Device for measuring absorption coefficient and scattering coefficient of aerosol

Abstract

The device comprises a light source module, a silencing cavity, a photon counter, a calculation module and a photodiode, the silencing cavity comprises a luminosity ball and absorption cavities located at the two ends of the luminosity ball, and the absorption cavities at the two ends are symmetrically arranged on the two sides of the luminosity ball respectively. A gas inlet and a gas outlet are formed in the tops of the two ends of the absorption cavity, and a light inlet optical glass fixing frame and a light outlet optical glass fixing frame are arranged at two ports of the absorption cavity. The light-in optical glass is fixed at the axis center of one end of the absorption cavity close to the gas inlet, the light-out optical glass is fixed at the axis center of one end of the absorption cavity close to the gas outlet, and the top end of the photometric ball is provided with a scattered signal collection port. According to the utility model, the integrating sphere scattering measurement technology and the cavity ring-down spectroscopy technology are combined, the absorption coefficient of the aerosol is measured by using the cavity ring-down spectroscopy technology, the scattering coefficient is measured by using an integrating sphere enhanced scattering signal, and the synchronous measurement of the absorption coefficient and the scattering coefficient of the aerosol is realized.

Description

Technical Field

[0001] The utility model relates to the technical field of atmospheric aerosol measurement, in particular to a device for measuring aerosol absorption coefficient and scattering coefficient. Background Art

[0002] Atmospheric aerosol is a suspension system of liquid or solid particles in the air. They can serve as condensation nuclei for water droplets and ice crystals, absorbers and scatterers of solar radiation, and participate in various chemical cycles. They are an important component of the atmosphere. Although the content of aerosol in the atmosphere is relatively small, its role in atmospheric processes cannot be ignored. Its prominent role is reflected in the fact that aerosol not only has a lot of influence on atmospheric visibility, solar scattering and radiation, atmospheric temperature, etc., but also because of its small particle size and large surface area, it provides a reaction bed for atmospheric environmental chemistry, thereby affecting various chemical reactions in the atmosphere and affecting human health. Therefore, the accurate detection of aerosol absorption coefficient and scattering coefficient is of great significance.

[0003] The integrating sphere scattering measurement technology is based on the Beer-Lambert law and uses a special structural design to detect the aerosol scattering coefficient, so that the response value of the detector is proportional to the integral value of the scattered light at all scattering angles, thereby inverting the scattering coefficient.

[0004] Cavity ring-down spectroscopy is a gas absorption spectroscopy detection technology. A pair of highly reflective mirrors with a reflectivity of over 99.99% form an optical resonant cavity, which greatly increases the number of light reflections in the cavity, thereby increasing the absorption optical path of the gas to be measured. The concentration of the gas to be measured in the cavity is detected based on the ring-down time of the light in the cavity, and it is easy to achieve an accuracy of less than 1ppm.

[0005] At present, most of the instruments for measuring the absorption coefficient and scattering coefficient of aerosols are mainly based on measuring a single optical characteristic parameter. The measurement results are inevitably affected by the cumulative measurement errors of different instruments, sample inhomogeneity and differences in experimental conditions. Therefore, it is of great significance to develop an in-situ measurement device for aerosol optical characteristic parameters. Utility Model Content

[0006] In order to solve the technical problems mentioned in the background technology, the utility model provides a device for measuring aerosol absorption coefficient and scattering coefficient.

[0007] The utility model adopts the following technical scheme: a device for measuring aerosol absorption coefficient and scattering coefficient, comprising a light source module, an anechoic cavity, a photon counter, a calculation module, and a photodiode;

[0008] The interior of the anechoic cavity is integrally connected and includes a photometric sphere and absorption cavities at both ends thereof;

[0009] The photometric sphere is used as an integral turbidity cavity, and is generally of an inner circular outer square structure, with a hollow spherical shape inside;

[0010] The absorption cavities at both ends have the same structure and are constructed along the central axis of the photometric sphere and symmetrically arranged on both sides of the photometric sphere;

[0011] The absorption cavity is an axially penetrating cylindrical cavity;

[0012] The tops of both ends of the absorption chamber are provided with gas inlets and gas outlets;

[0013] A light inlet optical glass fixing frame and a light outlet optical glass fixing frame are arranged at two ends of the absorption cavity;

