Apparatus and method for measuring dissolved carbon dioxide concentration in seawater at different depths using the bubbling method

Abstract

An apparatus and method for measuring dissolved carbon dioxide concentration in seawater at different depths using the bubbling method are disclosed. The apparatus includes a bubbling measuring bottle, a cap, an outlet pipe, an inlet pipe, a solenoid valve, a carbon dioxide meter, a three-way valve, an air pump, a motor, a check valve, a weight, and a data acquisition and processing center. The bottom of the bottle is equipped with a water inlet, temperature and humidity sensors, a water pressure sensor, a salinity sensor, and a liquid level sensor. The inlet pipe, bubbling measuring bottle, outlet pipe, solenoid valve, carbon dioxide meter, three-way valve, and air pump form an airflow loop. The motor is connected to the weight, and the temperature, humidity, water pressure sensors, salinity sensor, and pressure sensor are electrically connected to the data acquisition and processing center. The dissolved carbon dioxide concentration is calculated in real time by observing the entry and exit of carbon dioxide molecules onto the surface of the bubbling measuring bottle to reach equilibrium. This invention features a simple structure and convenient operation, enabling continuous real-time monitoring of changes in carbon dioxide content in seawater, laying a solid foundation for marine carbon dioxide research.

Description

Technical Field

[0001] This invention relates to a technique for measuring dissolved carbon dioxide in seawater, and in particular to an apparatus and method for accurately measuring the concentration of dissolved carbon dioxide in seawater at different depths in real time using a bubbling device. Background Technology

[0002] Carbon dioxide is a common greenhouse gas, and global warming and the greenhouse effect have become a major environmental issue of widespread concern to the international community, governments, and the public. This gas is a primary contributor to global warming. The rapidly increasing CO2 concentration and its greenhouse effect have profound impacts on global ecosystems and the human environment. The ocean's ability to absorb, store, and transfer carbon dioxide from the atmosphere has an undeniable influence on the trend of atmospheric carbon dioxide levels. However, the ocean's absorption of CO2 leads to significant changes in the marine carbonate system. Measuring the dynamic changes in CO2 in seawater can help us better understand the marine carbon cycle and ocean acidification, providing essential tools for monitoring my country's marine ecological environment.

[0003] Currently, the main methods for measuring dissolved gases in seawater include: sampling-laboratory analysis, in-situ measurement of dissolved gases in seawater based on optical sensing technology, and in-situ measurement technology based on hydrophobic and breathable membranes combined with gas sensing. Sampling-laboratory analysis primarily targets surface seawater dissolved gas measurement, using water samplers or sampling bottles to collect samples at different depths and locations during navigation. However, the data obtained from continuous measurements has poor temporal resolution. In-situ measurement technology based on optical sensing technology is a more advanced detection technique with significant application potential in areas with high dissolved gas concentrations. As a high-precision, non-contact measurement technology, it shows promising application prospects in the field of in-situ seawater measurement. In-situ measurement technology based on hydrophobic and breathable membranes combined with gas sensing uses a hydrophobic and breathable membrane to separate water vapor in situ, followed by gas sensing technology for measurement, achieving rapid and high-precision measurement of dissolved gases. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned shortcomings of the prior art and provide an apparatus and method for measuring the concentration of dissolved carbon dioxide in seawater at different depths by bubbling method. It can achieve continuous real-time monitoring of carbon dioxide content in seawater without sampling the water body. The measurement and detection accuracy is high, the process is simple, and the operation is convenient, stable and reliable.

[0005] The technical solution of the present invention is: a device for measuring the concentration of dissolved carbon dioxide in seawater at different depths by bubbling method, comprising a bubbling measuring bottle, a bottle cap, an outlet sleeve, a weight rope, an inlet sleeve, an outlet pipe, an inlet pipe, a solenoid valve, a carbon dioxide measuring instrument, a three-way valve, an air pump, a motor, a one-way valve, a weight, and a data acquisition and processing center.

