CN111855514A - Dry sedimentation rate measuring device and measuring method thereof - Google Patents
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Abstract
The invention relates to the technical field of dry sedimentation rate determination, in particular to a dry sedimentation rate determination device and a determination method thereof, wherein the determination device comprises: the device comprises a wind tunnel, an aerosol generator, a hygrothermograph, a rectifying chamber, a particle deposition chamber, a first particle counter and an induced draft device; the wind tunnel is of a cylindrical structure with an inner cavity, and the aerosol generator, the hygrothermograph, the rectifying chamber, the particulate matter deposition chamber and the induced draft device are sequentially arranged in the inner cavity from left to right; the rectifying chamber is internally provided with an air speed sensor and a second particle counter, the particle deposition chamber is provided with a cover body which can be opened and closed, and the particle deposition chamber is provided with plant blades during testing. The measuring device and the measuring method can effectively overcome the problem of inaccurate measuring result caused by wall adsorption effect.
Description
Technical Field
The invention relates to the technical field of dry sedimentation rate determination, in particular to a dry sedimentation rate determination device and a determination method thereof.
Background
The information disclosed in this background of the invention is only for enhancement of understanding of the general background of the invention and is not necessarily to be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
The particles can settle on the surface of the plant leaf by means of retention, adhesion, etc., and dry settling is one of the main ways to remove particles that have entered the atmosphere. The Dry settling rate (V) of different plants can be used according to the Dry settling capacity of the plants on the particles under the influence of the physical and biochemical properties of the surface of the leavesd) And (4) quantitatively evaluating. The dry sedimentation rate meansAt a certain wind speed, the concentration of atmospheric particulates per unit time, the total number of aerosol particles deposited per unit blade area:
Vd＝N(u)/A·T·C
wherein, N (u) is the total amount of the settled particles in the time T when the wind speed is u, A is the total area of the blades, and C is the steady-state concentration of the atmospheric particles in the atmospheric environment. At present, the measurement of plant leaf VdThe method mainly comprises an elution method, an air stripping method, an indoor smoke box simulation experiment method, an empirical formula method and the like. The elution method comprises washing the particles retained by the plant leaves with water to separate the particles from the leaf surface, filtering, oven drying, and weighing the eluate to estimate the amount of the particles adsorbed by the leaf surface, thereby calculating Vd. The stripping method comprises blowing up the particles retained by the plant leaves with strong wind, measuring the mass of the stripped particles, and calculating Vd. The indoor smoke box simulation experiment method is characterized in that a blade is placed in an artificial smoke box to be simulated, the concentration range and the determination time length of particulate matters in the smoke box are determined, the exponential decay change rule of the concentration of the particulate matters along with time is further determined, a mathematical model is established to determine a decay rate constant, and the measured blade sample is deduced to form the PM according to the two obtained decay rate constants2.5Dry sedimentation rate ofdAnd (4) calculating a formula. The empirical formula method is mainly based on empirical values, and is simple and convenient to calculate.
However, the elution method results in a large mass loss due to the presence of partially soluble salts in the atmospheric particulates. The blow-off method can cause incomplete blow-off and smaller measured values because the particles are held by other forces except gravity. The indoor smoke box simulation method is an indirect measurement method based on a self-settling rule and a deduction method, and the measurement value is small due to the fact that the inner wall adsorption effect is obvious. Each parameter of the empirical formula method is derived from an empirical value, is simple and convenient to calculate, lacks regional accuracy and is not suitable for PM2.5。
Disclosure of Invention
Aiming at the problems, the invention provides a dry sedimentation rate measuring device and a measuring method thereof, which can effectively overcome the problem of inaccurate measuring result caused by wall adsorption effect. In order to achieve the above object, the technical solution of the present invention is as follows.