[0014] The light-incoming optical glass is fixed at the axis center of one end of the absorption cavity close to the gas inlet through a light-incoming optical glass fixing frame;

[0015] The light-emitting optical glass is fixed at the axis center of one end of the absorption cavity close to the gas outlet through a light-emitting optical glass fixing frame;

[0016] The top of the photometric sphere is provided with a scattering signal collecting port for installing a photomultiplier tube;

[0017] The scattered signal collection port is centrally arranged between the two absorption cavities and located on the cross section where the inner sphere and the outer cube of the photometric sphere are tangent;

[0018] The photomultiplier tube is used to collect scattered signals and send them to a photon counter;

[0019] The light source module includes a plurality of switchable visible light single laser light sources, which are perpendicular to the light-incoming optical glass and along the central axis of the light-incoming side absorption cavity to jointly inject a single wavelength light beam into the light-incoming side absorption cavity to excite the aerosol to generate a photoacoustic signal;

[0020] The photodiode is located in the light-emitting side absorption cavity, and is used to collect the signal after multiple reflections and send it to the photon counter;

[0021] The photon counter is used to count the photons of the scattered signal sent by the photomultiplier tube and the signal received by the photodiode, and send the obtained photon counting signal to the calculation module;

[0022] The calculation module is used for real-time analysis and processing of the photon counting signal sent by the photon counter.

[0023] Furthermore, the gas inlet and the gas outlet are both provided with solenoid valves to control the opening and closing states.

[0024] Furthermore, the gas inlet is connected to a drying tube and a vacuum pump through a pipeline.

[0025] Furthermore, the light-incoming optical glass and the light-emitting optical glass are both high-reflection mirrors with a reflectivity exceeding 99.99%, and the center distance between the light-incoming optical glass and the light-emitting optical glass is 500 mm.

[0026] Furthermore, a magnesium oxide coating is evenly applied on the inner wall of the spherical cavity of the photometric sphere, and the reflectivity of the magnesium oxide coating is above 99%.

[0027] Furthermore, the light source module includes a light source 1 for detecting barium sulfate aerosol, with a wavelength at 405nm in the visible blue light; and a light source 2 for detecting black carbon aerosol, with a wavelength at 700nm in the visible red light.

[0028] Compared with the prior art, the advantages of the utility model are: the device designed by the utility model for measuring the aerosol absorption coefficient and scattering coefficient has a simple structure, a unified standard, simple operation, and stable operation. Compared with a single aerosol optical property parameter detection device, it combines the integrating sphere scattering measurement technology with the cavity ring-down spectroscopy technology, uses the cavity ring-down spectroscopy technology to measure the aerosol absorption coefficient, and uses the integrating sphere to enhance the scattering signal to measure the scattering coefficient, thereby realizing the synchronous measurement of the aerosol absorption coefficient and the scattering coefficient. Compared with the detection effect of superimposing multiple single aerosol optical property parameter detection devices, the utility model eliminates the step of converting the measured parameters to the same wavelength for analysis according to the wavelength of light after measuring different data by multiple devices, thereby avoiding the influence of the cumulative measurement errors of different instruments, sample inhomogeneity, and differences in experimental conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the overall structure of the device for measuring aerosol absorption coefficient and scattering coefficient of the utility model;

[0030] Figure 2 This is a schematic diagram of the connection relationship of the utility model for transporting the aerosol to be tested;

[0031] Figure 3 It is a schematic diagram of the three-dimensional structure of the muffler chamber of the utility model.

[0032] in:

[0033] 1-light-incoming absorption cavity, 2-light-incoming optical glass fixing frame, 3-light-incoming optical glass, 4-gas inlet, 5-photometric ball, 6-scattering signal collection port, 7-gas outlet, 8-light-emitting optical glass, 9-light-emitting optical glass fixing frame, 10-light source module, 11-photon counter, 12-computing module, 13-photodiode, 14-drying tube, 15-vacuum pump, 16-solenoid valve, 17-photomultiplier tube. DETAILED DESCRIPTION

[0034] In order to facilitate those skilled in the art to understand the technical solution of the utility model, further description is now made with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the utility model.

