A method and apparatus for laser spectroscopy of greenhouse gases

Abstract

The present application relates to the technical field of laser measurement, and particularly relates to a greenhouse gas laser spectrum measurement method and device. The method comprises the following steps: emitting laser to a ring-down cavity containing a to-be-measured gas by using a plurality of lasers with different wavelengths, obtaining a plurality of first absorption cross sections and a plurality of first ring-down times; the laser wavelengths of the plurality of lasers correspond to the strongest absorption peak wavelengths of a plurality of greenhouse gases one by one; emitting laser to the ring-down cavity containing the to-be-measured gas by using a plurality of lasers with different wavelengths, obtaining a plurality of second absorption cross sections and a plurality of second ring-down times; the laser wavelengths of the plurality of lasers correspond to the weakest absorption peak wavelengths of the plurality of greenhouse gases one by one; and calculating the concentrations of different greenhouse gases in the to-be-measured gas by using the plurality of first absorption cross sections, the plurality of second absorption cross sections, the plurality of first ring-down times and the plurality of second ring-down times. The present application provides a greenhouse gas laser spectrum measurement method and device, which can measure the concentration of greenhouse gas on line.

Description

Technical Field

[0001] This invention relates to the field of laser measurement technology, and in particular to a method and apparatus for laser spectral measurement of greenhouse gases. Background Technology

[0002] To monitor changes in the greenhouse effect and achieve the "dual carbon" target as soon as possible, greenhouse gas measurements are necessary. The World Meteorological Organization (WMO) has provided information on the types of greenhouse gases of concern, their current concentrations, and recommended measurement accuracies. Greenhouse gases include carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), with recommended measurement accuracies for each of these three gases being very high, specifically 0.2 ppm, 2 ppb, and 0.1 ppb. This level of accuracy is beyond the reach of semiconductor sensors and traditional tunable semiconductor laser absorption spectroscopy (TDLAS). Furthermore, measurement methods with high accuracy, such as gas chromatography (GC), mass spectrometry (MS), or gas chromatography-mass spectrometry (GC-MS), require sampling and analysis of the analyte under laboratory conditions, making online measurement impossible.

[0003] Therefore, in order to address the above shortcomings, there is an urgent need for a method and device that can measure greenhouse gas concentrations online. Summary of the Invention

[0004] This invention provides a laser spectral measurement method and apparatus for greenhouse gases, which can measure greenhouse gas concentrations online.

[0005] In a first aspect, embodiments of the present invention provide a method for measuring greenhouse gases using laser spectroscopy, comprising:

[0006] Multiple lasers with different wavelengths are used to emit lasers into a ring-down cavity containing the gas to be tested, thereby obtaining multiple first absorption cross-sections and multiple first ring-down times; wherein, the laser wavelengths of the multiple lasers correspond one-to-one with the strongest absorption peak wavelengths of various greenhouse gases.

[0007] Multiple lasers with different wavelengths are used to emit lasers into a ring-down cavity containing a gas to be tested, thereby obtaining multiple second absorption cross-sections and multiple second ring-down times; wherein, the laser wavelengths of the multiple lasers correspond one-to-one with the weakest absorption peak wavelengths of various greenhouse gases.

[0008] The concentrations of different greenhouse gases in the gas to be measured are calculated using multiple first absorption cross-sectional areas, multiple second absorption cross-sectional areas, multiple first decay times, and multiple second decay times.

[0009] In one possible design, each of the lasers can obtain a first absorption cross-sectional area for greenhouse gases and a first absorption cross-sectional area for water vapor;

[0010] Each of the lasers can obtain a second absorption cross-sectional area for greenhouse gases and a second absorption cross-sectional area for water vapor;

[0011] The laser spectroscopy measurement method further includes:

[0012] Adjust the wavelength of a laser so that it produces the strongest absorption peak for water vapor;

[0013] The laser is used to emit a laser beam into a ring-down cavity containing the gas to be measured, thereby obtaining the third absorption cross-sectional area and the third ring-down time.

[0014] The calculation of the concentrations of different greenhouse gases in the gas to be measured using multiple first absorption cross-sectional areas, multiple second absorption cross-sectional areas, multiple first ring-down times, and multiple second ring-down times includes:

[0015] The concentrations of different greenhouse gases in the gas to be measured are calculated using multiple first absorption cross-sectional areas, multiple second absorption cross-sectional areas, multiple first decay times, multiple second decay times, the third absorption cross-sectional area, and the third decay time.

