METHOD AND AEROSOL MEASURING DEVICE FOR DETERMINING A SOURCE-DEPENDENT PARTICLE SIZE DISTRIBUTION OF AN AEROSOL

Abstract

A method for determining a source-dependent particle size distribution of an aerosol by an aerosol measuring device. First, a fraction parameter is determined that corresponds to a fraction of a source-dependent aerosol part of the aerosol. In addition, a particle size distribution of the aerosol particles is determined such that the source-dependent particle size distribution of the aerosol is determined from the fraction parameter and the particle size distribution. In terms of the device, the invention comprises an aerosol measuring device for determining a source-dependent particle size distribution of an aerosol, by means of which aerosol measuring device a fraction parameter can be determined that corresponds to a fraction of a source-dependent aerosol part of the aerosol. A particle size distribution of the aerosol particles can be determined such that the source-dependent particle size distribution of the aerosol can be determined from the fraction parameter and the particle size distribution.

Claims

1. A method for determining a source-dependent particle size distribution of an aerosol via an aerosol measuring device, the method comprising: illuminating aerosol particles of the aerosol flowing through a measuring cell with a light beam; detecting scattered light by a sensor, scattered light signals of the aerosol particles being detected spectroscopically in terms of intensity; creating a size distribution of the scattered light signals representative of a particle size distribution; determining a fraction parameter that corresponds to a fraction of a source-dependent aerosol part of the aerosol; determining a particle size distribution of the aerosol particles; and determining the source-dependent particle size distribution of the aerosol from the fraction parameter and the particle size distribution.

2. The method according to claim 1, wherein the fraction parameter is determined from a comparison of two particle size distributions of the aerosol.

3. The method according to claim 1, wherein the fraction parameter is determined from a comparison of a parameter of at least one gas component of the aerosol with a source-dependent reference value.

4. The method according to claim 3, wherein the parameter of the at least one gas component corresponds to a concentration of the gas component of the aerosol and/or in that the source-dependent reference value corresponds to a source-dependent concentration of the gas component.

5. The method according to claim 4, wherein, to determine the fraction parameter, the concentration of carbon dioxide in the aerosol is compared with a reference value of between 1% and 10%, or between 3% and 5%, or with a reference value k.sub.ref of 4%.

6. The method according to claim 3, wherein the parameter of the at least one gas component and/or the reference value is corrected.

7. The method according to claim 1, wherein the method is terminated if the fraction parameter falls below a first user-defined value and/or if the fraction parameter exceeds a second user-defined value.

8. The method according to claim 1, wherein the determined particle size distribution of the aerosol is corrected.

9. The method according to claim 1, wherein the source-dependent particle size distribution is determined by multiplying the particle size distribution of the aerosol by the fraction parameter.

10. The method according to claim 1, wherein a quality parameter of the aerosol is determined from at least part of the source-dependent particle size distribution.

11. The method according to claim 10, wherein the step of determining the quality parameter comprises summing at least part of the source-dependent particle size distribution.

12. The method according to claim 10, wherein the step of determining the quality parameter comprises a weighting operation that depends on the particle size of the aerosol particles and/or depends on the concentration of at least one gas component of the aerosol and/or depends on the relative humidity of the aerosol.

13. The method according to claim 1, wherein determining the fraction parameter and/or the particle size distribution and/or the source-dependent particle size distribution and/or the quality parameter comprises determining individual values and a statistical evaluation of the individual values.

14. An aerosol measuring device to determine a source-dependent particle size distribution of an aerosol, the measuring device comprising: a measuring cell, wherein aerosol particles of the aerosol are arranged in the measuring cell such that the aerosol particles are adapted to be illuminated by a light beam; and a sensor to detect scattered light of the aerosol particles, wherein scattered light signals of the aerosol particles are spectroscopically detected in terms of intensity such that a size distribution of the scattered light signals that is representative of a particle size distribution is created, wherein a fraction parameter is determined that corresponds to a fraction of a source-dependent aerosol part of the aerosol, wherein a particle size distribution of the aerosol particles is determined, and wherein the source-dependent particle size distribution of the aerosol is determined from the fraction parameter and the particle size distribution.

15. The aerosol measuring device according to claim 14, wherein the aerosol measuring device has an electronic processor that determines the fraction parameter, that determines the particle size distribution, or that determines the source-dependent particle size distribution.

16. The aerosol measuring device according to claim 14, further comprising a gas measuring unit that determines a concentration of at least one gas component of the aerosol, the gas measuring unit being configured to detect at least one of the following substances and/or parameters: carbon oxides, nitrogen oxides, sulfur oxides, ozone, volatile organic compounds, or relative humidity.

17. The aerosol measuring device according to claim 14, wherein the light beam has polychromatic light.

18. The aerosol measuring device according to claim 14, wherein a direction of movement of the aerosol particles in the measuring cell, the direction of the light beam in the measuring cell and the direction of the scattered light are arranged in pairs perpendicular to one another.

