A method for simulating the change of particle number concentration and particle size spectrum distribution during the generation of new particles

Abstract

The present invention provides a method for simulating changes in particle number concentration and particle size spectrum distribution during new particle generation, including calculating relevant characteristic parameters during a new particle generation event; calculating the impact of atmospheric transport on the new particle number concentration during a new particle generation event; determining upper and lower boundaries of the simulation based on actual measurements of the particle number concentration and particle size spectrum distribution; and simulating changes in the particle number concentration and particle size spectrum distribution during a new particle generation event using aerosol dynamics. The present invention improves existing dynamic equations for calculating new particle generation events, considers the impact of atmospheric transport on changes in particle number concentration, and improves the accuracy of simulating changes in particulate matter during new particle generation events. The present invention can quantitatively evaluate the impact of various parameters on the particle number concentration during a new particle generation event, which helps to evaluate the impact of new particle generation events on atmospheric particulate matter. It can also evaluate the causes of atmospheric pollution and provide an analytical method for global climate change analysis.

Description

Technical Field

[0001] The present invention relates to the technical field of particle number concentration and particle size spectrum simulation, and in particular to a method for simulating changes in particle number concentration and particle size spectrum distribution during the generation of new particles. Background Art

[0002] New particle formation (NPF) refers to the process in which gaseous precursors in the atmosphere collide and form particles through condensation and continue to grow through condensation and other processes. As one of the world's important sources of atmospheric aerosols, it can occur in most regions of the world (including cities, forests, oceans, etc.). After growing to a certain particle size, new particles can activate into atmospheric cloud condensation nuclei (CCN) and affect the evolution of clouds, thereby affecting the global climate. In addition, the new particles that have grown can also increase the particle reaction area, promote the particle-gas-particle distribution process and the heterogeneous reaction process, thereby exacerbating secondary atmospheric pollution.

[0003] The contribution of new particle generation events to atmospheric particulate matter is influenced by multiple factors, including the generation rate, growth rate, background particle distribution, and atmospheric transport. The generation rate describes the rate at which new particles are generated. A higher generation rate results in a higher concentration of new particles in the atmosphere per unit time. This means more particles are available for growth and activation into CCN. The growth rate refers to the rate at which new particle size increases. A higher growth rate allows new particles to more quickly activate into cloud condensation nuclei, reducing collision losses with background particles. The background particle distribution significantly influences the atmospheric lifetime of gaseous precursors and new particles. High concentrations of large background particles can quickly remove new particles through collisions, thereby reducing their number concentration. Atmospheric transport, on the other hand, can bring new particles generated elsewhere to a local area or dilute them, affecting the concentration and size distribution of new particles in the atmosphere. The impact of new particle generation events on atmospheric particle number concentration varies significantly across regions and from different new particle generation events. This variation may be due to significant differences in the parameters of different new particle generation events.

[0004] Current research on new particle generation events primarily focuses on observational studies of parameters such as the generation rate, but lacks a means to quantitatively assess the impact of these parameters on particle number concentration. Existing models have been constructed to simulate the evolution of particle matter during localized new particle generation events. This approach has been used to assess the impact of parameters such as the generation rate on changes in particle number concentration. However, these models ignore the influence of atmospheric transport processes on changes in particle number concentration. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention provides a method for simulating the change in particle number concentration and particle size spectrum distribution during the generation of new particles.

[0006] The technical solution of the present invention is: a method for simulating the change in particle number concentration and particle size spectrum distribution during the generation of new particles, comprising the following steps:

[0007] S1), calculating the relevant characteristic parameters during the new particle generation event;

[0008] S2), calculate the effect of atmospheric transmission on the number concentration of new particles during the new particle generation event;

[0009] S3), determining the upper and lower boundaries of the simulation based on the actual measured particle number concentration and particle size spectrum distribution;

[0010] S4) Use aerosol dynamics to simulate the changes in particle number concentration and size spectrum distribution during new particle generation events; and evaluate the impact of changing simulation conditions on the changes in particle number concentration during new particle generation events.

