Persistent Organic Pollutant Air-Surface Exchange Sampler Based on Fugacity Principle

Abstract

A persistent organic pollutant soil-air exchange sampler based on the fugacity principle, comprising: a sampling chamber (1), a base (2), an air pump (3), a flowmeter (4), a particulate pollutant collection tube (5), a gaseous pollutant collection tube (6) and an electronic control module. Among them, a circular hole is provided in the middle of the base (2), the sampling chamber (1) is connected to the circular hole, the sampling chamber (1), the particulate pollutant collection tube (5), the gaseous pollutant collection tube (6), the air pump (3), and the flowmeter (4) are sequentially connected through rubber tubes, and the electronic control module is connected to the air pump (3) and the flowmeter (4). The persistent organic pollutant soil-air exchange sampler based on the fugacity principle provided by the present disclosure is easy to disassemble and assemble, convenient to carry, and only requires battery power supply, which is suitable for short-term sampling in remote areas. The sampling height of this device is only 30 mm, which can effectively avoid the sampling error caused by the vertical distribution of atmospheric pollutants and make the obtained soil-air exchange data closer to the true value.

Description

Technical Field

[0001] The present disclosure relates to the technical field of atmospheric pollutant monitoring, and particularly to a persistent organic pollutant ground-air exchange sampler based on the fugacity principle. Background Art

[0002] Persistent organic pollutants (POPs) are globally migrating pollutants with semi-volatility, and their volatilization or sedimentation behaviors affected by temperature are important links in the global migration and transport process. Therefore, accurately evaluating the exchange direction and flux of POPs at the atmospheric-surface interface is a key link in studying the global transport of POPs. The atmospheric content of POPs pollutants is generally at trace levels. With the current analytical and testing capabilities, large-volume sampling and enrichment are required to ensure the detection of target compounds. This results in the inability to directly conduct real-time observations of the atmospheric-surface flux of POPs.

[0003] The current research on the atmospheric-surface exchange of POPs is mainly completed by means of the fugacity method: calculating the fugacity of POPs in the atmosphere and soil based on concentration and environmental parameters, and then estimating the atmospheric-surface exchange direction and flux. To simplify the calculation process of the fugacity formula, when comparing POPs at different locations or different time periods, the soil-air partition coefficient (K SA ) is often used to directly characterize the volatilization or sedimentation trend of POPs at the soil-air interface. Generally, it is considered that the higher the K SA value of the same compound at different locations or time periods, the more it tends to volatilize into the atmosphere; and vice versa.

[0004] The fugacity formula estimation method has obvious systematic defects: the standard height of the sampling port of the large-volume sampler is 1.5 meters. However, there are often large vertical gradient changes in the pollutant concentration near the surface, and the gaseous pollutant concentration at the soil-air interface may be several times or even an order of magnitude higher than that at 1.5 meters. Therefore, using the atmospheric POPs concentration collected by a common large-volume sampler for fugacity calculation may cause large deviations. In addition, the core component of the large-volume sampler is a high-power air pump, which has high power requirements and is not suitable for conducting research work in remote areas; and large-volume sampling will significantly change the air flow around the sampler, changing the actual atmospheric content and the ground-air exchange situation. Therefore, in view of the current deficiencies, it has become an urgent task to develop a low-power sampler that can be used for collecting surface atmospheric POPs. Summary of the Invention

[0005] In view of the above problems, the present invention provides a persistent organic pollutant ground-air exchange sampler based on the fugacity principle to at least solve some of the above problems.

[0006] The present disclosure provides a persistent organic pollutant soil-air exchange sampler based on the fugacity principle, comprising: a sampling chamber 1, a base 2, an air pump 3, a flowmeter 4, a particulate pollutant collection tube 5, a gaseous pollutant collection tube 6, and an electronic control module; wherein, a circular hole is provided in the middle of the base 2, and the sampling chamber 1 is connected to the circular hole; the sampling chamber 1, the particulate pollutant collection tube 5, the gaseous pollutant collection tube 6, the air pump 3, and the flowmeter 4 are sequentially connected through rubber hoses; the electronic control module is connected to the air pump 3 and the flowmeter 4 for supplying power to the air pump 3 and the flowmeter 4.

