A device and method for measuring wet deposition removal coefficient of small-size aerosol particles

Abstract

The present invention provides a device and method for measuring the wet deposition clearance coefficient of small-size aerosol particles, which solves the problem that the current deposition amount is difficult to be accurately weighed, and the measurement of the wet deposition coefficient is ultimately erroneous due to the inability to distinguish aerosol particles of different particle sizes. The present invention measures the dry deposition velocity v of the corresponding particle size for the aerosol particle size whose wet deposition clearance coefficient needs to be measured. TS ; Then, aerosol particles are input through the aerosol generator. When the environmental conditions for measuring the dry deposition velocity are reached, the aerosol particles are left to stand for a period of time to allow for uniform distribution, and then the spray device is turned on. Finally, the wet deposition removal coefficient Λ of the aerosol particles of the corresponding particle size is obtained based on the data obtained by the particle size spectrometer.

Description

Technical Field

[0001] The invention relates to the technical field of aerosol particle testing, and in particular to a device and method for measuring the wet deposition clearance coefficient of small-diameter aerosol particles. Background Art

[0002] There are a large number of tiny particles in the atmosphere, which seriously affect the environment and human health, especially particles with an aerodynamic diameter of less than 10μm. PM10 particles settle extremely slowly in the atmosphere and stay in the air for a long time. All kinds of harmful substances in the air, such as bacteria and viruses, are almost all attached to particles with a diameter of less than 10μm, further aggravating the harmfulness of suspended aerosol particles.

[0003] The removal of aerosols by spraying is an important process for maintaining the balance of aerosol particles in the atmosphere and the self-cleaning of the atmosphere. A deep understanding of the wet deposition process and mechanism of aerosol particles is of great significance to protecting the atmospheric environment and promoting human health. Therefore, it is necessary to accurately measure the wet deposition removal coefficient of suspended aerosol particles under spraying conditions.

[0004] The wet deposition removal coefficient Λ is generally measured based on the removal coefficient definition:

[0005]

[0006] Among them, Δt is the wet deposition test time, Δm is the mass of aerosol particles removed due to wet deposition within Δt, and m is the total mass of aerosol particles at the initial moment.

[0007] At present, the following difficulties exist in the measurement using the definition of wet deposition removal coefficient shown in formula (1): the suspended aerosol particles are very small and the sedimentation speed is slow, so the aerosol particle sedimentation amount obtained within an acceptable time range is very small. Limited by the accuracy of the electronic balance, the sedimentation amount is difficult to be accurately weighed. In addition, it is impossible to distinguish aerosol particles of different particle sizes in the process, so it is impossible to give the sedimentation amount of aerosol particles of a specified particle size, which further causes errors in the measurement of the wet deposition removal coefficient. Summary of the invention

[0008] The present invention provides a device and method for measuring the wet deposition clearance coefficient of small-size aerosol particles, which are used to solve the problem that the current deposition amount is difficult to be accurately weighed, and the deposition amount of aerosol particles of a certain specified particle size cannot be given due to the inability to distinguish aerosol particles of different particle sizes, which ultimately leads to a large error in the measurement of the wet deposition coefficient.

[0009] To achieve the above object, the technical solution of the present invention is as follows:

[0010] A device for measuring the wet deposition removal coefficient of small-size aerosol particles, which is special in that it includes an experimental cabin, a spray device, an aerosol generator, a particle size spectrometer and a data acquisition device; the spray device is installed at the top of the experimental cabin to provide a spray environment;

[0011] The aerosol generator is connected to the experimental cabin, and the output end of the aerosol generator is located at the upper end of the experimental cabin; the input end of the particle size spectrometer is located at the lower end of the experimental cabin, and the output end of the particle size spectrometer is connected to the input end of a data acquisition device, and the data acquisition device is used to display and save the data collected by the particle size spectrometer.

