Method for simulating particle number concentration particle size spectrum distribution change in new particle generation period

Abstract

The invention provides a particle number concentration particle size spectrum distribution change simulation method in a new particle generation period. The method comprises the following steps: calculating related characteristic parameters in a new particle generation event period; calculating the influence of the atmospheric transmission effect on the new particle number concentration during the new particle generation event; determining upper and lower boundaries of simulation based on the actually measured particle number concentration particle size spectrum distribution; and simulating particle number concentration particle size spectrum distribution change during a new particle generation event by adopting aerosol dynamics. According to the method, the dynamic equation during the period of calculating the new particle generation event in the prior art is improved, the influence of the atmospheric transmission effect on the particle number concentration change is considered, and the accuracy of simulating the particle change in the new particle generation event is improved; according to the method, the influence of each parameter on the particle number concentration in the new particle generation event can be quantitatively evaluated, and the influence of the new particle generation event on the atmospheric particles can be evaluated; the air pollution cause can be evaluated, and an analysis method is provided for global climate change analysis.

Description

Technical Field

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

[0002] New particle generation (NPF) refers to the process in which gaseous precursors in the atmosphere form particulate matter through condensation and coalescence and continue to grow through condensation and other effects. As one of the important global sources of atmospheric aerosols, it can occur in most regions of the world (including cities, forests, oceans, etc.). After the new particles grow to a certain particle size, they can be activated into atmospheric cloud condensation nuclei (CCN) and affect the evolution process of clouds, thereby affecting the global climate. In addition, the grown new particles can also increase the reaction area of particulate matter, promote the gas-particle partitioning process and heterogeneous reaction process of particulate matter, thus exacerbating atmospheric secondary pollution.

[0003] The contribution of new particle generation events to atmospheric particulate matter is affected by multiple factors, such as generation rate, growth rate, background particulate matter distribution, and atmospheric transport effects. The generation rate describes the rate of new particle generation. The higher the generation rate, the higher the concentration of new particles increased in the atmosphere per unit time. And the more particulate matter that can grow and be activated into CCN. The growth rate refers to the particle size growth rate of new particles. When the growth rate of new particles is higher, the new particles can be activated into cloud condensation nuclei faster, and can also reduce the coalescence loss with background particulate matter. The background particulate matter distribution has an important impact on the atmospheric lifetime of gaseous precursors and new particles. High-concentration and large-particle-size background particulate matter can quickly remove new particles through coalescence, thereby reducing the number concentration of new particles. And the atmospheric transport effect will bring new particles generated in other places to the local area, or dilute the new particles generated locally, thus affecting the concentration and particle size distribution of atmospheric new particles. There are great differences in the impact of different regions and different new particle generation events on the number concentration of atmospheric particulate matter. This difference may come from the significant differences in the parameters of different new particle generation events.

[0004] At present, the research on new particle generation events mainly focuses on the observational research of parameters such as generation rate, and there is temporarily a lack of means to quantitatively evaluate the influence of each parameter on particulate number concentration. And there is a model that has been constructed to simulate the evolution process of particulate matter in local new particle generation events. Based on this method, the influence of parameters such as generation rate on the change of particulate number concentration has been evaluated. However, the model ignores the influence of the atmospheric transport process on the change of particulate number concentration during the calculation. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a method for simulating the change of particulate number concentration size spectrum distribution during new particle generation.

[0006] The technical solution of the present invention is as follows: A simulation method for the change of the particle number concentration size spectrum distribution during the generation of new particles, comprising the following steps:

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

[0008] S2), calculating the influence of atmospheric transport on the new particle number concentration during the new particle generation event;

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

[0010] S4), using aerosol dynamics to simulate the change of the particle number concentration size spectrum distribution during the new particle generation event; and by changing the simulation conditions, evaluating the influence on the change of the particle number concentration during the new particle generation event.

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

[0015] Preferably, in step S1), the particle number concentration distribution spectrum during the new particle generation event is fitted by using a single-modal lognormal 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] Preferably, in step S1), the generation rate J of the new particles k is calculated as:

[0019]

[0020] where is the particle number concentration in the particle size range from Dp k to Dp u ; Dp k and Dp u are respectively the upper and lower limits of the particle size for calculating the new particle generation rate; β(i，g) is the collision rate of particulate matter with a particle size of Dp i and Dp g ; n u is the distribution function of particulate matter with a particle size of Dp u ; GR u is the growth rate of particulate matter with a particle size of Dp u .