In a first aspect of the present invention, there is disclosed a dry sedimentation rate measuring apparatus comprising: the device comprises a wind tunnel, an aerosol generator, a rectification chamber, a particle deposition chamber, a first particle counter and an induced draft device; the wind tunnel is of a cylindrical structure with an inner cavity, and the inner cavity is sequentially provided with the aerosol generator, the rectifying chamber, the particulate matter deposition chamber and the air inducing device from left to right. The rectifying chamber is internally provided with an air speed sensor and a second particle counter, the particle deposition chamber is provided with a cover body which can be opened and closed, and the particle deposition chamber is provided with plant blades during testing.
Furthermore, the induced draft device is a stepless speed change fan, and the induced draft device mainly has the main function of pumping air in the inner cavity of the wind tunnel to the outside so as to carry particulate matters generated by the aerosol generator to flow from the left end to the right end of the wind tunnel.
Furthermore, the rectification chamber is formed by isolating two rectification nets fixed in an inner cavity of the wind tunnel, and particulate matters generated by the aerosol generator are rectified by the rectification nets and then uniformly enter the particulate matter deposition chamber.
Further, the lid sets up on the roof of particulate matter deposit room, and is provided with the handle on the surface of lid to put into plant leaf after opening fast.
Furthermore, a hook for hanging the plant leaves is arranged on the inner wall of the cover body.
Further, a hygrothermograph is arranged between the aerosol generator and the rectification chamber and is mainly used for measuring the background environment condition, and because the humidity and the temperature can influence the dry sedimentation rate to a certain extent, the hygrothermograph can be used for further analyzing the relationship between the background environment and the sedimentation rate in subsequent researches.
In a second aspect of the present invention, there is disclosed a method for dry sedimentation rate measurement using the above-mentioned measuring apparatus, comprising the steps of:
(1) keeping the inner cavity of the wind tunnel clean, opening all instruments in the inner cavity, and repeatedly adjusting the guideThe rotating speed of the wind device and the flow of the aerosol generator enable the reading of the wind speed sensor to reach a preset experimental wind speed value, meanwhile, the reading of the second particle counter reaches a preset value C, and the value C is the annual average PM of the measurement area2.5And (4) after various numerical values are stable, entering a stable operation stage.
(2) Recording the readings of the hygrothermograph, reading the readings of the first particle counter and the second particle counter, respectively marked as C0、C0' if there is a difference in the concentration of the particulate matter due to the wall adsorption effect, the difference is recorded as Δ C0＝C0-C0’。
(3) When the dry settlement experiment formally starts, the cover body above the experimental section is removed, the other cover body hung with the experimental plant leaves is quickly replaced, the total area of the plant leaves is A, and the moment of starting the test is marked as t0From t due to dust retention of the blades0The difference between the readings of the two particle counters at the beginning of the time varies and is a function of the time t, denoted Δ C(t)After a time T, the particles retained by the blade reach saturation level, and the difference between the readings of the two particle counters reaches Δ C again0And (3) finishing the test, and obtaining the total amount of particles retained on the blade as shown in the formula (1):
in the formula (1), S (unit m)2) The cross section area of the inner cavity of the wind tunnel is shown, and u (unit m/s) is the wind speed under the test working condition, and is measured by a wind speed sensor. In the actual calculation, dt is replaced by sampling interval time, so that the dust retention amount N (u) (unit mu g) of the blade of the species and the blade within the time T (unit s) under the specified wind speed and the specified particulate matter concentration can be calculated.
(4) Dry settling rate (V) of particulate matterd) Defined as the ratio of the total number of aerosol particles deposited per unit area per unit time to the number concentration of aerosol particles in the atmosphere as shown in equation (2):
Vd＝N(u)/A·T·C
in the formula (2), N (u) (in. mu.g) is the total number of particles settled in the time T (in s) at the wind speed u, which is measured in the step (3), A (in m)2) C (unit. mu.g/m) is the total area of the leaf3) The average dry settling rate of the plant leaf is derived from the concentration of such particles in the atmosphere.