[0012] A method for measuring the wet deposition removal coefficient of small-size aerosol particles is special in that: based on the above-mentioned device for measuring the wet deposition removal coefficient of small-size aerosol particles, the steps are as follows:

[0013] Step 1), put a given powder material into the powder storage container of the aerosol generator, turn on the aerosol generator, input aerosol particles of a specified particle size into the experimental chamber, turn on the particle size spectrometer at the same time, and observe the data measured by the particle size spectrometer;

[0014] When the particle size spectrometer measures the concentration of aerosol particles of the specified particle size in the experimental chamber to be about 10 5 ~10 6 cm -3 When the aerosol generator is turned off;

[0015] Step 2) Use a particle size spectrometer to continuously measure the aerosol particle concentration C(t) in the experimental chamber to obtain the relationship between the concentration of aerosol particles of a specified particle size and time; according to the relationship between the aerosol particle concentration and its change over time, obtain the dry deposition velocity v of aerosol particles of a specified particle size TS ;

[0016] Step 3), when the aerosol particle concentration in the experimental chamber drops to the background level, the aerosol generator is turned on again, aerosol particles are input into the experimental chamber, and the measurement data of the particle size spectrometer is observed at the same time. When the aerosol particle size in the experimental chamber is consistent with the aerosol particle size pre-set in step 1), and the aerosol particle number concentration reaches the concentration level in step 1) again, the aerosol generator is turned off;

[0017] Step 4), let it stand for a period of time to make the aerosol particles in the experimental chamber evenly distributed;

[0018] Step 5), pre-set the spray intensity of the spray device, start the spray device to spray, and use the particle size spectrometer to continuously monitor the concentration of aerosol particles to obtain the relationship between the concentration of aerosol particles of a specified particle size and time. When the concentration of aerosol particles drops to the environmental background level, stop spraying;

[0019] Step 6), obtain the relationship between the concentration of aerosol particles of a specified particle size and time through step 5), and combine the dry deposition velocity of the aerosol particles obtained in step 2) to obtain the wet deposition clearance coefficient Λ of the aerosol particles of the specified particle size.

[0020] Further, in step 2), the dry settling velocity v of the aerosol particles is obtained by the following formula: TS :

[0021] v TS =-k1H

[0022] Where H represents the aerosol particle settling height, which is the net height in the experimental cabin, and the unit is m; k1 is the slope of the linear fitting curve between the natural logarithm of the aerosol particle concentration during dry deposition, lnC(t), and the dry deposition test time t.

[0023] Further, in step 6), the aerosol particle wet deposition removal coefficient Λ of the preset aerosol particle size is obtained by the following formula:

[0024]

[0025] Among them, v TS is the dry settling velocity of aerosol particles, in m / s; H represents the settling height of aerosol particles, in m;

[0026] k' is the slope of the linear fitting curve between the natural logarithm of the aerosol particle concentration lnC(t)' during wet deposition and the wet deposition test time t'.

[0027] Furthermore, in step 4, the aerosol particles in the experimental chamber are evenly distributed after standing for about 2 minutes or observing that the concentration data measured by the particle size spectrometer shows a gentle change trend.

[0028] Furthermore, in step 1), before turning on the aerosol generator, it is necessary to clean the experimental chamber, spray device, aerosol generator, particle size spectrometer and connecting pipes to ensure that all components and connecting pipes are clean to prevent the aerosol particles deposited therein from clogging the air path or being brought into the experimental chamber, thereby adversely affecting the subsequent experimental measurement process.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] In the present invention, there is no need to measure the wet deposition flux or deposition mass of aerosol particles. The wet deposition removal coefficient of aerosol particles of a specified particle size under spraying conditions can be obtained only by monitoring the relationship between the concentration of aerosol particles of a specified particle size and time using a particle size spectrometer.

[0031] The method is simple and easy to operate, and the data is easy to measure. It can distinguish different particle sizes of aerosol particles and complete the wet deposition removal coefficient measurement of various small-size aerosol particles in a single measurement process. It also brings small errors and is easier to measure the wet deposition removal coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a structural schematic diagram of an embodiment of the present invention;

[0033] The specific reference numerals are as follows:

[0034] 1. Experimental chamber, 2. Spraying device, 3. Aerosol generator, 4. Particle size spectrometer, 5. Data acquisition equipment. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods.

[0036] like Figure 1 As shown, a device for measuring the wet deposition removal coefficient of small-size aerosol particles includes an experimental chamber 1, a spray device 2 arranged on the top of the experimental chamber 1, an aerosol generator 3, a particle size spectrometer 4 and a data acquisition device 5.

