CN103048284A - Novel method for measuring extinction coefficient of atmospheric aerosol - Google Patents

Abstract

The invention discloses a new method for measuring the extinction coefficient of atmospheric aerosol by using a coated glass tube. , the light of a certain wavelength is transmitted in the glass tube filled with aerosol at a certain angle for a long distance between the tube walls, the attenuation information of the light by the aerosol can be obtained by measuring the detectors at both ends of the glass tube, and the light passes through the glass tube many times Reentry greatly increases the sensitivity to aerosol extinction. The invention establishes a measurement formula for the multi-wavelength extinction coefficient, and the relative calculation method based on the ratio avoids the measurement error caused by the light intensity fluctuation in the photoelectric conversion process, and has the characteristics of simple principle, convenient operation and fast detection speed.

Description

A New Method for Measuring Extinction Coefficient of Atmospheric Aerosol Using Coated Glass Tube

technical field

The invention relates to the field of aerosol extinction coefficient measurement, in particular to a new method for directly measuring atmospheric aerosol extinction coefficients, which can measure the atmospheric aerosol extinction coefficients of multiple wavelengths in real time.

Background technique

Atmospheric aerosols are an important part of the atmosphere and an important factor in the physical and chemical processes of the atmosphere. Atmospheric aerosols have important direct and indirect effects on climate change. They absorb and scatter solar radiation through aerosol particles and directly change the earth- Energy budget of gas system. Based on atmospheric light scattering, the measurement of aerosol optical properties, especially the extinction coefficient at different wavelengths, and the establishment of wavelength conversion relationships can deepen the understanding of aerosol optical properties and expand the research on radiation transmission of lasers in the atmosphere, which is more accurate The assessment of the radiative forcing and climate impact of atmospheric aerosols has important academic significance and potential application value.

The methods of measuring the aerosol extinction coefficient can be roughly divided into the following types, 1. Forward detection method: one end actively emits a laser light source, and the other end receives transmitted light, transmitted light and incident light at a certain distance (50m~2000m) The ratio of the ratio is the transmittance and then converted into the extinction coefficient. 2 Backward detection method: laser radar and other active detection methods measure the backscattering signal of the aerosol to obtain the extinction coefficient. 3 Lateral detection method: the visibility meter is the measurement The detection method measures the lateral (33°) scattering signal of the aerosol and inverts the extinction coefficient to obtain the extinction coefficient. The 4 reflection method: the extinction coefficient can also be retrieved through the reflection of an object on natural light and the contrast of surrounding objects. All of the above methods have certain limitations, for example: the forward detection method requires a certain measurement distance (optical path), while the backward, lateral and reflection methods are all inversion methods, not direct measurement. In addition, the above methods are generally is the extinction coefficient measured at a certain wavelength. The extinction coefficients at many wavelengths can only be obtained by model derivation ^[7] , so it is meaningful to study the extinction coefficients of aerosols at different wavelengths.

A new method of measuring the extinction coefficient of atmospheric aerosols using a coated glass tube overcomes the shortcomings of the above methods. It adopts a direct forward measurement method, and can achieve tens of meters of light transmission in a one-meter-long glass tube to achieve long-distance transmission. The purpose is to truly reflect the transmission of light in the atmosphere and its interaction with aerosols. Use a semiconductor laser as the incident light source, the wavelength can be 532nm, 635 nm, 650 nm, 660 nm, 808 nm and 980 nm, as long as the wavelength available on the market can be used, it can also be a continuous laser light source, these advantages will be great Expansion of aerosol extinction research and its application fields.

Contents of the invention

The purpose of the present invention is to provide a new method with ingenious structure, high precision and real-time measurement aiming at the deficiency of existing atmospheric aerosol extinction coefficient measurement technology. The method can effectively measure atmospheric aerosol extinction coefficients at various wavelengths; the method has the characteristics of simple principle, convenient operation, high detection sensitivity and the like.

