System and method for measuring NO3 free radicals in atmosphere based on open light path

Abstract

The invention relates to the technical field of optical measurement, and discloses an atmosphere NO3 free radical measurement system and method based on an open light path, and the system comprises a light source module, a first convex lens, a first high-reflectivity lens, a second high-reflectivity lens, a detachable cavity, a second convex lens and a spectrometer. Air between high-reflectivity lenses can be directly sampled, and the wall loss of NO3 free radicals in active sampling is avoided, so that the sensitivity and accuracy of measurement are improved. Meanwhile, the design of a detachable cavity is introduced, so that flexible switching between zero air sampling and actual atmosphere sampling is realized. The introduction of the zero spectrum library method effectively compensates the influence of temperature and humidity changes on the light source and the spectrometer, the spectrum shift caused by environmental changes is eliminated through dynamic calibration, in addition, the input of the real-time water vapor absorption cross section can accurately remove the influence of water vapor absorption on NO3 free radical measurement, and the reliability of the measurement result is further improved.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement technology, and more specifically, to an atmospheric NO3 free radical measurement system and method based on an open optical path. Background Art

[0002] The monitoring of NO3 free radicals in the atmosphere is particularly important. NO3 free radicals are a gas that is active at night. They play an important role in atmospheric chemical reactions and participate in the formation of various atmospheric reactions, especially in the formation of secondary atmospheric pollution and secondary organic aerosols. Therefore, accurately measuring the concentration of NO3 free radicals in the atmosphere can provide important data for air quality monitoring, pollutant emission control and environmental science research.

[0003] At present, there are some air pollution monitoring systems on the market that use spectral analysis to detect NO3 free radicals in the atmosphere. However, most of the existing measurement systems have problems such as closed optical paths, which easily cause NO3 free radical wall loss, and the measurement accuracy is greatly affected by the external environment. Especially under high humidity and large temperature changes, the measurement results are highly unstable and have low accuracy. Summary of the invention

[0004] In order to overcome the defects of low precision and instability in the existing NO3 free radical measurement technology, the present invention proposes the following technical solution:

[0005] In a first aspect, the present invention provides an atmospheric NO3 free radical measurement system based on an open optical path, comprising:

[0006] A light source module, used for emitting a light beam of a specific wavelength;

[0007] A first convex lens, used for focusing the light beam emitted by the light source module;

[0008] A first high reflectivity lens, arranged behind the first convex lens;

[0009] The second high reflectivity lens is arranged opposite to the first high reflectivity lens, and together they form an optical resonant cavity, so that the light beam is reflected multiple times between the first high reflectivity lens and the second high reflectivity lens;

[0010] A detachable cavity is disposed between the first high reflectivity lens and the second high reflectivity lens, and is used to form a closed sampling cavity when collecting a zero-point spectrum and calibrating reflectivity. After the detachable cavity is removed, an open optical path is formed between the first high reflectivity lens and the second high reflectivity lens;

[0011] A second convex lens is arranged behind the second high reflectivity lens and is used to focus the light beam after multiple reflections in the open light path;

[0012] The spectrometer is used to receive the spectrum information of the light beam focused by the second convex lens to obtain the concentration of NO3 free radicals in the atmosphere.

[0013] As a preferred technical solution, the system further includes a first optical fiber and a second optical fiber.

[0014] The light beam emitted by the light source module is transmitted to the first convex lens through the first optical fiber;

[0015] The light beam focused by the second convex lens is transmitted to the spectrometer through the second optical fiber.

[0016] As a preferred technical solution, a first air inlet is provided on one side of the light emitting surface of the first high reflectivity lens, and a second air inlet is provided on one side of the light incident surface of the second high reflectivity lens.

[0017] As a preferred technical solution, the light source module is an LED light source, and the wavelength range of the light beam emitted by the LED light source covers 640-680nm, and the central wavelength is 660nm.

[0018] As a preferred technical solution, the system also includes a temperature and humidity sensor, which is used to measure the temperature and humidity of the environment in real time.

[0019] As a preferred technical solution, the system further includes a zero-point spectrum library module, which is used to collect zero-point spectra under different temperature and humidity conditions and store them in the zero-point spectrum library.