[0007] Preferably, the sampling chamber 1 is hemispherical, made of stainless steel, and has a fully open circular bottom.

[0008] Preferably, the circular hole and the circular bottom of the sampling chamber 1 have the same size, and the radius of both is 250 mm.

[0009] Preferably, the base 2 is composed of nine square stainless steel plates of the same size arranged in a 3×3 array, wherein a circular hole is provided in the center of the stainless steel plate at the center position.

[0010] Preferably, the joints between the nine square stainless steel plates are sealed with sealing film or rubber strips.

[0011] Preferably, the size of the base 2 is 1 m×1 m.

[0012] Preferably, the base 2 further includes a plurality of floor feet 10 with a height of 30 mm.

[0013] Preferably, the flow rate of the air pump 3 is 3 - 5 L / min -1 .

[0014] Preferably, the electronic control module includes a switch 7, a voltage regulator 8, and a mobile power source 9.

[0015] Preferably, the filter element in the particulate pollutant collection tube 5 is a glass fiber filter membrane, and the sampling element in the gaseous pollutant collection tube 6 is polyurethane foam, XAD resin, or activated carbon.

[0016] At least one of the above technical solutions adopted in the embodiments of the present disclosure can achieve the following beneficial effects:

[0017] The persistent organic pollutant soil-air exchange sampler based on the fugacity principle provided by the present disclosure is relatively easy to disassemble, assemble, and carry, convenient to move, and only requires battery power supply, making it suitable for short-term sampling in remote areas; the sampling port of the sampler is only 30 mm above the ground, which can effectively avoid sampling errors caused by the vertical distribution of atmospheric pollutants, making the obtained soil-air exchange data closer to the true value. Description of the Drawings

[0018] To more fully understand the present disclosure and its advantages, reference will now be made to the following description in conjunction with the accompanying drawings, in which:

[0019] Figure 1 Schematically shows a schematic diagram of a persistent organic pollutant soil-air exchange sampler based on the fugacity principle provided by an embodiment of the present disclosure;

[0020] Figure 2 Schematically shows a comparison schematic diagram of soil-air partition coefficients obtained by a persistent organic pollutant soil-air exchange sampler based on the fugacity principle provided by an embodiment of the present disclosure and a large-volume sampler;

[0021] Figure 3 Schematically shows a comparison schematic diagram of fugacity ratios at each sampling point obtained by a persistent organic pollutant soil-air exchange sampler based on the fugacity principle provided by an embodiment of the present disclosure; Detailed implementation manners

[0022] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the following detailed description, for the sake of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, obviously, one or more embodiments can also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present disclosure.

[0023] The terms used herein are merely for describing specific embodiments and are not intended to limit the present disclosure. The terms "including", "comprising" and the like used herein indicate the presence of the described features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0024] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0025] Referring to Figure 1 , the present disclosure provides a persistent organic pollutant soil-air exchange sampler based on the fugacity principle, including: a sampling chamber 1, a base 2, an air pump 3, a flowmeter 4, a particulate pollutant collection tube 5, a gaseous pollutant collection tube 6, and an electronic control module.

