A single-component atmospheric particle thickness measurement method based on transmission electron microscope images

Abstract

The present invention provides a method for measuring the thickness of single-component atmospheric particles based on transmission electron microscopy (TEM) images. The method comprises the following steps: S1. preparing a reference set of standard particles, collecting particles to be measured in the atmosphere, and obtaining TEM images of the standard particles and the particles to be measured; S2. analyzing the TEM images using ImageJ to obtain a baseline grayscale value; S3. obtaining the grayscale values ​​of the standard particles at different particle sizes, removing the baseline grayscale value, and taking the absolute value; S4. establishing a functional relationship between the standard particle size and the absolute grayscale value; S5. partitioning the particles to be measured and calculating the absolute value of the grayscale values ​​of the particles within the partition after removing the baseline grayscale value; S6. substituting the absolute grayscale values ​​of the particles within each partition into the function between the standard particle size and the absolute grayscale value to calculate the thickness of the particles in each partition. By correlating the grayscale value changes in the particle TEM images with the standard particles of different particle sizes, the present invention can quickly and conveniently determine the thickness of single-component atmospheric particles.

Description

Technical Field

[0001] The invention relates to the field of environmental aerosols, in particular to a method for measuring the thickness of single-component atmospheric particles based on transmission electron microscope images. Background Art

[0002] Ambient aerosols have a complex and diverse composition. In addition to solid particles, liquid particles, and organic components, they also contain some biological bacteria and viruses. The mixed presence of various particles pollutes the atmospheric environment. Measuring and analyzing the thickness of single particles in ambient aerosols can help us understand climate change and mitigate its impact on the atmosphere. Single-component atmospheric particles are particles composed of a specific component, such as black carbon and dust. Black carbon is a chain-like polymer of carbon globules with strong light absorption properties, making it a significant absorptive aerosol. Dust particles are primarily composed of minerals and soil particles. Transmission electron microscopy is often used in atmospheric environmental research to analyze the microscopic morphology of particles. However, analysis based on transmission electron microscopy is generally limited to two-dimensional area and perimeter, and cannot address three dimensions. To quickly and easily determine the thickness of single-component particles in ambient aerosols and facilitate optical calculations of aerosol particles, it is necessary to measure the thickness of single-component particles based on transmission electron microscopy images.

[0003] Existing methods for analyzing atmospheric particle micromorphology have significant shortcomings in rapidly measuring the thickness of single-component particles. In 2014, Zhou Jinhua et al. from the University of Science and Technology of China proposed a method for measuring particle size based on image grayscale microscopy. By capturing particle images through a microscope, a characteristic curve between the particle's equivalent diameter and true diameter was established based on the images, allowing accurate determination of the true diameter of unknown particles. In 2015, Bai Benfeng et al. from Tsinghua University proposed a method for measuring the size of individual nanoparticles. By acquiring dark-field microscopy images of scattered light spots from nanoparticles, they established a relationship between the intensity of the scattered light spots and the particle size, enabling particle size measurement. In 2021, Chu Huaqiang et al. from Anhui University of Technology proposed an ImageJ-based method for measuring the size and area of ​​soot particles. Using Photoshop to remove the background from soot TEM images, they achieved more accurate size and area measurements. However, this method cannot measure the thickness of single-component particles using TEM images. Therefore, developing a method for measuring the thickness of single-component atmospheric particles based on transmission electron microscopy images is of great significance for aerosol environmental analysis. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for measuring the thickness of single-component atmospheric particles based on transmission electron microscope images. The method uses transmission electron microscope TEM image analysis technology to construct a grayscale value-particle size-thickness correlation, and obtains the thickness of single-component atmospheric particles simply and quickly.

[0005] The present invention is achieved in that:

[0006] The present invention samples standard particles and particulate matter in the atmosphere, analyzes transmission electron microscope images, obtains a standard particle size-grayscale absolute value function relationship, partitions single-component particles in the atmosphere (particles of the same component), and substitutes the grayscale in each partition into the standard particle size-grayscale absolute value function to calculate the thickness of single-component atmospheric particles. The method of the present invention can conveniently and quickly realize particle thickness detection, and can also perform three-dimensional morphological modeling of the particle surface microstructure.

[0007] A method for measuring the thickness of single-component atmospheric particles based on transmission electron microscope images comprises the following steps:

[0008] S1. Prepare standard particles: Prepare aqueous solutions of spherical particle samples of different particle sizes, dilute and sonicate them, and then drop the spherical particle sample solutions onto a copper mesh. The standard particles are carbon spheres and silica particles.

