Method for determining the particle size distribution of an aerosol and aerosol measuring device

Abstract

The present invention relates to a method and an aerosol measuring device for determining the particle size distribution of an aerosol by means of an aerosol measuring device. In a measuring unit, an aerosol particle of an aerosol flowing through the measuring unit is irradiated with a light beam. The scattered light is recorded by a detector, so that the optical signal of the aerosol particle is detected according to intensity by spectroscopy. Thereby, the size distribution of the optical signal representing the particle size distribution is obtained. A known standard particle size distribution of dry aerosol particles is matched to the measured particle size distribution, so as to eliminate the humidity influence on the measured particle size distribution in this way.

Description

Field of the Invention

[0001] The present invention relates to a method for determining the particle size distribution of an aerosol by means of an aerosol measuring device, wherein aerosol particles of the aerosol flowing through the measuring unit are irradiated with a light beam in the measuring unit, scattered light is recorded by a sensor, and the scattered light signal of the aerosol particles is detected according to intensity by spectroscopy, and the size distribution of the scattered light signals representing the particle size distribution is obtained.

[0002] Furthermore, the present invention relates to an aerosol measuring device for determining the particle size distribution of an aerosol, wherein the aerosol particles of the aerosol are arranged in the measuring unit in such a way that the aerosol particles can be irradiated with a light beam, wherein the sensor can record the scattered light of the aerosol particles and can detect the scattered light signal of the aerosol particles according to intensity by spectroscopy, so that the size distribution of the scattered light signals representing the particle size distribution can be obtained. Background Art

[0003] Methods for determining the particle size distribution of aerosol particles of an aerosol are known from the prior art. In the sense of the present invention, an aerosol means a mixture of a gas with solid and / or liquid suspended particles (aerosol particles), such as water droplets, soot particles, finely ground material particles, pollen, and other organic chemical substances. The particle size distribution means the concentration of aerosol particles related to the particle size of the aerosol particles and gives information about which particle sizes are present in the aerosol with what frequency.

[0004] Common methods can be used to determine the fine dust load of an aerosol. However, here, all aerosol particles are always measured regardless of the particle type. However, the influence of one or more aerosol particle types often has a destructive effect on the measurement result and may distort the measurement result. In particular, with known methods, in the case of high air humidity, water particles and / or particles whose size changes due to water condensation also distort the measurement, that is, cause measurement errors. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to eliminate the disadvantages of the prior art and to develop a more accurate method and device for determining the particle size distribution of an aerosol.

[0006] The above technical problem is solved by a method having the features of claim 1, an aerosol measuring device having the features of claim 9, a computer program having the features of claim 12, and a computer-readable medium having the features of claim 13.

[0007] The method according to the invention is characterized in that a known standard particle size distribution of dry aerosol particles is matched to the measured particle size distribution, and in this way the humidity influence on the measured particle size distribution is eliminated. The aerosol measuring device according to the invention is characterized in that the aerosol measuring device is equipped with a device which is designed to enable a known standard particle size distribution of dry aerosol particles to be matched to the measured particle size distribution and to be able to eliminate the humidity influence on the measured particle size distribution in this way.

[0008] The invention is based on the consideration that by matching a standard particle size distribution which is not influenced by humidity or has a humidity influence which is negligible in most cases to the measured particle size distribution, the humidity influence can be calculated to a large extent, so that in particular a reliable statement can be made about the fine dust load of the aerosol to be measured.

[0009] Preferably, the standard particle size distribution is matched to the measured particle size distribution only for the particle sizes within the matching interval. Particularly preferably, the matching interval includes particle sizes having a diameter of up to a maximum of 3 μm. Functionally, the matching interval serves as a sampling point for the matching of the standard particle size distribution to the measured particle size distribution. In this region, in particular, the humidity influence on the particle size distribution is negligible, which enables a more accurate matching.

[0010] In particular, values of the particle size distribution of the particle sizes can be provided within a target size interval which preferably includes particle diameters of up to a maximum of 50 μm, particularly preferably up to a maximum of 20 μm, in particular up to 15 μm. This region generally has a significant humidity influence on the measured particle size distribution and is also of interest for the assessment of the fine dust load of the aerosol.

