Gas photolysis rate measurement method

Abstract

The present invention provides a method for measuring gas photolysis rate. Specifically, the solar spectrum in the atmosphere is first received by a quartz receiving head with uniform angular response in all directions, and the spectrum information is uniformly transmitted to a spectrometer through a quartz light guide rod and an optical fiber to obtain spectrum data; then, the measured spectrum data is converted into spectrum radiance by integrating sphere radiation calibration; finally, the photolysis rate of different gas substances is obtained by using an integral formula and the spectrum function data of each gas, that is, the absorption cross section σ and quantum yield φ of each gas. The present invention has a simple overall structure, a compact size, a high degree of integration, and greatly saves costs.

Description

Technical Field

[0001] The invention belongs to the field of environmental monitoring, and in particular relates to a method for measuring gas photolysis rate. Background Art

[0002] The overall system of the photolysis spectrometer currently available on the market consists of a quartz receiving head, a spectrometer, and an industrial control computer. First, the quartz receiving head (diffuser) collects solar radiation from all directions, and transmits the light radiation collected by the quartz light guide rod to the spectrometer through a quartz fiber bundle. The spectrometer obtains spectral information within a fixed wavelength range, and then transmits the spectrometer data to the computer using a connecting line. The computer calibrates the spectrometer data and directly converts it into photochemical flux F(λ), and then uses the integral formula to compare the obtained photochemical flux data with the known gas absorption cross section and quantum yield Calculations are performed. Ultimately, the instrument can obtain the photolysis rates of important substances and free radicals in the atmosphere in real time. In the formula, J represents the photolysis rate of the substance being measured, σ is the absorption cross section of the gas, is the quantum yield in the photolysis reaction, and F(λ) is the photochemical flux.

[0003] Since photochemical flux refers to the amount of solar radiation incident on a spherical surface and capable of causing photolysis of atmospheric components, it is the only effective quantity for calculating the photolysis rate. It has highly variable spatial and spectral distributions, which are mainly affected by the solar zenith angle, the scattering absorption of clouds and aerosols in the atmosphere, and the surface albedo. Therefore, the measurement of photochemical flux requires high requirements for the optical receiving head, that is, the optical receiving head needs to be able to achieve a uniform angular response to light radiation within an angle of 2πsr (sr is a steradian, which is the unit of solid angle), which requires the optical receiving head to have a more complex hardware structure design, and the manufacturing design cost is high. Since the photochemical flux is directly obtained after calibration, improper operation may cause confusion between physical quantities, and it is easy to confuse it with another physical quantity, irradiance, making the measurement result unclear. In addition, most of the current photolysis spectrometers on the market are large in size and weight, which are not convenient for installation and measurement in outdoor experiments. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a gas photolysis rate measurement method, which adopts an improved algorithm for measuring the photolysis rate of gas substances, obtains radiance data by directly measuring the spectrum and then calibrating it, and then gradually converts the radiance data into photochemical flux through layer-by-layer deduction of units, and finally obtains the photolysis rate through integral calculation, so that the overall theoretical basis structure of the instrument is clear and the data volume is clear. At the same time, the overall structure of the instrument is simplified, which is easy to carry and saves costs.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A gas photolysis rate measurement method is performed by using a gas photolysis rate measurement instrument, wherein the gas photolysis rate measurement instrument comprises a quartz receiving head, a spectrometer, and an industrial control computer;

[0007] First, the solar spectrum in the atmosphere is received by a quartz receiving head, and then transmitted to an industrial computer through a quartz light guide rod and an optical fiber. The spectrum data is measured by a spectrometer. Then, the radiance of the integrating sphere is calibrated to convert the spectrum data into radiance. The unit of radiance is μW·cm -2 nm -1 sr -1 , and convert its units:

[0008] The conversion relationship between the physical quantity mol / s and the power unit W is:

[0009]

[0010] So the constant Planck constant h = 6.626*10 -34 J·s, speed of light c = 3.0*10 8 m / s and Avogadro's constant NA = 6.022*10 23 Substituting into formula (1) we get:

[0011]

[0012] The quantitative relationship in formula (2) is only related to the wavelength λ. When calculating the photolysis rate of most gases, the central wavelength is 300nm, so the wavelength λ is approximately 300nm, and the result is:

[0013]

[0014] Then we get:

[0015] 1μW=2.505×10 -12 mol / s (4)

[0016] Therefore, according to formula (4), the unit obtained by calibration is μw·cm -2 nm -1 sr -1 The radiance is converted to another unit of radiance, mol cm -2 nm -1 sr -1 s -1 ;

[0017] Then according to the relationship between photochemical flux and radiance, that is:

[0018]

[0019] The unit of photochemical flux is mol cm -2 nm -1 s -1 ; where θ is the solar zenith angle, is the solar azimuth; is the radiance;

[0020] Since the gas absorption cross section σ is in cm 2 ·molecule -1 , quantum yield No units, according to the following photolysis rate formula:

[0021]

[0022] Finally, the unit of photolysis rate J is s -1 ;

[0023] Then, after determining the time and place, use a quartz receiving head with uniform angular response in all directions to constantize the determined radiance data, move it outside the integral sign, and then solve the remaining definite integral. Substitute the calculated result into the integral formula of the photolysis rate, and finally use the discrete integration method to obtain the photolysis rate of the measured gas.