Compared with the prior art, the invention has the following beneficial effects:
(1) determination of the differences caused by the wall adsorption effect: when the experiment is carried out, all objects in the test section are emptied, the debugging equipment enables the reading of the wind speed sensor to reach a preset experiment wind speed value, and meanwhile, the reading of the particle counter is close to a preset value C (the annual average PM of a measuring area is measured)2.5Concentration). After stable operation, reading and recording the hygrothermograph, and observing the readings (respectively recorded as C) of two particle counters before and after the experimental section0、C0') has no significant difference. If there is a difference in the concentration of the particles due to the wall adsorption effect, the value Δ C is recorded0＝C0-C0’。
(2) Determination of the total amount of particles retained on the blade: when the dry sedimentation experiment formally starts, the top cover above the experimental section is removed, and the other top cover hung with the experimental blades (the pretreatment of the experiment is carried out, and the total area A of the blades is measured) is quickly replaced. This time is denoted t0. Due to the dust retention of the blades, it is possible to predict the time from t0At the beginning of the moment, the difference between the readings of the two particle counters before and after the moment changes, and the difference is a function of time t and is recorded as deltaC(t)After a time T, the particles retained by the blade reach the saturation level, and the difference between the readings of the two particle counters reaches Δ C again0This experiment was completed, and the total amount of particles remaining on the blade was summarized as shown in the above formula (2).
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.
FIG. 1 is a schematic view showing the structure of a dry sedimentation rate measuring apparatus according to an embodiment of the present invention.
Figure 2 is a graph of the dry settlement rate of the same plot vegetation in an example of the invention.
FIG. 3 is a graph comparing the dry settling rates of PM2.5 for three plant types in examples of the invention.
The scores in the figure represent: 1-wind tunnel, 2-aerosol generator, 3-hygrothermograph, 4-rectification chamber, 5-particle deposition chamber, 6-first particle counter, 7-induced air device, 8-wind speed sensor, 9-second particle counter, 10-cover body, 11-plant blade, 12-rectification net and 13-handle.
Detailed Description
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular is intended to include the plural unless the context clearly dictates otherwise. Furthermore, it will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
For convenience of description, the words "up", "down", "left" and "right" in the present invention, if any, merely indicate that the directions of movement are consistent with those of the drawings, and do not limit the structure, but merely facilitate the description of the invention and simplify the description, rather than indicate or imply that the referenced device or element needs to have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the invention.
Term interpretation section: the terms "mounted," "connected," "fixed," and the like in the present invention are to be understood in a broad sense, and for example, the terms "mounted," "connected," and "fixed" may be fixed, detachable, or integrated; the two components can be connected mechanically, directly or indirectly through an intermediate medium, or connected internally or in an interaction relationship, and the terms used in the description are understood by those skilled in the art as having specific meanings according to the specific situation.
As mentioned above, the current elution method results in a large mass loss due to the presence of partially soluble salts in the atmospheric particulates. The blow-off method can cause incomplete blow-off and smaller measured values because the particles are held by other forces except gravity. The indoor smoke box simulation method is an indirect measurement method based on a self-settling rule and a deduction method, and the measurement value is small due to the fact that the inner wall adsorption effect is obvious. Each parameter of the empirical formula method is derived from an empirical value, is simple and convenient to calculate, lacks regional accuracy and is not suitable for PM2.5. Therefore, the present invention provides a dry sedimentation rate measuring device and a measuring method thereof, and the present invention will be further described with reference to the drawings and the specific examples in the specification.
Referring to fig. 1 and 2, the dry settling rate measuring apparatus shown in the drawings comprises: the device comprises a wind tunnel 1, an aerosol generator 2, a hygrothermograph 3, a rectifying chamber 4, a particle deposition chamber 5, a first particle counter 6 and an induced draft device 7; wherein:
the wind tunnel 1 is a cylindrical structure having an inner cavity, and in this embodiment, the inner cavity of the wind tunnel 1 is sequentially fixed with the aerosol generator 2, the hygrothermograph 3, the rectification chamber 4, the particulate matter deposition chamber 5, and the air inducing device 6 from left to right.
