Laser spectroscopy online observation of atmospheric water vapor stable isotopes and calibration method

Abstract

This invention discloses an online observation and calibration method for stable isotopes of atmospheric water vapor using laser spectroscopy. The method includes: acquiring standard water vapor and atmospheric water vapor stable isotope data; performing memory effect calibration by selecting a specific time period and limiting the standard deviation range to eliminate residual errors; calculating the minute drift between two consecutive concentrated standard sample tests to perform drift effect calibration over time; establishing a nonlinear fitting relationship between the difference in standard water vapor concentration and the difference in stable isotopes to perform concentration effect calibration; and finally, establishing a linear mapping relationship between the instrument's average test value at the reference concentration and the true value of the standard sample to complete the true value standardization. This invention systematically eliminates the comprehensive systematic errors such as memory, drift, and concentration generated in online laser spectrometer observations, ensuring the long-term accuracy and reliability of the observation data.

Description

Technical Field

[0001] This invention relates to the field of isotope testing technology, and in particular to a method for online observation and calibration of stable isotopes of atmospheric water vapor using laser spectroscopy. Background Technology

[0002] Stable water isotopes, as natural tracers of atmospheric water cycle processes such as evaporation, transport, mixing, and precipitation, have significant application value in research fields such as hydrology, climatology, and meteorology. Traditional atmospheric water vapor stable isotope determination mainly relies on cryogenic cold trap technology for water vapor collection, followed by offline testing using isotope mass spectrometry. However, this traditional method has limitations such as cumbersome operation, time-consuming and labor-intensive processes, and low sample collection temporal resolution. In recent years, with the rapid development of laser spectroscopy, atmospheric water vapor stable isotope analysis technology based on laser spectrometers has gradually matured. With its high sensitivity and high degree of automation, this technology makes real-time, continuous, and high temporal resolution online observation of atmospheric water vapor stable isotopes a reality, greatly promoting in-depth research in related disciplines.

[0003] Although laser spectroscopy technology demonstrates significant advantages in online continuous observation, in practical applications, interference from factors such as the instrument's internal optical structure and the external testing environment can easily lead to systematic errors in online observation, causing the instrument's direct measurements to deviate from the sample's true values. Specifically, existing technologies mainly face the following three accuracy obstacles: First, the memory effect: when samples are alternately introduced into the instrument's optical cavity, the residue from previous samples is often difficult to remove instantly and completely, thus introducing background interference to the testing of subsequent samples; second, the drift effect: with long-term continuous operation of the instrument, aging of optical components and attenuation of the cavity lens reflectivity can cause a non-negligible baseline drift in the test results of samples of the same concentration over time; and finally, the concentration effect: due to the differences in spectral absorption peaks at different water vapor concentrations, water vapor with the same isotopic true value exhibits linear or non-linear testing deviations under different concentration conditions. In summary, the industry currently lacks a systematic, scientific, standardized observation procedure and calibration method to simultaneously eliminate the combined errors caused by the memory effect, drift effect, and concentration effect, making it difficult to guarantee the long-term accuracy and reliability of online observation data. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the aforementioned existing problems, this invention is proposed. Therefore, this invention provides a method for online observation and calibration of stable isotopes of atmospheric water vapor using laser spectroscopy, to address the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for online observation and calibration of stable isotopes of atmospheric water vapor using laser spectroscopy, comprising: Stable isotope data of water vapor in standard samples and stable isotope data of atmospheric water vapor are acquired using a laser spectrometer and its standard sample transmission module. The stable isotope data of water vapor in standard samples includes test data at a reference water vapor concentration and other different water vapor concentrations. The test data is acquired through routine standard sample testing and periodic centralized standard sample testing. The obtained standard water vapor stable isotope data and atmospheric water vapor stable isotope data are calibrated for memory effect. By extracting test data for a specific time period and limiting the standard deviation range of the data, error data caused by memory effect is eliminated, and calibrated data that meets the accuracy requirements is retained. Drift effect calibration is performed on the stable isotope data of standard water vapor after calibration based on memory effect. By calculating the drift rate of the stable isotope of standard water vapor at the reference water vapor concentration during two consecutive centralized standard sample tests, the drift compensation of the stable isotope data of standard water vapor and atmospheric water vapor isotope data is performed over time. Concentration effect calibration is performed on the stable isotope data of standard water vapor after drift effect calibration. By establishing a nonlinear fitting relationship between the concentration difference of standard water vapor relative to the reference water vapor concentration at different concentrations and the stable isotope difference, the concentration offset of atmospheric water vapor stable isotope data is calculated and compensated. Based on the concentration effect-calibrated atmospheric water vapor stable isotope data, true value standardization processing is performed. By establishing a linear mapping relationship between the instrument's average stable isotope test value at the reference water vapor concentration and the true value of the standard sample, the concentration effect-calibrated atmospheric water vapor stable isotope data is transformed into the final atmospheric water vapor stable isotope true values.