[0037] The aerosol generator 3 is connected to the experimental cabin 1 , and the output end of the aerosol generator 3 is located at the upper end of the experimental cabin 1 .

[0038] The input end of the particle size spectrometer 4 is connected to the lower end of the experimental cabin 1, and the output end of the particle size spectrometer 4 is connected to the input end of the data acquisition device 5. The data acquisition device 5 adopts a personal terminal notebook.

[0039] A method for measuring the wet deposition removal coefficient of small-size aerosol particles based on the above device has the following specific steps: The particle size of the aerosol particles in this embodiment does not exceed 8 microns.

[0040] Step 1: Clean the experimental device and its connecting pipes to ensure that the experimental device and its connecting pipes are clean, reduce the background level of aerosol particles in the experimental device and its connecting pipes, and prevent the aerosol particles deposited therein from blocking the air path or being brought into the experimental chamber, thereby adversely affecting the experimental process and introducing new errors.

[0041] Step 2, turn on the particle size spectrometer 4 to monitor the aerosol particle concentration and aerosol particle size in the experimental chamber 1 in real time, so as to facilitate the monitoring of the experimental process.

[0042] Step 3, turn on the aerosol generator 3, input aerosol particles into the experimental chamber 1, and observe the measurement data of the particle size spectrometer 4 at the same time. When the particle size of the aerosol particles in the experimental chamber meets the target particle size and the concentration reaches an appropriate level, turn off the aerosol generator 3.

[0043] Since the aerosol generation technology of certain specific particle sizes and materials is difficult in itself, the particle size of artificially generated aerosol particles may not meet the target requirements. In addition, the experimental chamber 1 cannot be completely sealed, so the particle size of aerosol particles inside it is also affected by the external environment. Therefore, before measuring the wet deposition clearance coefficient of aerosol particles, it is necessary to first confirm that the particle size of aerosol particles in the experimental chamber 1 is consistent with the particle size of aerosol particles whose wet deposition clearance coefficient needs to be measured. This is the so-called "the particle size spectrum of aerosol particles in the experimental chamber 1 meets the target particle size"; in this technical solution, a given powder material capable of generating a target particle size is placed in the powder storage container of the aerosol generator 3, so that the aerosol generator 3 generates aerosol particles of the target particle size. The concentration reaches an appropriate level, which means that the concentration of aerosol particles of a specific particle size should be significantly higher than the environmental background level, but it should not be too high to avoid too rapid coagulation. Because the higher the concentration, the faster the coagulation, which is not conducive to the measurement of sedimentation velocity. The concentration of aerosol particles of a specified particle size reaches 10 5 ~10 6 cm -3 It is appropriate.

[0044] Step 4, using the particle size spectrometer 4 to continuously measure the aerosol particle concentration in the experimental chamber 1, obtain the relationship between the concentration of aerosol particles of a specified particle size and time (under no spraying conditions), select the data points in the dry deposition stage, and because the data in the initial stage is unstable and the aerosol particle concentration in the later stage is too low, the initial stage and the later stage are eliminated, and the remaining data points are fitted and related subsequent calculations are performed to obtain the dry deposition velocity of aerosol particles of this particle size.

[0045] The calculation method is as follows:

[0046] When small-size aerosol particles undergo dry deposition in the experimental chamber 1, the relationship between their concentration and time is:

[0047]

[0048] The meaning of each symbol is:

[0049] C(t) represents the concentration of aerosol particles of specified size in the experimental chamber 1 at time t during the dry deposition process, in m -3 ;

[0050] C0 represents the concentration of aerosol particles of a specified size in the experimental chamber 1 at the initial time (t=0) during the dry deposition process, in m -3 ;

[0051] v TS It indicates the dry deposition velocity of aerosol particles during dry deposition, in m / s;

[0052] t represents the dry sedimentation test time, in seconds;

[0053] H represents the aerosol particle settling height, in meters.