[0020] In a second aspect, the present invention further proposes a method for measuring atmospheric NO3 free radicals based on an open optical path, which is applied to an atmospheric NO3 free radical measurement system based on an open optical path as in any scheme of the first aspect, comprising:

[0021] Installing the detachable cavity between the first high reflectivity lens and the second high reflectivity lens to form a closed sampling cavity;

[0022] Introducing nitrogen into the closed sampling cavity through the first air inlet and the second air inlet;

[0023] The light beam is emitted through the light source module, and after being transmitted to the first convex lens for focusing, the light beam is reflected by the closed sampling cavity between the first high-reflectivity lens and the second high-reflectivity lens, and finally focused by the second convex lens and transmitted to the spectrometer;

[0024] The spectrometer receives the light beam and records the spectrum information as a zero-point spectrum, and stores the zero-point spectrum in a zero-point spectrum library;

[0025] removing the removable cavity to form an open optical path between the first high reflectivity lens and the second high reflectivity lens;

[0026] The light beam is emitted again through the light source module, and after being transmitted to the first convex lens for focusing, the light beam is reflected by the open sampling cavity between the first high-reflectivity lens and the second high-reflectivity lens, and finally is focused by the second convex lens and transmitted to the spectrometer;

[0027] The spectrometer receives the light beam and records the spectral information as a sampled spectrum;

[0028] The sampled spectrum is compared with the zero-point spectrum in the zero-point spectrum library to determine the concentration of NO3 free radicals in the atmosphere.

[0029] As a preferred technical solution, the sample spectrum is compared with the zero-point spectrum in the zero-point spectrum library to determine the concentration of NO3 free radicals in the atmosphere, including:

[0030] Select a zero-point spectrum from the zero-point spectrum library as the reference spectrum I0;

[0031] According to the reference spectrum, the material absorption coefficient α(λ) is calculated, and its expression is as follows:

[0032]

[0033] Wherein, I is the sampling spectrum, R(λ) is the reflectivity of the high reflectivity lens at wavelength λ, and d is the effective cavity length between the first high reflectivity lens and the second high reflectivity lens;

[0034] The concentration of NO3 free radicals was calculated by the least squares fitting method based on the absorption coefficients α(λ) of multiple substances.

[0035] As a preferred technical solution, a zero-point library method is used to select a zero-point spectrum from the zero-point spectrum library as the reference spectrum I0, including:

[0036] For each sample spectrum I i (i=1,2,...,m) and all zero-point spectra I in the zero-point spectrum library 0j (j=1,2,...,n), calculate the absorption coefficient α1 in the 645-650nm and 668-673nm bands respectively ij and α2 ij ;

[0037] For each pair of sampled spectra I i and zero-point spectrum I 0j , calculate α1 ij and α2 ij The mean values ​​α1_mean and α2_mean and the standard deviations α1_std and α2_std;

[0038] According to the following formula, calculate the deviation degree X between the sampling spectrum and the zero-point spectrum

[0039] X=|α1_mean-α2_mean+α1_std+α2_std|

[0040] Repeat the above steps for all zero-point spectra in the zero-point spectrum library to obtain a set of X values;

[0041] Find the minimum value from the X value set and use the zero-point spectrum corresponding to the minimum value as the reference spectrum.

[0042] As a preferred technical solution, the concentration of NO3 free radicals is calculated by the least squares fitting method according to the absorption coefficient α(λ) of multiple substances, including:

[0043] Measure the current ambient temperature and humidity in real time, and calculate the absorption cross section of water vapor at wavelength λ based on the current ambient temperature and humidity;

[0044] According to the absorption coefficient α(λ) of multiple substances, the absorption contribution of NO3 radicals, NO2 and water vapor is calculated, and the expression is as follows:

[0045] α(λ)=n NO3 σ NO3 (λ)+n NO2 σ NO2 (λ)+n H2O σ H2O (λ)

[0046] Among them, n NO3 、n NO2 and n H2O Respectively represent the concentrations of NO3 free radicals, NO2 and water vapor, σ NO3 (λ) and σ NO2 (λ) represents the absorption cross section of NO3 radical and NO2 at wavelength λ, σ H2O (λ) represents the absorption cross section of the current water vapor at wavelength λ;

[0047] According to the absorption contributions of NO3 radicals, NO2 and water vapor, the concentration of NO3 radicals was extracted using the least squares fitting method.