[0007] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By strictly setting the data extraction time window (excluding the first 5 minutes and the last 30 seconds) and limiting the standard deviation range of the data ( and It can accurately filter out the interference of residual background values ​​of previous samples caused by the alternation of samples, and retain high-precision effective data.

[0008] 2. By combining routine testing with centralized standard sample testing every two months, the minute drift is calculated to dynamically compensate for baseline drift caused by aging of instrument optical components and attenuation of lens reflectivity, effectively overcoming the time accumulation error caused by long-term instrument operation.

[0009] 3. By conducting gradient standard sample tests over a very wide concentration range (4000ppmv to 40000ppmv), a univariate quadratic polynomial nonlinear fitting equation was constructed between the difference in water vapor concentration of the standard samples and the difference in stable isotopes, which effectively corrected the test deviation caused by the difference in spectral absorption peaks under different water vapor concentrations.

[0010] 4. By establishing a linear univariate mapping relationship between the calibrated average test value at the reference water vapor concentration and the true value of the liquid standard sample, the instrument observations are ultimately transformed into the standard true values. This allows online observation data to be directly compared with test results from traditional cold trap technology or other analytical instruments, greatly improving the data's versatility and scientific research application value. Attached Figure Description

[0011] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a flowchart illustrating the overall process of an online observation and calibration method for stable isotopes of atmospheric water vapor using laser spectroscopy, according to one embodiment of the present invention. Figure 2 This is a comparison chart of the online observation data after calibration and the results of atmospheric water vapor stable isotope collection by cold trap, based on the laser spectroscopy method for online observation and calibration of atmospheric water vapor stable isotopes according to an embodiment of the present invention. Detailed Implementation

[0012] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0013] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0014] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0015] This invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of this invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not be construed as limiting the scope of protection of this invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0016] Furthermore, in the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In addition, the terms "first," "second," or "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0017] Unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" in this invention should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; similarly, they can refer to mechanical connections, electrical connections, or direct connections, or indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0018] Reference Figure 1 and Figure 2 This is the first embodiment of the present invention, which provides a method for online observation and calibration of stable isotopes of atmospheric water vapor using laser spectroscopy, including: S1: Obtain stable isotope data of standard water vapor and stable isotope data of atmospheric water vapor.

[0019] Furthermore, stable isotope data of standard water vapor and stable isotope data of atmospheric water vapor were acquired using a laser spectrometer and its Standards Delivery Module System (SDM). The specific process is as follows: First, two liquid standard samples with known stable isotope values ​​are extracted from the standard sample bag and injected into the vaporization chamber to vaporize into water vapor. This process is to vaporize the liquid standard samples while avoiding isotope fractionation. Simultaneously, an air pump is used to sequentially pass the air in the chamber through a filter, a flow restrictor, and a drying tube to convert it into dry air with a water vapor concentration below a preset threshold (300 ppmv). Subsequently, the water vapor from the standard samples and the dry air are thoroughly mixed in the vaporization chamber and then delivered to the optical cavity of the laser spectrometer for testing.

[0020] Furthermore, in terms of observation mode, test data are obtained through routine standard sample testing and periodic centralized standard sample testing.

[0021] Specifically, routine standard sample testing is conducted every 24 hours, with each test lasting approximately 2.5 hours. By adjusting the injection rate of the standard sample, three different water vapor concentrations are set for testing. One of these concentrations is set as a reference water vapor concentration of 20000±1000 ppmv, while the other two are set based on the range of atmospheric water vapor concentration variations during the observation.