[0011] Particularly preferably, the standard particle size distribution is determined on the basis of the particle size distribution which has already been measured, in particular the particle size distribution of the measurements which have already been carried out at the same location where the method according to the invention is also carried out. With regard to the compensation of the humidity influence on the measured particle size distribution which has already been described, the particle size distribution which has already been measured may have been measured at a time when the concentration of water particles in the aerosol is negligible, i.e. in dry weather with low air humidity, for example at a relative air humidity of up to 60%.

[0012] Further preferably, the standard particle size distribution is a particle size distribution which is mathematically modeled and is in particular related to the power ν of the particle diameter d p wherein, in particular, the power ν has a value between -10 and -0.1. Thus, in particular, c n ' = f(d p γ) Examples of such particle size distributions are known as early distributions (Junge - Verteilung), which describe the particle size distribution of aerosols without water in a modeled way and can be mathematically represented by the following formula:

[0013]

[0014] where r is the particle radius, which is half of the particle diameter.

[0015] For example, in the matching interval, the standard particle size distribution can be matched to the measured particle size distribution, especially by changing the parameters of the standard particle size distribution. Mathematically, this is called adaptation or fitting. The matching is carried out until the error parameter, such as the RMS error (root mean square) or the QMW error (quadratischer Mittelwertfehler (root mean square error)), is minimized. Thus, a matched particle size distribution that fits the measured concentration distribution as best as possible is obtained. Subsequently, the matched particle size distribution can be extrapolated for the particle diameters within the target size range.

[0016] Based on the matched particle size distribution, especially in combination with the measured particle size distribution, a parameter corresponding to the mass fraction of aerosol particles in the aerosol can be calculated. Preferably, this parameter can correspond to the volume fraction of aerosol particles. Particularly preferably, the PM 10 value can be calculated as such a parameter of the mass fraction. The PM 10 value corresponds to the fraction of aerosol particles in the aerosol with a diameter less than 10 μm. These aerosol particles are inhalable. In a corresponding manner, the PM 2.5 value can be calculated, and the PM 2.5 value corresponds to the fraction of aerosol particles with a diameter less than 2.5 μm. These particles can pass through the lungs. Finally, the PM 0.1 value can be calculated, which corresponds to the fraction of ultrafine particles with a diameter less than 0.1 μm. By calculating the parameters of the mass fraction of the mentioned specific aerosol particles based on the particle size distribution with the humidity effect eliminated, more accurate statements about the fine dust load of the aerosol can be made in particular.

[0017] Preferably, after matching the standard particle size distribution, based on the matched particle size distribution and in combination with the measured particle size distribution, the content of water particles in the aerosol particles is determined. The content of water particles can be described mathematically, especially by a humidity parameter, which corresponds to a measure of the humidity effect on the measured particle size distribution. For example, preferably, only for the particle sizes within the target size range, the difference between the measured particle size distribution and the matched particle size distribution can be determined as the humidity parameter, and based on this difference, the water condensation part in the aerosol particles can be deduced.

[0018] Preferably, after determining the content of water particles in the aerosol particles, the humidity influence on the measured particle size distribution is eliminated only if the content of water particles is greater than a predefined limit value, which is in particular a limit value of a humidity parameter. For example, such a limit value for the content of water particles in the aerosol particles is 0.1 μg / m 3 .

[0019] According to the present invention, it can be arranged that the target size interval at least partially overlaps with the matching interval. Preferably, all particle diameters in the target size interval are greater than the particle diameters in the matching interval.

[0020] Preferably, the aerosol measuring device has a device suitable for performing the above-mentioned method steps.