[0026] Among them, a round hole is provided in the middle of the base 2, and the sampling chamber 1 is connected to the round hole; the sampling chamber 1, the particulate pollutant collection pipe 5, the gaseous pollutant collection pipe 6, the air pump 3, and the flow meter 4 are sequentially connected by rubber hoses. The particulate pollutant collection pipe 5 is used to filter solid pollutants, and the gaseous pollutant collection pipe 6 is used to collect gaseous POPs, etc.; the electronic control module is connected to the air pump 3 and the flow meter 4 and is used to supply power to the air pump 3 and the flow meter 4. The sampling chamber 1 is hemispherical, made of stainless steel, with a fully open circular bottom. The space of the sampling chamber 1 is mainly used for air mixing. The round hole and the circular bottom of the sampling chamber 1 have the same size, with a radius of 250 mm. The bottom of the sampling chamber 1 is welded to the round hole. Optionally, mechanical structures such as screws and card slots can also be used in combination with sealing strips to connect them together. The base 2 is composed of nine square stainless steel plates of the same size arranged in a 3×3 array. Among them, a round hole is provided in the center of the stainless steel plate at the center position. The joints between the nine square stainless steel plates are sealed with sealing film or rubber strips. The size of the base 2 is 1 m×1 m. The base 2 also includes a plurality of floor feet 10, with a length of 30 mm. The floor feet 10 enable the base 2 to be placed flat 30 mm above the ground surface, forming a space with a height of 30 mm and an area of 1 m 2 between the stainless steel base 2 and the ground surface.

[0027] Preferably, the flow rate of the air pump 3 is 3 - 5 L / min. Due to the small flow rate of the air pump 3, the air slowly flows in the space formed between the stainless steel base 2 and the ground surface. Theoretically, there is sufficient time to contact the ground surface to reach the atmospheric-surface equilibrium state of POPs.

[0028] Preferably, the electronic control module includes a switch 7, a voltage regulator 8, and a movable power source 9. Among them, the movable power source 9 can be a battery pack or a small mobile charging power source.

[0029] Preferably, the filter core in the particulate pollutant collection pipe 5 is a glass fiber filter membrane, and the sampling core in the gaseous pollutant collection pipe 6 is polyurethane foam, XAD resin, or activated carbon, which can be adjusted according to actual application situations.

[0030] The design key points of the persistent organic pollutant (POP) air-soil exchange sampler based on the fugacity principle provided by the present disclosure are as follows: to enable the near-surface air to fully contact the soil, so as to ensure the equilibrium of POPs at the air-soil interface; meanwhile, the minimum sampling volume required for POPs testing should be taken into account. Therefore, parameters such as flow rate, sampling time, and the height of the stainless steel plate from the ground (i.e., the volume of the interface equilibrium region) need to be tested and optimized to determine the optimal sampling conditions. Through testing, when the height of the base 2 from the ground exceeds 50 mm, the sampling is easily affected by strong airflows such as wind, and the flow rate cannot be effectively controlled. When the height of the base 2 from the ground is lower than 10 mm, the air resistance during the operation of the air pump 3 is relatively large, and the flow rate fluctuates significantly. Therefore, a compromise choice is made to set the height of the base 2 from the ground at 30 mm. Under the condition of a 30-mm height from the ground, the POPs concentration obtained at an air flow rate of 3 - 5 L / min is the most stable. Considering the minimum quantitative standard for analysis and testing, the operating conditions for each sampling of this sampler are finally determined to continuously sample for 4 - 6 days at a flow rate of 3 - 5 L / min.

[0031] In one embodiment of the present disclosure, the method for using the POP air-soil exchange sampler based on the fugacity principle is as follows: First, splice 9 stainless steel plates and the hemispherical sampling cover, and fix the hemispherical sampling cover to the middle plate with screws; then, separately install the glass fiber filter membrane and polyurethane foam (abbreviated as PUF foam) into the metal tubes. Before sampling, the PUF foam needs to be pre-cleaned with dichloromethane by Soxhlet extraction for 16 hours; successively connect the sampling cover, the metal tube containing the glass fiber filter membrane, the metal tube containing the PUF foam, the air pump 3, and the flowmeter 4 with white rubber tubes, and check the airtightness of the connection points; finally, turn on the power supply 9, and sampling starts. The flow rate of the air pump 3 is 3 - 5 L / min, and the specific flow rate can be adjusted according to the actual situation. During the sampling process, mainly rely on the PUF foam (with a diameter of 3 cm and a length of 7.5 cm) as the adsorption medium to collect organic pollutants in the atmosphere. The sampling period is 4 - 6 days. After sampling is completed, wrap the PUF foam with clean tin foil paper and store it in an environment of -20 °C for analysis.

