FR3005353A1 - AEROSOL COLLECTION DEVICE - Google Patents

Abstract

The invention relates to a device (10) for collecting aerosols, characterized in that it comprises: - a plate (11) having a surface (12) for depositing aerosols, and - at least one projection (13) projecting from said surface, adapted to form an obstacle to a flow of aerosol-laden air flowing through the plate and generate turbulence in said air flow to promote the deposition of aerosols on the surface. The invention also relates to an aerosol recovery system, comprising: a device (10) for collecting aerosols, and a cover adapted to be fixed on the collection device, comprising a flat plate in which is arranged at least one groove adapted to receive all the bosses of the collection device when the cover is fixed on the collection device, and to form in cooperation with the plate of the collection device a flow channel of a fluid.

Description

FIELD OF THE INVENTION The invention relates to the field of the collection of aerosols in air, to study their composition and their behavior in terms of dry deposition (deposit in the absence of rainy precipitation) on surfaces exposed to the air.

STATE OF THE ART Aerosols are particles suspended in a gaseous medium, typically air, of negligible rate of fall, on which pollutants of various origins, for example gases and organic, inorganic or radioactive. Aerosols become vectors of these pollutants, which therefore follow the same movements, for example by convective movements or mechanical turbulence. The study of the atmospheric dispersion and the deposition of certain pollutant thus leads to study these aerosols. To study aerosol deposition, several types of collectors have been developed. A first type of collector simply consists of a rainwater collector. The rain, falling, captures aerosols and flaps them to the ground (wet deposit) and lays aerosols deposited on the collector in dry weather. The recovered rainwater contains the aerosols present in the air on the site. It can be used to measure the presence of pollutants by evaluating their concentration in rainwater. The disadvantage of this type of device is that the deposit is considered as a total deposit (dry + wet) which is not representative of the only dry deposit. It has also been developed electrical devices for collecting aerosols on suction filter, but these devices require a connection to a source of electricity. In addition, the aerosol suction in a given environment provides information only on the average aerosol concentration in the air on the sampling time, not on the amount transferred by dry deposition. There are also devices for collecting aerosols by dry deposition in the form of large plastic bins protected from the rain that is positioned in a site and whose content is then recovered for analysis. However the presence of the side walls of a tank prevents to know the level of turbulence prevailing inside, the capacity of the air to be renewed there, thus the estimate of the dry deposition by turbulence in this tank. In addition, the electrostatic forces between the aerosols and the plastic constituting the tank vary the amount of aerosols deposited by a factor of up to 10. Finally, when a plastic bin is placed in the sun to collect aerosols, it s heats up under the effect of radiation. However, the particles, by thermophoresis, have a natural tendency to move in the air from hot regions to cold regions, so that the dry deposit decreases in the collector when its surface is hotter than air. The results obtained by the use of such devices are therefore not sufficient and reliable enough to estimate dry deposition in a given environment.

SUMMARY OF THE INVENTION The object of the invention is to overcome at least one of the disadvantages of the prior art presented above. In particular, one of the aims of the invention is to provide an aerosol collecting device which does not require electricity to operate, and which makes it possible to obtain more reliable information on the concentration in the air of the aerosols. aerosols and their dry deposition in a site. In this respect, the invention proposes an aerosol collection device, characterized in that it comprises: a plate having an aerosol deposition surface, and at least one boss projecting from said surface, adapted to forming an obstacle to a flow of aerosol-laden air flowing through the plate and generating turbulence in said air flow to promote the deposition of aerosols on the surface.

