the slope delta m/delta t by the bottom area A of the hard box to calculate the emission flux F of the greenhouse gas,
Figure BDA0003917977420000031
m 1 ’,m 2 ’,m 3 ' and m 4 The way' is calculated as follows:
Figure BDA0003917977420000032
Figure BDA0003917977420000033
Figure BDA0003917977420000034
Figure BDA0003917977420000035
wherein c is 1 ,c 2 ,c 3 ,c 4 Representing the gas production times at 0, t,2t and 3tConcentration of the target greenhouse gas, P represents the pressure inside the static tank, which is the actual pressure of the outside atmosphere, T represents the absolute temperature of the gas inside the static tank, V represents the volume of the gas inside the static tank, P 0 Denotes the atmospheric pressure, T, in the standard state 0 Denotes the absolute temperature, V, of the gas in the standard state 0 Represents the molar volume of the gas in the standard state, and M represents the molar mass of the target greenhouse gas.
The invention has the beneficial effects that: according to the greenhouse gas constant-pressure acquisition device and method and the emission flux calculation method thereof, the flexible air bag is set as the polyester air bag, so that the situation that the air pressure is reduced due to gas extraction in the process of acquiring gas by the static box, the actual greenhouse gas emission rate of soil or water surface greenhouse gas is changed, and the system error caused by the change of the air pressure in the greenhouse gas calculation process can be avoided; the polyester air bag is used as a flexible air bag, has the characteristics of light weight and thin thickness, can increase the volume which is the same as that of the flexible air bag according to the sampling volume, effectively solves the problem of change of gas volume caused by gas extraction in the process of collecting gas by adopting balance gas and a static box, and can improve the calculation accuracy of greenhouse gas emission flux; the polyester air bag has the characteristics of low adsorption, low gas permeability and no odor and pollution, and the problems of large adsorption of the air bag on target greenhouse gases and permeation and leakage of the gases through the air bag in the sampling process are solved; the invention does not need expensive gas analysis equipment and a sampling device with overlarge volume, and can quickly and rapidly collect greenhouse gas in the field by matching a small static sampling box with balance gas. And the air pressure in the box is ensured to be constant in the gas production process.
Drawings
FIG. 1 is a schematic structural diagram of a constant pressure collecting device for greenhouse gases in the present invention.
The reference numbers in the figures are as follows: 1-an exhaust pipe; 2-a gas collection tube; 3-a flexible airbag; 4-hard case.
Detailed Description
The present invention is further described with reference to the accompanying drawings, and the following examples are only for clearly illustrating the technical solutions of the present invention, and should not be taken as limiting the scope of the present invention.
As shown in figure 1, the invention discloses a greenhouse gas constant-pressure collecting device which comprises a hard box 4, a flexible air bag 3, an exhaust pipe 1 and a gas collecting pipe 2, wherein a manual gas valve is arranged on the gas collecting pipe 2. The hard case 4 is square in shape and has an opening at the lower part. The hard box 4 is used for placing vegetation on the ground or above the water surface, and the volume of the box cannot be changed. The top, front, back, left and right box bodies of the hard square box are combined by 5 transparent or non-transparent acrylic material plates and are bonded by PVC glue. A small hole with the diameter of 4mm is formed in the top plate, a PU hose is inserted to serve as an exhaust pipe 1, and a gap between the box body and the hose is sealed by neutral glass cement. A flexible gas sack 3 is then connected to the gas sack in the region of the gas sack discharge line 1 located inside the rigid square box 4. Compared with a flexible air bag, the flexible air bag adopts a medical drainage bag, a medical appliance or an infusion bag in a veterinary appliance, an intestinal tract flushing bag or an infusion bag for conveying nutrient solution to trees in the landscaping industry. This embodiment's flexible air pocket 3 adopts polyester odor air pocket, and polyester odor air pocket can not have and kick-backs, just keeps not having the state that gas got into after exhausting gas, finds through experimental determination that this air pocket can effectively perceive the variation of box internal pressure and can not produce the adsorption effect to greenhouse gas. A small hole with the diameter of 4mm is formed in a side plate of the hard box 4, a PU hose is inserted to serve as a gas collecting pipe 2, and a gap between the box body and the hose is sealed by neutral glass cement.
The invention also discloses a greenhouse gas constant-pressure acquisition method, which comprises the following steps:
step one, emptying: the gas in the soft air bag is completely discharged.