[0021] Further preferably, the light beam of the light source of the aerosol measuring device is multi-color light, which enables a more accurate determination of the particle size distribution compared to monochromatic light. In another design, the light beam has coherent light, especially laser. In order to detect the scattered light, the aerosol measuring device, especially its detector, can have at least four light channels, which are designed as spectral channels, for example. Description of the Drawings

[0022] Other advantages and features result from the claims and from the following description, in which embodiments of the present invention are described in detail with reference to the drawings. Herein:

[0023] Figure 1 A schematic diagram of an aerosol measuring device in the aerosol to be measured is shown;

[0024] Figure 2 Shows Figure 1 the schematic structure of the aerosol measuring device in;

[0025] Figure 3 A flowchart of the method according to the present invention is shown; and

[0026] Figures 4 to 6 The measured particle size distributions of different aerosols and the matching particle size distributions are shown. Detailed Description of the Invention

[0027] Figure 1 An aerosol 10 is schematically shown, which contains solid and liquid aerosol particles 11 in a gas 12, such as air. The aerosol particles 11 are, for example, water droplets, soot particles, finely ground material particles, pollen, and / or other organic chemicals.

[0028] In the region of the aerosol 10, there is arranged an aerosol measuring device 13 in the form of an aerosol spectrometer. The aerosol measuring device 13 measures the particle size distribution c of the aerosol particles 11 of the aerosol 10 according to the particle diameter d of the aerosol particles 11 p of the aerosol particles 11 of the aerosol 10 n . For this purpose, the aerosol particles 11 are sucked through the inlet 14 of the aerosol measuring device 13 and through the flow tube 15 by means of a pump (not shown) arranged downstream. In the schematic structure of the aerosol measuring device 13 according to Figure 2 , the flow tube 15 is arranged perpendicular to the plane of the figure

[0029] In the flow tube 15, a collimated beam 18 formed by polychromatic light from a light source 16 and a lens 17 irradiates the aerosol particles 11 in a direction perpendicular to the flight direction of the aerosol particles 11. Due to the resulting scattering process, the aerosol particles 11 emit scattered light 19, and the scattered light 19 reaches the converging lens 20 perpendicular to the flight direction of the aerosol particles 11 and perpendicular to the irradiation direction of the light from the light source 16. The converging lens 20 focuses the scattered light 19 onto the photoelectric sensor 21, and the photoelectric sensor 21 converts the scattered light 19 into an electrical signal. The electronic processing unit 22 determines the particle size distribution c according to these electrical signals according to the particle diameter d p of the aerosol particles 11 n . The spatial overlap of the beam 18, the measured scattered light 19, and the partial aerosol particles 11 in the detected flow tube 15 defines a virtual space measurement unit 23, and the particle size distribution c is determined in the virtual space measurement unit 23 n .

[0030] During the measurement, the light intensity of the scattered light 19, and thus the intensity of the electrical signal generated thereby, is also a measure of the particle size of the aerosol particles 11, and the particle size of the aerosol particles 11 is correspondingly associated with the particle diameter d p . The measured particle size distribution c n is related to the particle diameter d p , and thus it holds that: c n = f(d p ).

[0031] Although during the measurement, the particle size distribution c is always determined for discrete particle diameters d as measurement points p , where usually up to 256 channels are used, when analyzing in the electronic processing unit 22, the trend of the measured particle size distribution c n between the measurement points is interpolated, so as to obtain a continuous trend as shown in n . There, the measured particle size distribution c is plotted as a thin dotted curve with respect to the particle diameter d Figures 4 to 6 . p , and the measured particle size distribution c n, including region e1, which reproduces the humidity effect. In addition, in Figures 4 to 6 the dry aerosol particles 11, i.e., the standard particle size distribution c without humidity effect, are shown n '. It can be seen that for particle diameters d between 0.2 μm and a maximum of 3 μm p , the humidity effect on the particle size distribution c n is negligible within the matching interval Δd2, which will be further described below. In contrast, in the target size interval Δd1, which includes particle diameters d from 3 μm to 50 μm and will also be further described below p , the humidity effect on the particle size distribution c n is quite obvious. For clarity, Figures 4 to 6 only the trend of particle diameters d between 0.2 μm and 20 μm is shown on a double-logarithmic scale p . Therefore, it can be inferred that, by size, in the target size interval Δd1, it is mainly the water particles in the aerosol 10.

[0032] Below, the method according to the present invention will be described based on Figure 3 : In the first method step A, the particle size distribution c is determined in the manner already described by means of the aerosol measuring device 13 n . As shown in Figures 4 to 6 , the particle size distribution c n has a humidity effect.

