WO2020225770A1

WO2020225770A1 - Device and method for measuring the concentration of elementary carbon in the atmospheric particulate

Info

Publication number: WO2020225770A1
Application number: PCT/IB2020/054347
Authority: WO
Inventors: Dario MASSABÒ; Paolo PRATI; Gianluca CAZZULI
Original assignee: Dado Lab S.R.L.; Pm_Ten S.R.L.
Priority date: 2019-05-09
Filing date: 2020-05-07
Publication date: 2020-11-12
Also published as: IT201900006685A1

Abstract

The present invention relates to a device (1) of measuring the concentration di Black Carbon (BC) in a sample of particulate extracted by a flow of ambient air, comprising: - a main body (10) comprising a measurement chamber (11) shaped in such a way as to be crossed by a flow of ambient air; - a filtering element (5) housed within the measurement chamber (11) in a position interposed between said inlet opening (52) and outlet opening (53), further configured to collect a sample of particulate suspended in the ambient air flow; - a light source (7), configured to radiate the particulate sample collected; - a sensor (91) of detecting the light intensity, faced towards the particulate sample collected in such a way as to detect the light intensity reflected by the particulate sample collected.

Description

DEVICE AND METHOD FOR MEASURING THE CONCENTRATION OF ELEMENTARY CARBON IN THE ATMOSPHERIC PARTICULATE

DESCRIPTION

Technical field of the invention

The present invention relates to a method a to a corresponding system for detecting elementary carbon, alternatively known as“Black carbon”, in a sample of atmospheric particulate.

Background

Atmospheric particulate (PM) or atmospheric aerosol plays a key role in the dynamics of the atmosphere, with a mainly negative impact. The particulate particles that are suspended in the atmosphere act as condensation cores of the clouds, cause a reduction in visibility, affect global climate change and are harmful to human health.

With particular reference to the urban environment, carbonaceous aerosol (CA) represents one of the main fractions of PM; the combustion of fossil fuels (FF) and the combustion of biomass (BB) represent the main sources of carbon compounds. Fossil fuels pollution is increasing due to the growing energy contribution necessary for transport and production activities.

In addition, the impact of biomass combustion is continuously increasing, especially in association with energy purposes: the wood combustion provides a significant contribution to the high concentrations of atmospheric aerosols observed in different areas of the world. In fact, the carbonaceous material, present above all in the breathable atmospheric particulate, is emitted directly by combustion processes and consists of a first organic fraction, called precisely organic carbon, and a second oxidation resistant fraction at a temperature below 400°C. When the two fractions are distinguished according to their respective thermal properties, the second fraction is called elemental carbon (EC), while if their optical properties are considered, the second fraction is called“black” carbon (BC), due it has a high light absorbing power.

Carbon aerosols significantly contribute to the ongoing climate change since elemental carbon (EC) - or, depending on the technique used to reveal it, Black Carbon (BC) - effectively absorbs electromagnetic radiation throughout the interval between infrared and ultraviolet. Furthermore, biomass combustion releases organic compounds into the atmosphere which significantly absorb light at high frequency and in the ultraviolet spectrum (the expression Brown Carbon, BrC, was introduced precisely with reference to this feature).

Considering everything mentioned, to safeguard the health of the environment and the population, it is required to carry out a precise characterization and monitoring of the atmospheric particulate sources, and the quantification of their impact. To date, the characterization of carbonaceous particulates follows a methodological approach which requires long analysis times, complex structures and can only be operated by qualified personnel. Therefore, the measurement of the concentration of Black Carbon (BC), although codified by national and European regulations, is subjected to continuous speculation and, to date, no methodology seems to combine simplicity of use and sufficient reliability.

The currently most widespread technique for obtaining information on carbonaceous particulates is thermo-optical analysis, which exploits various characteristics of evolution of organic and inorganic carbon in an inert/oxidizing atmosphere, as a function of the temperature. However, this technique has some disadvantages, among which we note in particular: the destructive nature of the test, which does not allow the reuse of the analysed sample, the possibility of being applied only in association with quartz filters and the fact that it is an“offline” measurement (with the consequent impossibility of producing real time information).

Another widely used approach involves the analysis only of the optical properties of particulates. Various instruments capable of providing an estimate of the concentration of Black Carbon in samples of particulates are currently on the market.

Using these instruments, the BC concentration is obtained by measuring the light absorption or attenuation operated by the particulates. In the latter case, it is necessary to apply corrections to the results obtained according to the characteristic parameters of the site considered, and therefore the use of auxiliary equipment, which is complex to use, is required.