[0048] The beneficial effects of the present invention include at least:

[0049] First, through the design of an open optical path, the system can directly sample the air between the high-reflection lenses, avoiding the wall loss of NO3 radicals in traditional active sampling, thereby improving the sensitivity and accuracy of the measurement. At the same time, the introduction of the design of a detachable cavity not only realizes the flexible switching between zero air and actual atmospheric sampling, but also ensures that the light beam is not obstructed during multiple reflections, ensuring the stability and accuracy of the spectral signal. Secondly, the introduction of the zero-point spectral library method effectively compensates for the effects of temperature and humidity changes on the light source and spectrometer, eliminates the spectral shift caused by environmental changes through dynamic calibration, and further improves the reliability of the measurement results. Finally, the input of the real-time water vapor absorption cross section can remove the influence of water vapor absorption on the measurement of NO3 radicals and improve the accuracy of the measurement. Overall, the present invention provides a high-precision, flexible and stable atmospheric NO3 radical measurement scheme with a wider range of application potential, particularly suitable for fields such as atmospheric environmental monitoring and pollutant emission assessment. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A schematic diagram of the structure of an atmospheric NO3 free radical measurement system based on an open optical path provided in an embodiment of the present invention.

[0051] Figure 2 A schematic flow chart of a method for measuring atmospheric NO3 free radicals based on an open optical path provided in an embodiment of the present invention.

[0052] Figure 3 A schematic diagram of a process for matching the optimal zero-point spectrum provided in an embodiment of the present invention.

[0053] Figure 4 A schematic flow chart of a real-time water vapor absorption cross-section calculation method provided in an embodiment of the present invention.

[0054] Among them, there are a light source module 1, a first convex lens 2, a first high reflectivity lens 3, a second high reflectivity lens 4, a detachable cavity 5, a second convex lens 6, a spectrometer 7, a first optical fiber 8, a second optical fiber 9, a first air inlet 10, and a second air inlet 11. DETAILED DESCRIPTION

[0055] The following will describe the embodiments of the present invention with reference to the accompanying drawings and preferred technical solutions. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred technical solutions are only for illustrating the present invention, not for limiting the scope of protection of the present invention.

[0056] It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and thus the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0057] In the following description, numerous details are discussed to provide a more thorough explanation of the embodiments of the present invention. However, it is obvious to those skilled in the art that the embodiments of the present invention can be implemented without these specific details. In other embodiments, well-known structures and devices are shown in the form of block diagrams rather than in detail to avoid making the embodiments of the present invention difficult to understand.

[0058] Example 1

[0059] This embodiment proposes an atmospheric NO3 free radical measurement system based on an open optical path, such as Figure 1 As shown, Figure 1 A structural schematic diagram of an atmospheric NO3 free radical measurement system based on an open optical path provided in this embodiment includes: a light source module 1, a first convex lens 2, a first high reflectivity lens 3, a second high reflectivity lens 4, a detachable cavity 5, a second convex lens 6 and a spectrometer 7.

[0060] Among them, the light source module 1 is used to emit a light beam of a specific wavelength. The first convex lens 2 is used to focus the light beam emitted by the light source module 1. The first high reflectivity lens 3 is arranged behind the first convex lens 2, and the second high reflectivity lens 4 is arranged opposite to the first high reflectivity lens 3, and together they form an optical resonant cavity, so that the light beam is reflected multiple times between the first high reflectivity lens 3 and the second high reflectivity lens 4. The detachable cavity 5 is arranged between the first high reflectivity lens 3 and the second high reflectivity lens 4, and is used to form a closed sampling cavity when collecting zero-point spectrum and calibrating reflectivity. After the detachable cavity 5 is removed, an open light path is formed between the first high reflectivity lens 3 and the second high reflectivity lens 4. The second convex lens 6 is arranged behind the second high reflectivity lens 4, and is used to focus the light beam after multiple reflections in the open light path. The spectrometer 7 is used to receive the spectral information of the light beam focused by the second convex lens 6 to obtain the concentration of NO3 free radicals in the atmosphere.