[0016] In one possible design, multiple lasers of different wavelengths are used to emit laser light into a ring-down cavity containing the gas to be measured, thereby obtaining multiple first absorption cross-sections and multiple first ring-down times; wherein the laser wavelengths of the multiple lasers correspond one-to-one with the strongest absorption peak wavelengths of various greenhouse gases, including:

[0017] A first laser is used to emit a laser beam into a ring-down cavity containing the gas to be tested, thereby obtaining the first methane absorption cross-sectional area, the first water vapor absorption cross-sectional area, and the first methane ring-down time; wherein, the laser wavelength of the first laser is the same as the wavelength of the strongest absorption peak of methane.

[0018] A second laser is used to emit a laser beam into a ring-down cavity containing the gas to be measured, thereby obtaining the first carbon dioxide absorption cross-sectional area, the second water vapor absorption cross-sectional area, and the first carbon dioxide ring-down time; wherein, the laser wavelength of the second laser is the same as the wavelength of the strongest absorption peak of carbon dioxide.

[0019] A third laser is used to emit a laser beam into a ring-down cavity containing the gas to be tested, thereby obtaining the first nitrous oxide absorption cross-sectional area, the third water vapor absorption cross-sectional area, and the first nitrous oxide absorption cross-sectional area; wherein the laser wavelength of the third laser is the same as the wavelength of the strongest absorption peak of nitrous oxide.

[0020] In one possible design, multiple lasers of different wavelengths are used to emit laser light into a ring-down cavity containing the gas to be measured, thereby obtaining multiple second absorption cross-sections and multiple second ring-down times; wherein the laser wavelengths of the multiple lasers correspond one-to-one with the weakest absorption peak wavelengths of various greenhouse gases, including:

[0021] The first laser is used to emit a laser into a ring-down cavity containing the gas to be tested, thereby obtaining the second methane absorption cross-sectional area, the fourth water vapor absorption cross-sectional area, and the second methane ring-down time; wherein, the laser wavelength of the first laser is the same as the wavelength of the weakest absorption peak of methane.

[0022] The second laser is used to emit a laser into a ring-down cavity containing the gas to be measured, thereby obtaining the second carbon dioxide absorption cross-sectional area, the fifth water vapor absorption cross-sectional area, and the second carbon dioxide ring-down time; wherein, the laser wavelength of the second laser is the same as the wavelength of the weakest absorption peak of carbon dioxide.

[0023] The third laser is used to emit a laser beam into a ring-down cavity containing the gas to be tested, thereby obtaining the second nitrous oxide absorption cross-sectional area, the sixth water vapor absorption cross-sectional area, and the second nitrous oxide absorption cross-sectional area; wherein, the laser wavelength of the third laser is the same as the wavelength of the weakest absorption peak of nitrous oxide.

[0024] In one possible design, the third absorption cross-sectional area includes a strong water vapor absorption cross-sectional area and a third methane absorption cross-sectional area;

[0025] The methane concentration in the gas to be tested is obtained by the following formula:

[0026]

[0027] Where Y is the methane concentration, c is the speed of light, and t is the velocity of light. a1 t is the first methane decay time. a2 t is the second methane oscillation time. a3 For the third oscillation time, Sh a1 Sh is the first water vapor absorption cross-sectional area. a2 Sh is the fourth water vapor absorption cross-sectional area. a3 Where is the cross-sectional area for strong water vapor absorption, Sy a1 Sy is the first methane absorption cross-sectional area. a2 The second methane absorption cross-sectional area, Sy a3 The third methane absorption cross-sectional area is given.

[0028] In one possible design, the concentration of water vapor in the gas to be measured is obtained by the following formula:

[0029]

[0030] Where H represents the concentration of water vapor.

[0031] In one possible design, the carbon dioxide concentration in the gas to be measured is obtained by the following formula:

[0032]

[0033] Where X is the concentration of carbon dioxide, t b1 t is the first carbon dioxide oscillation time. b2 The second carbon dioxide oscillation time, Sh b1 Sh is the second water vapor absorption cross-sectional area. b2 Sx is the fifth water vapor absorption cross-sectional area. b1 Sx is the first carbon dioxide absorption cross-sectional area. b2 This is the second carbon dioxide absorption cross-sectional area.

[0034] In one possible design, the concentration of nitrous oxide in the gas to be tested is calculated using the following formula:

[0035]

[0036] Where Z is the concentration of nitrous oxide, t c1 t is the first nitrous oxide oscillation time. c2 The second nitrous oxide oscillation time, Sh c1 Sh is the third water vapor absorption cross-sectional area. c2 Sz is the sixth water vapor absorption cross-sectional area. c1 Sz is the absorption cross-sectional area of ​​the first nitrous oxide. c2 This represents the absorption cross-sectional area of ​​the second nitrous oxide.