The aforementioned tools can operate in an“online” mode, meaning they are able to produce information in real time. This aspect represents an advantage indeed for the detection of episodic phenomena or for responding to the possible need to have immediately (or almost) information although at the same time determines the need to have a detection unit for each monitoring site and implies continuous and often economically demanding maintenance.

Summary of the invention

The technical problem posed and solved by the present invention is therefore to provide a methodology for measuring the concentration of Black Carbon in the atmospheric particulate which allows to overcome the above mentioned drawbacks with reference to the prior art.

The aforementioned drawbacks are solved precisely by a measurement method according to claim 1.

Furthermore, the present invention provides a computer program according to claim 3 and a device suitable for allowing the implementation of the aforementioned method, as defined in claim 4.

Preferred features of the present invention are the subject of the dependent claims.

The present invention provides a method for measuring the concentration of Black Carbon in an atmospheric particulate sample, which provides the analysis of optical properties of the sample according to a non-destructive technique.

The idea behind the invention is to use a single optical measurement in reflection to determine the amount of Black Carbon existing in a sample of atmospheric particulate, collected on a filtration support. The reflection measure (RFN) is correlated with the sample absorption (ABS) by means of an empirical equation, obtained from the analysis of a certain number of reference samples.

The number of samples of reference particulates requires to be statistically relevant by number, as well as by variety of concentration and composition. To achieve such result, according to a preferred embodiment of the invention, the relationship between the reflection value (RFN) and the absorption value (ABS) was determined starting from the analysis of more than 450 samples, representative of concentrations and compositions of atmospheric particulate also very different one from another. Samples collected in different locations were considered, for example urban sites such as those of Genoa, Marseille and Milan, rural and mountain sites such as Propata and Valle d’Aosta and particular sites such as the rainforest of the Amazon and the desert of Niger.

Once the absorption has been obtained through the aforementioned report, it is possible to determine the BC concentration value in the sample, because these values are reciprocally proportional.

Advantageously, this method can be implemented by devices which can be integrated into, or connectable to, standard sequential samplers.

Advantageously, it is possible to associate an“online” measurement (in real time) of the BC concentration carried out by the invention with a measurement carried out with standard sequential samplers compliant with the current legislation in force, which consists of a gravimetric determination of the concentration of PM 10 and/or PM2.5, without the latter being altered in any way.

Other advantages, characteristics and methods of use of the present invention will become apparent from the following detailed description of several embodiments, presented by way of non-limiting example.

Brief description of the drawings

Reference will be made to the attached Figures, in which:

Figure 1 shows a graph showing the absorption values (ABS) and reflection (RFN, for a reflection angle equal to 125°) related to a plurality of atmospheric particulate samples analysed;

Figure 2 shows a top view from above of a first preferred embodiment of a measuring device according to the present invention;

Figure 3 shows a first cross-sectional view of the measuring device of Figure 2, according to the section plane Y-Y indicated in Figure 2;

Figure 4 shows a second cross-sectional view of the measuring device of Figure 2, according to the section plane X-X indicated in Figure 2;

Figure 5 shows a schematic view of the path of the light beam emitted by a light source of the measuring device of Figure 2 and reflected by the sample of particulates being measured by a measuring device according to the present invention; and

Figure 6 shows an exemplary block diagram of a further preferred embodiment of a measuring device according to the present invention.

The figures indicated above are to be intended only as an example and not for limiting purposes. Detailed description of preferred embodiments

The present invention relates to a method for measuring the concentration of Black Carbon (BC) in a particulate sample. The particulate sample, suspended in a flow of ambient air, is collected on a surface, for example on the surface of a filter, to allow analysis by using the aforementioned method.

A further object of the invention is a device configured to implement this method.

The method according to the invention allows to measure the BC concentration in a sample of particulates, without involving the destruction of the sample itself.

The method involves calculating the concentration value starting from the absorption values (ABS) and the mass impact section aabs characteristics of the sample under investigation, by applying the following mathematical relationship:

BC = ABS /a_abs The value of the mass impact section cabs is known with reference to the sample being measured, or is calculated in accordance with already known methods.

The mass impact section cabs (Mass Absorption Cross-section, otherwise known as MAC) represents the proportionality coefficient existing between the optical property of absorption of the particulates (ABS) and the concentration of BC. The assignment of a MAC value is therefore required to“convert” the optical absorbance (ABS) value into a BC concentration. This parameter is not constant as the analysed samples vary, because it depends heavily on the composition and aging of the atmospheric aerosol particles. Therefore, the MAC value for each sample can take significantly different values depending on the respective measurement site.