[0032] The following further illustrates a POP air-soil exchange sampler based on the fugacity principle provided by the present disclosure in combination with specific embodiments.

[0033] Example 1

[0034] In this embodiment, the air-soil exchange sampler based on the fugacity principle is used for the study of POPs air-surface exchange under different surface conditions on the Qinghai-Tibet Plateau. The content of POPs in environmental media on the Qinghai-Tibet Plateau is extremely low, and many research sites lack basic power supply facilities, which is an excellent location to test the operation of the sampler under extreme conditions.

[0035] The three test sites of this embodiment are all located in the Tibet Autonomous Region: (1) Lulang: with an altitude of 3300 m, located in southeastern Tibet, the surface is covered with forest vegetation; (2) Namcha Barwa: with an altitude of 4730 m, located in the central part of the Qinghai-Tibet Plateau, the surface is covered with alpine meadow vegetation; (3) Ngari: with an altitude of 4270 m, located in the western part of the Qinghai-Tibet Plateau, the surface is alpine desert.

[0036] At each of the above test sites, two plots within 100 meters apart were selected to install two soil-air exchange samplers based on the fugacity principle, both with a slow flow rate of 4 L min -1 and a sampling period of 5 days for surface air sampling. Each sample obtained an average air volume of approximately 30 m 3 . Two sampling periods (referring to summer and winter) were carried out each year to study the seasonal variation of POPs air-soil exchange, with each period being 20 days.

[0037] In this embodiment, large-volume samplers were used as the control group. Large-volume samplers were installed in the three regions of Lulang, Namcha Barwa, and Ngari to measure the atmospheric POPs concentration. The sampler was 1.5 m above the ground surface. The large-volume sampler used fiberglass membranes to intercept atmospheric particulate matter and PUF foam sampling column cores (diameter 6 cm × 7.5 cm) to adsorb gaseous organic pollutants. Each sample collected approximately 600 m 3 of air.

[0038] In this embodiment, soil samples were also collected. During the atmospheric sampling period, surface 5-cm soil samples were collected around the sampling points and thoroughly mixed.

[0039] The experimental analysis and experimental results of this embodiment are as follows.

[0040] The atmospheric POPs concentration C a , the gaseous POPs concentration C sa at the soil-air interface, and the soil POPs concentration C s were obtained respectively by the large-volume sampler, the soil-air exchange sampler, and the soil sample determination. Thus, the POPs soil-air partition coefficients K SA and K SA-real based on the atmospheric concentration and the soil-air interface concentration were calculated respectively. Among them, the calculation formulas for K SA and K SA-real are as follows:

[0041]

[0042]

[0043] Generally, K SA can be used to characterize the distribution of POPs at the air-soil interface, which is usually related to the properties of the compound (i.e., the octanol-air partition coefficient KOA ) There is a linear relationship. From Figure 2 it can be seen that the K SA value (K SA ) obtained based on the large-volume sampler is SA higher than the K SA-real value (K

[0044] ) obtained based on the soil-air exchange sampler by 1 to 4 orders of magnitude.

[0045]

[0046] f a = C a / RT; (4)

[0047]

[0048] Among them, f s and f a respectively represent the fugacity (Pa) of POPs in soil and atmosphere, is the proportion of organic matter in dry soil, K oa is the octanol-air partition coefficient of POPs, R is the ideal gas constant (8.31 Pa m 3 ·mol -1 ·K -1 ), and T is the temperature (K). FF is the fugacity ratio. When FF > 0.53, it indicates that the pollutant volatilizes from the soil; when FF < -1.2, it indicates that the pollutant sediments from the atmosphere to the soil; when FF is between -1.2 and 0.53, it is considered that POPs are in an equilibrium state at the soil-atmosphere interface.