[0061] In this embodiment, the system further includes a first optical fiber 8 and a second optical fiber 9 .

[0062] The light beam emitted by the light source module is transmitted to the first convex lens 2 through the first optical fiber 8;

[0063] The light beam focused by the second convex lens 6 is transmitted to the spectrometer 7 through the second optical fiber 9 .

[0064] In this embodiment, a first air inlet 10 is provided on a light emitting surface side of the first high reflectivity lens 3 , and a second air inlet 11 is provided on a light incident surface side of the second high reflectivity lens 4 .

[0065] In this embodiment, the light source module 1 is an LED light source, which is coaxially arranged with the first high reflectivity lens 3 and the first high reflectivity lens 4. The wavelength range of the light beam emitted by the LED light source covers 640-680nm, and the central wavelength is 660nm.

[0066] In this embodiment, the system further includes a temperature and humidity sensor, which is used to measure the temperature and humidity of the environment in real time.

[0067] In this embodiment, the system further includes a zero-point spectrum library module, which is used to collect zero-point spectra under different temperature and humidity conditions and store them in the zero-point spectrum library.

[0068] It is understandable that, through the design of the open optical path, the system can directly sample the air between the high-reflection lenses, avoiding the wall loss of NO3 radicals in traditional active sampling, thereby improving the sensitivity and accuracy of the measurement. At the same time, the introduction of the design of the detachable cavity 5 not only realizes the flexible switching of zero air and actual atmospheric sampling, but also the LED light source and the first high-reflectivity lens 3 and the first high-reflectivity lens 4 are coaxially arranged to ensure that the light beam is not obstructed during multiple reflections, ensuring the stability and accuracy of the spectral signal. Secondly, the introduction of the zero-point spectral library method effectively compensates for the influence of temperature and humidity changes on the light source and spectrometer 7, eliminates the spectral shift caused by environmental changes through dynamic calibration, further improves the reliability of the measurement results, and the input of the real-time water vapor absorption cross section accurately eliminates the influence of water vapor absorption on NO3 radical measurement, thereby improving the accuracy of the measurement results. Overall, the present invention provides a high-precision, flexible and stable atmospheric NO3 radical measurement scheme, which has a wider application potential and is particularly suitable for fields such as atmospheric environment monitoring and pollutant emission assessment.

[0069] Example 2

[0070] like Figure 2 As shown, this embodiment proposes an atmospheric NO3 free radical measurement method based on an open optical path, which is applied to an atmospheric NO3 free radical measurement system based on an open optical path as in the above embodiment, including:

[0071] S1: Install the detachable cavity 5 between the first high reflectivity lens 3 and the second high reflectivity lens 4 to form a closed sampling cavity. At this time, the optical path in the cavity is closed, and the zero-point spectrum can be collected and the reflectivity can be calibrated. The installation of the cavity ensures that the propagation of the light beam in the optical system is not disturbed by external gases, which is suitable for stable measurement of background signals.

[0072] S2: Nitrogen is introduced into the closed sampling chamber through the first air inlet 10 and the second air inlet 11. The role of nitrogen is to clear the air in the chamber to avoid interference from gases such as water vapor. At the same time, nitrogen as a purge gas can also protect the high reflectivity lens from particulate contamination. By introducing nitrogen, it can be ensured that when collecting the zero-point spectrum, there are no other gas components in the system that may affect the spectral analysis.

[0073] S3: Start the light source module 1 and emit a light beam through the light source module 1. After being focused by the first convex lens 2, the light beam passes through the installed closed sampling cavity and is reflected between the first high reflectivity lens 3 and the second high reflectivity lens 4. After multiple reflections, the light beam is finally focused again by the second convex lens 6 and transmitted to the spectrometer 7.

[0074] S4: The spectrometer receives the light beam and records the spectrum information as the zero-point spectrum, and stores the zero-point spectrum in the zero-point spectrum library. Since the cavity is in a nitrogen environment, the measured spectrum data is the zero-point spectrum. The zero-point spectrum is stored in the zero-point spectrum library module as a comparison benchmark for subsequent actual sampling.