[0037] Secondly, embodiments of the present invention also provide a laser spectral measurement device for greenhouse gases, used to implement any of the methods described in the above embodiments, the device comprising a first laser unit, a second laser unit, a third laser unit, a ring-down cavity, and a receiving unit;

[0038] The ring-down cavity is composed of four cavity mirrors. The first laser unit, the second laser unit, and the third laser unit are used to emit wavelength-tunable lasers into the ring-down cavity so that the lasers are reflected and transmitted in the four cavity mirrors.

[0039] The receiving unit is used to receive the laser emitted from the ring-down cavity in order to obtain the ring-down time and absorption cross-sectional area.

[0040] In one possible design, the first laser unit, the second laser unit, and the third laser unit all include a laser and an optical path shaping module, and the receiving unit includes a receiver and a focusing lens.

[0041] Compared with the prior art, the present invention has at least the following beneficial effects:

[0042] In this embodiment, high-precision gas concentration measurements can be obtained using laser spectroscopy. Specifically, the wavelengths of multiple lasers are adjusted so that each laser's wavelength produces the strongest absorption peak for each greenhouse gas. Multiple lasers with different wavelengths are emitted into the ring-down cavity using these lasers, resulting in multiple first absorption cross-sections and multiple first ring-down times. Then, the wavelengths of the multiple lasers are adjusted so that each laser's wavelength produces the weakest absorption peak for each greenhouse gas, equivalent to the cavity ring-down time. Multiple lasers with different wavelengths are emitted into the ring-down cavity, resulting in multiple second absorption cross-sections and multiple second ring-down times. These multiple second absorption cross-sections and multiple second ring-down times correspond to a standard zero value. Using these multiple second absorption cross-sections and multiple second ring-down times as a standard, combined with the first absorption cross-section and first ring-down time under the strong absorption peak, the concentrations of different greenhouse gases in the gas being measured can be obtained.

[0043] It should be noted that the wavelengths of both the strongest and weakest absorption peaks can be obtained through calculation. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of a laser spectroscopy measurement method provided in an embodiment of the present invention.

[0046] In the picture:

[0047] 1-First laser;

[0048] 2-Second laser;

[0049] 3-Third laser;

[0050] 4-Laparoscope;

[0051] 5-Optical path shaping module;

[0052] 6-Focusing lens;

[0053] 7- Receiver. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0055] In the description of the embodiments of the present invention, unless otherwise expressly specified and limited, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; unless otherwise specified or stated, the term "multiple" refers to two or more; the terms "connected," "fixed," etc., should be interpreted broadly. For example, "connected" can be a fixed connection, a detachable connection, an integral connection, or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0056] In this specification, it should be understood that the directional terms such as "upper" and "lower" used in the description of the embodiments of the present invention are used to describe the angles shown in the accompanying drawings and should not be construed as limiting the embodiments of the present invention. Furthermore, in the context, it should also be understood that when it is mentioned that one element is connected "upper" or "lower" to another element, it can be directly connected to the other element "upper" or "lower," or indirectly connected to the other element "upper" or "lower" through an intermediate element.

[0057] This invention provides a method for measuring greenhouse gases using laser spectroscopy, comprising:

[0058] Multiple lasers with different wavelengths are used to emit lasers into a ring-down cavity containing the gas to be tested, thereby obtaining multiple first absorption cross-sections and multiple first ring-down times; wherein, the laser wavelengths of the multiple lasers correspond one-to-one with the strongest absorption peak wavelengths of various greenhouse gases.

[0059] Multiple lasers with different wavelengths are used to emit lasers into a ring-down cavity containing the gas to be measured, thereby obtaining multiple second absorption cross-sections and multiple second ring-down times; wherein, the laser wavelengths of the multiple lasers correspond one-to-one with the weakest absorption peak wavelengths of various greenhouse gases.

[0060] The concentrations of different greenhouse gases in the gas to be measured are calculated using multiple first absorption cross-sectional areas, multiple second absorption cross-sectional areas, multiple first ring-down times, and multiple second ring-down times.

[0061] In this embodiment, high-precision gas concentration measurements can be obtained using laser spectroscopy. Specifically, the wavelengths of multiple lasers are adjusted so that each laser's wavelength produces the strongest absorption peak for each greenhouse gas. Multiple lasers with different wavelengths are emitted into the ring-down cavity using these lasers, resulting in multiple first absorption cross-sections and multiple first ring-down times. Then, the wavelengths of the multiple lasers are adjusted so that each laser's wavelength produces the weakest absorption peak for each greenhouse gas, equivalent to the cavity ring-down time. Multiple lasers with different wavelengths are emitted into the ring-down cavity, resulting in multiple second absorption cross-sections and multiple second ring-down times. These multiple second absorption cross-sections and multiple second ring-down times correspond to a standard zero value. Using these multiple second absorption cross-sections and multiple second ring-down times as a standard, combined with the first absorption cross-section and first ring-down time under the strong absorption peak, the concentrations of different greenhouse gases in the gas being measured can be obtained.