Advantageously, but optionally, the invention furthermore proposes at least one of the following characteristics: the bosses are studs regularly distributed over the aerosol deposition surface to maximize the turbulences generated in the air flow traversing the plate . - The boss or bosses are arranged on the surface so as to form between them a network of contiguous channels. the device comprises a plurality of bosses distributed in a spiral on the aerosol deposition surface. The device comprises a plurality of bosses distributed in concentric circles on the aerosol deposition surface. the cylindrical pins have a height of between 0.5 and 3 cm and a diameter of between 2 and 10 mm. - The plate has the shape of a flat disk to ensure a homogeneous and isotropic deposition of aerosols. According to one embodiment, an aerosol recovery system is proposed, comprising: an aerosol collection device, and a cover, adapted to be fixed on the collection device, comprising a flat plate in which is arranged at less a groove adapted to receive all the bosses of the collection device when the cover is fixed on the collection device, and to form in cooperation with the plate of the collection device a flow channel of a fluid. Advantageously, but optionally, the aerosol recovery system further comprises means for sealing the fluid flow channel when the hood is attached to the collection device.

The invention also relates to a method for collecting aerosols used by a recovery system according to the invention, comprising the steps of: positioning a device for collecting aerosols in a sampling site, at a given height relative to the ground, so that the device is protected from the rain, and for a determined duration, at the end of the determined duration, fix a cover on the collection device to form a flow channel of a fluid injecting a fluid into the channel to collect the aerosols deposited on the device, and recovering the fluid containing said aerosols.

The invention also proposes a method for determining a dry deposition flux of aerosols in a given type of environment, characterized in that it comprises the steps of: collecting a quantity of aerosols in said environment by the method previously described, and deducing from the quantity of aerosols collected a stream of dry deposition of aerosols on the device in the environment, - from the average wind speed in said environment during the collection, determine a dry deposition rate of aerosols on the device, - deduce from the dry deposition rate and the dry deposition flux on the device an atmospheric concentration of aerosols in the environment, and - determine, from a deposition rate Dry aerosols in the environment and atmospheric concentration of aerosols, an aerosol dry deposition flux specific to the environment.

The invention finally proposes a method for determining a dry deposition rate of aerosols on an aerosol collection device, as a function of a wind speed, comprising the steps of: placing a device in a medium closed end provided with a blower system or in an open environment, said medium comprising aerosols in predetermined concentration, - implementing the previously exposed aerosol collection method, for different wind speeds generated by the blower system, and deduce from the quantity of aerosols collected for each wind speed and aerosol concentration in the environment a dry deposition flux of aerosols on the device for the given wind speed. DESCRIPTION OF THE FIGURES Other characteristics, objects and advantages of the present invention will appear on reading the detailed description which follows, with reference to the appended figures, given by way of non-limiting examples and in which: FIG. an aerosol collection device according to one embodiment of the invention. - Figure 2 shows a hood that can be fixed on a device of Figure 1 to allow the recovery of collected aerosols. - Figure 3 shows an aerosol recovery system comprising a collection device and a cover for the recovery of collected aerosols. - Figure 4 shows the main steps of an aerosol collection process. FIG. 5 represents the main steps of determining a dry deposition rate of aerosols in a particular environment implemented by means of the collection device.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION FIG. 1 shows an aerosol collection device 10 according to one embodiment of the invention. This device comprises a plate 11, preferably having a disk shape, that is to say that the plate is flat and circular in section. A circular surface 12 of the plate 11 is an aerosol deposition surface on which aerosols contained in the ambient air of a sampling site are deposited when the plate is placed in the site. The plate 11 is preferably made of a material having a thermal capacity making it possible to minimize the temperature differences between the atmosphere and the plate, in order to avoid thermoforetic phenomena, an example of a suitable material being aluminum or steel. stainless. The flat disk shape allows isotropic trapping of aerosols. In addition, the absence of flanges makes it possible not to influence the movements of air near the deposition surface. On the deposition surface 12 is arranged at least one boss 13 projecting from said surface. This boss makes it possible to generate turbulences in the aerosol-laden air flow that travels through the plate, this making it possible to promote the deposition of aerosols on the surface 12.