[0075] S5: Before the actual measurement, the detachable cavity 5 is first removed from the system. After the cavity is removed, an open optical path is formed between the first high reflectivity lens 3 and the second high reflectivity lens 4. At this time, the optical path is no longer closed, and the system is in direct contact with the atmospheric environment.

[0076] S6: Re-emit the light beam for actual sampling. Start the light source module 1 and re-emit the light beam. After being focused by the first convex lens 2, the light beam passes through the open light path between the first high reflectivity lens 3 and the second high reflectivity lens 4, and in the process interacts with molecules such as NO3 free radicals in the external atmosphere to generate a spectral absorption signal.

[0077] S7: After being reflected, the light beam is focused by the second convex lens 6 and transmitted to the spectrometer 7. At this time, the light beam received by the spectrometer 7 carries the characteristic spectrum information of NO3 free radicals in the atmosphere.

[0078] S8: The spectrometer 7 receives the light beam and records the spectrum information as a sample spectrum.

[0079] S9: Compare the sampled spectrum with the zero-point spectrum in the zero-point spectrum library to determine the concentration of NO3 free radicals in the atmosphere.

[0080] In this embodiment, the sample spectrum is compared with the zero-point spectrum in the zero-point spectrum library to determine the concentration of NO3 free radicals in the atmosphere, including:

[0081] A zero-point spectrum is selected from the zero-point spectrum library as the reference spectrum I0.

[0082] According to the reference spectrum, the material absorption coefficient α(λ) is calculated, and its expression is as follows:

[0083]

[0084] Wherein, I is the sampling spectrum, R(λ) is the reflectivity of the high reflectivity lens at wavelength λ, and d is the effective cavity length between the first high reflectivity lens 3 and the second high reflectivity lens 4.

[0085] The concentration of NO3 free radicals was calculated by the least squares fitting method based on the absorption coefficients α(λ) of multiple substances.

[0086] It should be noted that the periodic changes in the day and night temperature and relative humidity in the atmosphere will have a significant impact on the light source and spectrometer 7 of the measurement system. This impact will cause the sampled spectrum to shift to varying degrees, thereby causing deviations in the NO3 radical concentration obtained by spectrum analysis. In addition, since the system uses an open optical path for passive sampling, the traditional chemical titration method cannot obtain a dynamic zero point. The present invention innovatively proposes a zero-point spectral library method, which aims to effectively eliminate the impact of temperature and relative humidity changes on the sampled spectrum.

[0087] The zero-point spectrum library of the present invention covers a large number of zero-point spectra reflecting the day-night changes in temperature and relative humidity. In practical applications, when calculating the absorption coefficient α, the system will intelligently select the zero-point spectrum closest to the current sampled spectrum I temperature and relative humidity as I0. This method can effectively eliminate the sampling spectrum offset caused by changes in environmental factors, thereby making the calculated absorption coefficient α more accurate and closer to the actual situation.

[0088] LED light sources have an inherent temperature drift phenomenon. As the temperature of the light source changes, the light intensity characteristics and emission wavelength of the LED will change accordingly. In addition, the CCD in the spectrometer 7 will also be affected by temperature during operation, causing the collected spectrum to present varying degrees of noise. If a fixed zero-point spectrum I0 is still used in this case, when the light source has a temperature drift, the band of the sampled spectrum I will mismatch with I0. This mismatch will cause the baseline drift of the absorption coefficient α, ultimately resulting in a large uncertainty in the NO3 radical concentration obtained by the spectrum analysis.

[0089] The present invention ensures that the environmental influences on the light source and the spectrometer 7 are basically consistent by selecting a zero-point spectrum that is highly consistent with the temperature and relative humidity of the sampling spectrum I. This strategy can largely eliminate the drift effect caused by temperature and relative humidity changes on the light source and the spectrometer 7 when calculating the absorption coefficient α, thereby significantly improving the accuracy and reliability of the measurement. Among them, there are many choices for the zero-point spectrum, and the nitrogen spectrum can be selected as the zero-point spectrum library. The sampling spectrum at noon (without NO3 free radical absorption) can also be selected as the zero-point spectrum. When the sampling spectrum at noon is used as the zero-point spectrum, the influence of partial water vapor absorption and particulate matter absorption can be eliminated at the same time.