The main function of the aerosol generator 2 is to simulate the production of particles in the atmosphere, so as to measure the dry settling rate of the particles after being captured by the dust retention of the plant leaves 11. The installation of the aerosol generator 2 at the end of the wind tunnel 1 also facilitates a series of numerical tuning and monitoring requirements.
And the rectifying chamber 4 is internally provided with a wind speed sensor 8 and a second particle counter 9 which are respectively used for testing the wind speed in the wind tunnel 1 and the particles passing through the counter.
Further, the particle deposition chamber 5 is provided with a cover 10 capable of being opened and closed, and a plant leaf 11 is placed in the particle deposition chamber 5 during testing so as to test the dry settling rate of the plant leaf on particles in air.
Further, in other embodiments, the air inducing device 6 is selected as a stepless speed-changing fan, and the main function of the fan is to draw air in the inner cavity of the wind tunnel 1 to the outside, so as to carry the particles generated by the aerosol generator 2 from the left end to the right end of the wind tunnel 1.
Further, in other embodiments, the rectification chamber 4 is formed by two rectification nets 12 fixed in the inner cavity of the wind tunnel 1 in an isolated mode, and the particulate matters generated by the aerosol generator 2 enter the particulate matter deposition chamber 5 more uniformly after being rectified by the rectification nets 12.
Further, in other embodiments, the cover 10 is disposed on the top wall of the particulate matter deposition chamber 5, and the outer surface of the cover 10 is provided with a handle 13 for placing the plant leaves 11 after being opened quickly.
Further, in other embodiments, hooks for hanging the plant leaves 11 are provided on the inner wall of the cover 10.
In order to test the effect of the dry settlement rate measuring device shown in fig. 1, in this embodiment, plant leaves of 23 common afforestation tree species in shenzhen city in the growing season of 2019 are used as test objects (including 12 common evergreen broadleaf species in subtropical zone, 3 deciduous broadleaf species, and 8 evergreen shrubs), and a test including the following steps is performed:
(1) in subtropical monsoon climate of Shenzhen city, the growth period of the plant is May to September, the sampling time is set in the growth period of the plant, and the sampling time is set in three days after rainfall so that the rainwater washes away the particulate matters on the surface of the leaf. The sampling place is located in Shenzhen Liyue university city to ensure that the growing environment is similar. 4 standard trees were selected for each tree species. These trees grew well, were similar in age, and had diameters similar to chest height (DBH). Assuming that all leaves of a tree are similar to the sampled leaves and are exposed to the same concentration of contamination under field conditions, the diameter at breast (DBH), height (H) and crown diameter (C) are measured on site using tape measures and DBH scales, and the Leaf Area Index (LAI) and the perpendicular projected area (St) of the crown are measured for estimating the total leaf area.
(2) According to the structure of the tree, branches and leaves are collected from branches in four different directions (east, south, west and north) of different crown layers (low, middle and high crown layers), and the leaves are required to be complete and free from diseases and insect pests. During sampling, branches containing 10-20 leaves are collected by using pruning shears according to the size of the leaves at 12 sampling points of each tree, the branches are packaged in a sealing bag and transported back to a laboratory, and the branches are washed by 1000 ml of deionized water in the laboratory and dried. According to wind speed data of the Shenzhen city meteorological monitoring station every five minutes in 2019, the average wind speed of the Shenzhen city in the whole year is statistically found to be 1.9m/s, and 2m/s is taken as the constant wind speed in the wind tunnel experiment. According to the atmospheric particulate data of Shenzhen city in 2019, the data interval is 5 minutes, and the average PM of Shenzhen city in all years is statistically found2.5The concentration is 24 mug/m3. The laboratory experiments were conducted in an environment where the contaminant concentration was close to the average concentration.
(3) Keeping the inner cavity of the wind tunnel clean, opening all instruments in the inner cavity, and then repeatedly adjusting the rotating speed of the induced draft device 6 and the flow of the aerosol generator 2 to enable the reading of the wind speed sensor 8 to reach a preset experimental wind speed value, and simultaneously enabling the reading of the second particle counter 9 to reach a preset value C, wherein the value C is the annual average PM of the measurement area2.5And (4) after various numerical values are stable, entering a stable operation stage.