The technical scheme adopted in the present invention is:

The new method for measuring the extinction coefficient of atmospheric aerosols by using a coated glass tube is characterized in that: it comprises a glass tube, the inner and outer walls of the glass tube are coated with a high reflection film, and an aerosol inlet, an outlet, and a light beam inlet and outlet are provided. The inlet and outlet of the sol are located at both ends of the glass tube and are perpendicular to the glass tube, the aerosol inlet is provided with an air valve, and the aerosol outlet is provided with an air pump, and the beam inlet and outlet are respectively located at both ends of the glass tube and are connected to the The glass tube forms a certain angle, the beam entrance is equipped with laser diodes of multiple wavelengths as the light source, the optical path between the laser diode and the beam entrance is equipped with a parallel light tube and a beam splitter, and the beam emitted by the laser diode passes through the parallel light The tube collimates the beam, and then produces two collimated beams with the same beam quality through the beam splitter, which are used as the reference light and the incident light respectively. The entire energy of the reference light enters the photodetector 1 and is converted into a corresponding electrical signal. The light beam outlet is provided with a photodetector two, and the incident light enters the photodetector two after being reflected in the glass tube, and the electric signal output terminals of the photodetector one and the photodetector two are connected to the single-chip microcomputer of the AD converter, and the single-chip microcomputer also Control and connect the laser diode, air valve, and air pump, and the single-chip microcomputer is connected to the computer through the connected USB interface; the specific measurement process includes the following steps:

(1) Install a filter at the aerosol inlet of the glass tube, let the incident light with a wavelength of λ enter the glass tube at a certain angle, transmit it through the clean air without aerosol, and record the incident light detected by the photodetector 2 at The electrical signal when there is no aerosol particle in the glass tube is i ₂ (λ), and the reference light with a wavelength of λ directly enters the photodetector 1, and the electrical signal corresponding to the wavelength λ detected by the photodetector 1 is i ₁ (λ );

(2) Remove the filter at the aerosol inlet of the glass tube, let the aerosol enter the glass tube evenly, turn on the air pump at the aerosol outlet of the glass tube, and use the air pump to pump air to make the aerosol particles flow evenly in the glass tube, Let the incident light with a wavelength of λ enter the glass tube at a certain angle and pass through the atmospheric aerosol to be measured. The scattered light intensity of the aerosol particles is weak and is consumed by the reflection on the inner wall of the glass tube, and the absorption of the aerosol particles is converted into molecules Thermal movement, the incident light is scattered and absorbed by the aerosol particles and reaches the photodetector 2 to convert into a corresponding electrical signal. Record the electrical signal detected by the photodetector 2 at this time as i ₃ (λ);

(3) In steps (1) and (2), the electrical signals detected by photodetector 1 and photodetector 2 are respectively converted into digital signals and processed by a single-chip microcomputer before being connected to a computer. Aerosol extinction coefficient measurement formula:

Where D is the optical path of the light in the glass tube;

From this, the extinction coefficient β _ext(λ) of the aerosol at the wavelength λ is calculated.

Principle of the present invention is:

The measurement system consists of a light emitting unit, a coated glass tube, two photodetection units, and a control and signal processing unit. A glass tube coated with a high-reflectivity film on the inner and outer surfaces is used as the light transmission tube. The numerical calculation is combined with the method of laboratory measurement. The inner diameter of the glass tube is d, the length of the glass tube is L, and the incident angle of the beam is . Obviously have:

Beam return times N:

The journey P of light in the glass tube between two reflections is:

P=tgθ·d

The total transmission distance of the beam in the aerosol:

It can be seen that the transmission distance has nothing to do with the inner diameter of the glass tube, but only with the length of the glass tube and the incident angle. If an incident angle of 1° is used, the transmission distance of light in the aerosol medium will be magnified by 57.3 times compared with the direct measurement, which greatly improves the sensitivity of the measurement of the aerosol extinction coefficient. Of course, the minimum incident angle is also related to factors such as the sensitivity of the detector, the size of the opening, the incident aperture of the beam, and the reflectivity of the inner wall of the glass tube. The length of the glass tube of the device is 860 mm, the diameter is 30 mm, the incident light angle is 1 degree, and the light transmission is nearly 50 meters.