[0009] S2. Perform transmission electron microscopy on the standard particles and obtain the absolute grayscale value of the standard particles based on their transmission electron microscopy images; the absolute grayscale value of the standard particles is obtained by subtracting the copper mesh carbon film reference grayscale value from the standard particle grayscale value;

[0010] S3. Establish a rectangular coordinate system based on the standard particle size and the grayscale absolute value, draw a scatter plot of the standard particle size and its corresponding grayscale absolute value, and obtain a functional relationship curve between the standard particle size and its corresponding grayscale absolute value by fitting;

[0011] S4. Use an aerosol single-particle sampler to collect airborne particles. Direct the airflow containing particles into a heat diffuser set to a preset temperature to remove impurities from the particle surface. The particles are then attached to a copper mesh.

[0012] S5. Analyze the particles attached to the copper mesh using a transmission electron microscope, identify black carbon and dust in the particles, and save the corresponding transmission electron microscope images.

[0013] S6. Partition the transmission electron microscope images of black carbon and dust, respectively, so that the area of ​​the partitioned regions is equal to the minimum particle size of standard particles of the same composition;

[0014] S7. Read the grayscale value of the single-component particles in each partition of the transmission electron microscope image of the black carbon and dust, subtract the grayscale value of the copper mesh carbon film baseline, and then take the absolute value;

[0015] S8. Substitute the grayscale absolute value of the single-component particles in each partition into the functional relationship between the particle size and the grayscale absolute value of the standard particles of the corresponding component to calculate the thickness value of the single-component particles in each partition.

[0016] In the above solution, step S4 can be performed after step S1, that is, preparing standard particles and atmospheric particulate matter to be measured on the same copper mesh. The atmospheric particulate matter to be measured generally includes black carbon and dust.

[0017] In the above scheme, in step S5, black carbon and dust in the particulate matter are first identified based on the microscopic morphology of the image in the transmission electron microscope image. If black carbon and dust cannot be identified based on the microscopic morphology, they are then identified with the help of an X-ray spectrometer.

[0018] Preferably, the calculation method of the copper mesh carbon film reference grayscale value in steps S2 and S7 is as follows: read the grayscale value distribution of the copper mesh carbon film in the transmission electron microscope image, select several points in the grayscale value distribution of the copper mesh carbon film and take the average grayscale value to obtain the copper mesh carbon film reference grayscale value.

[0019] Preferably, the functional relationship between the standard particle size and its corresponding grayscale absolute value in step S3 is a linear function relationship.

[0020] Preferably, the method further includes step S9, wherein a 3D drawing tool is used to obtain a three-dimensional model of the surface microstructure of the single-component particles according to the thickness values ​​of the single-component particles in each partition.

[0021] Preferably, the preset temperature in step S4 is 500-600°C.

[0022] The present invention measures the thickness of single-component atmospheric particles based on transmission electron microscope images. When a high-energy electron beam from a transmission electron microscope is used to irradiate particles, the grayscale on the image obtained by the interaction between the electron beam and a substance of the same component reflects the depth, i.e., the thickness, of the electron beam penetrating the substance, and the grayscale is not affected by the morphology of the substance. Therefore, by correlating the grayscale value changes in the particle TEM image with standard particles of different particle sizes, accurate measurement of the thickness of single-component particles is achieved. A three-dimensional morphological model can also be constructed to simplify optical calculations of aerosol particles, thereby reducing the influence of the image on the thickness measurement of single-component particles, effectively reducing errors in the image processing process, and concretely depicting the three-dimensional morphology. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flow chart of the method of the present invention.

[0024] Figure 2 It is a transmission electron microscope image of the standard granular silicon dioxide and the collected dust in the air in the embodiment of the present invention.

[0025] Figure 3 3 is a fitting curve diagram of the particle size and grayscale absolute value of the standard granular silicon dioxide in the embodiment of the present invention.

[0026] Figure 4 It is a schematic diagram of dividing the sand and dust in the air collected by an embodiment of the present invention into different zones.

[0027] Figure 5 1 is a graph showing the thickness test results of several zones of sand and dust in the air collected according to an embodiment of the present invention. DETAILED DESCRIPTION

[0028] Combine Figure 1 The present invention provides a method for measuring the thickness of single-component atmospheric particles based on transmission electron microscope images, which specifically includes the following steps:

[0029] S1. Make standard particles: Prepare different particle sizes D1...D for carbon spheres and silica respectively. m A carbon sphere and silica aqueous solution sample (m ≥ 2) was prepared. The carbon spheres and silica prepared here were all solid spherical structures. The carbon sphere and silica aqueous solution samples were diluted using a pipette and ultrasonicated to obtain relatively dispersed carbon spheres and silica. A certain amount of the diluted sample solution was then pipetted onto a clean copper mesh to obtain standard carbon sphere and silica particles.