[0024] Furthermore, the quartz receiving head is composed of five parts: an ellipsoidal receiving head made of quartz material, a quartz light guide rod, a shadow ring, a drying box and an optical fiber adapter; wherein the quartz light guide rod uniformly converges the spectrum received by the quartz receiving head onto the optical fiber; the shadow ring limits the field of view of the quartz receiving head to within 2πsr; and the drying box is used to prevent water mist condensation inside the quartz receiving head, thereby affecting the measurement accuracy.

[0025] Beneficial effects:

[0026] 1. The present invention has a relatively simple quartz receiving head structure;

[0027] 2. The present invention directly converts the received spectrum into radiance through calibration of the integrating sphere;

[0028] 3. The present invention clarifies the calculation of the photolysis rate by converting each physical quantity unit;

[0029] 4. The present invention provides a new measurement algorithm for photolysis rate, which makes the designed instrument relatively simple.

[0030] The purpose of the present invention is firstly to make the physical quantities in each step of the measurement clear and definite through formula derivation and conversion between units. Secondly, since the improved algorithm obtains the relationship between spectral data and photolysis rate, compared with directly measuring the photochemical flux, the requirements for the optical receiving head are relatively lower. Similarly, the design of its hardware structure is relatively simple, making the instrument simple and portable as a whole, thereby saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the structure of the photolysis spectrometer of the present invention;

[0032] Figure 2 It is an algorithm structure diagram of the photolysis spectrometer of the present invention;

[0033] Figure 3 The schematic diagram of the calibration of the internal integrating sphere of the photolysis spectrometer in the present invention;

[0034] Figure 4a This is a comparison chart of HCHO measurements by the present invention and foreign instruments on June 3;

[0035] Figure 4b This is a comparison chart of the measurement of HONO by the present invention and foreign instruments on June 3. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] like Figure 1 As shown, the gas photolysis rate measuring instrument of the present invention includes a quartz receiving head, a spectrometer, and an industrial control computer. The quartz receiving head is mainly composed of five parts: an ellipsoidal receiving head made of quartz material, a quartz light guide rod, a shadow ring, a drying box, and an optical fiber adapter. Among them, the quartz light guide rod can evenly converge the spectrum received by the quartz receiving head onto the optical fiber; the shadow ring limits the field of view of the quartz receiving head to within 2πsr; the drying box is used to prevent water mist condensation inside the quartz receiving head, which affects the measurement accuracy.

[0038] The working principle of the gas photolysis rate measuring instrument of the present invention is as follows:

[0039] like Figure 3As shown, the gas photolysis rate measuring instrument first receives the solar spectrum in the atmosphere through a quartz receiving head, transmits it to the industrial control computer through a quartz light guide rod and an optical fiber, and obtains the spectrum data through the measurement of the spectrometer. Then, the radiance of the integrating sphere is calibrated to convert the spectrum data into radiance. At this time, the calibrated radiance unit is μW·cm -2 nm -1 sr -1 In order to convert it into photolysis rate, the following unit conversion is required.

[0040] First, we consult the data to get the conversion relationship between the physical quantity mol / s and the power unit W:

[0041]

[0042] Then the constant Planck constant h = 6.626*10 -34 J·s, speed of light c = 3.0*10 8 m / s and Avogadro's constant NA = 6.022*10 23 Substituting into formula (1) we get:

[0043]

[0044] The quantitative relationship in formula (2) is only related to the wavelength λ. When calculating the photolysis rate of most gases, the central wavelength is 300nm, so here the wavelength λ is approximately taken as 300nm, so the result is:

[0045]

[0046] Then we get:

[0047] 1μW=2.505×10 -12 mol / s (4)

[0048] Therefore, according to formula (4), the unit obtained by calibration can be converted to μw·cm -2 nm -1 sr -1 The radiance is converted to another unit of radiance, mol cm -2 nm -1 sr -1 s -1 .