In this respect, the boss or bosses 13 are advantageously regularly distributed over the deposition surface 12. The bosses may advantageously be cylindrical pins 13, distributed for example in concentric circles or in a spiral, the distance between two adjacent pins being constant. The pins 13 advantageously have a height less than 3 cm, preferably between 0.5 and 3 cm, and a diameter of between 2 and 10 mm. Alternatively, the surface 12 may comprise one or more continuous bosses, forming for example a spiral or concentric circles. The circles or spiral then have a height also less than 3 cm, preferably between 0.5 and 3 cm, and a width, equal to the distance between two successive circles in the case of concentric circles, between 2 and 10 mm. The distribution of the boss or bosses 13 in the spiral is particularly advantageous for subsequently recovering the trapped aerosols. Referring to Figure 2, there is shown a cover 20 for the recovery of said aerosols once deposited on the device 10. This cover comprises a flat plate 21, said plate being advantageously circular and of the same section as the device 10, as shown on the face. On a surface 22 of this cover can be made at least one groove, and preferably a single groove 23, adapted to receive all the bosses 13 of the device 10, by positioning the cover 20 on the device 10, and to form a sealed fluid flow channel in which the bosses are located when the cover is fixed on the device 10. Advantageously, the boss or bosses form a network of contiguous channels, and the groove advantageously has the complementary shape of the network of contiguous channels formed by the bosses, so that the fluid flow channel corresponds to said network.

The geometry of the groove therefore depends on that of the bosses. The cover may not even have a groove, for example when the device comprises a continuous boss protruding from the deposition surface 12. In this case, the cover is a plane disc 21, which forms a channel with the boss 13 when it is fixed on the device 10.

In the case where the device has a plurality of discontinuous bosses such as pins 23, it is however necessary for the cover 20 to comprise a groove 23.

The groove 23 may be a groove dug in the surface 22, the depth of said groove being greater than or equal to the height of the bosses 13 of the device. According to an alternative embodiment, the groove 23 is made by arranging one or more walls projecting from the surface 22, said walls forming the edges of the groove 23, so that the gap between two adjacent walls, or two adjacent elements of the same wall, forms the groove in which the bosses are received. The wall then has a height greater than or equal to that of the bosses 13 of the trapping device.

For example, in the case where the groove 23 is a spiral, the wall itself has a spiral shape. Very advantageously, the fluid flow channel formed when the cover 20 is fixed on the device 10 interconnects all the bosses, and traverses the entire deposition surface 12 of the device, for a use described below. In a very preferred example, the device 10 comprises a plurality of spikes 13 arranged in a spiral extending from the center of the surface 12 to the periphery thereof, and the cover 20 has a single groove 23 also in shape. spiral, the dimensions of which correspond to those of the spiral formed by the bosses. Thus, it is possible to fix the cover 20 on the device so that all the bosses 13 are received in the groove 23, the fluid flow channel being formed by the walls of the groove 23 and by the surface 11 of the device entrapment against said walls. Advantageously, the device 10 and the cover 20 are provided with elements 14, 25 24 for fixing the cover on the device, also ensuring the sealing of the aerosol recovery system obtained, shown in FIG. 3 when the cover is fixed on the device, sealingly closing any gap that may remain between the surface 11 of the device 10 and the cover 20. The fastening elements are, for example, orifices passing through the plates 11 and 21, arranged regularly along the periphery plates, and identically on the two plates to be opposite when the cover is fixed on the device. We can then fix the cover on the device for example by bolting.

In the case described above where the bosses 13 and the groove 23 are spiral, the channel formed when the cap is attached to the device has a spiral shape, and has a first mouth 25 at the periphery of the spiral, and a second mouth 25 'in the center of the spiral.

This configuration makes it possible to flow a liquid, for example water, into the channel thus formed, in order to recover all the aerosols deposited on the plate 12. In particular, it is thus possible to easily recover the aerosols deposited in the vicinity. For example, a quantity of liquid is injected through the second mouth into the center of the spiral, and the liquid exiting is recovered through the first mouth of the spiral. FIG. 4 shows a method 100 for collecting aerosols used with the trapping device 10 and the hood described above. During a first step 110, the trapping device is positioned in a sampling site, the device being preferably placed on a flat support raised above the ground, the device being for example at least 5 cm from the ground preferably between 50 cm and 1.5 m from the ground. This allows the wind speed in the vicinity of the device is not altered by irregularities of the ground, for example plants etc.