[0035] In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present invention. However, it is apparent that one or more embodiments may be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0036] See also Figure 1 , which is a schematic diagram of the overall structure of the device for measuring aerosol absorption coefficient and scattering coefficient of the utility model, including a light source module 10, a silencing cavity, a photon counter 11, a calculation module 12, and a photodiode 13, wherein the interior of the silencing cavity is connected as a whole, such as Figure 3 As shown, it includes a photometric sphere 5 and an absorption cavity 1 located at both ends thereof. The photometric sphere 5 is used as an integral turbidity cavity, which only allows light beams in the directions of 0° to 4° and 176° to 180° to escape. The absorption cavities 1 at both ends have the same structure, are constructed along the central axis of the photometric sphere 5, and are symmetrically arranged on both sides of the photometric sphere 5. The photometric sphere 5 is an inner circle and outer square structure. In specific implementation, the inner diameter of the inner sphere is d=180mm, the substrate is 304 stainless steel, and the interior is a hollow spherical shape. The inner wall is evenly coated with magnesium oxide, and the reflectance of the magnesium oxide coating is above 99%. The absorption cavity 1 is an axially through cylindrical cavity. In specific implementation, the cross-sectional diameter is d=75mm, the length is L=320mm, and the substrate is 304 stainless steel. There are gas inlet 4 and gas outlet 7 at the top of the two ends of the absorption cavity 1. In some embodiments, the gas inlet 4 and the gas outlet 7 are both equipped with solenoid valves 16 to control the opening and closing state. The two ports of the absorption cavity 1 are designed with a light-incoming optical glass fixing frame 2 and a light-outgoing optical glass fixing frame 9. The light-incoming optical glass 3 is fixed to the center of the axis of the absorption cavity 1 by the light-incoming optical glass fixing frame 2, and the light-outgoing optical glass 8 is fixed to the center of the axis of the other end of the absorption cavity 1 by the light-outgoing optical glass fixing frame 9. Both optical glasses are high-reflection mirrors with a reflectivity exceeding 99.99%. In specific implementation, the center distance between the light-incoming optical glass 3 and the light-outgoing optical glass 8 is 500 mm. A scattered signal collecting port 6 for installing a photomultiplier tube is provided at the top of the photometric sphere 5. The scattered signal collecting port 6 is located on the cross section where the inner sphere and the outer cube of the photometric sphere 5 are tangent, and the scattered signal collecting port 6 is centrally arranged between the two absorption cavities 1.

[0037] Since the light source with a central wavelength in the visible light band has a more obvious scattering effect on aerosols, the light source with a central wavelength in the visible red light band and blue light band has a more obvious absorption effect on some types of aerosols. In order to further ensure the detection effect, in this embodiment, the multiple light sources of the light source module 10 include: a light source 1 for barium sulfate aerosol detection, with a wavelength in the visible blue light 405nm, and a light source 2 for black carbon aerosol detection, with a wavelength in the visible red light 700nm. Using multiple light sources with different central wavelengths to detect different types of aerosols is helpful for the source analysis of aerosols, the characterization of aerosol components, the determination of the proportion of aerosols with different components, and the improvement of aerosol absorption and scattering spectra. The light source module 10 injects a single wavelength light beam into the light-incoming side absorption cavity 1 along the central axis of the light-incoming side absorption cavity 1 perpendicular to the light-incoming optical glass 3, to excite the aerosol to generate a photoacoustic signal. A photomultiplier tube 17 is installed on the scattered signal collection port 6 to collect the scattered signal and send it to the photon counter 11. The photodiode 13 is used to collect the signal after multiple reflections and also sends it to the photon counter 11. The photon counter 11 is used to count the photons of the scattered signal sent by the photomultiplier tube and the signal received by the photodiode 13, and send the obtained photon counting signal to the calculation module 12. The calculation module 12 performs real-time analysis and processing on the photon counting signal sent by the photon counter 11.

[0038] like Figure 2 As shown, in some embodiments, the gas path for conveying the aerosol to be tested also includes a drying tube 14 and a vacuum pump 15 for drying the aerosol gas.