[0054] Taking the logarithm of both sides of equation (2), we get:

[0055]

[0056] According to formula (3), when small-size aerosol particles undergo dry deposition in the experimental chamber 1, the natural logarithm of the concentration of aerosol particles of a specified size in the experimental chamber 1 at time t during the dry deposition process, lnC(t), is linearly related to the dry deposition test time t, and its slope k1 is:

[0057]

[0058] According to the measured data, the lnC(t)-t relationship curve is drawn and linear fitting is performed to obtain the slope k1 of the fitting curve. The dry deposition velocity v of the aerosol particles can be obtained. TS for:

[0059] v TS =-k1H (5)

[0060] In the above data processing process, the data C(t) and C0 used are measured by the particle size spectrometer 4 in step 4. H is related to the size of the experimental chamber 1, the aerosol particle injection speed and other parameters. Under the condition of small particle size, the sedimentation height is the net height in the experimental chamber 1, which can be obtained through measurement.

[0061] Step 5, after the aerosol particle concentration drops to the background level, turn on the aerosol generator 3 again, input aerosol particles into the experimental chamber 1, and observe the measurement data of the particle size spectrometer 4 at the same time. When the aerosol particle size spectrum in the experimental chamber 1 meets expectations and the concentration reaches an appropriate level, turn off the aerosol generator.

[0062] The background level is the content of aerosol particles in the environment (atmosphere), which can be considered stable when the external environment does not change.

[0063] Step 6: Let it stand for a while until the concentration of aerosol particles in the experimental chamber 1 is evenly distributed.

[0064] The method to determine whether it is uniform is as follows:

[0065] First, based on experience, for the experimental chamber and powder materials used in this application, they can usually be considered basically uniform after being left to stand for about 2 minutes; second, observe the concentration data measured by the particle size spectrometer. If the concentration change trend is relatively gentle, it can be considered basically uniform.

[0066] After standing, the sediment will also settle and the concentration will change. However, the standing time is usually only a few minutes, and it takes several hours or even more than ten hours for the concentration to drop to the background level. Therefore, during this period of standing, the concentration drop can be ignored.

[0067] Step 7, pre-set the spray intensity and spray time, turn on the spray device 2, spray according to the set spray intensity and spray time, and use the particle size spectrometer 4 to continuously monitor the aerosol particle concentration.

[0068] The spray intensity is set according to the user's needs and the actual situation of the measuring device. If you need to measure the aerosol particle concentration corresponding to a certain spray intensity, set the spray intensity to the corresponding value.

[0069] The basis for determining the spraying time is: based on the aerosol particle concentration monitoring data, when the aerosol particle concentration is close to the environmental background level, the spraying can be stopped.

[0070] Step 8, perform data processing according to the following formulas (6) to (9) to obtain the relationship between the number concentration of aerosol particles of a specified particle size and time, and combine the dry deposition velocity and deposition height data obtained in step 4 to obtain the wet deposition removal coefficient of aerosol particles of this particle size.

[0071] The calculation process of aerosol particle wet deposition removal coefficient is as follows:

[0072] When small-size aerosol particles are wet deposited in the experimental chamber 1, the relationship between their concentration and time is:

[0073]

[0074] Taking the logarithm of both sides of equation (6), we get:

[0075]

[0076] The meaning of each symbol is:

[0077] C(t)' represents the concentration of aerosol particles of specified size in the experimental chamber 1 at time t' during the wet deposition process, in m -3 ;

[0078] C0' represents the concentration of aerosol particles of a specified size in the experimental chamber 1 at the initial time (t'=0) during the wet deposition process, in m -3 ;

[0079] v TS It represents the dry deposition velocity of aerosol particles during wet deposition, in m / s;

[0080] t' represents the wet deposition test time, in seconds;

[0081] Λ represents the wet deposition removal coefficient;

[0082] H represents the aerosol particle settling height, in meters.

[0083] The data C(t)′ and C0′ used are measured and obtained by the particle size spectrometer 4 in step 7 .

[0084] According to formula (6), there is a linear relationship between the natural logarithm of the concentration of small-size aerosol particles in the experimental chamber 1, lnC(t)', and the wet deposition test time t'. The lnC(t)'-t' relationship curve is fitted, and the slope k' of the curve is:

[0085]

[0086] The wet deposition removal coefficient Λ is:

[0087]

[0088] Dry settling velocity v TS Obtained from the control dry deposition experiment in step 4 above, according to formula (6)~

[0089] (9) Based on the concentration data monitored by the particle size spectrometer, the wet deposition removal coefficient Λ of small-size aerosol particles can be determined.