[0049] Then according to the relationship between photochemical flux and radiance, that is:

[0050]

[0051] where θ is the solar zenith angle, is the solar azimuth, and the radiance is related to both;

[0052] It can be concluded that the unit of photochemical flux is mol cm -2 nm -1 s -1 Since the gas absorption cross section σ is in cm 2 ·molecule -1 , and the quantum yield There are no units. So according to the following photolysis rate formula:

[0053]

[0054] Finally, the unit of photolysis rate is s -1 The above derivation process provides a detailed analysis of the theoretical basis of the instrument, making the amount of data involved particularly clear.

[0055] For algorithm design in instruments, such as Figure 2 As shown, firstly, according to the above formula (5), there is an integral conversion relationship between radiance and photochemical flux. Due to the uniformity of the spectrum received by the designed quartz receiving head in all directions, after determining the measurement time and location (that is, the solar zenith angle and the solar azimuth angle), the radiance obtained by integrating sphere calibration can be approximated by constantization, as shown in the following formula (7):

[0056]

[0057] The right side of formula (7) is the definite integral, which can be calculated as follows:

[0058]

[0059] After that, the approximate relationship between the radiance L and the photochemical flux F in formula (8) is substituted into the formula (6) for solving the photolysis rate, and the integral is discretized to obtain:

[0060]

[0061] Since the radiance is obtained by integrating sphere calibration based on the spectral data, after the resolution is determined, formula (9) expresses the relationship between the photolysis rate and the spectral data, and the photolysis rate of the gaseous substance is measured by the instrument accordingly.

[0062] The present invention designs and manufactures an optical receiving head in the hardware part of the existing photolysis spectrometer, uses a quartz light guide rod for light homogenization, and improves the algorithm, making the theoretical calculation clearer without changing the measurement accuracy.

[0063] The comparison results with foreign instruments are as follows Figure 4a , Figure 4b As shown, a total of O 3 、NO 2 , HONO, HCHO, H 2 O 2 The photolysis rates of several gaseous substances are highly correlated with the measurement results of the UF-CCD photolysis spectrometer produced by Metcon Company of Germany, and the measurement errors of several substances are all within 10%.

[0064] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. 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 present invention.

Claims

1. A method for measuring gas photolysis rate, Features: The measurement is performed by a gas photolysis rate measuring instrument, wherein the gas photolysis rate measuring instrument comprises a quartz receiving head, a spectrometer, and an industrial control computer; First, the solar spectrum in the atmosphere is received by a quartz receiving head, and transmitted to an industrial control computer through a quartz light guide rod and an optical fiber. The spectrum data is measured by a spectrometer. Then, the radiance of the spectrum is calibrated by an integrating sphere to convert the spectrum data into radiance. The unit of the calibrated radiance is μW·cm -2 nm -1 sr -1 , the units need to be converted: The conversion relationship between the physical quantity mol / s and the power unit W is: （1） So the constant Planck constant h=6.626 10 -34 J·s, speed of light c=3.0 10 8 m / s and Avogadro's constant NA = 6.022 10 23 Substituting into formula (1) we get: （2） The quantitative relationship in formula (2) is only related to the wavelength λ. When calculating the photolysis rate of most gases, the central wavelength is 300nm, so the wavelength λ is taken as 300nm, and the result is: （3） Then we get: （4） Therefore, according to formula (4), the unit obtained by calibration is μw·cm -2 nm -1 sr -1 The radiance is converted to another unit of radiance, mol cm -2 nm -1 sr -1 s -1 ; Then according to the relationship between photochemical flux and radiance, that is: （5） The unit of photochemical flux is mol cm -2 nm -1 s -1 ; where θ is the solar zenith angle and φ is the solar azimuth angle; is the radiance; Since the gas absorption cross section σ is in cm 2 ·molecule -1 , the quantum yield φ has no unit and is based on the following photolysis rate formula: （6） Finally, the unit of photolysis rate is s -1 ; Then, after determining the time and place, use a quartz receiving head with uniform angular response in all directions to constantize the determined radiance data, move it outside the integral sign, and then solve the remaining definite integral. Substitute the calculated result into the integral formula of the photolysis rate, and finally use the discrete integration method to obtain the photolysis rate of the measured gas.

2. A method for measuring gas photolysis rate according to claim 1, Features: The quartz receiving head consists of five parts: an ellipsoidal receiving head made of quartz material, a quartz light guide rod, a shadow ring, a drying box and an optical fiber adapter. The quartz light guide rod evenly converges the spectrum received by the quartz receiving head onto the optical fiber. The shadow ring limits the field of view of the quartz receiving head to within 2πsr. The drying box is used to prevent water mist condensation inside the quartz receiving head, which affects the measurement accuracy. sr is steradian, which is the unit of solid angle.

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