[0011] Preferably, in step S1), the relevant characteristic parameters during the new particle generation event include the generation rate and growth rate of new particles and the background particle number concentration and particle size spectrum distribution.

[0012] Preferably, in step S1), the calculation expression of the growth rate GR of the new particles is:

[0013]

[0014] Where Dp nuc is the particle size of the new particles.

[0015] Preferably, in step S1), the particle number concentration distribution spectrum during the new particle generation event is fitted by using a single-mode log-normal distribution fitting, that is:

[0016]

[0017] Where, is the particle number concentration distribution spectrum, N is the particle number concentration, σ is the fitting parameter, and Dp is the particle size.

[0018] As a preference, in step S1), the generation rate J of the new particles k The calculation formula is:

[0019]

[0020] Where, For particle size range Dp k To Dp u The particle number concentration between k With Dp u are the upper and lower limits of the particle size for calculating the new particle generation rate; β(i，g) The particle size is Dp i With Dp g Particle collision rate; n u The particle size is Dp u Particle distribution function; GR u The particle size is Dp u The growth rate of particulate matter.

[0021] Preferably, in step S1), the background particle number concentration and particle size spectrum distribution is selected as the average value of the particle number concentration distribution at 0-6 o'clock on the day of the new particle generation event.

[0022] As a preferred step, in step S2), for a specific particle size of Dp k The change in number concentration of particulate matter due to atmospheric transmission is calculated by the following formula:

[0023]

[0024]

[0025] Where TR k represents the atmospheric transmission term; N k Indicates particle size as Dp k The concentration of particulate matter; β (k，i) Indicates particle size as Dp k With Dp i Particle collision rate; N i Indicates particle size as Dp i the concentration of particulate matter; Indicates particle size as Dp i and Particle collision rate; N i 、 The particle size is Dp i 、 The concentration of particulate matter; n k The particle size is D Pk The particle distribution function; Dp k 、Dp i Respectively represent particle size.

[0026] As a preference, in step S3), the upper boundary Dp of the simulation up The change of (t) with time is determined by the following formula:

[0027] Dp up (t) = GR·(tt start )

[0028] Where GR is the growth rate of new particles; t startThe time when the new particle spawning event begins.

[0029] As a preference, in step S3), the lower boundary Dp of the simulation down The change of (t) with time is determined by the following formula:

[0030] Dp down (t) = GR·(tt end ).

[0031] Where, t end The time when the generation of new particles ends, that is, no new particles are observed to continue to be generated.

[0032] Preferably, in step S4), the change in particle number concentration of new particle generation events is simulated by aerosol dynamics, and the lower limit of particle size k is measured. * The change in particle number concentration is simulated by the following formula:

[0033]

[0034] in, k is the lower limit of particle size * The particle number concentration, k is the lower limit of particle size * The particle generation rate, The particle size is The particle distribution function; The particle size is The particle number concentration; The particle size is Dp i and The particle collision rate; Ni is the particle size Dp i The particle number concentration.

[0035] Preferably, in step S4), the change in the number concentration of particles with other particle sizes k is simulated by the following formula:

[0036]

[0037] Where N k Indicates particle size as Dp k The concentration of particulate matter; n k 、n k-1 Respectively represent the particle size Dp k With Dp k-1 The particle distribution function; GR represents the growth rate of new particles; Indicates particle size D Pi and The particle collision rate of Ni, Represents Dp i and The particle number concentration of TR k Indicates that the particle size caused by atmospheric transmission is Dp k Changes in particle number concentration.