Claims

1. A method for measuring the wet deposition removal coefficient of small-size aerosol particles, characterized in that: A device for measuring the wet deposition removal coefficient of small-size aerosol particles is used, comprising an experimental chamber (1), a spray device (2), an aerosol generator (3), a particle size spectrometer (4) and a data acquisition device (5); The spray device (2) is installed at the top of the experimental cabin (1) to provide a spray environment; The aerosol generator (3) is connected to the experimental chamber (1), and the output end of the aerosol generator (3) is located at the upper end of the experimental chamber (1); The input end of the particle size spectrometer (4) is located at the lower end of the experimental cabin (1), and the output end of the particle size spectrometer (4) is connected to the input end of a data acquisition device (5), and the data acquisition device (5) is used to display and save the data collected by the particle size spectrometer (4); The steps are as follows: Step 1), put a given powder material into the powder storage container of the aerosol generator (3), turn on the aerosol generator (3), input aerosol particles of a specified particle size into the experimental chamber (1), turn on the particle size spectrometer (4), and observe the data measured by the particle size spectrometer (4); When the particle size spectrometer (4) measures that the concentration of aerosol particles of a specified particle size in the experimental chamber (1) reaches 10 5 ~10 6 cm -3 When the aerosol generator (3) is turned off; Step 2), using a particle size spectrometer (4) to continuously measure the aerosol particle concentration C(t) in the experimental chamber (1), and obtain the relationship between the concentration of aerosol particles of a specified particle size and time; according to the relationship between the aerosol particle concentration and its change over time, obtain the dry settling velocity v of the aerosol particles of the specified particle size TS ; The dry deposition velocity v of aerosol particles is obtained by the following formula: TS : in TS =-k1H Wherein, H represents the aerosol particle settling height, which is the net height in the experimental chamber (1) in meters, and k1 is the slope of the linear fitting curve between the natural logarithm of the aerosol particle concentration lnC(t) during the dry deposition process and the dry deposition test time t; Step 3), when the aerosol particle concentration in the experimental chamber (1) drops to the background level, the aerosol generator (3) is turned on again, aerosol particles are input into the experimental chamber (1), and the measurement data of the particle size spectrometer (4) is observed at the same time. When the aerosol particle size in the experimental chamber (1) is consistent with the aerosol particle size pre-set in step 1), and the aerosol particle number concentration reaches the concentration level in step 1) again, the aerosol generator (3) is turned off; Step 4), leaving the chamber to stand for a period of time so that the aerosol particles in the experimental chamber (1) are evenly distributed; Step 5), presetting the spray intensity of the spray device (2), turning on the spray device (2) for spraying, and simultaneously continuously monitoring the concentration of aerosol particles using a particle size spectrometer (4) to obtain the relationship between the concentration of aerosol particles of a specified particle size and time, and stopping the spraying when the concentration of aerosol particles drops to the environmental background level; Step 6), obtaining the relationship between the concentration of aerosol particles of a specified particle size and time through step 5), and combining the dry deposition velocity of the aerosol particles obtained in step 2) to obtain the wet deposition clearance coefficient Λ of the aerosol particles of the specified particle size; The aerosol particle wet deposition removal coefficient Λ of the preset aerosol particle size is obtained by the following formula: Among them, v TS is the dry settling velocity of aerosol particles, in m / s; H represents the settling height of aerosol particles, in m; k' is the slope of the linear fitting curve between the natural logarithm of the aerosol particle concentration lnC(t)' during wet deposition and the wet deposition test time t'.

2. The method for measuring the wet deposition clearance coefficient of small-size aerosol particles according to claim 1, characterized in that: In step 4), the aerosol particles in the experimental chamber (1) are evenly distributed if the concentration data measured by the particle size spectrometer is observed to have a gentle change trend while standing for 2 minutes.

3. The method for measuring the wet deposition clearance coefficient of small-size aerosol particles according to claim 2, characterized in that: In step 1), before starting the aerosol generator (3), it is necessary to clean the experimental chamber (1), the spray device (2), the aerosol generator (3), the particle size spectrometer (4) and the connecting pipes to ensure that all components and connecting pipes are clean to prevent the aerosol particles deposited therein from clogging the air path or being brought into the experimental chamber, thereby adversely affecting the subsequent experimental measurement process.

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