[0006] The bubbling measuring bottle has a three-dimensional conical structure with multiple water inlets at the bottom. Temperature, humidity, water pressure, and salinity sensors are located at the bottom inside the bubbling measuring bottle. A pressure sensor is located at the air inlet of the carbon dioxide measuring instrument. Two liquid level sensors are located on the upper and lower inner walls of the bubbling measuring bottle, respectively.

[0007] The outlet sleeve, weight rope sleeve, and inlet sleeve are respectively installed on the bottle cap. The outlet pipe is inserted into the outlet sleeve, and the inlet pipe is inserted into the inlet sleeve. The inlet pipe extends into the bottom of the bubbling measuring bottle. The inlet end of the outlet pipe extends into the bubbling measuring bottle. The outlet end of the outlet pipe is connected to the inlet end of the carbon dioxide measuring instrument through a solenoid valve. The outlet end of the carbon dioxide measuring instrument is connected to the first inlet of the three-way valve. The second inlet of the three-way valve is connected to the atmosphere. The outlet of the three-way valve is connected to the inlet end of the air pump. The outlet end of the air pump is connected to the inlet of the one-way valve. The outlet of the one-way valve is connected to the inlet end of the inlet pipe.

[0008] The motor output end suspends a heavy object via a traction rope. The traction rope passes through the weight rope loop on the bottle cap and the water inlet at the bottom of the bubbling measuring bottle, causing the heavy object to sink into the seawater. The solenoid valve, carbon dioxide meter, three-way valve, air pump, motor, temperature, humidity and water pressure sensors, salinity sensor, pressure sensor, and two liquid level sensors are electrically connected to the data acquisition and processing center via wired or wireless means.

[0009] A further technical solution of the present invention is that the end of the air inlet pipe that extends into the bubbling measuring bottle is a porous cavity.

[0010] Another technical solution of the present invention is: a method for measuring the concentration of dissolved carbon dioxide in seawater at different depths using the aforementioned bubbling method, comprising a measurement process and a calculation process.

[0011] I. Measurement Process

[0012] The weight at the lower end of the motor traction rope is submerged in the water. Seawater enters the bubble measuring bottle through the water inlet at the bottom. The data from the two liquid level sensors control the three-way valve, air pump, and check valve, causing the device for measuring the dissolved carbon dioxide concentration in seawater at different depths using the bubble method to sink to the depth of the seawater where the carbon dioxide concentration is to be measured.

[0013] Open the solenoid valve and check valve, start the air pump, and connect the first air inlet and outlet of the three-way valve. The bubbles that are bubbling out of the bubbling measurement bottle come into contact with the seawater in the bubbling measurement bottle and are bubbled out from the liquid surface in the bubbling measurement bottle. They enter the carbon dioxide measuring instrument through the air outlet pipe and solenoid valve, and flow out of the carbon dioxide measuring instrument into the three-way valve, air pump, and check valve, and finally flow back into the bubbling measurement bottle to form an airflow loop.

[0014] After the airflow stabilizes, the carbon dioxide meter measures the carbon dioxide concentration in the bubbling gas; and sends the measured temperature, water pressure at the bottom of the bubbling measuring bottle, salinity, pressure in the upper space of the bubbling measuring bottle, and liquid level position signals of the bubbling measuring bottle to the data acquisition and processing center.

[0015] II. Calculation Process

[0016] When measuring the concentration of dissolved carbon dioxide in seawater, it is necessary to measure the solubility of carbon dioxide and convert the concentration from the gas phase to the water phase; the concentration of carbon dioxide in the atmosphere and water phase remains constant over time, and a carbon dioxide concentration equilibrium is reached between water and circulating air.

[0017] The measured temperature and salinity were substituted into the following empirical equation for the solubility of gases in seawater in relation to water temperature and salinity to calculate the solubility coefficient K0 of carbon dioxide:

[0018]

[0019] Where T is the temperature measured by the temperature, humidity, and water pressure sensors, in Kelvin; S is the salinity measured by the salinity sensor, in grams per kilogram; and K0 is the solubility coefficient of carbon dioxide, in mol (L·atm). -1 .