[0038] The beneficial effects of the present invention are:

[0039] 1. This invention improves the existing dynamic equations for calculating new particle generation events, taking into account the impact of atmospheric transport on changes in particle number concentration, and improves the accuracy of simulating particle changes during new particle generation events;

[0040] 2. The present invention can quantitatively evaluate the impact of various parameters on the particle number concentration in new particle generation events, which helps to evaluate the impact of new particle generation events on atmospheric particulate matter;

[0041] 3. The method of the present invention can evaluate the causes of air pollution and provide an analytical method for global climate change analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic diagram of the process of Example 1 of the present invention;

[0043] Figure 2 This is a distribution diagram of new particle generation events observed in Panyu District, Guangzhou City, Guangdong Province on December 12, 2014 in Example 2 of the present invention;

[0044] Figure 3 This is a graph showing changes in the growth rate of new particles during a new particle generation event in Example 2 of the present invention;

[0045] Figure 4 This is a graph showing the distribution of the number concentration and particle size spectrum of background particles in Example 2 of the present invention;

[0046] Figure 5 This is a graph showing the effect of atmospheric transport on particulate matter concentration during a new particle generation event in Example 2 of the present invention;

[0047] Figure 6 The particle number concentration and particle size spectrum distribution change diagram of Example 2 of the present invention, wherein (a) the actual measured particle number concentration and particle size spectrum distribution change diagram; (b) the simulated particle number concentration and particle size spectrum distribution change diagram; (c) the actual observed and simulated particle number concentration (N CN ) graph.

[0048] Figure 7 The actual measured particle number concentration and particle size spectrum distribution of Example 2 of the present invention and the particle number concentration and particle size spectrum distribution simulated using different parameters are shown. DETAILED DESCRIPTION

[0049] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0050] Example 1

[0051] like Figure 1 As shown, this embodiment provides a method for simulating changes in particle number concentration and particle size spectrum distribution during new particle generation, including the following steps:

[0052] S1), calculating the relevant characteristic parameters during the new particle generation event;

[0053] In this embodiment, the relevant characteristic parameters during the new particle generation event include the new particle generation rate, growth rate, and background particle number concentration and particle size spectrum distribution.

[0054] The calculation expression of the growth rate GR of the new particles is:

[0055]

[0056] Where Dp nuc For the new particle p nuc particle size.

[0057] In this embodiment, the particle number concentration distribution spectrum during the new particle generation event is fitted by using a single-mode log-normal distribution fitting, that is:

[0058]

[0059] Where, is the particle number concentration distribution spectrum, N is the particle number concentration, σ is the fitting parameter, D P is the particle size.

[0060] The generation rate of new particles J k The calculation formula is:

[0061]

[0062] Where, For particle size range Dp k To Dp u The particle number concentration between k With Dp u are the upper and lower limits of the particle size for calculating the new particle generation rate; β (i，g) The particle size is Dp i With Dp g Particle collision rate; n u The particle size is Dp u Particle distribution function; GR u The particle size is Dp u The growth rate of particulate matter.

[0063] In this embodiment, the particle size is D Pi With D Pg The particle collision rate β (i，g) Expressed as:

[0064]

[0065] Where, Respectively represent the particle size Dp i With Dp g The calculation of intermediate quantity; Di, D g Respectively represent the particle size Dp i With Dp g The particle diffusion coefficient; Respectively represent the particle size Dp i With Dp g The average particle velocity;

[0066] in,

[0067]

[0068]

[0069]

[0070]

[0071]

[0072] Where T is the Kelvin temperature; k is the Boltzmann constant; m i Indicates particle size as Dp i The mass of particulate matter; i Indicates particle size as Dp i The mean free path of particles; C c is the Cunningham correction factor, and ρ is the particle density.

[0073] The background particle number concentration and particle size spectrum distribution is selected as the average value of the particle number concentration distribution at 0-6 o'clock on the day when the new particle generation event occurs.