Step two, replacing gas inside the hard square box: and shaking the hard square box in the measured atmosphere to ensure that the gas in the box is fully exchanged with the ambient atmosphere of the measurement area so as to eliminate the influence of old gas.
Step three, setting a measuring system: in order to set a completely closed gas measuring system, the hard square box is inserted into soil or a water body for 5-10 cm, and a completely closed gas space is formed between the box body and the ground or the water surface.
Step four, greenhouse gas collection: gas is drawn from the gas collection tube using an injector or an air extractor, 0s, ts,2ts and 3ts, respectively, after the rigid square box is placed. Wherein the volume and time t of gas withdrawal are operated according to the experimental design outline. Wherein the total volume of gas collection must be less than the volume of the flexible gas pouch 3.
Step five, gas analysis: storing and transporting the gas sample, and using gas chromatography to treat CO 2 、CH 4 、N 2 O isothermal gas concentration.
In the invention, the emission flux calculation method of the greenhouse gas constant-pressure acquisition device is as follows:
firstly, calculating the quality of target greenhouse gas in a static box at a certain gas production moment, wherein the formula is as follows:
Figure BDA0003917977420000051
wherein m represents the mass of the target greenhouse gas in the static box at the gas production time, and c represents the concentration of the target greenhouse gas in the static box at the gas production time. P represents the pressure inside the static tank, T represents the absolute temperature of the gas inside the static tank, and V represents the volume of the gas inside the static tank; p 0 Indicates the atmospheric pressure (101.325 kPa), T, in the standard state 0 Represents the absolute temperature (273.15K), V, of the gas in the standard state 0 Represents the molar volume of the gas in the standard state (22.4L mol) -1 ). M represents the molar mass of the target greenhouse gas.
In the process of collecting greenhouse gases by adopting the constant-pressure collecting device, in order to ensure that the gas pressure in the static box is kept unchanged, the volume of the gases in the static box is continuously reduced, and because the polyester odor air bag is arranged as the flexible air bag, the flexible air bag can increase the volume which is the same as that of the flexible air bag according to the sampling volume, and the gas pressure in the static box can be ensured to be kept unchanged. Therefore, the following modifications are made to compensate for the change in gas volume during flux acquisition using the flux calculations for gas acquisition of the present invention.
The static box is just placed when the gas is collected for the first time, and at the moment, the soil or the water surface is considered not to discharge the greenhouse gas into the box. The mass of the target greenhouse gas inside the static tank at this time was:
Figure BDA0003917977420000061
wherein m is 1 ，c 1 And V 1 Respectively representing the mass, concentration and volume of the target greenhouse gas in the static box at the gas production moment. After the interval of t seconds, when gas is collected for the second time, the soil or the water surface is considered to discharge a certain amount of greenhouse gas to the inside of the box, and the quality of the target greenhouse gas in the static box at the moment is as follows:
Figure BDA0003917977420000062
by analogy, the mass of the target greenhouse gas in the static box after the interval of 2t and 3t seconds is m respectively 3 And m 4 . In addition, V 2 And V 1 The difference of (A) is the volume V of gas collected each time m . The mass of the target greenhouse gas inside the static box at the moment of four gas collection can be calculated respectively. Greenhouse gas emission flux, expressed as the change in mass of greenhouse gas in the box over time, was calculated as follows:
Figure BDA0003917977420000071
and the change of the quality of the target greenhouse gas in the static box at each moment comprises the greenhouse gas emission and the change of the quality of the greenhouse gas in the box caused by the collected gas, so the change of the quality of the greenhouse gas in the box caused by the collected gas needs to be compensated and calculated in the calculation process, and therefore the quality of the target greenhouse gas in the static box after the compensation gas is collected after the gas is collected for t,2t and 3t seconds can be calculated as follows:
Figure BDA0003917977420000072
Figure BDA0003917977420000073
Figure BDA0003917977420000074
Figure BDA0003917977420000075
using m 1 ’,m 2 ’,m 3 ' and m 4 ' Linear regression with measurement times 0, t,2t and 3t, with slope Δ m/Δ t, and final calculation of flux F. F is the emission flux of the target greenhouse gas in mg m -2 s -1 。
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention, and such modifications and adaptations are intended to be within the scope of the invention.