[0062] It should be noted that the wavelengths of both the strongest and weakest absorption peaks can be obtained through calculation.

[0063] In some embodiments of the present invention, each laser can obtain a first absorption cross-sectional area for a greenhouse gas and a first absorption cross-sectional area for water vapor.

[0064] Each laser can obtain a second absorption cross-section for a greenhouse gas and a second absorption cross-section for water vapor;

[0065] Laser spectroscopy measurement methods also include:

[0066] Adjust the wavelength of a laser so that it produces the strongest absorption peak for water vapor;

[0067] The laser is used to emit a laser beam into a ring-down cavity containing the gas to be measured, thereby obtaining the third absorption cross-sectional area and the third ring-down time.

[0068] The concentrations of different greenhouse gases in the analyte are calculated using multiple first absorption cross-sections, multiple second absorption cross-sections, multiple first ring-down times, and multiple second ring-down times, including:

[0069] The concentrations of different greenhouse gases in the gas to be measured are calculated using multiple first absorption cross-sectional areas, multiple second absorption cross-sectional areas, multiple first decay times, multiple second decay times, a third absorption cross-sectional area, and a third decay time.

[0070] Water vapor in the gas being tested can affect the measured concentration of greenhouse gases in the gas. Therefore, it is necessary to calculate the water vapor content in the gas being tested and then correct the greenhouse gas content based on the water vapor content to obtain a high-precision, low-error greenhouse gas concentration.

[0071] In some embodiments of the present invention, multiple lasers of different wavelengths are used to emit laser light into a ring-down cavity containing a gas to be measured, thereby obtaining multiple first absorption cross-sections and multiple first ring-down times; wherein the laser wavelengths of the multiple lasers correspond one-to-one with the strongest absorption peak wavelengths of various greenhouse gases, including:

[0072] A first laser is used to emit a laser beam into a ring-down cavity containing the gas to be measured, thereby obtaining the first methane absorption cross-sectional area, the first water vapor absorption cross-sectional area, and the first methane ring-down time; wherein, the laser wavelength of the first laser is the same as the wavelength of the strongest absorption peak of methane.

[0073] A second laser is used to emit a laser beam into a ring-down cavity containing the gas to be measured, thereby obtaining the first carbon dioxide absorption cross-sectional area, the second water vapor absorption cross-sectional area, and the first carbon dioxide ring-down time; wherein, the laser wavelength of the second laser is the same as the wavelength of the strongest absorption peak of carbon dioxide.

[0074] A third laser is used to emit a laser beam into a ring-down cavity containing the gas to be tested, thereby obtaining the first nitrous oxide absorption cross-sectional area, the third water vapor absorption cross-sectional area, and the first nitrous oxide absorption cross-sectional area; wherein, the laser wavelength of the third laser is the same as the wavelength of the strongest absorption peak of nitrous oxide.

[0075] Greenhouse gases in the air mainly include methane, carbon dioxide, and nitrous oxide. A first laser emits a laser beam that produces the strongest absorption peak for methane and is incident on a ring-down cavity to obtain the first methane absorption cross-sectional area, the first water vapor absorption cross-sectional area, and the first methane ring-down time. A second laser emits a laser that produces the strongest absorption peak for carbon dioxide and is incident on a ring-down cavity to obtain the first carbon dioxide absorption cross-sectional area, the second water vapor absorption cross-sectional area, and the first carbon dioxide ring-down time. A third laser emits a laser that produces the strongest absorption peak for nitrous oxide and is incident on a ring-down cavity to obtain the first nitrous oxide absorption cross-sectional area, the third water vapor absorption cross-sectional area, and the first nitrous oxide ring-down time.

[0076] In some embodiments of the present invention, multiple lasers of different wavelengths are used to emit laser light into a ring-down cavity containing a gas to be measured, thereby obtaining multiple second absorption cross-sections and multiple second ring-down times; wherein the laser wavelengths of the multiple lasers correspond one-to-one with the weakest absorption peak wavelengths of various greenhouse gases, including:

[0077] A first laser is used to emit a laser beam into a ring-down cavity containing the gas to be measured, thereby obtaining the second methane absorption cross-sectional area, the fourth water vapor absorption cross-sectional area, and the second methane ring-down time; wherein, the laser wavelength of the first laser is the same as the wavelength of the weakest absorption peak of methane.