[0022] Specifically, the periodic centralized standard sample testing cycle is set at two months. During this testing, the injection rate of the liquid standard sample is adjusted to gradually increase and then decrease the mixed water vapor concentration between 4000 ppmv and 40000 ppmv in 2000 ppmv increments. Each water vapor concentration is tested twice in the centralized standard sample test to fully characterize the concentration effect and ensure its stability. After the standard sample test is completed, the laser spectrometer automatically switches to online observation mode for stable isotopes of atmospheric water vapor. The atmospheric water vapor inlet is installed in an open, unobstructed environment, connected to a PTFE pipe equipped with a pump. Atmospheric water vapor enters the laser spectrometer through this pipe for stable isotope testing. This process only requires manual operation during the initial setup of the water vapor inlet device; once operational, online observation is automatically performed by the laser spectrometer.

[0023] S2: Perform memory effect calibration.

[0024] Furthermore, the acquired stable isotope data of standard water vapor and atmospheric water vapor were screened using the data processing software built into the laser spectrometer to eliminate memory effect errors caused by incomplete removal of residues from previous samples. The specific procedures are as follows: First, for each set of test data, data from the first 5 minutes of the test and the last 30 seconds of the test were removed. Second, the standard deviation range of the data was limited: the oxygen isotope standard deviation in each standard water vapor stable isotope data after removal must be less than 0.2‰ (i.e., The standard deviation of hydrogen isotopes must be less than 0.5‰ (i.e., For data that does not meet the standard, mark it and view its trend over time. Repeat the above elimination and screening steps for a relatively stable time period until the standard deviation requirement is met. Finally, after screening, recalculate. If the total duration of the remaining continuous test data is less than 5 minutes, the data is considered invalid and deleted. The data calibrated for memory effect is retained and will be used in subsequent calculations.

[0025] S3: Perform drift effect calibration.

[0026] Furthermore, as the instrument is used over time, factors such as the aging of optical components can cause baseline drift in the test results. Based on the data calibrated for the memory effect, drift compensation is performed by calculating the minute drift between two consecutive tests of the central standard sample. The formula for calculating the minute drift is as follows: in, This represents the calculated drift per minute. This represents the average stable isotope value of water vapor at a reference water vapor concentration (20000±1000ppmv) during the first centralized standard sample test. This represents the average stable isotope value of water vapor at the same reference water vapor concentration during the second centralized standard sample test. This indicates the time interval between two consecutive centralized standard sample tests, in minutes.

[0027] Furthermore, time-varying drift compensation was then performed on the stable isotope data of the standard water vapor, calculated using the following formula: in, This represents the stable isotope value of water vapor in the standard sample after calibration for the drift effect; This represents the stable isotope value of water vapor in the standard sample before drift effect calibration (i.e., after only memory effect calibration); This indicates the drift time corresponding to this test data, in minutes.

[0028] It should be noted that, assuming the standard sample test results and the actual atmospheric water vapor observation results have the same minute drift, similarly, drift calibration of the atmospheric water vapor stable isotope data can be performed to obtain the drift-calibrated atmospheric water vapor stable isotope values. .

[0029] S4: Perform concentration effect calibration.

[0030] Furthermore, because the spectral absorption peaks differ at different water vapor concentrations, concentration-dependent calibration is required. Based on the drift-effect calibrated standard water vapor stable isotope data, two difference variables are pre-calculated: the water vapor concentration difference and the stable isotope difference. Furthermore, the formula for calculating the water vapor concentration difference is: in, This represents the difference in water vapor concentration. These are the actual water vapor concentration values ​​for different concentration subsamples; For reference water vapor concentration values.

[0031] Furthermore, the formula for calculating the stable isotope difference is: in, To stabilize isotope differences; Stable isotope values ​​of standard water vapor at different water vapor concentrations; The average stable isotope value at a reference water vapor concentration (20000±1000ppmv) after drift effect calibration.