[0030] In a specific embodiment, the standard particles produced in this step can be any one of carbon spheres and silicon dioxide, or standard particles of both can be produced.

[0031] S2. Obtain a transmission electron microscope image of the standard particles using a transmission electron microscope. Import the transmission electron microscope image of the standard particles into imageJ, convert the RGB image into an 8-bit image for analysis, read the grayscale value distribution of the copper mesh carbon film in the image, and select some points V1-V in the grayscale value distribution of the copper mesh carbon film. n (n≥2) is averaged and the grayscale value of the carbon film is calculated as a benchmark. Copper mesh carbon film benchmark grayscale value V L The calculation formula is as follows:

[0032]

[0033] Among them, V L is the reference gray value of the copper mesh carbon film, select some points V n Sum and average.

[0034] S3. In the transmission electron microscope (TEM) image of the standard particles, the grayscale at the center of the standard particles corresponds to the thickness and diameter. Take a certain amount of standard particles of different sizes for analysis and use imageJ to confirm the particle size D1...D of the standard particles in the image. m Read the gray value C1...C at the center of the circle of the standard particle on the image. m (m≥2) and then remove the reference gray value V L , and obtain different particle sizes D1...D mThe absolute value of the true grayscale value of the standard particles under the condition is taken, and the calculation formula is as follows:

[0035] V1...V m =|C1...C m -V L | (2)

[0036] Among them, V1…V m is the absolute value of grayscale of standard particles with different particle sizes, C1…C m is the gray value of the standard particle on the image, V L is the reference grayscale value of the copper mesh carbon film.

[0037] S4. According to the different particle sizes of the standard particles and their corresponding grayscale absolute values, a plane rectangular coordinate system is established with different particle sizes of the standard particles D1...D m As the X-axis, the grayscale absolute value V1...V m As the Y axis, draw a scatter plot. In the scatter plot, different particle sizes and their corresponding grayscale absolute values ​​show a monotonic trend. Select a certain functional relationship to fit the scatter points to obtain the functional relationship between the grayscale absolute values ​​of different particle sizes of standard particles. The curve formula generated by the fitting is as follows:

[0038] y=a+bx (3)

[0039] For both carbon spheres and silica standard particles, the functional relationship between particle size and grayscale absolute value can be obtained through steps S2 to S4. For standard particles, their particle size and thickness are the same. Therefore, the functional relationship between particle size and grayscale absolute value obtained for standard particles can be converted into the functional relationship between particle thickness and grayscale absolute value.

[0040] S5. Use an aerosol single particle sampler to collect particulate matter in the air. By introducing an airflow containing particulate matter into a heat diffuser set to an appropriate temperature to remove impurities from the surface of black carbon and / or dust, the particulate matter is collected on a copper mesh with standard particles attached. (Of course, it is also possible to collect particulate matter on other copper meshes, but the copper mesh for collecting standard particles and the copper mesh for atmospheric sampling need to be placed under an electron microscope at the same time, or at least the electron microscope operating conditions for both need to be the same.) Standard particles of different particle sizes are attached to the copper mesh as a reference group for the actual particulate matter collected in the air.

[0041] This step can be performed in parallel with step S1. That is, before calculating the functional relationship between the thickness and grayscale value of the standard particles, standard particles and atmospheric particles to be measured can be collected on the copper mesh. On the same copper mesh, the standard particles serve as a reference group.

[0042] S6. Use a transmission electron microscope to analyze the particles attached to the copper mesh. Select the electron microscope to observe the particles in the field of view. First, carbon balls and silica standard particles can be identified by morphology. Secondly, the collected particles are classified. If the collected black carbon and dust can be identified by morphology, the corresponding transmission electron microscope image can be directly saved; otherwise, the sample needs to be subjected to an X-ray energy spectrum analyzer, and the collected black carbon and dust can be further identified by the X-ray energy spectrum analysis results, and finally the corresponding transmission electron microscope image is saved.