Claims (8)

1. The constant-pressure greenhouse gas collecting device is characterized in that: the gas collecting device is characterized by comprising a hard box (4), wherein the lower part of the hard box (4) is opened, a flexible gas bag (3) is arranged in the hard box (4), an exhaust pipe (1) is connected to the flexible gas bag (3), the exhaust pipe (1) penetrates through the hard box (4) in a sealing mode, a gas collecting pipe (2) is arranged on the hard box (4) in a sealing mode, and a manual gas valve is arranged on the gas collecting pipe (2).
2. The constant pressure collecting device for greenhouse gases as claimed in claim 1, wherein: the hard box (4) is in a cube shape, the hard box (4) is composed of five acrylic material plates, and the adjacent acrylic material plates are bonded through PVC glue.
3. The constant pressure collecting device for greenhouse gases as claimed in claim 1, wherein: the flexible airbag (3) is a polyester airbag.
4. A method for collecting a greenhouse gas constant pressure collecting device as claimed in any one of claims 1 to 3, which comprises the steps of: the method comprises the following steps:
completely discharging the gas in the flexible gas bag;
shaking the hard box in the measured atmosphere to ensure that the gas in the hard box is fully exchanged with the ambient atmosphere of the measurement area;
inserting the hard box into soil or a water body for a certain depth to form a completely closed gas space between the box body and the ground or the water surface;
respectively extracting gas samples from the gas collecting pipe at a plurality of sampling time points after the hard box is placed, wherein the total sampling volume of the gas samples is smaller than that of the flexible air bag;
storing and transporting the gas sample, and measuring the concentration of the gas sample by using a gas chromatograph.
5. The collecting method of the greenhouse gas constant pressure collecting device according to claim 4, wherein the collecting method comprises the following steps: the depth of the hard box inserted into soil or water is 5-10 cm.
6. The collecting method of the greenhouse gas constant pressure collecting device according to claim 4, wherein the collecting method comprises the following steps: the number of sampling times is four, sampling time points are 0s, ts,2ts and 3ts respectively, and t is sampling interval time.
7. A method for calculating the emission flux of a greenhouse gas constant-pressure acquisition device is characterized by comprising the following steps: the collecting method of the greenhouse gas constant pressure collecting device based on claim 6, comprising the following steps:
respectively calculating the sum of the target greenhouse gas mass in the hard box corresponding to the four sampling points and the target greenhouse gas mass in the existing gas sample, and respectively recording the sum as m 1 ’,m 2 ’,m 3 ' and m 4 ’；
Using m 1 ’,m 2 ’,m 3 ' and m 4 Performing linear regression with the measuring time 0, t,2t and 3t, and calculating to obtain a slope delta m/delta t;
dividing the slope delta m/delta t by the bottom area A of the hard box to calculate the emission flux F of the greenhouse gas,
Figure FDA0003917977410000021
8. the method for calculating the emission flux of the constant pressure greenhouse gas collection device according to claim 7, wherein the method comprises the following steps: m is 1 ’,m 2 ’,m 3 ' and m 4 ' is calculated as follows:
Figure FDA0003917977410000022
Figure FDA0003917977410000023
Figure FDA0003917977410000024
Figure FDA0003917977410000025
wherein c is 1 ,c 2 ,c 3 ,c 4 The concentration of the target greenhouse gas in the box at the gas production time of 0, t,2t and 3t is shown, and the pressure in the static box is the actual pressure of the external atmosphereStrong, T represents the absolute temperature of the gas inside the static tank, V represents the volume of the gas inside the static tank, P 0 Denotes the atmospheric pressure in the standard state, T 0 Denotes the absolute temperature, V, of the gas in the standard state 0 Represents the molar volume of the gas in the standard state, and M represents the molar mass of the target greenhouse gas.
CN202211344824.1A 2022-10-31 2022-10-31 Greenhouse gas constant-pressure acquisition device and method and emission flux calculation method thereof Pending CN115561038A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116380574A (en) * 2023-06-06 2023-07-04 四川发展环境科学技术研究院有限公司 Greenhouse gas collection method

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116380574A (en) * 2023-06-06 2023-07-04 四川发展环境科学技术研究院有限公司 Greenhouse gas collection method
CN116380574B (en) * 2023-06-06 2023-08-18 四川发展环境科学技术研究院有限公司 Greenhouse gas collection method

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