[0020] Substitute the carbon dioxide solubility coefficient K0 calculated by formula (1) into the following formula to calculate the equilibrium concentration of carbon dioxide in water at carbon dioxide equilibrium:

[0021]

[0022] Among them, A [(aq)] The concentration of CO2 dissolved in seawater. This represents the partial pressure of CO2 in the gas phase under equilibrium conditions.

[0023] Partial pressure of gaseous CO2 under equilibrium conditions Represented as:

[0024]

[0025] in, For measuring the mole fraction of carbon dioxide in the blown gas using a carbon dioxide measuring instrument 9, P 总 The carbon dioxide measuring instrument 9 measures the total gas pressure inside the room.

[0026] Substituting formulas (1) and (3) into formula (2), we obtain the dissolved carbon dioxide concentration when the device is placed in seawater at different depths. The calculation formula is as follows:

[0027]

[0028] A further technical solution of the present invention is as follows: The specific operation procedure for sinking the device for measuring the dissolved carbon dioxide concentration in seawater at different depths using the bubbling method to the depth of the desired carbon dioxide concentration in seawater is as follows: the solenoid valve is closed, and the motor controls the weight at the lower end of the traction rope to sink the device; when the liquid surface inside the device contacts the higher liquid level sensor, the motor stops working and the weight stops sinking; the air pump is turned on, connecting the second air inlet and outlet of the three-way valve, and external air is pumped into the upper space of the device through the air pump and the one-way valve, which increases the air pressure in the upper space of the bubbling measuring bottle, causing the liquid surface inside to move downward; when the liquid surface touches the lower liquid level sensor, the air pump is turned off, and the motor controls the weight at the lower end of the traction rope to continue to pull the device downward, repeating this process until the desired measurement depth is reached.

[0029] A further technical solution of the present invention is: the formula for calculating the depth of the device in seawater is:

[0030]

[0031] Where L is latitude, in degrees; P is underwater pressure measured by temperature, humidity and water pressure sensors, in decibars (1 decibar = 0.01 MPa); and ρ is the density of seawater, in kg / m³. 3 g is the acceleration due to gravity, with units of m / s². 2 P0 is the atmospheric pressure at the sea surface, measured in Pa; Z is the depth, measured in meters.

[0032] A further technical solution of the present invention is: the formula for calculating the depth of the device in seawater is:

[0033]

[0034] Where L is latitude, in degrees; P is underwater pressure measured by temperature, humidity and water pressure sensors, in decibars (1 decibar = 0.01 MPa); and ρ is the density of seawater, in kg / m³. 3 Z represents depth, measured in meters (m).

[0035] Compared with the prior art, the present invention has the following characteristics:

[0036] (1) The device for measuring carbon dioxide concentration of the present invention has a simple structure, is easy to use, and does not require water sampling, which greatly saves measurement costs.

[0037] (2) The method for measuring carbon dioxide concentration in this invention is simple and highly sensitive, reduces various factors that affect the observation data of carbon dioxide in seawater, and improves the measurement accuracy.

[0038] (3) The present invention can realize continuous real-time detection and monitor the changes in carbon dioxide content in seawater, and the observation data of carbon dioxide in seawater is more stable and accurate.

[0039] The detailed structure of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0040] Appendix Figure 1 This is a schematic diagram of the carbon dioxide concentration measuring device according to Embodiment 1 of the present invention;

[0041] Appendix Figure 2 This is a schematic diagram of the bottom structure of the bubbling device;

[0042] Appendix Figure 3 This is a schematic diagram of the carbon dioxide concentration measuring device according to Embodiment 2 of the present invention. Detailed Implementation

[0043] Example 1, as shown in the appendix Figure 1-2 As shown, the device for measuring the concentration of dissolved carbon dioxide in seawater at different depths using the bubbling method includes a bubbling measuring bottle 1, a bottle cap 2, an outlet pipe sleeve 3, a weight rope sleeve 4, an inlet pipe sleeve 5, an outlet pipe 6, an inlet pipe 7, a solenoid valve 8, a carbon dioxide measuring instrument 9, a three-way valve 10, an air pump 11, a motor 12, a one-way valve 13, a weight 14, and a data acquisition and processing center (not shown in the figure).