[0039] The working principle of this embodiment is as follows:

[0040] The light beam generated by the light source module 10 enters the extinction cavity through the light-incoming optical glass 3, and a high-reflection mirror with a reflectivity of more than 99.99% forms an optical resonant cavity. After passing through the first high-reflection mirror, most of the light is reflected, and the transmitted light oscillates back and forth in the resonant cavity, and the number of oscillations can reach tens of thousands of times, which greatly increases the absorption optical path. According to the Lambert-Beer law, when a beam of incident light enters the resonant cavity and begins to decay, the photodiode 13 detects that the light signal decays exponentially until the light power signal decays to 1 / e of the initial signal. This period of time is the cavity decay time. The decay time of light is called the cavity decay time, which is inversely proportional to all losses in the cavity. Therefore, by measuring the light decay time in the sample cavity instead of the total intensity, the absorption rate can be determined, directly providing the loss on an absolute scale. When no gas is introduced into the sample cavity, the loss is only determined by the reflectivity of the cavity reflector, and the introduction of sample gas into the cavity will result in greater light loss, thereby shortening the decay time.

[0041] When in an empty cavity without sample gas, the time constant t0 of light attenuation depends on the reflection loss of the mirror and can be expressed as:

[0042]

[0043] Where c is the speed of light in vacuum, L is the length of the optical cavity, and R is the reflectivity of the cavity mirror.

[0044] When the sample gas fills the cavity, the 1 / e decay time of this exponentially decaying light intensity is called the decay time t1, which can be expressed as:

[0045]

[0046] Where d is the length of the sample and α is the absorption coefficient of the sample.

[0047] In getting t 0 and t 1 After obtaining the data, the absorption coefficient α can be calculated.

[0048] The photosphere 5 enhances the scattering signal of aerosol particles. The inner wall of the sphere is covered with a high-reflectivity magnesium oxide coating to achieve the effect of a Lambertian reflector. The photosphere 5 acts as an integrating turbidity meter, allowing only light beams from 0° to 4° and 176° to 180° to escape, thereby increasing the collection of scattered light at the photomultiplier tube and improving the intensity of the scattered signal, thereby maximizing the scattered signal detected by the photomultiplier tube and minimizing the deviation of the scattered signal collected from different scattering angles. Ultimately, the absorption coefficient and scattering coefficient of the aerosol are detected synchronously.

[0049] The embodiment of the utility model also proposes a corresponding method for synchronous detection of aerosol absorption coefficient and scattering coefficient, which is used to realize synchronous detection of aerosol absorption coefficient and scattering coefficient in the above synchronous detection device, and is performed according to the following steps:

[0050] Step 1: Turn on the system and preheat to the set temperature.

[0051] Step 2: The aerosol is output from the drying tube 14 and the vacuum pump 15 and enters the silencer chamber from the air inlet 4 until the aerosol concentration in the silencer chamber no longer changes. At this time, the solenoid valves 16 of the air inlet 4 and the air outlet 7 work to close their valves, forming a closed air chamber in the silencer chamber.

[0052] Step 3: Start the light source module 10, and select a light source with a matching central wavelength according to the type of aerosol to be tested. The light source with a central wavelength in the visible light band has a more obvious scattering effect on the aerosol, while the light source with a central wavelength in the visible red light band and blue light band has a more obvious absorption effect on some types of aerosol. In order to further ensure the effective detection effect, the multiple light sources of the light source module 10 include: a light source 1 for barium sulfate aerosol detection, with a wavelength in the visible blue light band of 405nm; and a laser 2 for black carbon aerosol detection, with a wavelength in the visible red light band of 700nm. Using multiple light sources with different wavelengths to detect different types of aerosols is helpful for source analysis of aerosols, determining the proportion of aerosols with different components, and improving the aerosol absorption spectrum and scattering spectrum.

[0053] Step 4: The light source selected in step 3 is incident on the light-incoming side absorption cavity 1 along the central axis of the optical glass 3. The scattered light of the aerosol to be measured is reflected multiple times in the photometric sphere 5, which increases the number of interactions between the scattered light and the aerosol particles, thereby enhancing the scattering signal of the aerosol. The generated scattering signal is collected by a photomultiplier tube. The laser light beam is reflected back and forth multiple times between the high-reflectivity mirrors of the light-incoming absorption cavity 1 and the light-outgoing absorption cavity 1 to form an extremely long absorption light path, thereby deriving the absorption coefficient.