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

[0022] Preferably, in step S2), for particulate matter with a specific particle size of Dp k , the change in number concentration caused by atmospheric transport is calculated by the following formula:

[0023]

[0024]

[0025] In the formula, TR k represents the atmospheric transport term; N k represents the concentration of particulate matter with a particle size of Dp k ; β (k，i) represents the collision rate of particulate matter with a particle size of Dp k and Dp i ; N i represents the concentration of particulate matter with a particle size of Dp i ; represents the collision rate of particulate matter with a particle size of Dp i and ; N i , are respectively the concentrations of particulate matter with particle sizes of Dp i , ; n k is the distribution function of particulate matter with a particle size of D Pk ; Dp k , Dp i respectively represent the particle sizes.

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

[0027] Dp up (t) = GR · (t - t start )

[0028] In the formula, GR is the growth rate of the new particle; t startThe time when the new particle generation event starts.

[0029] Preferably, in step S3), the lower boundary Dp down (t) changes with time and is determined by the following formula:

[0030] Dp down (t) = GR · (t - t end ).

[0031] In the formula, t end is the time when the new particle generation ends, that is, no new particles are observed to continue to be generated.

[0032] Preferably, in step S4), the change in the number concentration of particulate matter in the new particle generation event is simulated by aerosol dynamics, and the change in the number concentration of particulate matter with a lower measurement particle size limit k * is simulated by the following formula:

[0033]

[0034] Where, is the number concentration of particulate matter with a lower particle size limit k * , is the generation rate of particles with a lower particle size limit k * , is the particulate matter distribution function with a particle size of ; is the number concentration of particulate matter with a particle size of ; is the collision rate of particulate matter with a particle size of Dp i and ; Ni is the number concentration of particulate matter with a particle size of Dp i .

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

[0036]

[0037] In the formula, N k represents the concentration of particulate matter with a particle size of Dp k ; n k , n k-1 respectively represent the particulate matter distribution functions with particle sizes of Dp k and Dp k-1 ; GR represents the growth rate of new particles; represents the collision rate of particulate matter with a particle size of D Pi and ; Ni, respectively represent Dp i and Number concentration of particulate matter; TR k Indicates the change in the number concentration of particulate matter with a particle size of Dp due to atmospheric transport k Change in the number concentration of particulate matter

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

[0039] 1. The present invention improves the existing dynamic equation during the calculation of new particle generation events, takes into account the influence of atmospheric transport on the change in particulate matter number concentration, and improves the accuracy of simulating the change in particulate matter during new particle generation events;

[0040] 2. The present invention can quantitatively evaluate the influence of each parameter on the particulate matter number concentration during 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 analysis method for global climate change analysis. Brief Description of the Drawings

[0042] Figure 1 Is a schematic flow chart of the method of Embodiment 1 of the present invention;

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

[0044] Figure 3 Is a change curve graph of the new particle growth rate during the new particle generation event in Embodiment 2 of the present invention;

[0045] Figure 4 Is a curve graph of the particle size spectrum distribution of the background particulate matter number concentration in Embodiment 2 of the present invention;

[0046] Figure 5 Is a curve graph of the influence of the atmospheric transport term on the particulate matter concentration during the new particle generation event in Embodiment 2 of the present invention;

[0047] Figure 6 Is a change diagram of the particle size spectrum distribution of the particulate matter number concentration in Embodiment 2 of the present invention, where (a) is the change diagram of the actually measured particle size spectrum distribution of the particulate matter number concentration; (b) is the simulated particle size spectrum distribution change diagram of the particulate matter number concentration; (c) is the curve graph of the actual observation and simulation of the particulate matter number concentration (N CN )

[0048] Figure 7 Is the actually measured particle size spectrum distribution of the particulate matter number concentration in Embodiment 2 of the present invention and the particle size spectrum distribution diagrams of the particulate matter number concentration simulated with different parameters. Detailed Description of the Invention

[0049] The following further describes the specific embodiments of the present invention in conjunction with the accompanying drawings:

[0050] Embodiment 1

[0051] As Figure 1 shown, this embodiment provides a simulation method for the change of particle number concentration size spectrum distribution during the generation of new particles, including the following steps:

[0052] S1), Calculate 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 generation rate, growth rate of new particles, and the background particle number concentration size spectrum distribution. Among them:

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

[0055]

[0056] In the formula, Dp nuc is the particle size of new particle p nuc

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

[0058]

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

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

[0061]

[0062] In the formula, is the particle number concentration in the particle size range from Dp k to Dp u ; Dp k and Dp u are respectively the upper and lower limits of the particle size for calculating the new particle generation rate; β (i，g) is the collision rate of particles with particle size Dp i and Dp g ; n u is the particle distribution function with particle size Dp u ; GR u is the growth rate of particles with particle size Dp u ​​

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

[0064]

[0065] In the formula, respectively represent the calculation intermediate quantities for particle sizes Dp i and Dp g ; Di, D g respectively represent the diffusion coefficients of particles with particle sizes Dp i and Dp g ; respectively represent the average speeds of particles with particle sizes Dp i and Dp g ;

[0066] Among them,

[0067]

[0068]

[0069]

[0070]

[0071]

[0072] In the formula, T is the Kelvin temperature; k is the Boltzmann constant; m i represents the mass of particles with particle size Dp i ; l i represents the mean free path of particles with particle size Dp i ; C c is the Cunningham correction factor, and ρ is the particle density.