The ABS absorption value of the sample is instead obtained as described below.

Initially, a certain number of reference particulate samples is considered, preferably detected at different locations for characteristics such as latitude, altitude, degree of human activity, etc. A reflectance value RFN and an absorption value ABS are measured for each of the aforementioned samples, in particular the reflectance value is measured for a given reflection angle value, equal for each sample.

Once this measurement has been carried out, for each of the reference samples a point of coordinates corresponding to the respective RFN and ABS absorption reflectance values, recorded for each sample, is represented on a Cartesian diagram, which has an abscissa axis corresponding to the absorption value ABS and an ordinate axis corresponding to the reflectance value RFN for a given reflection angle value.

The next step provides to determine the mathematical equation of a curve, for example a polynomial curve, such as to interpolate those points shown on the Cartesian diagram. The number of reference particulate samples is preferably increased until the correlation coefficient R² of the mathematical equation of the aforementioned polynomial curve, with respect to the diagram points which are interpolated therefrom, has a value greater than or equal to 0.9.

According to experimental tests, a number of reference particulate samples equal to at least 450 ensures to calculate a polynomial curve equation that is sufficiently accurate in the interpolation of the diagram points (R² > 0.9) and statistically representative of the variability of the relationship between RFN and ABS in different sites and periods.

When the value of the correlation coefficient R² satisfies the requirement barely stated, the mathematical equation of the polynomial curve is determined, in such a way as to express the ABS absorption as a function of the reflectance RFN.

The polynomial curve equation is:

ABS = (A ± DA) X RFN² + (B ± DB ) X RFN + (C ± AC) wherein:

A, B and C are coefficients whose value depends on the phenomenon of multiple scattering which occurs among the particles and the filtering support matrix, while DA, DB e AC represent the uncertainties related to the relative coefficients A, B and C.

In particular, the phenomenon of multiple scattering produces an increase in the optical path of light within the system, causing a non-linearity of the reflectance signal as the absorption increases.

Such coefficients further depend on the reflectance angle at which the measurement is performed, on the optical thickness of the particle-filter system (t) and on the single scattering albedo (co), i.e. the ratio between the diffused and extinct radiation, via the relation: ABS = t (1— w)

Furthermore, the ABS absorption calculation takes into account the particle asymmetry parameter and the surface roughness of the filter used.

The equation thus formulated allows to obtain the ABS absorption value for any sample of particulates - once the RFN reflectance value is known for the considered sample - with reference to the same value of the reflection angle considered for the reference samples.

Thereby, considering a new sample whose BC concentration is desired to be obtained, it is first necessary to measure its RFN reflectance value, for the aforementioned reflection angle value. In addition, it is necessary to determine, according to known methods, the value of the mass impact section aabs of the new sample.

Subsequently, the corresponding absorption value ABS is calculated by means of the mathematical equation of the interpolation curve, as described above.

Once the ABS absorption value has been calculated, the BC concentration is calculated by applying the equation:

BC = ABS /a_abs

Considering the example of Figure 1 , it is specified that the analysed values were obtained using an MWAA (Multi Wavelength Absorption Analyser) optical instrument, using a light source with a wavelength of 635nm (red), with a reflection angle of 125° with respect to the direction of the LASER beam incident on the sample. With reference to the polynomial correlation curves of the diagram in Figure 1 , it is to be noted that this interpolates the points with considerable precision (correlation coefficient R² = 0.985), confirming the possibility of using the reflectance measurement to evaluate Black Carbon concentration values and suggesting the parameters to be used for the conversion of the data measured in concentration measurement.

Obviously, a skilled person will understand that the aforementioned configuration is not binding for the extrapolation of information; for example, the use of a light source with different wavelength or the evaluation of the light diffusion coefficient at a different reflection angle allow to determine a different correlation curve between reflectance (RFN) and absorption (ABS), and however to correctly implement the method of the invention.

As anticipated, in accordance with the aforementioned preferred method of implementation of the invention, the RFN reflectance value of the reference samples, as well as the reflectance value of the sample under investigation, is measured for a reflectance angle equal to 125°. The reference samples analysed were 450.