In addition, for the trapping device only collects dry aerosol deposition, it is advantageously positioned sheltered from the rain. Advantageously, it is then also protected from the sun, which prevents the device from heating. This shelter can be made by a protective device such as a parasol, said device preferably not having to obstruct the lateral air currents, so as not to limit the deposition of aerosols. The trapping device is thus left for a predetermined period, for example a day or a month. Then, the device is retrieved and positioned on the cover 20, so that the groove 23 of the cover receives all the bosses and forms a fluid flow channel. The hood is fixed on the device so as to make the channel tight. During a step 130, the aerosols deposited on the device 10 are recovered. To do this, a solvent, for example water, is injected into the channel via a mouth, and the entire amount of the aerosol is recovered. water injected by the other mouth.

Thanks to the arrangement described above of the cover 20 and the device 10, the injected water has thus traversed the entirety of the deposition surface 12, and carries with it the deposited aerosols. The recovered water thus contains the aerosols deposited, and can be deduced during a step 140, the flow of dry deposition of aerosols during the duration of the collection, and per unit area. To do this, the quantity of aerosols deposited, either in kg or in Becquerel, is determined by measuring the concentration of said aerosols, and this quantity is divided by the surface of the device 10 and the collection duration, in order to obtain a flow F in kg.rn-2.s-1 or in Bq.m-2.s-1. Referring now to FIG. 5, use will be made of the device 10 for determining a flow of dry aerosol deposition in a given type of environment, an environment being characterized in particular by the composition of the surface. on which aerosols are deposited: meadows, urban areas, vegetation with trees etc. During a first step 100, the aerosol collection method described above is implemented by positioning the device in the environment for which it is desired to determine the flow of dry aerosol deposition. From the quantity of aerosols collected, as indicated above, the flow of dry aerosol deposition on the device 10 and specific to this environment is deduced. During the entire duration of the collection, the wind speed in the environment is furthermore measured during a step 100 '. The speed of the wind in the environment makes it possible to deduce, during a step 200, the dry deposition rate of the aerosols on the device 10 in ms-1, since this dry deposition rate depends on both the speed of the wind and deposit surface. For this purpose, a law making it possible to deduce a dry deposition rate of aerosols on the device 10 as a function of a wind speed is established by carrying out the following operations. A device 10 is positioned in a closed environment provided with a blower system or in an open environment. Aerosols are available in the air contained in the medium at a predetermined concentration. Then, the collection method 100 described above is implemented for different wind speeds, each speed being constant during the collection period, and generated using the blower system or in an open environment.

The quantity of aerosols collected makes it possible to deduce the dry deposition flux of aerosols on the surface, for example in kg.m-2s-1, as indicated above. However, the dry deposition rate Vd is related to the dry deposition flux F by the following relation: IVdI = 1F1 Where C is the concentration of aerosols in the air (contained in the closed medium). The repetition of this collection operation 100 for different wind speeds and for the same concentration of aerosols thus makes it possible to obtain a relationship between the dry deposition flux and the dry deposition rate. Returning to FIG. 5, during a step 300, measured measurements are deduced from an average concentration of aerosols C in the atmosphere during the collection in the studied environment. This concentration is obtained by the following relation: C = Vd Where F is the dry deposition flux measured at the end of step 100, in kg.m-2.s-1 or in Bq.m-2.s -1, and Vd is the dry deposition rate on the device 10 for the average wind speed during collection, determined during step 200. However, according to the same relationship, the flow of dry deposition of aerosols on the soil of the studied environment (and no longer on the device 10) is obtained by the following relation: IF I = C. IVd I, where Vd is this time the dry deposition rate of the aerosols on the soil type of the environment studied. However, the dry deposition rate Vd for different types of environment is listed in the literature. Therefore, during a step 400, the aerosol dry deposition flux specific to the environment studied is deduced.