[0090] like Figure 3 As shown, the present invention adopts a high-power monochromatic LED red light source, whose central wavelength is at 660nm and the effective wavelength range covers 640-680nm. This wavelength range just includes the main absorption peak of NO3 free radical near 662nm.

[0091] Based on the spectral characteristics of NO3 radicals, in actual observations, the absorption coefficients α of non-NO3 radical absorption bands such as 640-650nm and 668-680nm should remain relatively stable and close in value. However, the temperature drift of the light source will cause the absorption coefficients of these two bands to change accordingly.

[0092] Utilizing this principle, the present invention designs Figure 4 The exact screening steps shown:

[0093] For each sample spectrum I i (i=1,2,...,m) and all zero-point spectra I in the zero-point spectrum library 0j (j=1,2,...,n), calculate the absorption coefficient α1 in the 645-650nm and 668-673nm bands respectively ij and α2 ij ;

[0094] For each pair of sampled spectra I i and zero-point spectrum I 0j , calculate α1 ij and α2 ij The mean values ​​α1_mean and α2_mean and the standard deviations α1_std and α2_std;

[0095] According to the following formula, the deviation degree X between the sample spectrum and the zero-point spectrum is calculated:

[0096] X=|α1_mean-α2_mean+α1_std+α2_std|

[0097] Repeat the above steps for all zero-point spectra in the zero-point spectrum library to obtain a set of X values;

[0098] Find the minimum value from the X value set and use the zero-point spectrum corresponding to the minimum value as the reference spectrum.

[0099] This process finds the best matching zero-point spectrum I0 for each sampled spectrum I. In this way, the spectral shift caused by temperature drift and other environmental factors can be effectively compensated, thereby greatly improving the accuracy of NO3 radical concentration measurement. It is worth noting that this screening method not only considers the overall shape of the spectrum, but also evaluates the stability of the spectrum by calculating the standard deviation, which makes the selection process more comprehensive and reliable. By performing this screening step for each sampled spectrum, a highly matched set of zero-point spectra I0 is finally obtained, laying a solid foundation for the subsequent calculation of NO3 radical concentration.

[0100] In this embodiment, the concentration of NO3 free radicals is calculated by the least squares fitting method according to the absorption coefficient α(λ) of multiple substances, including:

[0101] Measure the current ambient temperature and humidity in real time, and calculate the absorption cross section of water vapor at wavelength λ based on the current ambient temperature and humidity;

[0102] According to the absorption coefficient α(λ) of multiple substances, the absorption contribution of NO3 radicals, NO2 and water vapor is calculated, and the expression is as follows:

[0103] α(λ)=n NO3 σ NO3 (λ)+n nO2 σ NO2 (λ)+n H2O σ H2O (λ)

[0104] Among them, n NO3 、n NO2 and n H2O Respectively represent the concentrations of NO3 free radicals, NO2 and water vapor, σ NO3 (λ), σ NO2 (λ) and σ H2O (λ) represents the absorption cross sections of NO3 free radical, NO2 and water vapor at wavelength λ, respectively.

[0105] According to the absorption contributions of NO3 radicals, NO2 and water vapor, the concentration of NO3 radicals was extracted using the least squares fitting method.

[0106] In this embodiment, Figure 4As shown in the figure, when calculating the real-time water vapor absorption cross section, it is first necessary to download the high-resolution spectrum data of water from the HITRAN database. Each spectral line will be broadened due to the thermal motion of molecules. This phenomenon is mainly manifested as the Doppler effect under low pressure conditions, resulting in the broadening of the spectral line conforming to the Gaussian distribution, that is, Gaussian broadening. This broadening is mainly affected by temperature. Under high pressure conditions, frequent collisions of molecules or atoms will cause the frequency width of radiation to increase. This broadening increases linearly with the particle density and the pressure of the external particles, which is called pressure broadening. At this time, the distribution of spectral line broadening conforms to the Lorentz distribution, also called Lorentz broadening, which is mainly affected by pressure and the collision cross section of molecules.