[0044] The bubbling measuring bottle 1 has a three-dimensional conical structure with multiple water inlets 1-1 at its bottom. When the bubbling measuring bottle 1 is placed in seawater, seawater can enter the interior of the bubbling measuring bottle 1 through the multiple water inlets 1-1. Temperature, humidity, and water pressure sensors 15 and a salinity sensor 16 are located at the bottom of the bubbling measuring bottle 1 to measure the temperature T and water pressure F1 at the bottom of the bubbling measuring bottle 1, as well as the salinity S of the seawater. A pressure sensor 17 is located at the air inlet of the carbon dioxide meter 9. During measurement, the air inlet section is connected to the upper space of the bubbling measuring bottle 1, and the pressure F2 in the upper space of the bubbling measuring bottle 1 can be accurately determined by the reading of the pressure sensor 17. Two liquid level sensors 18 are respectively located on the upper and lower inner walls of the bubbling measuring bottle 1 to define the upper and lower limits of the liquid level in the bubbling measuring bottle 1.

[0045] The air outlet sleeve 3, the weight rope sleeve 4, and the air inlet sleeve 5 are respectively installed on the bottle cap 2. The air outlet pipe 6 is inserted into the air outlet sleeve 3, and the air inlet pipe 7 is inserted into the air inlet sleeve 5. The air inlet pipe 7 extends into the bottom of the bubbling measuring bottle 1 to facilitate sufficient contact between the air entering through the air inlet pipe 7 and the seawater. The air inlet end of the air outlet pipe 6 extends into the bubbling measuring bottle 1, and the air outlet end of the air outlet pipe 6 is connected to the air inlet end of the carbon dioxide measuring instrument 9 through the solenoid valve 8. The air outlet end of the carbon dioxide measuring instrument 9 is connected to the first air inlet A of the three-way valve 10, the second air inlet C of the three-way valve 10 is connected to the atmosphere, the air outlet B of the three-way valve 10 is connected to the air inlet end of the air pump 11, the air outlet end of the air pump 11 is connected to the air inlet of the one-way valve 13, and the air outlet of the one-way valve 13 is connected to the air inlet end of the air inlet pipe 7. The output end of motor 12 suspends a weight 14 via a traction rope. The traction rope passes through the weight rope loop 4 on the bottle cap 2 and the water inlet 1-1 at the bottom of the bubbling measuring bottle 1, causing the weight 14 to sink into the seawater, thereby reducing the impact of underwater ocean current disturbances on the device during the measurement process. The solenoid valve 8, carbon dioxide meter 9, three-way valve 10, air pump 11, motor 12, temperature, humidity and water pressure sensors 15, salinity sensor 16, pressure sensor 17, and two liquid level sensors 18 are electrically connected to the data acquisition and processing center via wired or wireless means for data transmission and processing.

[0046] Example 2 is basically similar in structure to Example 1, except that, as shown in Example 2... Figure 3 As shown, in order to facilitate the generation of more bubbles from the air entering through the air inlet pipe 7 and to allow them to come into contact with the water in the bubbling measuring bottle 1, the end of the air inlet pipe 7 that extends into the bubbling measuring bottle 1 is designed as a porous cavity.

[0047] Example 3: A method for measuring the concentration of dissolved carbon dioxide in seawater at different depths using the bubbling method applied in Example 1 or Example 2, including the measurement process and the calculation process.

[0048] I. Measurement Process

[0049] The weight 14 at the lower end of the traction rope of the motor 12 is submerged in the water. Seawater enters the bubble measuring bottle 1 through the water inlet 1-1 at the bottom of the bubble measuring bottle 1. The data from the two liquid level sensors 18 are used to control the three-way valve 10, the air pump 11 and the one-way valve 13, so that the device for measuring the concentration of dissolved carbon dioxide in seawater at different depths by the bubble method sinks into the seawater at the depth of the carbon dioxide concentration to be measured.