The proposed collection device and method therefore makes it possible to simply determine a dry deposition flow of aerosols specific to a particular type of environment. In particular, the dry deposition rate of the aerosols on the device is well characterized as a function of the wind speed during the collection, which makes it possible to easily deduce dry deposition flux values on the device the corresponding flow values in the device. environment studied. This is also allowed by the circular geometry of the device which allows an isotropic character of the aerosol deposition.

Claims (12)

REVENDICATIONS1. Device (10) for collecting aerosols, characterized in that it comprises: - a plate (11) having an aerosol deposition surface (12), and - at least one projection (13) projecting from said surface , adapted to form an obstacle to a flow of aerosol-laden air flowing through the plate and generate turbulence in said airflow to promote the deposition of aerosols on the surface. 2. Device (10) for collecting aerosols according to claim 1, wherein the bosses (13) are regularly distributed pimples on the aerosol deposition surface to maximize the turbulence generated in the air flow through the plate . 3. Device (10) for collecting aerosols according to one of claims 1 or 2, wherein the boss or bosses are arranged on the surface so as to form between them a network of contiguous channels. 4. Device (10) for collecting aerosols according to one of claims 1 to 3, comprising a plurality of bosses (13) distributed spirally on the aerosol deposition surface. 5. Device (10) for collecting aerosols according to one of claims 1 to 3, comprising a plurality of bosses (13) distributed in concentric circles on the aerosol deposition surface. 6. Device (10) for collecting according to one of claims 2 to 5, wherein the cylindrical pins have a height of between 0.5 and 3 cm and a diameter of between 2 and 10 mm. 7. Device (10) for collecting aerosols according to one of the preceding claims, wherein the plate (11) has the shape of a flat disk to ensure a homogeneous and isotropic deposition of aerosols. Aerosol recovery system, comprising: an aerosol collecting device (10) according to one of the preceding claims, and a cover (20) adapted to be fixed on the collection device (10). , comprising a flat plate (21) in which is arranged at least one groove (23) adapted to receive all the bosses (13) of the collection device when the cover is fixed on the collection device, and to form in cooperation with the plate of the collection device a flow channel of a fluid. Aerosol recovery system according to the preceding claim, further comprising means (14, 24) for sealing the fluid flow channel when the cover (20) is attached to the collection device (10). . 10. A method of aerosol collection implemented by a recovery system according to one of claims 8 or 9, comprising the steps of: - Positioning (110) a device (10) for collecting aerosols in a site at a fixed height from the ground, so that the device is protected from the rain, and for a determined period of time, - at the end of the determined duration, fix (120) a cover (20) on the collecting device for forming a flow channel of a fluid, injecting a fluid (130) into the channel to collect the aerosols deposited on the device, and - recovering the fluid containing said aerosols. 11. A method for determining a flow of dry deposition of aerosols in a given type of environment, characterized in that it comprises the steps of: - collecting a quantity of aerosols in said environment by the method (100 ) according to claim 10, and deducing from the quantity of aerosols collected a stream of dry deposition of aerosols on the device (10) in the environment, - from the average wind speed in said environment during the collecting, determining (200) a dry aerosol deposition rate on the device (10), - deducing (300) the dry deposition rate and the dry deposition flux on the device (10) an atmospheric concentration of the aerosols in the device the environment, and - determining (400), from a dry deposition rate of aerosols in the environment and the atmospheric concentration of aerosols, an environment-specific dry deposition flux of aerosols. 12. A method for determining a dry deposition rate of aerosols on a device (10) according to one of claims 1 to 7, according to a wind speed, comprising the steps of: - placing a device (10) in a closed medium provided with a blower system or in an open medium, said medium comprising aerosols in predetermined concentration, - implementing the aerosol collection method (100) according to claim 11, for different wind speeds generated by the wind tunnel system, and deduce from the amount of aerosols collected for each wind speed and aerosol concentration in the environment a dry deposition flow of aerosols on the device for the wind speed given.