[0073] The number concentration size spectrum distribution of the background particles is selected as the average value of the particle number concentration distribution from 0 to 6 o'clock on the day of the new particle generation event.

[0074] S2), calculate the influence of atmospheric transport on the new particle number concentration during the new particle generation event;

[0075] In this embodiment, the atmospheric transport term refers to the change in the particle number concentration per unit time caused by atmospheric transport. For particles with a specific particle size Dp i , the change in the number concentration caused by atmospheric transport is calculated by the following formula:

[0076]

[0077]

[0078] In the formula, TR k represents the atmospheric transmission term; N k represents the concentration of particulate matter with a particle size of Dp k ; β (k，i) represents the collision rate of particulate matter with a particle size of Dp k and Dp i ; N i represents the concentration of particulate matter with a particle size of Dp i ; represents the collision rate of particulate matter with a particle size of Dp i and ; N i , are respectively the concentrations of particulate matter with particle sizes of Dp i , ; n k is the particle size distribution function of particulate matter with a particle size of Dp k ; Dp k , Dp i respectively represent the particle sizes.

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

[0080] In this embodiment, in simulating the new particle generation event, it is necessary to assume that except for the newly generated particulate matter, other particulate matters are not affected by condensation growth and coagulation between particulate matters. Therefore, it is necessary to determine the upper and lower boundaries of the simulated particle size during the simulation of the new particle generation process, so as to exclude other particle size particulate matters from the aerosol dynamics calculation. Since the particle size of particulate matter continuously increases 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] In this embodiment, the variation of the upper boundary Dp up (t) with time is defined as:

[0082] Dp up (t) = GR·(t - t start )

[0083] In the formula, GR is the growth rate of new particles; t start is the start time of the new particle generation event.

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

[0085] Dp downG(t) = GR·(t - t end ).

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

[0087] S4) Simulate the change of the particle number concentration size spectrum distribution during the new particle generation event by aerosol dynamics; and evaluate the influence on the change of the particle number concentration during the new particle generation event by changing the simulation conditions.

[0088] The change of the particle number concentration during the new particle generation event is simulated by aerosol dynamics. The change of the particle number concentration with the lower limit of the measured particle size k * is simulated by the following formula:

[0089]

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

[0091] For the change of the particle number concentration of particles with other particle sizes k, it is simulated by the following formula:

[0092]

[0093] Wherein, N k represents the concentration of particles with the particle size Dp k ; n k , n k-1 respectively represent the particle distribution functions with the particle sizes Dp k and Dp k-1 ; GR represents the growth rate of new particles; represents the collision rate of particles with the particle size D Pi and ; N i , respectively represent the particle number concentrations of Dp i and ; TR kIndicates the change in the number concentration of particulate matter with particle size Dp due to atmospheric transport k of particulate matter.

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

[0095] Example 2

[0096] From November 22, 2014 to January 3, 2015, an outdoor observation experiment was carried out on the top of Dazhengang Mountain in Panyu District, Guangzhou City, Guangdong Province. A scanning mobility particle sizer (SMPS) was used to measure the number concentration size spectrum distribution of particulate matter with a size of 10 - 400 nm. A typical new particle generation event on December 12 was selected for analysis. The new particle generation event occurred at around 9:30 in the morning. After the new particles were generated, they began to grow and grew to 50 - 60 nm at around 20:00.

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

[0098] Based on the number concentration size spectrum distribution of particulate matter on December 12, the number concentration size spectrum distribution from 00:00 to 6:00 was averaged to obtain the background particulate matter number concentration size spectrum distribution. As Figure 4 shown, it can be found that the particulate matter is mainly concentrated at around 150 nm.

[0099] Based on the observed number concentration size spectrum distribution of particulate matter, the method of Example 1 is used to calculate the influence of atmospheric transport on the number concentration of newly generated particulate matter. As Figure 5 can be seen, the atmospheric transport first increases the number concentration of newly generated particulate matter, and its influence is approximately within 0 - 260 cm -3 . Subsequently, its influence gradually turns negative, reducing the particulate matter number concentration, reaching a trough at 13:00, then slowly rising, turning from negative to positive at 14:00, and then remaining positive.