For this reflectance angle, an accurate equation has been determined - according to the method above described - which expresses the polynomial curve which interpolates points having the reflectance values (RFN) and absorption (ABS) of each reference sample as coordinates, of the type:

ABS= (-0,69 ± 0,03) ^* RFN² + (2,22 ± 0,04) ^* RFN + (0, 13 ± 0,01)

Once the ABS absorption value has been obtained, the concentration of Black Carbon (BC) can be calculated using the equation:

BC = ABS /a_abs

This equation, which allows to calculate ABS, contains the information to evaluate the results’ uncertainty and, consequently, the statistical error associated with the BC value. With reference to Figures 2 to 5, a first preferred embodiment of a device according to the present invention is shown, overall denoted by 1.

The device 1 comprises a main body 10 which is overall shaped to realize a measurement chamber 11 suitable for being flown by a flow of ambient air. This flow delivers atmospheric particulate in suspension. A measurement chamber is housed within the measurement chamber 11 to capture a sample of this particulate to be analysed in order to obtain the BC concentration thereof, as will be better described below.

In particular, the measurement chamber 11 comprises a first portion (or first chamber) 2 and a second portion (or second chamber) 3, which respectively have an overall truncated conical shape, to create a diffusion cone of the air flow.

To allow the flow of ambient air pass through device 1 , the measurement chamber 11 has two openings 52, 53 that put it in communication with the external environment. These openings 52, 53 are preferably mutually opposite, and even more preferably are located at opposite terminal ends of the measurement chamber 11.

According to the preferred implementation of the invention of Figures 3 and 4, the inlet opening 52 is configured to allow the flow of ambient air enter, while the outlet opening 53 is configured to allow the exit of the flow of ambient air. Preferably, the entrance opening 52 is arranged at the first portion 2, while the exit opening 53 is arranged at the second portion 3.

To achieve a flow of ambient air compliant with predetermined flow and speed parameters, the presence of forced circulation means 6 of the ambient air is preferably provided, configured to convey a flow of ambient air precisely from the entrance opening 52 to the outlet opening 53. Such means 6 can comprise a suction pump, and is preferably positioned at the outlet opening 53.

The means 6 can be further configured in such a way as to allow an operator, even remotely, to select operating parameters thereof, to adjust the flow of worked air, and/or the speed and/or orientation of the flow. Alternatively, for this purpose the device 1 can comprise user interface means, not shown in the attached figures.

The device 1 further comprises a filtering element 5, housed within the measurement chamber 11 to collect the particulate matter suspended in the flow of ambient air which passes through the same chamber 11. For this purpose, the filtering element 5 is arranged in an interposed position between the inlet opening 52 and outlet opening 53. In particular, the openings 52, 53 are arranged specularly with respect to the filtering element 5.

According to a preferred configuration of the invention, the first portion 2 and the second portion 3 have a truncated cone shape respectively, with an increasing volume towards said filtering element 5. In particular, the first portion 2 and the second portion 3 have a mutually specular conformation with respect to the filtering element 5, and are preferably juxtaposed at said element 5.

The filtering element 5 comprises a deposit surface 51 , configured to collect a sample of particulates suspended in the flow of ambient air which passes through the measurement chamber 11 along the path from the inlet opening 52 to the outlet opening 53. According to this configuration, the deposit surface 51 faces or faces towards the entrance opening 52, preferably according to an orientation orthogonal to the direction of advancement of the flow of ambient air which passes through the chamber. Therefore, preferably, the deposit surface 51 is arranged orthogonally to the passage section of the entrance opening 52.

The element 5 can comprise a filter membrane, for example made of glass fiber and/or other quartz material substantially transparent to a light radiation being radiated on the sample, as will now be described.

The device 1 comprises a light source 7, configured to radiate the deposit surface 51. Preferably, the light source 7 can be implemented, even remotely, by means of interface means. The light source 7 can be configured to emit a light beam focused on the filtering element 5 by means of one or more lenses, arranged downstream of the light source 7 and upstream of the deposit surface 51 , with reference to the path of the irradiated light beam. The device 1 comprises a sensor 91 for detecting the light intensity, facing the deposit surface 51 , such that when the particulate sample is settled at the deposit surface 51 and the light source 7 has been activated, the latter emits a light radiation towards the particulate sample and the sensor 91 detects the intensity of the light reflected by the latter. The two sensors 91 , 92 are preferably both arranged at the internal surface of the upper chamber 2. Also the light source 7 is preferably arranged at the upper chamber 2.

In particular, according to the preferred embodiment of the method above described, the light intensity detection sensor 91 is oriented to define a first reflection angle having an amplitude equal to 35° with respect to the deposit surface 51 , while the second sensor 92 of detection of the light intensity is oriented to define a second reflection angle b of amplitude equal to 75° with respect to the deposit surface 51.