(4) Record the reading of the hygrothermograph 3, read the readings of the first particle counter 6 and the second particle counter 9, respectively denoted as C0、C0' if there is a difference in the concentration of the particulate matter due to the wall adsorption effect, the difference is recorded as Δ C0＝C0-C0’。
(5) When the dry settlement experiment formally starts, the cover body above the experimental section is removed, the other cover body 8 hung with the experimental plant leaves 11 is quickly replaced, the total area of the leaves of the plant leaves 11 is A, and the moment of starting the test is recorded as t0From t due to dust retention of the blades0At the beginning of two particlesThe difference in the counter readings changes and is a function of time t, denoted as ac(t)After a time T, the particles retained by the blade reach saturation level, and the difference between the readings of the two particle counters reaches Δ C again0And (3) finishing the test, and obtaining the total amount of particles retained on the blade as shown in the formula (1):
in the formula (1), S (m)2) Is the cross-sectional area of the inner cavity of the wind tunnel, and u (m/s) is the wind speed under the test working condition, and is measured by a wind speed sensor 8. In the actual calculation, dt is replaced by sampling interval time, so that the dust retention quantity N (u) (mu g) of the blade of the species and the blade within the time T(s) under the specified wind speed and the specified particulate matter concentration can be calculated.
(6) Dry settling rate (V) of particulate matterd) Defined as the ratio of the total number of aerosol particles deposited per unit area per unit time to the number concentration of aerosol particles in the atmosphere as shown in equation (2):
Vd＝N(u)/A·T·C (2)
in the formula (2), N (u) (μ g) is the total number of particles settled in the time T(s) at the wind speed u, which is measured in the step (3), A (m)2) C (μ g/m) is the total area of the leaf3) The average dry settling rate of the plant leaves was derived from the concentration of such particles in the atmosphere (see figure 2).
PM of growing season2.5And PM10The greening tree species with the highest dry settlement rate is ficus microcarpa (evergreen broad leaf) which is 5.7cm & s respectively-1And 6.4cm · s-1Second, the defoliation wood (evergreen shrub) and the lime (evergreen shrub) are 4.23cm s each-1And 4.46cm · s-1And 2.66cm · s-1And 2.95cm · s-1。PM2.5And PM10The tree species with the lowest dry settlement rate was cabbage (evergreen broad leaf) and was 0.04 cm. multidot.s -1 and 0.37cm · s-1. The results show that for most tree species, PM is present10Dry settling rate greater than PM2.5The dry settling rate of (a) is,because of PM10The mass is larger, the gravity action is stronger, and the deposition speed is higher; and PM10High dry settlement rate of tree species, PM thereof2.5The dry settling rate is also higher. To illustrate, tree species to PM10And PM2.5The retention mechanism of (a) is similar.
Meanwhile, the vegetation is divided into three groups of evergreen broad leaves, evergreen fallen leaves and shrubs to compare whether the dry settlement rate of the three groups has obvious difference. As can be seen in fig. 3, at a confidence level of 95% (outliers removed), we found the median size of the dry sedimentation rate: evergreen broad leaf (1.60 cm. s)-1)>Deciduous broad leaf (1.39 cm. s)-1)>Evergreen shrubs (0.66 cm. s)-1). The mean dry settlement rate of evergreen shrubs is high, but the difference is large (1.67 cm. s)-1) And secondly evergreen broad leaf (1.64 cm. s)-1) Whereas deciduous and broad-leaved tree species have the lowest mean dry settlement rate and the smallest difference (1.16 cm. multidot.s)-1) The mean differences of the three types were found to be significant by ANOVA comparison, at PM10Similar laws were found in dry settling rates.
Finally, it should be understood that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention. Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.