[0054] Step 5: The scattered signal collected by the photomultiplier tube 17 is subjected to photon counting by the photon counter 11, and the obtained photon counting signal is uploaded to the calculation module 12; the ring-down signal is measured by the photodiode 13 at the light-emitting optical lens, and the photon counting is performed by the photon counter 11, and the obtained photon counting signal is uploaded to the calculation module 12.

[0055] Step 6: The calculation module 12 analyzes and processes the photon counting signal sent by the photon counter 11 to calibrate and invert the scattering coefficient and absorption coefficient of the aerosol to be measured.

[0056] The above embodiments are merely descriptions of the preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the protection scope determined by the claims of the present invention.

Claims

1. A device for measuring aerosol absorption coefficient and scattering coefficient, characterized in that: It comprises a light source module (10), an anechoic cavity, a photon counter (11), a calculation module (12), and a photodiode (13); The interior of the anechoic cavity is integrally connected and includes a photometric sphere (5) and absorption cavities (1) located at both ends thereof; The photometric sphere (5) serves as an integral turbidity cavity, and is generally of an inner circular and outer square structure, with the interior being a hollow spherical shape; The absorption cavities (1) at both ends have the same structure and are constructed along the central axis of the photometric sphere (5) and are symmetrically arranged on both sides of the photometric sphere (5); The absorption cavity (1) is an axially penetrating cylindrical cavity; The tops of both ends of the absorption chamber (1) are provided with a gas inlet (4) and a gas outlet (7); A light inlet optical glass fixing frame (2) and a light outlet optical glass fixing frame (9) are arranged at two ends of the absorption cavity (1); The light-incoming optical glass (3) is fixed to the axial center of one end of the absorption cavity (1) close to the gas inlet (4) through a light-incoming optical glass fixing frame (2); The light-emitting optical glass (8) is fixed to the axis center of one end of the absorption cavity (1) close to the gas outlet (7) by means of a light-emitting optical glass fixing frame (9); The top of the photometric sphere (5) is provided with a scattered signal collecting port (6) for installing a photomultiplier tube (17); The scattered signal collection port (6) is centrally arranged between the two absorption cavities (1) and is located on a cross section where the inner sphere and the outer cube of the photometric sphere (5) are tangent; The photomultiplier tube (17) is used to collect scattered signals and send them to the photon counter (11); The light source module (10) comprises a plurality of switchable visible light single laser light sources, which are configured to jointly emit a single wavelength light beam into the light-incoming side absorption cavity (1) along the central axis of the light-incoming side absorption cavity (1) perpendicular to the light-incoming optical glass (3) to excite the aerosol to generate a photoacoustic signal; The photodiode (13) is located in the light-emitting side absorption cavity (1) and is used to collect signals after multiple reflections and send them to the photon counter (11); The photon counter (11) is used to count the photons of the scattered signal sent by the photomultiplier tube (17) and the signal received by the photodiode (13), and send the obtained photon counting signal to the calculation module (12); The calculation module (12) is used to perform real-time analysis and processing on the photon counting signal sent by the photon counter (11).

2. The device for measuring aerosol absorption coefficient and scattering coefficient according to claim 1, characterized in that: The gas inlet (4) and the gas outlet (7) are both provided with a solenoid valve (16) to control the opening and closing states.

3. The device for measuring aerosol absorption coefficient and scattering coefficient according to claim 2, characterized in that: The gas inlet (4) is connected to a drying pipe (14) and a vacuum pump (15) via a pipeline.

4. The device for measuring aerosol absorption coefficient and scattering coefficient according to claim 3, characterized in that: The light-incoming optical glass (3) and the light-emitting optical glass (8) are both high-reflection mirrors with a reflectivity exceeding 99.99%, and the center distance between the light-incoming optical glass (3) and the light-emitting optical glass (8) is 500 mm.

5. The device for measuring aerosol absorption coefficient and scattering coefficient according to claim 4, characterized in that: The inner wall of the spherical cavity of the photometric ball (5) is evenly coated with a magnesium oxide coating, and the reflectance of the magnesium oxide coating is above 99%.

6. The device for measuring aerosol absorption coefficient and scattering coefficient according to claim 5, characterized in that: The light source module (10) comprises a light source 1 for detecting barium sulfate aerosol, the wavelength of which is located at 405 nm in the visible blue light; and a light source 2 for detecting black carbon aerosol, the wavelength of which is located at 700 nm in the visible red light.

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