[0078] A second laser is used to emit a laser beam into a ring-down cavity containing the gas to be measured, thereby obtaining the second carbon dioxide absorption cross-sectional area, the fifth water vapor absorption cross-sectional area, and the second carbon dioxide ring-down time; wherein, the laser wavelength of the second laser is the same as the wavelength of the weakest absorption peak of carbon dioxide.

[0079] A third laser is used to emit a laser beam into a ring-down cavity containing the gas to be tested, thereby obtaining the second nitrous oxide absorption cross-sectional area, the sixth water vapor absorption cross-sectional area, and the second nitrous oxide absorption cross-sectional area; wherein, the laser wavelength of the third laser is the same as the wavelength of the weakest absorption peak of nitrous oxide.

[0080] In this embodiment, the wavelength of the first laser is adjusted to the wavelength that produces the weakest absorption peak for methane. The first laser is used to emit laser light into the ring-down cavity to obtain the second methane absorption cross-sectional area, the fourth water vapor absorption cross-sectional area, and the second methane ring-down time. The second laser emits laser light that produces the weakest absorption peak for carbon dioxide and is incident on the ring-down cavity to obtain the second carbon dioxide absorption cross-sectional area, the fifth water vapor absorption cross-sectional area, and the second carbon dioxide ring-down time. The third laser emits laser light that produces the weakest absorption peak for nitrous oxide and is incident on the ring-down cavity to obtain the second nitrous oxide absorption cross-sectional area, the sixth water vapor absorption cross-sectional area, and the second nitrous oxide ring-down time.

[0081] In some embodiments of the present invention, the third absorption cross-sectional area includes a strong water vapor absorption cross-sectional area and a third methane absorption cross-sectional area.

[0082] The concentration of methane in the gas to be tested is obtained by the following formula:

[0083]

[0084] Where Y is the methane concentration, c is the speed of light, and t is the velocity of light. a1 The first methane decay time, t a2 The second methane decay time, t a3 For the third wave phase, Sh a1 Sh is the first water vapor absorption cross-sectional area. a2 The fourth water vapor absorption cross-sectional area, Sh a3 For the cross-sectional area of ​​strong water vapor absorption, Sy a1 Sy is the first methane absorption cross-sectional area. a2 The second methane absorption cross-section, Sy a3 This represents the third methane absorption cross-sectional area.

[0085] In some embodiments of the present invention, the concentration of water vapor in the gas to be measured is obtained by the following formula:

[0086]

[0087] Where H represents the concentration of water vapor.

[0088] In some embodiments of the present invention, the carbon dioxide concentration in the gas to be measured is obtained by the following formula:

[0089]

[0090] Where X is the concentration of carbon dioxide, t b1 The first carbon dioxide oscillation time, t b2 For the second carbon dioxide oscillation time, Sh b1 The second water vapor absorption cross-sectional area, Sh b2 Sx is the fifth water vapor absorption cross-sectional area. b1 Sx is the first carbon dioxide absorption cross-sectional area. b2 This represents the second carbon dioxide absorption cross-sectional area.

[0091] In some embodiments of the present invention, the concentration of nitrous oxide in the gas to be tested is calculated using the following formula:

[0092]

[0093] Where Z is the concentration of nitrous oxide, t c1 t is the first nitrous oxide oscillation time. c2 The second nitrous oxide oscillation time, Sh c1 For the third water vapor absorption cross-sectional area, Sh c2 Sz is the sixth water vapor absorption cross-sectional area. c1 Sz represents the first nitrous oxide absorption cross-section. c2 This represents the absorption cross-sectional area of ​​the second nitrous oxide layer.

[0094] Please refer to Figure 1 The present invention also provides another method for measuring greenhouse gases using laser spectroscopy, comprising:

[0095] Step 1: Setting up the device

[0096] Laser 1, laser 2, and laser 3 are all interband cascaded lasers with output center wavelengths of 3.27 μm, 4.24 μm, and 4.47 μm, respectively. The knife-edge method was used to obtain the output beam characteristics of laser 1, laser 2, and laser 3, including waist size and position. A ring-down cavity consisting of four cavity mirrors 4 was constructed. All four cavity mirrors 4 are high-reflectivity mirrors with a reflectivity better than 0.9999 in the 3 μm–5 μm wavelength range. Based on the ABCD matrix calculation results, four beam shaping modules 5 were constructed, and the spacing between the three lasers, their corresponding beam shaping modules 5, and the cavity mirrors 4 was determined. A focusing lens 6 was installed near the cavity mirror 4 at the output position, with the focal point placed on the target surface of the receiver 7. The receiver 7 uses a single-point mercury cadmium telluride detector, which has high measurement sensitivity.