[0033] In the second method step B, the parameterizable standard particle size distribution c of the already existing dry particles, i.e., with a negligible humidity effect n ', is matched to the measured particle size distribution c n , which is also mathematically referred to as fitting (Anfitten) or fitting (Fitting). The standard particle size distribution c n ' is related to at least one fitting parameter α i . The fitting parameter α i is changed until the standard particle size distribution c n ' has sufficient consistency with the measured concentration distribution c n . Here, the matching is only performed for the sampling points in the matching interval Δd2, i.e., for particle diameters d between 0.2 μm and 3 μm p . In Figures 4 to 6 , the discrete sampling points are shown as squares.

[0034] The early distribution (Junge-Verteilung) of the dry aerosol 10 is used as the standard particle size distribution c n ', and the early distribution of the aerosol 10 has no humidity effect and is described as follows:

[0035]

[0036] Here, r is the radius of the aerosol particle 11, and thus it applies: r = d p / 2. Thus, the standard particle size distribution c n ' is related to the power ν of the particle diameter d p , where ν has a value between -10 and -0.1 and is thus used as the fitting parameter α i . Alternatively, a predefined and / or already stored measured standard particle size distribution c n ' can also be used, but in any case, the standard particle size distribution c n ' is not allowed to have any significant humidity influence.

[0037] To evaluate a good enough match, in particular to calculate the error parameter β for the quality of the fit, in the case of the best match, the error parameter β is minimized. Such an error parameter β is, for example, defined as the RMS value (Root mean square) of the mean variance between the standard particle size distribution c n ' and the measured particle size distribution c n . As a result, the following standard particle size distribution c n ' is obtained, which matches the measured particle size distribution c n ' of the particle diameter d as well as possible in the matching interval Δd2 p . In n respectively, this curve approximates the measured particle size distribution c Figures 4 to 6 and is shown as a solid line respectively, but instead of the region e1, this curve has a region e2, and the region e2 no longer exhibits a significant humidity influence. n In the next method step C, the humidity influence on the measured particle size distribution c

[0038] is determined in the form of the humidity parameter γ, where the humidity parameter γ is defined as the deviation between the standard particle size distribution c n ' that matches the particle diameter d p in the target size interval Δd1 and the measured particle size distribution c n . Thus, the humidity parameter γ is n a measure of the area between the regions e1 and e2 of Figure 4 and represents the water condensation particle fraction on the aerosol particle 11.

[0039] After determining the humidity parameter γ, in the next method step D, it is queried whether the humidity parameter γ is greater than a predefined limit value γ GW , where, for example, it applies that γ GW = 0.001 water condensation particles / cm 3。

[0040] If the humidity parameter γ is less than the limit value γ GW , then for the measured particle size distribution c n there is only a negligible humidity influence. In this case, Figures 4 to 6 the regions e1 and e2 in Figure 3 approximate to coincide, and the following method step E shown on the p left is continued. Accordingly, the measured particle size distribution c n of the particle diameter d of the first size interval Δd1 is provided.

[0041] Subsequently, in method step F, a parameter corresponding to the specific mass fraction of the aerosol particles 11 is calculated from the measured particle size distribution c n . This is, for example, the PM 2.5 value, and the PM 2.5 value represents the mass fraction of all aerosol particles 11 with a particle diameter d p less than 2.5 μm in the entire aerosol 10, and is a measure of the fine dust load (Feinstaub - Belastung) of the aerosol 10.

[0042] If the inquiry according to method step D yields that the humidity parameter γ is greater than the limit value γ GW , then there is a significant humidity influence on the measured particle size distribution c n . This situation is shown separately in Figures 4 to 6 . In this case, the following method step G shown on the Figure 3 right is continued. There, a matched standard particle size distribution c p ' of the particle diameter d of the first size interval Δd1 is provided by extrapolation, the value of which has no humidity influence. In this way, the humidity influence is eliminated. In n , the modeled trend of the particle size distribution of the water particles of the aerosol is shown separately as a dashed line, which approximately coincides with the corresponding measured particle size distribution c Figures 4 to 6 in the region of the first size interval Δd1. Figures 4 to 6 in n .