[0032] Furthermore, a univariate quadratic polynomial nonlinear fitting relationship was established between the difference in water vapor concentration of the standard samples and the difference in stable isotopes: in, , and All are regression coefficients.

[0033] Furthermore, after obtaining the equation, compensation is performed on the stable isotope data of atmospheric water vapor. First, the atmospheric water vapor concentration difference is calculated. (in Substituting the atmospheric water vapor concentration into the above fitting equation, the atmospheric water vapor stable isotope shift value can be obtained. : Furthermore, the stable isotope values ​​of atmospheric water vapor after concentration effect calibration were calculated: in, These are the stable isotope values ​​of atmospheric water vapor after concentration effect calibration.

[0034] S5: Perform truth standardization.

[0035] Furthermore, to facilitate comparison with observations from other instruments, we need to convert the calibrated instrument test values ​​into data under the true value system of standard samples. First, we calculate the average stable isotope values ​​of the standard sample at the reference water vapor concentration (20000±1000ppmv) after concentration effect calibration. Secondly, this average value is compared with the true value of stable isotopes in liquid standard samples (…). The linear regression equation between the two variables is as follows: in, and These are the linear regression coefficients.

[0036] Furthermore, the atmospheric water vapor stable isotope data calibrated for concentration effects... Substituting these values ​​into the equation as independent variables transforms them into the final true values ​​of stable atmospheric water vapor isotopes. : It should be noted that, through the above process, all systematic errors can be calibrated online, resulting in high-precision atmospheric water vapor stable isotope observation data. (Refer to Table 1 and...) Figure 2 Comparative experiments conducted simultaneously using cold trap technology to collect atmospheric water vapor and perform stable isotope testing have demonstrated that the data calibrated by this method is basically consistent with the results collected by the cold trap, with the difference within a reasonable range, and is accurate and reliable.

[0037] Table 1

[0038] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0039] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0040] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0041] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0042] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0043] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for online observation and calibration of stable isotopes of atmospheric water vapor using laser spectroscopy, characterized in that, include: Stable isotope data of water vapor in standard samples and stable isotope data of atmospheric water vapor are acquired using a laser spectrometer and its standard sample transmission module. The stable isotope data of water vapor in standard samples includes test data at a reference water vapor concentration and other different water vapor concentrations. The test data is acquired through routine standard sample testing and periodic centralized standard sample testing. The obtained standard water vapor stable isotope data and atmospheric water vapor stable isotope data are calibrated for memory effect. By extracting test data for a specific time period and limiting the standard deviation range of the data, error data caused by memory effect is eliminated, and calibrated data that meets the accuracy requirements is retained. Drift effect calibration is performed on the stable isotope data of standard water vapor after calibration based on memory effect. By calculating the drift rate of the stable isotope of standard water vapor at the reference water vapor concentration during two consecutive centralized standard sample tests, the drift compensation of the stable isotope data of standard water vapor and atmospheric water vapor isotope data is performed over time. Concentration effect calibration is performed on the stable isotope data of standard water vapor after drift effect calibration. By establishing a nonlinear fitting relationship between the concentration difference of standard water vapor relative to the reference water vapor concentration at different concentrations and the stable isotope difference, the concentration offset of atmospheric water vapor stable isotope data is calculated and compensated. Based on the concentration effect-calibrated atmospheric water vapor stable isotope data, true value standardization processing is performed. By establishing a linear mapping relationship between the instrument's average stable isotope test value at the reference water vapor concentration and the true value of the standard sample, the concentration effect-calibrated atmospheric water vapor stable isotope data is transformed into the final atmospheric water vapor stable isotope true values.

2. The method for online observation and calibration of stable isotopes of atmospheric water vapor using laser spectroscopy as described in claim 1, characterized in that, The process of obtaining stable isotope data of standard water vapor includes: The liquid standard sample is injected into the vaporization chamber and vaporized into water vapor. The air is filtered and dried by a vacuum pump to dry air with a water vapor concentration less than a preset threshold. The water vapor of the standard sample and the dry air are mixed in the vaporization chamber and then transported to the optical cavity of the laser spectrometer for testing. The preset threshold is 300 ppmv, and the reference water vapor concentration is set to 20000±1000 ppmv.