[0097] Step 2: Gas Collection

[0098] The gas to be tested is drawn from the ambient air by a diaphragm pump or other intake device. The ambient air contains greenhouse gases such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Before entering the decay chamber, the ambient air passes through a particulate filter and a desiccant, thus achieving basic filtration of aerosol particles and water vapor in the ambient air.

[0099] The third step involves measuring using the wavelength that produces the strong absorption peak.

[0100] The output laser wavelength is changed by current modulation. The first measurement wavelength of the first laser 1 is set to 3270.42 nm, the first measurement wavelength of the second laser 2 is set to 4237.08 nm, and the first measurement wavelength of the third laser 3 is set to 4470.38 nm. The laser output from the first laser 1, after passing through its corresponding beam shaping module 5, is coupled into the ring-down cavity through its corresponding cavity mirror 4, transmitted through the cavity mirror 4 at the output position, and focused onto the target surface of the receiver 7 by the focusing lens 6. The laser output from the second laser 2, after passing through the beam shaping module 5, is coupled into the ring-down cavity through the cavity mirror 4, transmitted through the cavity mirror 4 at the output position, and focused onto the target surface of the receiver 7 by the focusing lens 6. The laser output from the third laser 3, after passing through the beam shaping module 5, is coupled into the ring-down cavity through the cavity mirror 4, transmitted through the cavity mirror 4 at the output position, and focused onto the target surface of the receiver 7 by the focusing lens 6. The receiver 7 performs an A / D conversion to convert the light intensity signal into a voltage digital signal. When the voltage signal reaches the set trigger threshold, the first laser 1, the second laser 2, and the third laser 3 respectively achieve optical shutdown by rapidly turning off their power supplies. At this time, the voltage signal exhibits a single exponential decay over time, thus forming three ring-down curves. The ring-down time is calculated from the ring-down curves using a ring-down time extraction algorithm. Therefore, the ring-down times at the three wavelengths can be obtained, denoted as t0. a1 t b1 and tc1 .

[0101] The fourth step involves measuring at the wavelength that produces the weak absorption peak.

[0102] By changing the output laser wavelength using current modulation, the second measurement wavelength of the first laser 1 was set to 3269.62 nm, the first measurement wavelength of the second laser 2 was set to 4237.95 nm, and the first measurement wavelength of the third laser 3 was set to 4471.38 nm. The gas to be measured was then measured using the second measurement wavelength. The measurement process was the same as in the third step, and the decay times at the three wavelengths were finally obtained, t0. a2 t b2 and t c2 ...

[0103] The fifth step involves measuring using the third measurement wavelength.

[0104] By changing the output laser wavelength through current modulation, the third measurement wavelength of the first laser 1 was set to 3271.87 nm, and the gas to be measured was measured using this third measurement wavelength. The measurement process was the same as steps three and four, yielding a ring-down time t. a3 .

[0105] Step 6: Concentration Inversion and Water Vapor Correction

[0106] Using the infrared absorption spectra of greenhouse gases and water vapor provided by the HITRAN database, the absorption cross-sections of greenhouse gases and water vapor at different wavelengths were calculated using the Voigt line shape function. Specific values ​​(absorption cross-section unit: cm) are provided. 2 ·molecule -1 The symbols and their representations are shown in the table below.

[0107] 3270.42 <![CDATA[Sx a1 =1.9×10 -28 ]]> <![CDATA[Sy a1 =1.9×10 -18 ]]> <![CDATA[Sz a1 =8.3×10 -24 ]]> <![CDATA[Sh a1 =2.8×10 -23 ]]> 4237.08 <![CDATA[Sx b1 =1.5×10 -17 ]]> <![CDATA[Sy b1 =1.1×10 -24 ]]> <![CDATA[Sz b1 =6.7×10 -23 ]]> <![CDATA[Sh b1 =3.0×10 -27 ]]> 4470.38 <![CDATA[Sx c1 =3.9×10 -24 ]]> <![CDATA[Sy c1 =2.4×10 -25 ]]> <![CDATA[Sz c1 =4.2×10 -18 ]]> <![CDATA[Sh c1 =6.7×10 -28 ]]> 3269.62 <![CDATA[Sx a2 =1.0×10 -28 ]]> <![CDATA[Sy a2 =1.7×10 -20 ]]> <![CDATA[Sz a2 =9.3×10 -24 ]]> <![CDATA[Sh a2 =1.4×10 -23 ]]> 4237.95 <![CDATA[Sx b2 =4.7×10 -19 ]]> <![CDATA[Sy b2 =3.3×10 -23 ]]> <![CDATA[Sz b2 =1.7×10 -23 ]]> <![CDATA[Sh b2 =1.8×10 -28 ]]> 4471.38 <![CDATA[Sx c2 =5.2×10 -25 ]]> <![CDATA[Sy c2 =3.5×10 -26 ]]> <![CDATA[Sz c2 =9.9×10 -20 ]]> <![CDATA[Sh c2 =1.2×10 -28 ]]> 3271.87 <![CDATA[Sx a3 =2.0×10 -28 ]]> <![CDATA[Sy a3 =4.9×10 -21 ]]> <![CDATA[Sz a3 =2.6×10 -25 ]]> <![CDATA[Sh a3 =5.1×10 -21 ]]>