The signal comparison method is used to avoid the influence of the glass tube wall and atmospheric molecules on the signal. A filter is installed on the air inlet, and the transmission information Ext ₂ of the signal light is measured when there is no aerosol in the glass tube, and then removed. Filter, let the aerosol enter the glass tube evenly, and measure the transmission information Ext ₃ of the signal light again. If the incident light intensity is Ext ₁ , the attenuation information of the aerosol at this time can be expressed as Ext _a =( Ext ₂ - Ext ₃ ) /Ext ₁ .

Advantage of the present invention and beneficial effect are:

1. In situ measurement, maintaining the objective interaction between light and atmospheric aerosol particles;

2. The measurement principle is direct and simple, the design is ingenious, the operation is convenient, the detection sensitivity is high, and the detection speed is fast;

3. The ratio calculation method eliminates the influence of light intensity fluctuations in photoelectric conversion on the measurement results;

4. Realize long-distance transmission of light over a limited distance.

The present invention uses a coated glass tube to measure the extinction coefficient of atmospheric aerosols. Based on the characteristics of light transmission in the coated glass tube, such as long optical path and low loss, light of a certain wavelength passes through the aerosol-filled glass tube at a certain angle. The long-distance transmission between the tube walls, the attenuation information of the aerosol to light can be measured by the detector at the end of the glass tube, and the multiple reentry of light in the glass tube greatly improves the sensitivity of the aerosol attenuation; Without changing the suspension state of the particles, the interference of the tube wall and air molecule light scattering is effectively deducted during the measurement, and continuous real-time online measurement of atmospheric aerosols can be carried out. characteristics, all show good application prospects.

Description of drawings

Figure 1 is a schematic diagram of the measurement of the extinction coefficient of the present invention.

Detailed ways

As shown in Figure 1, the new method of measuring the extinction coefficient of atmospheric aerosols by using a coated glass tube includes a glass tube 1, the inner and outer walls of the glass tube 1 are coated with a high-reflection film, and there are aerosol inlets, outlets 2, 3 and light beams. , outlet 4, 5, aerosol inlet, outlet 2, 3 are respectively located at the two ends of glass tube 1 and are all perpendicular to glass tube 1, aerosol inlet 2 is provided with air valve 6, aerosol outlet 3 is provided with air pump 7, The beam entrance and exit 4, 5 are respectively located at both ends of the glass tube 1 and form a certain angle with the glass tube. The beam entrance 4 is provided with a laser diode 8 with multiple wavelengths as a light source. A collimator and a beam splitter 9 are arranged on the optical path between them. The light beam emitted by the laser diode 8 passes through the collimator to collimate the beam, and then passes through the beam splitter 9 to produce two collimated beams with the same beam quality, which are respectively used as reference Light and incident light, all the energy of the reference light enters the photodetector 10 and converts it into a corresponding electrical signal. The beam exit 5 is provided with a photodetector 2 11, and the incident light enters the photodetector 11 after being reflected in the glass tube 1 , the electric signal output end of photodetector one 10, photodetector two 11 connects the single-chip microcomputer 12 of AD converter, and single-chip microcomputer 12 also controls and connects laser diode 8, air valve 6, air extraction pump 7, and single-chip microcomputer 12 connects through the USB interface Connect computer 13; Concrete measurement process comprises the following steps:

(1) Install a filter 14 at the aerosol inlet 2 of the glass tube 1, let the incident light with a wavelength of λ enter the glass tube 1 at a certain angle, transmit it through the clean air without aerosol, and record the photodetector 2 11 The electrical signal of the detected incident light when there are no aerosol particles in the glass tube 1 is i ₂ (λ), and the reference light with a wavelength of λ directly enters the photodetector 10, and records the corresponding wavelength λ detected by the photodetector 10. The electric signal of is i ₁ (λ);