[0074] S2), calculate the effect of atmospheric transmission on the number concentration of new particles during the new particle generation event;

[0075] In this embodiment, the atmospheric transport term refers to the change in particle number concentration per unit time due to atmospheric transport. i The change in number concentration of particulate matter due to atmospheric transmission is calculated by the following formula:

[0076]

[0077]

[0078] Where TR k represents the atmospheric transmission term; N k Indicates particle size as Dp k The concentration of particulate matter; β (k，i) Indicates particle size as Dp k With Dp i Particle collision rate; N i Indicates particle size as Dp i the concentration of particulate matter; Indicates particle size as Dp i and Particle collision rate; N i 、 The particle size is Dp i 、 The concentration of particulate matter; n k The particle size is Dp k The particle distribution function; Dp k 、Dp i Respectively represent particle size.

[0079] S3), determining the upper and lower boundaries of the simulation based on the actual measured particle number concentration and particle size spectrum distribution;

[0080] In this embodiment, when simulating new particle generation events, it is necessary to assume that other particles, except for the newly generated particles, are not affected by condensation growth or particle collisions. Therefore, it is necessary to determine the upper and lower boundaries of the simulated particle size during the new particle generation process to exclude particles of other sizes from the aerosol dynamics calculation. Because the particle size of the particles continues to increase during the new particle generation process, it is necessary to determine the upper and lower boundaries of the simulated particle size at different times.

[0081] The upper boundary Dp simulated in this embodiment up The change of (t) over time is defined as:

[0082] Dp up (t) = GR·(tt start )

[0083] Where GR is the growth rate of new particles; t start The time when the new particle spawning event begins.

[0084] Simulated lower boundary Dp down The change of (t) with time is determined by the following formula:

[0085] Dp down(t) = GR·(tt end ).

[0086] Where, t end The time when the generation of new particles ends, that is, no new particles are observed to continue to be generated.

[0087] S4) Use aerosol dynamics to simulate the changes in particle number concentration and size spectrum distribution during new particle generation events; and evaluate the impact of changing simulation conditions on the changes in particle number concentration during new particle generation events.

[0088] The particle number concentration changes of new particle generation events are simulated by aerosol dynamics, and the lower limit of particle size k is measured. * The change in particle number concentration is simulated by the following formula:

[0089]

[0090] in, k is the lower limit of particle size * The particle number concentration, k is the lower limit of particle size * The particle generation rate, The particle size is The particle distribution function; The particle size is The particle number concentration; The particle size is Dp i and Particle collision rate; N i The particle size is Dp i The particle number concentration.

[0091] For the change in particle number concentration of other particle sizes k, the following formula is used for simulation:

[0092]

[0093] Where N k Indicates particle size as Dp k The concentration of particulate matter; n k 、n k-1 Respectively represent the particle size Dp k With Dp k-1 The particle distribution function; GR represents the growth rate of new particles; Indicates particle size D Pi and Particle collision rate; N i 、 Represents Dp i and The particle number concentration of TR kIndicates that the particle size caused by atmospheric transmission is Dp k Changes in particle number concentration.

[0094] Based on the above steps, this embodiment uses Matlab software to simulate the new particle generation event. The simulation step size is set to 10 s. The input parameters include the calculated new particle growth rate, generation rate, background particle distribution, and atmospheric transport term.

[0095] Example 2

[0096] This study conducted field observations at the top of Gangshan Mountain in Dazhen, Panyu District, Guangzhou City, Guangdong Province, from November 22, 2014, to January 3, 2015. A scanning mobility aerosol spectrometer (SMPS) was used to measure the number concentration and size distribution of particles ranging from 10 to 400 nm. A typical new particle generation event on December 12th was selected for analysis. The new particle generation event occurred around 9:30 AM and began to grow after generation, reaching a size of 50 to 60 nm around 8:00 PM.

[0097] After measuring the change in the particle size spectrum distribution of the new particle generation event, this embodiment uses the method of Example 1 to calculate the generation rate J of new particles with a particle size of 10 nm. 10 .like Figure 3 As shown, J 10 It started to increase around 9:30 and reached a peak around 11:30 (about 7.2 cm -3 s -1 ), then dropped rapidly and reached 0 at around 12:30, indicating the end of the new particle generation phase.