[0043] S7. Partition the black carbon and dust in the TEM image separately. This partitioning is usually random uniform partitioning, that is, dividing a whole regular area including the particles to be measured into several small uniform areas. The more and smaller the number of blocks, the higher the final measurement accuracy. The uniform partitioning here refers to the uniform partitioning of a regular area including black carbon or dust, such as Figure 5 As shown in the figure, after partitioning, there are complete uniform partitions inside the particles to be measured (black carbon or dust), but there may be incomplete uniform partitions at the boundary lines of the particles to be measured. The complete uniform partitions mentioned here are Figure 5 Partitions shown in C and D are not complete uniform partitions. Partitions A, B, and E are not complete uniform partitions.

[0044] S8. Continue to analyze the TEM images of dust and black carbon particles collected in the air on the copper mesh using ImageJ. After reading the grayscale value of the single-component particles (dust or black carbon) in each partition (the grayscale value can be the grayscale value at the center of the partition), remove the copper mesh carbon film baseline grayscale value V L , and then take the absolute value to obtain the absolute value of the grayscale of single-component particles (sand or black carbon) in each partition.

[0045] S9. According to the functional relationship between the different particle sizes of the standard particles and their corresponding grayscale absolute values ​​in step S4, the grayscale absolute value distribution of the single-component particles collected from the air is analyzed and read from the TEM image in step S8, and the grayscale absolute value of the single-component particles of sand or black carbon in each partition is substituted into the function of the particle size and grayscale absolute value of the standard particles of silica or carbon balls, and the thickness distribution of the single-component particles of sand and black carbon in each partition is calculated, thereby realizing the single-component atmospheric particle thickness measurement based on TEM images.

[0046] When collecting airborne particles, most of the collected particles are irregular in shape, resulting in inconsistent grayscale values ​​across their projected areas and uneven thickness distribution. The present invention utilizes a particle size-grayscale absolute value correspondence method to accurately measure the thickness distribution of irregular particles, thereby allowing the calculation of their volume.

[0047] Based on the thickness information of different parts of the particles, the 3D drawing tool can be used to further construct a 3D morphological model of single-component particles. Figure 5 , Figure 5 The divided regions are uniform square blocks. Single-component particles are irregular in shape, so there are irregular blocks (such as blocks A, B, and E) at the boundaries of single-component particles, and complete square blocks (such as blocks C and D) inside. When the area of ​​a block inside a single-component particle is greater than 50% of the area of ​​a single square block, this block is taken into account in the 3D modeling process. The surface structure of the constructed morphological model is affected by the size of the block division. The smaller the block, the more accurately the surface microstructure of the particle can be reproduced, which facilitates subsequent optical calculations.

[0048] The following is a further detailed description of the single-component atmospheric particle thickness measurement method based on transmission electron microscope images provided by the present invention in conjunction with the accompanying drawings and specific embodiments. The described embodiment is only one embodiment of the present invention.

[0049] A standard particle reference group was prepared. The standard particles prepared in this embodiment are standard silica particles. Silica spheres of different particle sizes within the range of 115-130 nm were selected to make silica solutions. The silica solutions were diluted and ultrasonicated using a pipette, and then dropped onto a copper mesh to obtain standard silica particles. An aerosol single particle sampler was used to collect particulate matter from sandstorms in the north. The airflow containing particulate matter was introduced into a heat diffuser. The temperature of the heat diffuser was set to 550°C. After removing impurities on the surface of black carbon or sand and dust, the particulate matter was collected onto a copper mesh with standard particles attached. Under a transmission electron microscope, sand and dust are mainly composed of minerals and soil particles, showing an irregular, porous structure. The particles are large and have a rough surface, with different shapes and sizes, such as Figure 2 As shown, from Figure 2 Standard particles and dust particles can be identified. Save the transmission electron microscope image and use imageJ software to convert the RGB image into an 8-bit image. Select ten points in the gray value distribution of the copper mesh carbon film and calculate the copper mesh carbon film reference gray value V using formula (1). L The silica standard particles were analyzed and measured using imageJ software. Figure 2The particle size of the five available silica standard particles is obtained (there are two overlapping standard particles in the figure, which are not considered here because they overlap), and the central grayscale value of the silica standard particles is read. The grayscale value range is generally 0-255, and the grayscale absolute value of the silica standard particles is calculated by formula (2). According to the measurement results that the grayscale absolute value range of the silica standard particle image at a particle size of 115-130nm is 61.6-89.6, the functional relationship between the silica standard particle size and its corresponding grayscale absolute value is obtained by formula (3). At this time, the linear fitting equation is y=0.59569x+0.57402, as shown Figure 3 Continue to analyze the dust collected in the air through imageJ (in this embodiment, the collected particles to be tested are only dust), and include Figure 2 A square area including dust is randomly and evenly divided into multiple areas for processing. The processing results are as follows Figure 4 As shown. After reading the grayscale values ​​in each dust partition, remove the reference grayscale value V L (i.e. 136.6) and take the absolute value to get the grayscale absolute value of different dust partitions. Substitute the grayscale absolute value of each partition into the particle size-grayscale absolute value function of the silica standard particles to calculate the thickness of each partition. Figure 5 As shown in the figure, the thicknesses of the dust particles in the five subregions A, B, C, D, and E are 83.41 nm, 112.35 nm, 108.75 nm, 118.54 nm, and 90.87 nm, respectively. The thicknesses of dust particles occupying at least 50% of the total area of ​​the subregions are sequentially obtained. Using 3D drawing tools, a three-dimensional morphological model is constructed based on the thickness differences of the dust particles in the subregions. Cubes of varying heights are used to represent the thickness of the subregions. Because dust particles can have both hollow and solid portions, the solid portions are randomly distributed within the thickness range, making it impossible to determine the number and distribution of these solid portions. Therefore, a variety of different 3D morphological models can be constructed. The surface structure of the morphological model is affected by the size of the subregions. Smaller subregions provide a more accurate representation of the particle's surface microstructure, thus facilitating optical calculations of aerosol particles based on the surface microstructure model.