[0107] Under actual atmospheric conditions, the spectrum will show the characteristics of both Gaussian distribution and Lorentzian distribution. This distribution between the two is called Viogt distribution. Gaussian function and Lorentzian function are both analytical functions and can be directly solved, but Viogt function is a convolution function and there is no analytical solution. It can only be approximated by algorithm. In order to eliminate the influence of broadening, the Viogt integral approximation method is used to calculate the H2O absorption cross section under set temperature and pressure conditions. In this way, the H2O absorption cross section under specific conditions can be calculated, and then the high-resolution spectrum line and instrument function are used for convolution to obtain the H2O absorption cross section under the corresponding set conditions. This method not only improves the calculation efficiency, but also ensures the real-time input of the water vapor absorption cross section when decomposing the spectrum, making the calculation of NO3 radical concentration more accurate.

[0108] It should be noted that the aforementioned explanation of the embodiment of the atmospheric NO3 free radical measurement method based on an open optical path is also applicable to the atmospheric NO3 free radical measurement system based on an open optical path of this embodiment, and will not be repeated here.

[0109] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0110] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "N" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0111] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, fragment or portion of code comprising one or more executable instructions for implementing the steps of a custom logical function or process, and the scope of the preferred embodiments of the present application includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in reverse order depending on the functions involved, which should be understood by technicians in the technical field to which the embodiments of the present application belong.

[0112] It should be understood that the various parts of the present application can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiment, the N steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array, a field programmable gate array, etc.

[0113] A person skilled in the art may understand that all or part of the steps in the above-mentioned embodiment method may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

[0114] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. An atmospheric NO3 free radical measurement system based on an open optical path, characterized in that: include: A light source module (1) is used to emit a light beam of a specific wavelength; A first convex lens (2) is used to focus the light beam emitted by the light source module (1); A first high reflectivity lens (3) is arranged behind the first convex lens (2); The second high reflectivity lens (4) is arranged opposite to the first high reflectivity lens (3) and together forms an optical resonant cavity, so that the light beam is reflected multiple times between the first high reflectivity lens (3) and the second high reflectivity lens (4); A detachable cavity (5) is arranged between the first high reflectivity lens (3) and the second high reflectivity lens (4) and is used to form a closed sampling cavity when collecting a zero-point spectrum and calibrating reflectivity. After the detachable cavity (5) is removed, an open optical path is formed between the first high reflectivity lens (3) and the second high reflectivity lens (4); A second convex lens (6) is arranged behind the second high reflectivity lens (4) and is used to focus the light beam after multiple reflections in the open light path; The spectrometer (7) is used to receive the spectrum information of the light beam focused by the second convex lens (6) to obtain the concentration of NO3 free radicals in the atmosphere.

2. The atmospheric NO3 free radical measurement system based on an open optical path according to claim 1, characterized in that: The system further comprises a first optical fiber (8) and a second optical fiber (9); The light beam emitted by the light source module is transmitted to the first convex lens (2) through the first optical fiber (8); The light beam focused by the second convex lens (6) is transmitted to the spectrometer (7) via the second optical fiber (9).

3. The atmospheric NO3 free radical measurement system based on an open optical path according to claim 1, characterized in that: A first air inlet (10) is provided on one side of the light emitting surface of the first high reflectivity lens (3), and a second air inlet (11) is provided on one side of the light incident surface of the second high reflectivity lens (4).

4. The atmospheric NO3 free radical measurement system based on an open optical path according to claim 1, characterized in that: The light source module (1) is an LED light source. The wavelength range of the light beam emitted by the LED light source covers 640-680 nm, and the central wavelength is 660 nm.

5. The atmospheric NO3 free radical measurement system based on open optical path according to claim 1, characterized in that: The system also includes a temperature and humidity sensor, which is used to measure the temperature and humidity of the environment in real time.

6. The atmospheric NO3 free radical measurement system based on an open optical path according to any one of claims 1 to 5, characterized in that: The system further comprises a zero-point spectrum library module, which is used to collect zero-point spectra under different temperature and humidity conditions and store them in the zero-point spectrum library.