[0098] Based on the particle number concentration and size spectrum distribution on December 12, the particle number concentration and size spectrum distribution from 00:00 to 6:00 was selected for average calculation to obtain the background particle number concentration and size spectrum distribution, as shown in the following example: Figure 4 As shown, it can be found that the particles are mainly concentrated around 150nm.

[0099] Based on the observed particle size distribution, the method of Example 1 was used to calculate the effect of atmospheric transmission on the number concentration of newly generated particles. Figure 5 It can be seen that the atmospheric transmission first increases the number concentration of newly generated particles, and its influence is about 0-260cm -3 . Then its influence gradually turned negative, causing the particle number concentration to decrease and reach a trough at 13:00, then slowly rose and turned from negative to positive at 14:00, and has remained positive since then.

[0100] The new particle generation rate (J 10), growth rate (GR), background particle distribution and atmospheric transport, a model based on aerosol dynamics equations is used to simulate the new particle generation event. The simulation results are as follows Figure 6 As shown in (a), (b), and (c), it is found that the method of Example 1 can better capture the changes in the particle number concentration and particle size spectrum distribution during the new particle generation event, and the particle number concentration (N CN ) in terms of the change trend of the simulation results is also consistent with the actual observation value. Due to the influence of the primary emission, the observed particulate matter did not show a smooth downward trend during the period of 14:00-18:00. There were still some particles in the 10-30nm particle size range. However, due to the change of the simulation boundary, the change of this part of the particles was not taken into account. Therefore, the simulated N CN Still descending smoothly.

[0101] This embodiment can better simulate the change of particle number concentration and particle size spectrum distribution during the new particle generation event ( Figure 7 Based on (a) and (b), by adjusting the simulation input parameters (2 times and 0.5 times), including the growth rate (GR), generation rate (J), background particle distribution (PNSD) and atmospheric transport effect (TR), the factors that mainly affect the particle number concentration, particle size spectrum distribution and number concentration during the generation of new particles are analyzed. It can be found that the growth rate has the most significant effect on the change of particle size, such as Figure 7 (e)- Figure 7 (h) Under the 0.5 times GR scenario, the newly generated particles can only grow to about 40nm, while under the 2 times GR scenario, the newly generated particles can grow to about 100nm, and the concentration is higher than the 0.5 times GR scenario. However, the changes in J and PNSD do not affect the change in the particle size of the new particles, but mainly affect the change in concentration. Among them, 2 times J and 0.5 times PNSD will lead to an increase in the number concentration of newly generated particles, while 0.5 times J and 2 times PNSD will reduce the number concentration of particles. From the perspective of atmospheric transmission, Figure 7 (j)- Figure 7 (k) Atmospheric transport has little influence on the particle number concentration and size spectrum distribution of this new particle generation event.

[0102] Furthermore, this embodiment uses the effect of varying parameters on the number concentration of new particles during a new particle generation event to investigate the effects of varying parameters. It is found that a high generation rate significantly increases the number concentration of new particles, while a low generation rate has the most negative impact on the number concentration. A high growth rate and a low background particle distribution also increase the number concentration of new particles, while a low growth rate and a high background particle distribution result in a decrease in the number concentration of new particles.

[0103] The above embodiments and descriptions are only for explaining the principles and best embodiments of the present invention. Without departing from the spirit and scope of the present invention, the present invention may be subject to various changes and improvements, which shall fall within the scope of the invention to be protected.