Claims (7)
1. A dry settling rate measuring device, comprising: the device comprises a wind tunnel, an aerosol generator, a rectification chamber, a particle deposition chamber, a first particle counter and an induced draft device; the wind tunnel is of a cylindrical structure with an inner cavity, and the aerosol generator, the rectifying chamber, the particulate matter deposition chamber and the air inducing device are sequentially arranged in the inner cavity from left to right; the rectifying chamber is internally provided with an air speed sensor and a second particle counter, the particle deposition chamber is provided with a cover body which can be opened and closed, and the particle deposition chamber is provided with plant blades during testing.
2. The dry settling rate measuring device according to claim 1, wherein the air inducing device is a continuously variable fan.
3. The dry settling rate measuring device according to claim 1, wherein the rectifying chamber is isolated by two rectifying nets fixed in an inner cavity of the wind tunnel.
4. The dry sedimentation rate measurement device according to claim 1, wherein the cover is provided on a top wall of the particulate matter deposition chamber, and a handle is provided on an outer surface of the cover.
5. The dry sedimentation rate measuring apparatus according to any one of claims 1 to 4, wherein a hook for hanging a plant leaf is provided on an inner wall of the cover.
6. The dry sedimentation rate measuring device according to any one of claims 1 to 4, wherein a hygrothermograph is further provided between the aerosol generator and the rectifying chamber.
7. A method of dry sedimentation rate determination, wherein the method is performed using the dry sedimentation rate determination apparatus according to any one of claims 1 to 6, comprising the steps of:
(1) keeping the inner cavity of the wind tunnel clean, opening all instruments in the inner cavity, and then repeatedly adjusting the rotating speed of the induced draft device and the flow of the aerosol generator to enable the reading of the wind speed sensor to reach a preset experimental wind speed value, and simultaneously enabling the reading of the second particle counter to reach a preset numerical value C, wherein the numerical value C is the annual average PM of the measurement area2.5After various numerical values are stable, entering a stable operation stage;
(2) recording the reading of the hygrothermograph, reading the first particle meterReadings of the counter and the second particle counter, respectively, are denoted as C0、C0' if there is a difference in the concentration of the particulate matter due to the wall adsorption effect, the difference is recorded as Δ C0＝C0-C0’；
(3) When the dry settlement experiment formally starts, the cover body above the experimental section is removed, the other cover body hung with the experimental plant leaves is quickly replaced, the total area of the plant leaves is A, and the moment of starting the test is marked as t0From t due to dust retention of the blades0The difference between the readings of the two particle counters at the beginning of the time varies and is a function of the time t, denoted Δ C(t)After a time T, the particles retained by the blade reach saturation level, and the difference between the readings of the two particle counters reaches Δ C again0And (3) finishing the test, and obtaining the total amount of particles retained on the blade as shown in the formula (1):
in the formula (1), S (m)2) The cross section area of the inner cavity of the wind tunnel is shown, and u (m/s) is the wind speed under the test working condition and is measured by a wind speed sensor; in the actual calculation, dt is replaced by sampling interval time, so that the dust retention quantity N (u) (mug) of the blade of the species and the blade within the time T(s) under the specified wind speed and the specified particulate matter concentration can be calculated;
(4) dry settling rate (V) of particulate matterd) Defined as the ratio of the total number of aerosol particles deposited per unit area per unit time to the number concentration of aerosol particles in the atmosphere as shown in equation (2):
Vd＝N(u)/A·T·C
in the formula (2), N (u) (μ g) is the total number of particles settled in the time T(s) at the wind speed u, which is measured in the step (3), A (m)2) C (μ g/m) is the total area of the leaf3) The average dry settling rate of the plant leaf is derived from the concentration of such particles in the atmosphere.
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| CN115165687A (en) * | 2022-07-14 | 2022-10-11 | 西北核技术研究所 | Device and method for testing dry settling velocity of micron-sized solid particles |
| CN115356075A (en) * | 2022-08-26 | 2022-11-18 | 西北核技术研究所 | Method for measuring dry deposition speed of atmospheric boundary layer environment wind tunnel |
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| CN115165687A (en) * | 2022-07-14 | 2022-10-11 | 西北核技术研究所 | Device and method for testing dry settling velocity of micron-sized solid particles |
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