[0050] The specific operating procedure for sinking the device for measuring the dissolved carbon dioxide concentration in seawater at different depths using the bubbling method to the depth of the desired carbon dioxide concentration is as follows: The solenoid valve 8 is closed, and the motor 12 controls the weight 14 at the lower end of the traction rope to sink the device. When the liquid surface inside the device contacts the higher-positioned liquid level sensor 18, the motor 12 stops working, and the weight 14 stops sinking. The air pump 11 is turned on, connecting the second air inlet C and the air outlet B of the three-way valve 10, pumping external air into the upper space of the device through the air pump 11 and the one-way valve 13, increasing the air pressure in the upper space of the bubbling measuring bottle 1, causing the liquid surface inside to move downwards. When the liquid surface touches the lower-positioned liquid level sensor 18, the air pump 11 is turned off, and the motor 12 controls the weight 14 at the lower end of the traction rope to continue pulling the device downwards. This process is repeated until the desired measurement depth is reached.

[0051] Open the solenoid valve 8 and the one-way valve 13, start the air pump 11, and connect the first air inlet A and the air outlet B of the three-way valve 10. Under the action of the air pump 11, the bubbles bulging out of the bubble measuring bottle 1 enter the carbon dioxide measuring instrument 9 through the air outlet pipe 6 and the solenoid valve 8, and flow out of the carbon dioxide measuring instrument 9 into the three-way valve 10, the air pump 11, the one-way valve 13, and finally flow back into the bubble measuring bottle 1 to form an airflow loop.

[0052] Bubbles bulging from the bottom of the inlet pipe 7 come into contact with seawater in the bubbling measuring bottle 1 and then bubble out from the liquid surface inside the bottle 1. After contacting the seawater, the bubbles enter the carbon dioxide measuring instrument 9 through the outlet pipe 6. Once the airflow stabilizes, the carbon dioxide measuring instrument 9 measures the carbon dioxide concentration in the bulging gas. And the carbon dioxide concentration Temperature T, water pressure F1 at the bottom of bubbling measuring bottle 1, salinity S, pressure F2 in the upper space of bubbling measuring bottle 1, and liquid level position signals of bubbling measuring bottle 1, respectively, are measured by temperature and humidity sensor 15, water pressure sensor 16, pressure sensor 17, and two liquid level sensors 18 and sent to the data acquisition and processing center.

[0053] II. Calculation Process

[0054] When measuring the concentration of dissolved carbon dioxide in seawater, it is necessary to measure the solubility of carbon dioxide and convert the concentration from the gas phase to the water phase. Carbon dioxide molecules continuously enter or leave the ocean surface, and when the exchange rate is equal, an equilibrium state is reached. At this time, the concentration of carbon dioxide in the atmosphere and water phase remains unchanged over time, and the carbon dioxide concentration is in equilibrium between water and circulating air.

[0055] Substituting the measured temperature T and salinity S into the following empirical equation for gas solubility in seawater versus water temperature and salinity, the solubility coefficient K0 of carbon dioxide can be calculated:

[0056]

[0057] Where T is the temperature measured by temperature, humidity and water pressure sensor 15, in Kelvin; S is the salinity measured by salinity sensor 16, in grams per kilogram; and K0 is the solubility coefficient of carbon dioxide, in mol (L·atm). -1 .

[0058] Since the carbon dioxide concentration measured by the carbon dioxide meter 9 is the data when carbon dioxide reaches water / air equilibrium, the equilibrium concentration of carbon dioxide in the air measured by the carbon dioxide meter 9 is converted into the corresponding carbon dioxide concentration in the water, thus obtaining the carbon dioxide concentration in the seawater at that depth. The solubility coefficient K0 of carbon dioxide calculated by formula (1) is substituted into the following formula to calculate the equilibrium concentration of carbon dioxide in the water at carbon dioxide equilibrium:

[0059]

[0060] Among them, A [(aq)] The concentration of CO2 dissolved in seawater. This represents the partial pressure of CO2 in the gas phase under equilibrium conditions.

[0061] Partial pressure of gaseous CO2 under equilibrium conditions Represented as:

[0062]

[0063] in, For measuring the mole fraction of carbon dioxide in the blown gas using a carbon dioxide measuring instrument 9, P 总 The carbon dioxide measuring instrument 9 measures the total gas pressure in the room, i.e., F2.