[0049] Substitute the measured C sa value into formula (4) to replace the C a value and calculate the FF value. It can be found that: whether in the forest area (Lulang) with extremely high soil organic matter content or in the desert area (Ali), there are some samples with FF values greater than 0.53, that is, POPs show the state of volatilizing from the soil to the atmosphere ( Figure 3 ). The soil on the Qinghai-Tibet Plateau may be a secondary volatilization source of POPs. This partly overturns the conclusion of the early research that "the soil on the Qinghai-Tibet Plateau is a'sink' of POPs".

[0050] In summary, whether it is the comparison of the K SA value or the FF value, it shows that the soil-air exchange sampler based on the fugacity principle provided by the present disclosure has partly improved the deficiencies of the previous research compared with the large-volume sampler, and reduced the underestimation of the atmospheric concentration and the overestimation of the atmospheric sedimentation trend to the ground surface caused by using the large-volume sampler.

[0051] The fugacity principle-based persistent organic pollutant soil-air exchange sampler provided by the present disclosure is relatively easy to disassemble, assemble and carry, convenient for movement, and only requires battery power supply, making it suitable for short-term sampling in remote areas. The sampling port of the sampler is only 30 mm above the ground, which can effectively avoid the sampling error caused by the vertical distribution of atmospheric pollutants, making the obtained soil-air exchange data closer to the true value.

[0052] Those skilled in the art can understand that the features recited in the various embodiments and / or claims of the present disclosure can be combined or / and combined in various ways, even if such combinations or combinations are not explicitly recited in the present disclosure. In particular, without departing from the spirit and teachings of the present disclosure, the features recited in the various embodiments and / or claims of the present disclosure can be combined and / or combined in various ways. All such combinations and / or combinations fall within the scope of the present disclosure.

[0053] Although the present disclosure has been shown and described with reference to specific exemplary embodiments thereof, those skilled in the art should understand that various changes in form and detail may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents. Therefore, the scope of the present disclosure should not be limited to the above embodiments, but should be determined not only by the appended claims but also by the equivalents of the appended claims.

Claims

1. A persistent organic pollutant soil-gas exchange sampler based on the fugacity principle, characterized in that, Including: A sampling chamber (1), a base (2), an air pump (3), a flowmeter (4), a particulate pollutant collection tube (5), a gaseous pollutant collection tube (6), and an electronic control module; Among them, a circular hole is provided in the middle of the base (2), and the sampling chamber (1) is connected to the circular hole; the sampling chamber (1), the particulate pollutant collection tube (5), the gaseous pollutant collection tube (6), the air pump (3), and the flowmeter (4) are sequentially connected through rubber tubes; the electronic control module is connected to the air pump (3) and the flowmeter (4) for supplying power to the air pump (3) and the flowmeter (4); The flow rate of the air pump (3) is 3 - 5 L / min; The base (2) is composed of nine square stainless steel plates of the same size in a 3×3 array. Among them, a circular hole is provided at the center of the stainless steel plate at the center position; the joints between the nine square stainless steel plates are sealed with sealing film or rubber strips; the base (2) further includes a plurality of floor feet (10), and the floor feet (10) are 30 mm high.

2. The sampler according to claim 1, wherein The sampling chamber (1) is hemispherical, made of stainless steel, and the circular bottom is fully open.

3. The sampler according to claim 2, wherein The circular hole and the circular bottom of the sampling chamber (1) have the same size, and the radius of both is 250 mm.

4. The sampler according to claim 1, wherein, The size of the base (2) is 1 m × 1 m.

5. The sampler according to claim 1, characterized in that, The electronic control module includes a switch (7), a voltage regulator (8), and a mobile power supply (9).

6. The sampler according to claim 1, characterized in that, The filter element in the particulate pollutant collection tube (5) is a glass fiber filter membrane, and the sampling core in the gaseous pollutant collection tube (6) is polyurethane foam, XAD resin, or activated carbon.

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