19. A computer program having program code, which computer program is configured to carry out the steps of the method according to claim 1 when the computer program is executed on a computer or a corresponding computing unit or on an electronic processor of an aerosol measuring device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0027] FIG. 1 shows a schematic view of an aerosol measuring device in an aerosol to be measured;

[0028] FIG. 2 shows a schematic design of the aerosol measuring device of FIG. 1;

[0029] FIG. 3 shows a flowchart of a method according to the invention;

[0030] FIG. 4 shows a first particle size distribution having a first source-dependent particle size distribution;

[0031] FIG. 5 shows a second particle size distribution having a second source-dependent particle size distribution; and

[0032] FIG. 6 shows a third particle size distribution having a third source-dependent particle size distribution.

DETAILED DESCRIPTION

[0033] FIG. 1 shows a schematic view of an aerosol 10 in a closed region 11, the aerosol 10 containing solid and liquid aerosol particles 12 in a gas 13, for example air. Aerosol particles 11 are, for example, water droplets, soot particles, abraded material, pollen and/or other organic and chemical substances. A person is located in the region 11 as an aerosol source 14. It is assumed below that the aerosol 10 changes within the region 11 substantially as a result of the exhaled air of the person 14. The aerosol 10 of the region 11 therefore has a source-dependent aerosol part 10a, in this case the exhaled air, and a source-independent aerosol part 10b.

[0034] An aerosol measuring device 15 in the form of an aerosol spectrometer is arranged in the region 11 of the aerosol 10, which aerosol measuring device measures a particle size distribution c.sub.n of the aerosol particles 12 of the aerosol 10 as a function of their particle diameters d.sub.p. For this purpose, the aerosol particles 12 are drawn through an access opening 16 of the aerosol measuring device 15 and through a flow tube 17 by means of a conveyor arranged downstream, the conveyor being designed as a pump. In the outlined design of the aerosol measuring device 15 according to FIG. 2, the flow tube 17 is arranged perpendicularly to the plane of the drawing.

[0035] The aerosol particles 12 are irradiated in the flow tube 17, perpendicularly to their flight direction, with a collimated light beam 18 made up of polychromatic light from a light source 19 and a lens 20. Because of the scattering processes that take place as a result, the aerosol particles 12 emit scattered light 21 that impinges on a converging lens 22 perpendicularly to the flight direction of the aerosol particles 12 and perpendicularly to the irradiation direction of the light from the light source 19. The converging lens 22 focuses the scattered light 21 onto an optoelectrical sensor 23 that converts the scattered light 21 into electrical signals. An electronic processor 24 uses the electrical signals to determine the particle size distribution c.sub.n as a function of the particle diameter d.sub.p of the aerosol particles 12. The spatial overlap of the light beam 18 of the measured scattered light 21 and of the detected part of the aerosol particles 12 in the flow tube 17 defines a virtual spatial measuring cell 25 in which the particle size distribution c.sub.n is determined.

[0036] During the measurement, the light intensity of the scattered light 21 and thus also the resulting electrical signal strength is a measure of the particle size of the aerosol particles 12 to which a particle diameter d.sub.p is accordingly assigned. The measured particle size distribution c.sub.n depends on the particle diameter d.sub.p such that the following applies: c.sub.n=f(d.sub.p).

[0037] The determined particle size distribution c.sub.n is determined for discrete particle diameters d.sub.p as measuring points, up to 256 channels being used as a rule. In order to improve accuracy, the progression of the particle size distribution c.sub.n between the measurement points is locally interpolated by means of cubic splines during the evaluation in the electronic processor 24 such that a continuous progression results. To accelerate the method according to the invention described below, the particle size distribution c.sub.n is determined by means of downsampling for 32 channels.

[0038] A reference particle size distribution c.sub.r is subtracted from the determined particle size distribution c.sub.n, the reference particle size distribution c.sub.r being a model distribution that corresponds to normal room air and has a carbon dioxide concentration of approximately 400 ppm.

[0039] The aerosol measuring device 15 has a gas measuring unit 26 that is designed as a gas sensor and determines the concentration k.sub.CO2 of carbon dioxide (CO.sub.2) in the aerosol, which corresponds to the volume fraction of CO.sub.2 in the aerosol 10 within the context of the invention. This value is transmitted to the electronic processor 24.

[0040] An embodiment of the method according to the invention according to FIG. 2 is described below in which the source-dependent particle size distribution c.sub.n′ is determined, which corresponds to the source-dependent aerosol part 10a and is associated with the air exhaled by the person 14. Within the context of the invention, this particle size distribution c.sub.n′ is referred to as the source-dependent particle size distribution. In particular, the risk of infection within the region 11 as a result of the microbial contamination of the aerosol 10 is determined by the method.