[0100] After calculating the new particle generation rate (J 10) After considering the growth rate (GR), background particulate matter distribution, and atmospheric transport effects, a model based on the aerosol dynamics equation is used to simulate new particle formation events. The simulation results are as shown in Figure 6 (a), (b), and (c) in the figure. It is found that the method of Example 1 can better capture the changes in the particle number concentration size spectrum distribution during the new particle formation event. At the same time, in terms of the particle number concentration (N CN ), the change trend of the simulation results also agrees well with the actual observed values. Due to the influence of primary emissions, during the period from 14:00 to 18:00, the observed particulate matter did not show a smooth downward trend, and there was still some particulate matter distribution in the particle size range of 10 - 30 nm. However, due to the change of the simulation boundary, the change of this part of particulate matter was not considered, so the simulated N CN still decreased smoothly.

[0101] On the basis of better simulating the changes in the particle number concentration size spectrum distribution during the new particle formation event ( Figure 7 (a), (b)), by adjusting the simulation input parameters (2 times and 0.5 times), including the growth rate (GR), generation rate (J), background particulate matter distribution (PNSD), and atmospheric transport effect (TR), the factors mainly affecting the particle number concentration size spectrum distribution and number concentration during the new particle formation process are analyzed. It can be found that the growth rate has the most significant impact on the particle size change. As shown in Figure 7 (e)- Figure 7 (h), in the case of 0.5 times GR, the newly generated particles can only grow to about 40 nm, while in the case of 2 times GR, the newly generated particles can grow to about 100 nm, and the concentration is higher than that in the case of 0.5 times GR. The changes in J and PNSD do not affect the particle size change of the new particles, but mainly affect the concentration change. Among them, 2 times J and 0.5 times PNSD will lead to an increase in the number concentration of newly generated particulate matter, while 0.5 times J and 2 times PNSD will reduce the particle number concentration. From the analysis of the role of atmospheric transport, as shown in Figure 7 (j)- Figure 7 (k), the impact of atmospheric transport on the particle number concentration size spectrum distribution of this new particle formation event is not significant.

[0102] In addition, by using the influence of different parameter changes on the particle number concentration of new particles during the new particle formation event in this embodiment, it can be found that a high generation rate can most significantly increase the particle number concentration of new particles, while a low generation rate has the most negative impact on the particle number concentration of new particles. A high growth rate and a low background particulate matter distribution will also increase the particle number concentration of new particles, while a low growth rate and a high background particulate matter distribution will lead to a decrease in the particle number concentration of new particles.

[0103] The above-described embodiments and the description in the specification are only to illustrate the principles and the best embodiments of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed.

Claims

1. A method for simulating the change of particle number concentration and particle size spectrum 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 impact of atmospheric transport on the number concentration of new particles during the new particle generation event; 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 particle size spectrum distribution during new particle generation events; and evaluate the impact of changing the simulation conditions on the changes in particle number concentration during new particle generation events.

2. The method for simulating the change of particle number concentration and particle size spectrum distribution during the generation of new particles 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 particle size spectrum distribution of background particle number concentration.

3. The method for simulating the change of particle number concentration and particle size spectrum distribution during the generation of new particles 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 the change of particle number concentration and particle size spectrum distribution during the generation of new particles 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: In the formula, 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 the change of particle number concentration and particle size spectrum distribution during the generation of new particles according to claim 2, characterized in that: In step S1), the generation rate of the new particles is k The calculation formula is: In the formula, 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 The 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 particles.

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

7. The method for simulating the change of particle number concentration and particle size spectrum distribution during the generation of new particles according to claim 1, characterized in that: In step S2), for a specific particle size Dp k The change in number concentration of particles due to atmospheric transmission is calculated by the following formula: In the formula, 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 The particle collision rate; N i Indicates particle size as Dp i The concentration of particulate matter; Indicates particle size as Dp i and The 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 of Dp k 、Dp i Respectively represent particle size.

8. The method for simulating the change of particle number concentration and particle size spectrum distribution during the generation of new particles 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 at which the new particle generation event begins. As a preference, in step S3), the 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 It is the time when the generation of new particles ends, that is, no new particles are observed to continue to be generated.

9. The method for simulating the change of particle number concentration and particle size spectrum distribution during the generation of new particles 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 of The particle size is The particle number concentration; The particle size is Dp i and The particle collision rate; N i The particle size is Dp i The particle number concentration.

10. The method for simulating the change of particle number concentration and particle size spectrum distribution during the generation of new particles according to claim 9, characterized in that: In step S4), the change in the number concentration of particles with other particle sizes k is simulated by 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 as 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; N i , Respectively represent 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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