(2) Remove the filter 14 at the aerosol inlet of the glass tube 1, let the aerosol enter the glass tube 1 evenly, and turn on the air pump 7 at the aerosol outlet of the glass tube 1, and use the air pump 7 to pump air The sol particles flow uniformly in the glass tube 1, so that the incident light with a wavelength of λ enters the glass tube 1 at a certain angle and passes through the atmospheric aerosol to be measured. The scattered light intensity of the aerosol particles is weak and reflected by the inner wall of the glass tube 1 is consumed, the absorption of aerosol particles is converted into molecular thermal motion, the incident light is scattered and absorbed by the aerosol particles, reaches the photodetector 11 and converts it into a corresponding electrical signal, and records the electrical signal detected by the photodetector 2 11 at this time is i ₃ (λ);

(3) In steps (1) and (2), the electrical signals detected in photodetector one 10 and photodetector two 11 are respectively converted into digital signals and processed by single chip microcomputer 12 and connected to computer 13, and the internal software of computer 13 The measurement formula of aerosol extinction coefficient at different wavelengths is established:

Where D is the optical path of the light in the glass tube;

From this, the extinction coefficient β _ext(λ) of the aerosol at the wavelength λ is calculated.

Claims (1)

1. Utilize the new method of coated glass tube to measure atmospheric aerosol extinction coefficient, it is characterized in that: comprise glass tube, described glass tube inner and outer wall is coated with high reflection film, be provided with aerosol inlet, outlet and light beam inlet, outlet, all The aerosol inlet and outlet are respectively located at both ends of the glass tube and are all perpendicular to the glass tube. The aerosol inlet is provided with an air valve, and the aerosol outlet is provided with an air pump. The beam inlet and outlet are respectively located at both ends of the glass tube and Both form a certain angle with the glass tube. The beam entrance is equipped with laser diodes with multiple wavelengths as the light source. The optical path between the laser diode and the beam entrance is equipped with a parallel light tube and a beam splitter. The collimator collimates the light beam, and then produces two collimated beams with the same beam quality through the beam splitter, which are used as the reference light and the incident light respectively. All the energy of the reference light enters the photodetector 1 and is converted into Signal, beam exit is provided with photodetector two, and described incident light enters photodetector two after being reflected in glass tube, and the electrical signal output end of photodetector one, photodetector two connects the single-chip microcomputer of AD converter, The single-chip microcomputer also controls and connects the laser diode, the air valve, and the air pump, and the single-chip microcomputer is connected to the computer through the connected USB interface; the specific measurement process includes the following steps: (1) Install a filter at the aerosol inlet of the glass tube, let the incident light with a wavelength of λ enter the glass tube at a certain angle, transmit it through the clean air without aerosol, and record the incident light detected by the photodetector 2 at The electrical signal when there is no aerosol particle in the glass tube is i ₂ (λ), and the reference light with a wavelength of λ directly enters the photodetector 1, and the electrical signal corresponding to the wavelength λ detected by the photodetector 1 is i ₁ (λ ); (2) Remove the filter at the aerosol inlet of the glass tube, let the aerosol enter the glass tube evenly, turn on the air pump at the aerosol outlet of the glass tube, and use the air pump to pump air so that the aerosol particles flow evenly in the glass tube, Let the incident light with a wavelength of λ enter the glass tube at a certain angle and pass through the atmospheric aerosol to be measured. The scattered light intensity of the aerosol particles is weak and is consumed by the reflection on the inner wall of the glass tube, and the absorption of the aerosol particles is converted into molecules Thermal movement, the incident light is scattered and absorbed by the aerosol particles and reaches the photodetector 2 to convert into a corresponding electrical signal. Record the electrical signal detected by the photodetector 2 at this time as i ₃ (λ); (3) In steps (1) and (2), the electrical signals detected by photodetector 1 and photodetector 2 are respectively converted into digital signals and processed by a single-chip microcomputer before being connected to a computer. Aerosol extinction coefficient measurement formula: Where D is the optical path of the light in the glass tube; From this, the extinction coefficient β _ext(λ) of the aerosol at the wavelength λ is calculated.

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