[0043] Finally, in the last method step H, the already described PM n value is determined from the standard particle size distribution c 2.5 '. Accordingly, the humidity influence on the PM 2.5 value is also eliminated. Thus, despite the presence of water particles, the pure fine dust load of the aerosol 10 can also be reliably determined.

Claims

1. A method for determining the particle size distribution (c n ) of an aerosol (10) by means of an aerosol measuring device (13), wherein, In the measuring unit (23), the aerosol particles (11) of the aerosol (10) flowing through the measuring unit (23) are irradiated with a light beam (18), the scattered light signal (19) is recorded by the sensor (21), and the scattered light signal (19) of the aerosol particles (11) is detected according to the intensity by spectroscopy, and a size distribution of the scattered light signal (19) representing the particle size distribution (c n ) is obtained, wherein a known standard particle size distribution (c n ) of the dry aerosol particles is matched to the measured particle size distribution (c n ), and in this way the humidity influence on the measured particle size distribution (c n ) is eliminated, wherein after the standard particle size distribution (c n ) is matched, the content of the water particles in the aerosol particles (11) is determined according to the combination of the matched standard particle size distribution (c n ) and the measured particle size distribution (c n ). The standard particle size distribution (c n ') is a particle size distribution that is mathematically modeled as being related to the power ν of the particle diameter (d p ), where the power ν has a value between -10 and -0.1, and where the standard particle size distribution (c n ') is described by , where ν has a value between -10 and -0.1, and r is the particle radius, i.e., half of the particle diameter.

2. The method according to claim 1, characterized in that, The matching of the standard particle size distribution (c n ') and the measured particle size distribution (c n ) is only carried out for the particle sizes within the matching interval (Δd2).

3. The method according to claim 2, characterized in that, The matching interval (Δd2) includes particle sizes having a diameter (d p ) of up to 3 μm maximum.

4. The method according to any one of claims 1 to 3, characterized in that, Determine the standard particle size distribution (c n ) based on the already measured particle size distribution (c n ).

5. The method according to any one of claims 1 to 3, characterized in that, Based on the combination of the matched standard particle size distribution (c n ') and the measured particle size distribution (c n ), a parameter corresponding to the mass fraction of the aerosol particles (11) in the aerosol (10) is calculated.

6. The method according to any one of claims 1 - 3, characterized in that, After determining the content of water particles in the aerosol particles (11), the humidity influence on the measured particle size distribution (c GW ) is eliminated only if the content of water particles is greater than a predefined limit value (γ n ).

7. An aerosol measuring device (13) for determining the particle size distribution (c n ) of an aerosol (10), wherein, The aerosol particles (11) of the aerosol (10) are arranged in the measuring unit (23) in such a way that the light beam (18) can irradiate the aerosol particles (11), wherein the sensor (21) can record the scattered light signal (19) of the aerosol particles (11) and can detect the scattered light signal (19) of the aerosol particles (11) according to the intensity by spectroscopy, so that the size distribution of the scattered light signal (19) representing the particle size distribution (c n ) can be obtained, wherein the aerosol measuring device (13) is equipped with a device which is designed to match the known standard particle size distribution (c n ) of the dry aerosol particles to the measured particle size distribution (c n ), and to eliminate the humidity influence on the measured particle size distribution (c n ) in such a way, wherein the device is suitable for performing the steps of the method according to claims 1 to 6.

8. The aerosol measuring device according to claim 7, characterized in that, The light beam (18) of the light source (16) is polychromatic light.

9. The aerosol measuring device according to claim 7 or 8, characterized in that, The light beam (18) of the light source (16) is coherent light.

10. The aerosol measuring device according to claim 7 or 8, characterized in that, The aerosol measurement device (13) has at least four optical channels including spectral channels for detecting the scattered light signal (19).

11. A computer program having instructions that cause the aerosol measuring device (13) according to claims 7 to 10 to perform the method steps according to any one of claims 1 to 6.

12. A computer - readable medium having stored thereon the computer program according to claim 11.

Images