Claims

1. A method for simulating the change in particle number concentration and particle size distribution during the generation of new particles, characterized in that: The steps include: S1), calculating the relevant characteristic parameters during the new particle generation event; S2), calculate the effect of atmospheric transmission on the number concentration of new particles during the new particle generation event; For a specific particle size Dp k The change in number concentration of particulate matter due to atmospheric transmission is calculated by the following formula: Where TR k represents the atmospheric transmission term; N k Indicates particle size as Dp k The concentration of particulate matter; β (k,i) Indicates particle size as Dp k With Dp i Particle collision rate; N i Indicates particle size as Dp i the concentration of particulate matter; Indicates particle size as Dp i and Particle collision rate; N i 、 The particle size is Dp i 、 The concentration of particulate matter; n k The particle size is D Pk The particle distribution function; Dp k 、Dp i Respectively represent particle size; S3), determining the upper and lower boundaries of the simulation based on the actual measured particle number concentration and particle size spectrum distribution; S4) Use aerosol dynamics to simulate the changes in particle number concentration and size spectrum distribution during new particle generation events; and evaluate the impact of changing simulation conditions on the changes in particle number concentration during new particle generation events.

2. The method for simulating changes in particle number concentration and particle size distribution during new particle generation according to claim 1, characterized in that: In step S1), the relevant characteristic parameters during the new particle generation event include the generation rate and growth rate of new particles and the background particle number concentration and particle size spectrum distribution.

3. The method for simulating changes in particle number concentration and particle size distribution during new particle generation according to claim 2, characterized in that: In step S1), the calculation expression of the growth rate GR of the new particles is: Where Dp nuc is the particle size of the new particles.

4. The method for simulating changes in particle number concentration and particle size distribution during new particle generation according to claim 3, characterized in that: In step S1), the particle number concentration distribution spectrum during the new particle generation event is fitted by using a single-mode log-normal distribution fitting, that is: Where, is the particle number concentration distribution spectrum, N is the particle number concentration, σ is the fitting parameter, and Dp is the particle size.

5. The method for simulating changes in particle number concentration and particle size spectrum distribution during new particle generation according to claim 2, characterized in that: In step S1), the generation rate of the new particles J k The calculation formula is: Where, For particle size range Dp k To Dp u The particle number concentration between k With Dp u are the upper and lower limits of the particle size for calculating the new particle generation rate; β (i,g) The particle size is Dp i With Dp g Particle collision rate; n u The particle size is Dp u Particle distribution function; GR u The particle size is Dp u The growth rate of particulate matter.

6. The method for simulating changes in particle number concentration and particle size spectrum distribution during new particle generation according to claim 2, characterized in that: In step S1), the background particle number concentration and particle size spectrum distribution is selected as the average value of the particle number concentration distribution at 0-6 o'clock on the day of the new particle generation event.

7. The method for simulating changes in particle number concentration and particle size distribution during new particle generation according to claim 1, characterized in that: In step S3), the upper boundary Dp of the simulation up The change of (t) with time is determined by the following formula: Dp up (t)=GR·(t-t start ) Where GR is the growth rate of new particles; t start The time when the new particle generation event begins; Simulated lower boundary Dp down The change of (t) with time is determined by the following formula: Dp down (t)=GR·(t-t end ); Where, t end The time when the generation of new particles ends, that is, no new particles are observed to continue to be generated.

8. The method for simulating changes in particle number concentration and particle size distribution during new particle generation according to claim 1, characterized in that: In step S4), the change in particle number concentration of new particle generation events is simulated by aerosol dynamics, and the lower limit of particle size k is measured. * The change in particle number concentration is simulated by the following formula: in, k is the lower limit of particle size * The particle number concentration, k is the lower limit of particle size * The particle generation rate, The particle size is The particle distribution function; The particle size is The particle number concentration; The particle size is Dp i and Particle collision rate; N i The particle size is Dp i The particle number concentration.

9. The method for simulating changes in particle number concentration and particle size spectrum distribution during new particle generation according to claim 8, characterized in that: In step S4), the change in the number concentration of particles with other particle sizes k is simulated using the following formula: Where N k Indicates particle size as Dp k The concentration of particulate matter; n k 、n k-1 Respectively represent the particle size Dp k With Dp k-1 The particle distribution function; GR represents the growth rate of new particles; Indicates particle size D Pi and Particle collision rate; N i 、 Represents Dp i and The particle number concentration of TR k Indicates that the particle size caused by atmospheric transmission is Dp k Changes in particle number concentration.

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