7. A method for measuring atmospheric NO3 free radicals based on an open optical path, applied to an atmospheric NO3 free radical measurement system based on an open optical path as claimed in any one of claims 1 to 6, characterized in that: include: The detachable cavity (5) is installed between the first high reflectivity lens (3) and the second high reflectivity lens (4) to form a closed sampling cavity; Introducing nitrogen into the closed sampling cavity through the first air inlet (10) and the second air inlet (11); A light beam is emitted through a light source module (1), and after being transmitted to a first convex lens (2) for focusing, the light beam is reflected by a closed sampling cavity between a first high-reflectivity lens (3) and a second high-reflectivity lens (4), and finally focused by a second convex lens (6) and transmitted to a spectrometer (7); The spectrometer (7) receives the light beam and records the spectrum information as a zero-point spectrum, and stores the zero-point spectrum in a zero-point spectrum library; The detachable cavity (5) is removed to form an open optical path between the first high reflectivity lens (3) and the second high reflectivity lens (4); The light beam is emitted again through the light source module (1), and after being transmitted to the first convex lens (2) for focusing, the light beam is reflected by the open sampling cavity between the first high-reflectivity lens (3) and the second high-reflectivity lens (4), and finally focused by the second convex lens (6) and transmitted to the spectrometer (7); The spectrometer (7) receives the light beam and records the spectral information as a sampled spectrum; The sampled spectrum is compared with the zero-point spectrum in the zero-point spectrum library to determine the concentration of NO3 free radicals in the atmosphere.

8. The method for measuring atmospheric NO3 free radicals based on an open optical path according to claim 7, characterized in that: Compare the sampled spectrum with the zero-point spectrum in the zero-point spectrum library to determine the concentration of NO3 free radicals in the atmosphere, including: Select a zero-point spectrum from the zero-point spectrum library as the reference spectrum I0; According to the reference spectrum, the material absorption coefficient α(λ) is calculated, and its expression is as follows: Wherein, I is the sampling spectrum, R(λ) is the reflectivity of the high reflectivity lens at wavelength λ, and d is the effective cavity length between the first high reflectivity lens (3) and the second high reflectivity lens (4); The concentration of NO3 free radicals was calculated by the least squares fitting method based on the absorption coefficients α(λ) of multiple substances.

9. The method for measuring atmospheric NO3 free radicals based on an open optical path according to claim 8, characterized in that: Using the zero-point library method, a zero-point spectrum is selected from the zero-point spectrum library as the reference spectrum I0, including: For each sample spectrum I i (i=1,2,...,m) and all zero-point spectra I in the zero-point spectrum library 0j (j=1,2,...,n), calculate the absorption coefficient α1 in the 645-650nm and 668-673nm bands respectively ij and α2 ij ; For each pair of sampled spectra I i and zero-point spectrum I 0j , calculate α1 ij and α2 ij The mean values ​​α1_mean and α2_mean and the standard deviations α1_std and α2_std; According to the following formula, the deviation degree X between the sample spectrum and the zero-point spectrum is calculated: X=|α1_mean-α2_mean+α1_std+α2_std| Repeat the above steps for all zero-point spectra in the zero-point spectrum library to obtain a set of X values; Find the minimum value from the X value set, and use the zero-point spectrum corresponding to the minimum value as the reference spectrum.

10. The method for measuring atmospheric NO3 free radicals based on an open optical path according to claim 8, characterized in that: According to the absorption coefficient α(λ) of multiple substances, the concentration of NO3 free radicals is calculated by the least squares fitting method, including: Measure the current ambient temperature and humidity in real time, and calculate the absorption cross section of water vapor at wavelength λ based on the current ambient temperature and humidity; According to the absorption coefficient α(λ) of multiple substances, the absorption contribution of NO3 radical, NO2 and water vapor is calculated, and the expression is as follows: a(λ)=n NO3 s NO3 (λ)+n NO2 s NO2 (λ)+n H2O s H2O (l) Among them, n NO3 、n NO2 and n H2O Respectively represent the concentrations of NO3 free radicals, NO2 and water vapor, σ NO3 (λ) and σ NO2 (λ) represents the absorption cross section of NO3 radical and NO2 at wavelength λ, σ H2O (λ) represents the absorption cross section of the current water vapor at wavelength λ; According to the absorption contributions of NO3 radicals, NO2 and water vapor, the concentration of NO3 radicals was extracted using the least squares fitting method.

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