[0108] According to the World Meteorological Organization (WMO) data for global atmospheric greenhouse gas concentrations in 2020, carbon dioxide concentration was 413 ppm, methane concentration was 1.889 ppm, and nitrous oxide concentration was 0.333 ppm. However, at higher relative humidity levels, water vapor concentrations can reach tens of thousands of ppm or even higher, thus needing to be considered in the concentration retrieval process. As for the three greenhouse gases themselves, calculations based on absorption cross-sections show that their individual concentrations have little impact on the retrieval results, therefore they do not need to be considered.

[0109] The greenhouse gas inversion algorithm of this invention, which considers water vapor correction, is as follows:

[0110] The first step is to calculate the methane concentration Y and the water vapor concentration H.

[0111]

[0112]

[0113] The second step is to calculate the carbon dioxide concentration X.

[0114]

[0115] The third step is to calculate the nitrous oxide concentration Z.

[0116]

[0117] In the formula, c is the speed of light.

[0118] Step 7: Repeat Measurements

[0119] Repeat steps three through six to achieve n repeated measurements, continuously obtaining the concentrations of carbon dioxide, methane, and nitrous oxide, respectively (X1, X2, ..., X...). n (Y1,Y2,…,Y) n (Z1, Z2, ..., Z) n ).

[0120] Step 8: Stop measuring

[0121] Once the measurement data is confirmed to meet the measurement requirements, the first laser 1, the second laser 2, the third laser 3, the receiver 7, and other equipment / units / modules (such as laser controllers, data processing modules, diaphragm pumps, etc.) are powered off, and the measurement is stopped.

[0122] This invention also provides a laser spectral measurement device for greenhouse gases, used to implement any of the methods in the above embodiments. The device includes a first laser unit, a second laser unit, a third laser unit, a ring-down cavity, and a receiving unit.

[0123] The ring-down cavity consists of four cavity mirrors. The first laser unit, the second laser unit, and the third laser unit are used to emit wavelength-tunable lasers into the ring-down cavity so that the lasers are reflected and transmitted in the four cavity mirrors.

[0124] The receiving unit is used to receive the laser emitted from the ring-down cavity in order to obtain the ring-down time and absorption cross-sectional area.

[0125] In some embodiments of the present invention, the first laser unit, the second laser unit, and the third laser unit all include a laser and an optical path shaping module, and the receiving unit includes a receiver and a focusing lens.

[0126] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A laser spectral measurement method for greenhouse gases, characterized in that, include: Multiple lasers with different wavelengths are used to emit lasers into a ring-down cavity containing the gas to be tested, thereby obtaining multiple first absorption cross-sections and multiple first ring-down times; wherein, the laser wavelengths of the multiple lasers correspond one-to-one with the strongest absorption peak wavelengths of various greenhouse gases. Multiple lasers with different wavelengths are used to emit lasers into a ring-down cavity containing a gas to be tested, thereby obtaining multiple second absorption cross-sections and multiple second ring-down times; wherein, the laser wavelengths of the multiple lasers correspond one-to-one with the weakest absorption peak wavelengths of various greenhouse gases. Each of the lasers can obtain a first absorption cross-sectional area for a greenhouse gas and a first absorption cross-sectional area for water vapor; Each of the lasers can obtain a second absorption cross-sectional area for greenhouse gases and a second absorption cross-sectional area for water vapor; The laser spectroscopy measurement method further includes: Adjust the wavelength of a laser so that it produces the strongest absorption peak for water vapor; The laser is used to emit a laser beam into a ring-down cavity containing the gas to be measured, thereby obtaining the third absorption cross-sectional area and the third ring-down time; the third absorption cross-sectional area includes the strong absorption cross-sectional area of ​​water vapor and the third absorption cross-sectional area of ​​methane. The concentrations of different greenhouse gases in the gas to be measured are calculated using multiple first absorption cross-sectional areas, multiple second absorption cross-sectional areas, multiple first decay times, multiple second decay times, the third absorption cross-sectional area, and the third decay time.