[0050] Ultimately, it will be possible to measure the thickness of single-component atmospheric particles based on TEM images, characterize the thickness of different regions in single atmospheric particles, and deepen our understanding of the microstructure of single-component particles.

Claims

1. A method for measuring the thickness of single-component atmospheric particles based on transmission electron microscope images, characterized in that: The steps include: S1. Prepare standard particles: Prepare aqueous solutions of spherical particle samples of different particle sizes, dilute and sonicate them, and then drop the spherical particle sample solutions onto a copper mesh. The standard particles are carbon spheres and silica particles. S2. Perform transmission electron microscopy on the standard particles and obtain the absolute grayscale value of the standard particles based on their transmission electron microscopy images; the absolute grayscale value of the standard particles is obtained by subtracting the copper mesh carbon film reference grayscale value from the standard particle grayscale value; S3. Establish a rectangular coordinate system based on the standard particle size and the grayscale absolute value, draw a scatter plot of the standard particle size and its corresponding grayscale absolute value, and obtain a functional relationship curve between the standard particle size and its corresponding grayscale absolute value by fitting; S4. Use an aerosol single-particle sampler to collect airborne particles. Direct the airflow containing particles into a heat diffuser set to a preset temperature to remove impurities from the particle surface. The particles are then attached to a copper mesh. S5. Analyze the particles attached to the copper mesh using a transmission electron microscope, identify black carbon and dust in the particles, and save corresponding transmission electron microscope images. S6. Partition the transmission electron microscope images of black carbon and dust separately; S7. Read the grayscale value of the single-component particles in each partition of the transmission electron microscope image of the black carbon and dust, subtract the grayscale value of the copper mesh carbon film baseline, and then take the absolute value; S8. Substitute the grayscale absolute value of the single-component particles in each partition into the functional relationship between the particle size and the grayscale absolute value of the standard particles of the corresponding component to calculate the thickness value of the single-component particles in each partition.

2. The method for measuring the thickness of single-component atmospheric particles based on transmission electron microscope images according to claim 1, characterized in that: The calculation method of the copper mesh carbon film reference grayscale value in steps S2 and S7 is as follows: read the grayscale value distribution of the copper mesh carbon film in the transmission electron microscope image, select several points in the grayscale value distribution of the copper mesh carbon film and average the grayscale values ​​to obtain the copper mesh carbon film reference grayscale value.

3. The method for measuring the thickness of single-component atmospheric particles based on transmission electron microscope images according to claim 1, characterized in that: In step S3, the functional relationship between the standard particle size and its corresponding grayscale absolute value is a linear function relationship.

4. The method for measuring the thickness of single-component atmospheric particles based on transmission electron microscope images according to claim 1, characterized in that: The method further includes step S9, wherein a 3D drawing tool is used to obtain a three-dimensional model of the surface microstructure of the single-component particles according to the thickness values ​​of the single-component particles in each partition.

5. The method for measuring the thickness of single-component atmospheric particles based on transmission electron microscope images according to claim 1, characterized in that: The preset temperature in step S4 is 500-600°C.

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