According to the embodiment object of the present description, the two sensors are oriented in accordance with the aforementioned specific reflection angles, which are considered optimal angles for the implementation of the invention, since the equations binding absorption (ABS) and reflectance (RFN) have been obtained for these specific angles by means of the measurements performed by the MWAA, according to what has already been described. Therefore, it is to be understood that the person skilled in the art is able to determine, according to known methods, the relationship between the reflection (RFN) and any angle, according to different specific needs. The concept on the understanding, according to the invention, is the use of the information obtained for certain values of the reflection angle to derive the absorption value and therefore of the BC concentration.

Preferred variants of the invention provide that the sensors 91 , 92 are associated with respective handling means (not visible in the Figures), configured in such a way as to vary the position of the sensors themselves, in particular their angle and their distance from the deposit surface 51 , for example to allow the method of the invention to be applied according to different values of the reflection angle. Furthermore, the device can comprise means for moving the focusing lenses, in order to obtain focused light beams that can be customized. The means for moving can be implemented by means of dedicated interface means.

In essence, the present invention is based on the innovative technique of using a single optical reflection measurement to determine the amount of Black Carbon present in a sample of atmospheric particulate.

The advantage of being able to determine the concentration of BC starting from a single measurement in reflection lies in the fact that the described device can be implemented in a modular way, in order to be compatible with integration into standard sequential samplers, in order to support an“online” measurement of the BC concentration to the measurement required by law, without the latter coming in any way altered.

For this purpose, the light intensity detection sensors 91 , 92 can have respective means of data communication with the sampler with which the device of the invention is associated.

Alternatively, preferred embodiments of the device of the invention can operate as a standalone, remotely manageable measuring instrument.

According to this preferred embodiment, shown in Figure 6, the device T shows to integrate or comprise a data processing unit 19, or the main body 10 of the device T can be connected to the latter according to a wired or wireless mode. According to this implementation, the central unit 19 can be further arranged remotely with respect to the site where the main body 10 of the measuring device T is installed. Alternatively, the central unit 19 can be integrally comprised in the main body 10. The central unit 19 is configured, or better programmed, to implement the method of calculating the BC concentration in the particulate sample analysed in the main body 10. For this purpose, the central unit 19 can comprise a dedicated microprocessor and/or a memory unit 99 in which instructions to be implemented, algorithms and values of the calculation parameters (e.g. the MAC value) are stored. The central unit 19 can be programmed to use a predetermined MAC value. The MAC value assignment is arbitrary, for example, a MAC value of 10 m²g-¹ can be pre-set. Alternatively, the user can independently set and/or modify the MAC value to better adhere to the characteristics of the samples analysed (this operation can be carried out starting from the comparison between thermo-optical (EC) and absorption (ABS) measurements carried out on the sampling site).

Once the RFN reflectance value of the sample has been determined based on the data detected by the sensors 91 , 92, a mathematical equation has been provided expressing the ABS absorption value as a function of the RFN reflectance value and the MAC value has been provided, the central unit 19 automatically calculates an ABS absorption value using the above mathematical equation, and again automatically calculates a BC concentration value using the equation:

BC = ABS /a_abs Furthermore, the unit 19 can comprise, or be connected in a wireless or wired mode to, interface means for the selection and modification of operating parameters of the device T (for example: orientation and positioning of the light intensity detection sensors, orientation and positioning of the focusing lenses, intensity of the light beam emitted by the source, activation of the means of forced circulation of the ambient air, setting and modification of the MAC value). These interface means, as well as the central unit 19, can be implemented using an electronic calculator, or a smartphone, which appropriate software is installed thereon.

The present invention has so far been described with reference to preferred embodiments. It is to be understood that other embodiments may exist which pertain to the same inventive core, as defined by the scope of protection of the claims set forth below.