2. The laser spectral measurement method for greenhouse gases according to claim 1, characterized in that, The method involves emitting laser light into a ring-down cavity containing the gas to be measured using multiple lasers of different wavelengths, thereby obtaining multiple first absorption cross-sections and multiple first ring-down times; wherein the laser wavelengths of the multiple lasers correspond one-to-one with the strongest absorption peak wavelengths of various greenhouse gases, including: A first laser is used to emit a laser beam into a ring-down cavity containing the gas to be tested, thereby obtaining the first methane absorption cross-sectional area, the first water vapor absorption cross-sectional area, and the first methane ring-down time; wherein, the laser wavelength of the first laser is the same as the wavelength of the strongest absorption peak of methane. A second laser is used to emit a laser beam into a ring-down cavity containing the gas to be measured, thereby obtaining the first carbon dioxide absorption cross-sectional area, the second water vapor absorption cross-sectional area, and the first carbon dioxide ring-down time; wherein, the laser wavelength of the second laser is the same as the wavelength of the strongest absorption peak of carbon dioxide. A third laser is used to emit a laser beam into a ring-down cavity containing the gas to be tested, thereby obtaining the first nitrous oxide absorption cross-sectional area, the third water vapor absorption cross-sectional area, and the first nitrous oxide ring-down time; wherein the laser wavelength of the third laser is the same as the wavelength of the strongest absorption peak of nitrous oxide.

3. The laser spectral measurement method for greenhouse gases according to claim 2, characterized in that, The method involves emitting laser light into a ring-down cavity containing the gas to be measured using multiple lasers of different wavelengths, thereby obtaining multiple second absorption cross-sections and multiple second ring-down times; wherein the laser wavelengths of the multiple lasers correspond one-to-one with the weakest absorption peak wavelengths of various greenhouse gases, including: The first laser is used to emit a laser into a ring-down cavity containing the gas to be tested, thereby obtaining the second methane absorption cross-sectional area, the fourth water vapor absorption cross-sectional area, and the second methane ring-down time; wherein, the laser wavelength of the first laser is the same as the wavelength of the weakest absorption peak of methane. The second laser is used to emit a laser into a ring-down cavity containing the gas to be measured, thereby obtaining the second carbon dioxide absorption cross-sectional area, the fifth water vapor absorption cross-sectional area, and the second carbon dioxide ring-down time; wherein, the laser wavelength of the second laser is the same as the wavelength of the weakest absorption peak of carbon dioxide. The third laser is used to emit a laser beam into a ring-down cavity containing the gas to be tested, thereby obtaining the second nitrous oxide absorption cross-sectional area, the sixth water vapor absorption cross-sectional area, and the second nitrous oxide ring-down time; wherein, the laser wavelength of the third laser is the same as the wavelength of the weakest absorption peak of nitrous oxide.

4. The laser spectral measurement method for greenhouse gases according to claim 3, characterized in that, The methane concentration in the gas to be tested is obtained by the following formula: in, Y where c is the methane concentration, c is the speed of light, and t is the methane concentration. a1 t is the first methane decay time. a2 t is the second methane oscillation time. a3 S is the third oscillation time. h a1 S is the first water vapor absorption cross-sectional area. h a2 S is the fourth water vapor absorption cross-sectional area. h a3 S is the cross-sectional area for strong water vapor absorption. y a1 S is the first methane absorption cross-sectional area. y a2 S is the second methane absorption cross-sectional area. y a3 The third methane absorption cross-sectional area is given.

5. The laser spectral measurement method for greenhouse gases according to claim 4, characterized in that, The concentration of water vapor in the gas to be tested is obtained by the following formula: in, H This represents the concentration of water vapor.

6. The laser spectral measurement method for greenhouse gases according to claim 5, characterized in that, The carbon dioxide concentration in the gas to be tested is obtained by the following formula: in, X t represents the concentration of carbon dioxide. b1 t is the first carbon dioxide oscillation time. b2 S is the second carbon dioxide oscillation time. h b1 S is the second water vapor absorption cross-sectional area. h b2 S is the fifth water vapor absorption cross-sectional area. x b1 S is the first carbon dioxide absorption cross-sectional area. x b2 This is the second carbon dioxide absorption cross-sectional area.

7. The laser spectral measurement method for greenhouse gases according to claim 5, characterized in that, The concentration of nitrous oxide in the gas to be tested is calculated using the following formula: in, Z t represents the concentration of nitrous oxide. c1 t is the first nitrous oxide oscillation time. c2 S is the second nitrous oxide oscillation time. h c1 S is the third water vapor absorption cross-sectional area. h c2 S is the sixth water vapor absorption cross-sectional area. z c1 S is the absorption cross-sectional area of ​​the first nitrous oxide. z c2 This represents the absorption cross-sectional area of ​​the second nitrous oxide.

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