[0064] Substituting formulas (1) and (3) into formula (2), we obtain the dissolved carbon dioxide concentration when the device is placed in seawater at different depths. The calculation formula is as follows:

[0065]

[0066] The formula for calculating the depth of the device in seawater is as follows:

[0067]

[0068] Where L is latitude in degrees (°); P is the underwater pressure measured by temperature and humidity sensor 15 in decibar (1 decibar = 0.01 MPa); and ρ is the density of seawater in kg / m³. 3 g is the acceleration due to gravity, with units of m / s². 2 P0 is the atmospheric pressure at the sea surface, measured in Pa; Z is the depth, measured in meters.

[0069] The density ρ of seawater was calculated using the GSW Oceanography Toolbox based on TEOS-10 in conjunction with MATLAB or Python coding.

[0070] Example 4 is basically similar to Example 3, except that the formula for calculating the depth of the device in seawater is as follows:

[0071]

[0072]

[0073] Where L is latitude in degrees (°); P is the underwater pressure measured by temperature and humidity sensor 15 in decibar (1 decibar = 0.01 MPa); and ρ is the density of seawater in kg / m³. 3 Z represents depth, measured in meters (m).

Claims

1. A device for measuring the concentration of dissolved carbon dioxide in seawater at different depths using the bubbling method, characterized by: Includes bubbling measuring bottle, bottle cap, gas outlet sleeve, weight rope sleeve, gas inlet sleeve, gas outlet pipe, gas inlet pipe, solenoid valve, carbon dioxide measuring instrument, three-way valve, air pump, motor, one-way valve, weight, and data acquisition and processing center; The bubbling measuring bottle has a three-dimensional conical structure with multiple water inlets at the bottom. Temperature, humidity, water pressure, and salinity sensors are located at the bottom inside the bubbling measuring bottle. A pressure sensor is located at the air inlet of the carbon dioxide measuring instrument. Two liquid level sensors are located on the upper and lower inner walls of the bubbling measuring bottle, respectively. The outlet sleeve, weight rope sleeve, and inlet sleeve are respectively installed on the bottle cap. The outlet pipe is inserted into the outlet sleeve, and the inlet pipe is inserted into the inlet sleeve. The inlet pipe extends into the bottom of the bubbling measuring bottle. The inlet end of the outlet pipe extends into the bubbling measuring bottle. The outlet end of the outlet pipe is connected to the inlet end of the carbon dioxide measuring instrument through a solenoid valve. The outlet end of the carbon dioxide measuring instrument is connected to the first inlet of the three-way valve. The second inlet of the three-way valve is connected to the atmosphere. The outlet of the three-way valve is connected to the inlet end of the air pump. The outlet end of the air pump is connected to the inlet of the one-way valve. The outlet of the one-way valve is connected to the inlet end of the inlet pipe. The motor output end suspends a heavy object via a traction rope. The traction rope passes through the weight rope loop on the bottle cap and the water inlet at the bottom of the bubbling measuring bottle, causing the heavy object to sink into the seawater. The solenoid valve, carbon dioxide meter, three-way valve, air pump, motor, temperature, humidity and water pressure sensors, salinity sensor, pressure sensor, and two liquid level sensors are electrically connected to the data acquisition and processing center via wired or wireless means.

2. The apparatus for measuring the concentration of dissolved carbon dioxide in seawater at different depths using the bubbling method as described in claim 1, characterized in that: The end of the air inlet pipe that extends into the bubbling measuring bottle is a porous cavity.