Claims

1. A method of measuring the concentration di Black Carbon (BC) in a target sample of atmospheric particulate, which comprises the following steps:

- providing a certain number of reference atmospheric particulate samples, - measuring a reflectance value (RFN) and an absorption value (ABS) for each of said samples, wherein each of said samples is collected on a filtering support;

- for each of said samples, reporting on a Cartesian diagram, consisting of an abscissa axis corresponding to the absorption value (ABS) and an ordinate axis corresponding to the reflectance value (RFN) measured according to a predetermined reflection angle value, a point of coordinates corresponding to respective reflectance (RFN) and absorption (ABS) values;

- determining the mathematical equation of a polynomial curve that interpolates the points reported on the Cartesian diagram, wherein the mathematical equation expresses the absorption (ABS) as a function of the reflectance (RFN) and is a mathematical equation of the type:

ABS = (A ± AA) X RFN² + (fl ± AB) X RFN + (C ± AC) wherein:

A, B and C are coefficients whose value depends on the phenomenon of multiple scattering that occurs among the particles of said particulate samples and a matrix of the filtering support, while DA, DB and AC represent uncertainties respectively related to each of said coefficients A, B and C;

- measuring a reflectance value (RFN) of the target sample, according to said predetermined reflection angle value;

- calculating the corresponding absorption value (ABS) using said mathematical equation;

- calculating the concentration of Black Carbon (BC) in the target sample using the relation:

BC = ABS /a_abs wherein: aabs is known and is the mass impact section of the target sample, and the number of reference particulate samples is such that the correlation coefficient (R²) of said mathematical equation with respect to the interpolated points have a value greater than or equal to 0,9.

2. Method of measuring the concentration di Black Carbon (BC) in a sample di atmospheric particulate, which comprises the following steps:

- providing the value of the mass impact section (aabs) of the sample;

- measuring the reflectance value (RFN) of the sample for a detection angle of 125 and for a light source having wavelength equal to 635 nm; - calculating the absorption value (ABS) of the sample using the mathematical equation:

ABS= (-0,69 ± 0,03) * RFN² + (2,22 ± 0,04) * RFN + (0, 13 ± 0,01)] and

- calculating the concentration of Black Carbon (BC) in the sample by means of the equation: BC = ABS/a_abs.

3. Computer program, comprising a list of instructions which, when performed on an electronic computer, provided a reflectance value (RFN) of an atmospheric particulate sample, a mass impact section value (aabs) of said sample of atmospheric particulate and a mathematical equation according to claim 1 or 2, implement the following steps: calculating an absorption value (ABS) of said atmospheric particulate sample by means of said mathematical equation; calculating a concentration value of Black Carbon (BC) in said atmospheric particulate sample by means of the equation:

BC = ABS/a_abs.

4. A device (1 ) for measuring the concentration of Black Carbon (BC) in a sample of atmospheric particulate, apt to implement the method according to claim 1 or 2 and comprising:

- a main body (10) comprising a measurement chamber (11 ) shaped in such a way as to be crossed by a flow of ambient air in which atmospheric particulate is suspended, said measurement chamber (11 ) having an inlet opening (52) for the ambient air flow and an outlet opening (53) for the ambient air flow;

- a filtering element (5) housed within said measurement chamber (11 ) in a position interposed between said inlet opening (52) and outlet opening (53), and comprising a deposit surface (51 ), said filtering element (5) being configured to collect at said deposition surface (51 ) a sample of atmospheric particulate suspended in the flow of ambient air which passes through said measuring chamber (11 ) from said inlet opening (52) towards said outlet opening (53);

- a light source (7), configured to radiate said deposit surface (51 ); and

- a first sensor (91 ) for detecting light intensity, facing onto said deposit surface (51 ); the configuration of said device (1 ) being such that: when the particulate sample is deposited at said deposit surface (51 ) and said light source (7) and said first sensor (91 ) are activated, said light source (7) radiates the particulate sample and said first sensor (91 ) detects the intensity of light reflected by the particulate sample.

5. The device (1 ) according to claim 4, wherein said measuring chamber (11 ) comprises a first portion (2) and a second portion (3), therebetween said filtering element (5) being interposed, wherein said first portion (2) and second portion (3) presents respectively an overall frusto-conical shape, with volume increasing towards said filtering element (5).

6. The device (1 ) according to claim 4 or 5, wherein said first sensor (91 ) for detecting light intensity is orientated to define a first angle (a) equal to about 35° with respect to said deposit surface (51 ).

7. The device (1 ) according to any of claims 4 to 6, comprising means of forced circulation (6) of the ambient air, configured to convey a flow of ambient air from said inlet opening (52) to said outlet opening (53), preferably positioned at said outlet opening (53).

8. The device (1 ) according to any of claims 4 to 7, wherein said deposit surface (51 ) is arranged orthogonally to the passage section of the ambient air flow of said inlet opening (52).

9. The device (1 ) according to any of claims 4 to 8, further comprising, or being connected to, a central unit (19) for processing data detected by said first sensor (91 ) for detecting light intensity, wherein said central unit (19) comprises means for implementing a computer program according to claim 3.