3. The method for online observation and calibration of stable isotopes of atmospheric water vapor using laser spectroscopy as described in claim 2, characterized in that, The periodic centralized standard sample test is conducted every two months. In the centralized standard sample test, the injection rate of the liquid standard sample is adjusted so that the water vapor concentration after mixing gradually increases and then gradually decreases between 4000 ppmv and 40000 ppmv in intervals of 2000 ppmv, and each water vapor concentration is tested twice.

4. The method for online observation and calibration of stable isotopes of atmospheric water vapor using laser spectroscopy as described in claim 1, characterized in that, The operation of capturing a specific time period includes: For each set of test data, data from the first 5 minutes of the test and the last 30 seconds of the test were removed. After the elimination and filtering are completed, if the total duration of the remaining continuous test data is less than 5 minutes, the data is deemed invalid and deleted.

5. The method for online observation and calibration of stable isotopes of atmospheric water vapor using laser spectroscopy as described in claim 4, characterized in that, The range of standard deviations for the restricted data includes: The oxygen isotope standard deviation for each standard water vapor stable isotope data point must be less than 0.2‰ and the hydrogen isotope standard deviation must be less than 0.5‰. For data that does not meet the standard, the time period is reselected and repeatedly filtered by viewing the trend chart of its change over time until the standard deviation is met.

6. The method for online observation and calibration of stable isotopes of atmospheric water vapor using laser spectroscopy as described in claim 1, characterized in that, The operation of calculating drift rate specifically involves calculating the drift per minute, including: The isotope drift difference is obtained by subtracting the average stable isotope value of water vapor at the reference water vapor concentration during the second centralized standard sample test from the average stable isotope value of water vapor at the reference water vapor concentration during the first centralized standard sample test. The isotope drift difference is then divided by the time interval (in minutes) between the two consecutive centralized standard sample tests to obtain the minute drift amount.

7. The method for online observation and calibration of stable isotopes of atmospheric water vapor using laser spectroscopy as described in claim 6, characterized in that, The drift compensation includes: Multiply the minute drift amount by the drift time in minutes to obtain the drift compensation amount. Subtract this drift compensation amount from the standard sample water vapor stable isotope value and the atmospheric water vapor stable isotope value before drift calibration to obtain the standard sample water vapor stable isotope data and the atmospheric water vapor stable isotope data after drift effect calibration.

8. The method for online observation and calibration of stable isotopes of atmospheric water vapor using laser spectroscopy as described in claim 1, characterized in that, Before establishing the nonlinear fitting relationship, two difference variables are pre-calculated, including: The first difference variable is the water vapor concentration difference, which is calculated by subtracting the reference water vapor concentration value from the water vapor concentration value of different water vapor concentration subsamples. The second difference variable is the stable isotope difference, which is calculated by subtracting the average stable isotope value of the standard sample water vapor at the reference water vapor concentration from the stable isotope value of the standard sample water vapor at different water vapor concentrations.

9. The method for online observation and calibration of stable isotopes of atmospheric water vapor using laser spectroscopy as described in claim 8, characterized in that, The nonlinear fitting relationship is a univariate quadratic polynomial equation, which is generated by regression fitting with the water vapor concentration difference as the independent variable and the stable isotope difference as the dependent variable. When calculating the concentration shift of atmospheric water vapor stable isotope data, the difference between atmospheric water vapor concentration and reference water vapor concentration is substituted into the univariate quadratic polynomial equation as the independent variable to obtain the concentration shift. Finally, the atmospheric water vapor stable isotope value after drift effect calibration is subtracted from the concentration shift to obtain the atmospheric water vapor stable isotope value after concentration effect calibration.

10. The method for online observation and calibration of stable isotopes of atmospheric water vapor using laser spectroscopy as described in claim 1, characterized in that, The truth value normalization process includes: A linear regression equation was established, with the average stable isotope value of the reference water vapor concentration standard sample after concentration effect calibration as the independent variable and the true stable isotope value of the liquid standard sample as the dependent variable. The atmospheric water vapor stable isotope data calibrated for concentration effect are substituted into the linear regression equation and the calculated output is the true value of the atmospheric water vapor stable isotopes observed online.

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