3. A method for measuring the concentration of dissolved carbon dioxide in seawater at different depths using the bubbling method as described in claim 1 or 2, characterized in that: Including the measurement process and the calculation process, I. Measurement Process The weight at the lower end of the motor traction rope is submerged in the water. Seawater enters the bubble measuring bottle through the water inlet at the bottom of the bubble measuring bottle. The data of the two liquid level sensors are measured and the three-way valve, air pump and check valve are controlled so that the device for measuring the concentration of dissolved carbon dioxide in seawater at different depths by the bubble method sinks into the seawater at the depth of the carbon dioxide concentration to be measured. Open the solenoid valve and check valve, start the air pump, and connect the first air inlet and outlet of the three-way valve. The bubbles that are bubbling out of the bubbling measurement bottle come into contact with the seawater in the bubbling measurement bottle and are bubbled out from the liquid surface in the bubbling measurement bottle. They enter the carbon dioxide measuring instrument through the air outlet pipe and solenoid valve, and flow out of the carbon dioxide measuring instrument into the three-way valve, air pump, and check valve, and finally flow back into the bubbling measurement bottle to form an airflow loop. After the airflow stabilizes, the carbon dioxide meter measures the carbon dioxide concentration in the bubbling gas; and sends the measured temperature, water pressure at the bottom of the bubbling measuring bottle, salinity, pressure in the upper space of the bubbling measuring bottle, and liquid level position signals of the bubbling measuring bottle to the data acquisition and processing center. II. Calculation Process When measuring the concentration of dissolved carbon dioxide in seawater, it is necessary to measure the solubility of carbon dioxide and convert the concentration from the gas phase to the water phase; the concentration of carbon dioxide in the atmosphere and water phase remains constant over time, and a carbon dioxide concentration equilibrium is reached between water and circulating air. The measured temperature and salinity were substituted into the following empirical equation for the solubility of gases in seawater in relation to water temperature and salinity to calculate the solubility coefficient K0 of carbon dioxide: Where T is the temperature measured by the temperature, humidity, and water pressure sensors, in Kelvin; S is the salinity measured by the salinity sensor, in grams per kilogram; and K0 is the solubility coefficient of carbon dioxide, in mol (L·atm). -1 ; Substitute the carbon dioxide solubility coefficient K0 calculated by formula (1) into the following formula to calculate the equilibrium concentration of carbon dioxide in water at carbon dioxide equilibrium: Among them, A [(aq)] The concentration of CO2 dissolved in seawater. This represents the partial pressure of CO2 in the gas phase under equilibrium conditions. Partial pressure of gaseous CO2 under equilibrium conditions Represented as: in, To measure the mole fraction of carbon dioxide in the blown gas using a carbon dioxide measuring instrument, P 总 The carbon dioxide meter is used to measure the total gas pressure inside the room. Substituting formulas (1) and (3) into formula (2), we obtain the dissolved carbon dioxide concentration when the device is placed in seawater at different depths. The calculation formula is as follows:

4. The method as described in claim 3, characterized in that: The specific operating procedure for sinking the device for measuring the dissolved carbon dioxide concentration in seawater at different depths using the bubbling method to the depth of the desired carbon dioxide concentration is as follows: The solenoid valve is closed, and the motor controls the weight at the lower end of the traction rope to sink the device. When the liquid surface inside the device contacts the higher-positioned liquid level sensor, the motor stops working, and the weight stops sinking. The air pump is turned on, connecting the second air inlet and outlet of the three-way valve, pumping external air into the upper space of the device through the air pump and one-way valve, increasing the air pressure in the upper space of the bubbling measuring bottle, causing the liquid surface inside to move downwards. When the liquid surface touches the lower-positioned liquid level sensor, the air pump is turned off, and the motor controls the weight at the lower end of the traction rope to continue pulling the device downwards. This process is repeated until the desired measurement depth is reached.

5. The method as described in claim 3 or 4, characterized in that: The formula for calculating the depth of the device in seawater is as follows: Where L is latitude, in degrees; P is underwater pressure measured by temperature, humidity and water pressure sensors, in decibars (1 decibar = 0.01 MPa); and ρ is the density of seawater, in kg / m³. 3 g is the acceleration due to gravity, with units of m / s². 2 P0 is the atmospheric pressure at the sea surface, measured in Pa; Z is the depth, measured in meters.

6. The method as described in claim 3 or 4, characterized in that: The formula for calculating the depth of the device in seawater is as follows: Where L is latitude, in degrees; P is underwater pressure measured by temperature, humidity and water pressure sensors, in decibar, 1 decibar = 0.01 MPa; and Z is depth, in meters.

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