[0041] In a first step A of the method, the fraction parameter f is determined. For this purpose, the CO.sub.2 concentration k.sub.CO2 in the aerosol 10 is determined by the gas sensor 26 and transmitted to the electrical processor 24. A reference concentration k.sub.ref is subtracted from the CO.sub.2 concentration k.sub.CO2, which corresponds to the usual CO.sub.2 concentration of room air and is approximately 0.05% in the present example. The reference concentration k.sub.ref is determined by measuring the CO.sub.2 concentration of the aerosol 10 at an interval of one measurement per hour over a period of 24 hours and forming the minimum of these measured values. Because the source-dependent particle size distribution c.sub.n′ to be determined in the present example corresponds to breathing air, the reference concentration k.sub.ref is also subtracted from the CO.sub.2 concentration of exhaled air, in this case approximately 4%. The result is a corrected CO.sub.2 concentration k.sub.CO2′ of the aerosol 10 and a corrected reference concentration k.sub.ref. The quotient of these two variables results in an individual value f.sub.i for the fraction parameter f of the breathing air 10a in the aerosol 10. The individual values f.sub.i of the fraction parameter f are continuously determined over a period of 30 minutes, the fraction parameter f being formed from the individual values as a moving average value.

[0042] In a next step B, the fraction factor f is queried. If there is not a person 14 within the region 11, a value of 0 results for the fraction parameter f, whereupon the method is terminated C and the method restarts after a user-defined time interval.

[0043] If the query B results in a value for the fraction parameter greater than 0, the method is continued and the particle size distribution c.sub.n of the aerosol 11 is determined D in the manner described above. The aerosol measuring device 15 continuously determines the particle size distribution c.sub.n of the aerosol 10 at a measuring frequency of one measurement per minute and forms the particle size distribution c.sub.n used below as a moving average.

[0044] The source-dependent particle size distribution c.sub.n′ is then determined E by multiplying the particle size distribution c.sub.n of the aerosol 10 by the fraction parameter f, which is done for each measurement channel in the present example.

[0045] The determination E of the source-dependent particle size distributions c.sub.n′ is shown in FIGS. 4 to 6, which show an exemplary particle size distribution c.sub.n of the aerosol 10 on the left-hand side and a source-dependent particle size distribution c.sub.n′ on the right-hand side. The particle size distributions c.sub.n, c.sub.n′ are each illustrated there as bar charts as a function of the particle diameter d.sub.p. For reasons of clarity, the particle size distributions c.sub.n, c.sub.n′ each have 7 measured values. In FIG. 4, the fraction factor is approx. 0.28, in FIG. 5 approx. 0.3 and in FIG. 6 approx. 0.32. From this it can be seen that the fraction factor f has increased in the transition from the particle size distribution c.sub.n of FIG. 4 to the particle size distribution c.sub.n of FIG. 6. This indicates that the person 14 may have stayed in the region 11 for a longer period of time and that the fraction of breathing air 10a in the aerosol 10 is continuously increasing.

[0046] After the source-dependent particle size distribution c.sub.n′ is determined E, quality parameters g are determined F, which quality parameters are assigned to the source-dependent particle size distribution c.sub.n′ and are described below.

[0047] The total number g.sub.1 of aerosol particles 12 in the source-dependent particle size distribution c.sub.n′ is determined by summing up the source-dependent particle size distribution c.sub.n′ across all channels. Because the source-dependent particle size distribution c.sub.n′ in particular also includes microbial contamination of the aerosol 10, for example by bacteria or viruses, the total number g.sub.1 serves as an indicator of a risk of infection and is therefore also referred to as a “germ indicator.”

[0048] The PM.sub.2.5 parameter g.sub.2 is also determined from the source-dependent particle size distribution c.sub.n′, which reflects the mass fraction of all aerosol particles 12 having particle diameters d.sub.p of less than 2.5 μm in the source-dependent aerosol part 10a, i.e., the exhaled air and a further quality parameter g for, in particular, the fine dust pollution of the source-dependent aerosol 10a. The PM.sub.2.5 value also includes microbial contaminants in the air and thus also provides information about the microbial contamination of the source-dependent aerosol part 10a. In addition, a modified PM.sub.2.5 parameter g.sub.3 is determined, in which the calculation is based on a weighting depending on the relative humidity of the aerosol 10.

[0049] For a comprehensive assessment of the aerosol quality, the gas measuring unit 26 has further components not shown in FIG. 1, such as a hygrometer for determining the relative humidity, and sensors for determining volatile organic compounds, ozone, nitrogen oxides, sulfur oxides and/or carbon monoxide. Furthermore, parameters can be determined that are composed of a plurality of these parameters. For example, it is possible to determine an indicator of risk of infection which depends on the corrected particle rise distribution, concentrations of volatile organic compounds and CO.sub.2 and relative humidity.

[0050] The number concentration of colony-forming particles (kbP per m.sup.3) is also determined from the source-dependent particle size distribution c.sub.n′, which number concentration is a measure of the microbial contamination of the air.

[0051] The steps of the method described above are carried out continuously when a computer program according to the invention is executed on the processor 24.

[0052] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.