Calibration method for conversion relation between particle number and mass concentration

Abstract

The invention discloses a method for calibrating the conversion relation between the particle number and the mass concentration, and the method comprises the following steps: for aspheric particles, introducing a voltage correction coefficient through employing the concept of equivalent diameter, and obtaining a calculation formula of the mass concentration of the aspheric particles; in a test environment, the number of voltage pulses of the particulate matter sensor within a period of time is collected, the average value of peak voltage of each pulse is solved, and meanwhile, the PM2.5 mass concentration is collected by using a standard instrument; after the calibration coefficient and the proportionality coefficient are calculated and obtained by combining the mass concentration measured by the standard instrument and the quantity concentration detected by the particulate matter sensor, the calibration coefficient and the proportionality coefficient are substituted into a formula to calculate the mass concentration corresponding to the quantity concentration detected by the particulate matter sensor, and meanwhile, the measurement precision of the particulate matter sensor is guaranteed when the particulate matter concentration changes suddenly.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of particulate matter detection, in particular to a calibration method for the conversion relationship between particle number and mass concentration. BACKGROUND

[0002] PM2.5 is a particulate matter (fine particulate matter) with a diameter ≤2.5 microns in air dynamics. The smaller the particle size, the longer the residence time in the atmosphere, and the higher the respiratory absorption rate. Since most harmful substances are enriched on the surface of such particles, the health hazards show a particle size-dependent decreasing characteristic, that is, the health risks to the respiratory system, cardiovascular system, etc. of the human body increase exponentially with each order of magnitude decrease in particle size. This characteristic makes it one of the most threatening types of pollutants to public health in air pollution.

[0003] Therefore, the detection of air quality PM2.5 concentration is particularly important. At present, the existing technology mainly realizes the rapid and accurate detection of PM2.5 particulate matter through different principles of sensors (such as optical, electrochemical, mass spectrum, etc.). The optical sensor based on Mie scattering principle can identify the number concentration of particulate matter in the air, but cannot directly obtain the mass concentration of particulate matter. In order to obtain the mass concentration, the existing particulate matter sensor usually adopts a single linear model to calibrate the relationship between the number concentration and the mass concentration, so as to obtain the mass concentration of particulate matter in the air. The error of the mass concentration calculated by this calibration method when the PM2.5 concentration suddenly changes will exceed ±15%.

[0004] For the existing scattering principle sensor, the number concentration of particulate matter can be identified, but the mass concentration cannot be directly identified. The present application provides a calibration method for the conversion relationship between particle number and mass concentration. The current air PM2.5 concentration is directly calculated according to the calibrated formula through particle counting. For the problem that the existing sensor usually uses a single linear model to calibrate the relationship between the number concentration and the mass concentration, resulting in a large error when the particulate matter concentration suddenly changes, a polynomial calibration method is adopted to improve the calculation accuracy of the mass concentration. SUMMARY

[0005] The present application aims to provide a calibration method for the conversion relationship between particle number and mass concentration to solve the problems raised in the background.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solution: a calibration method for the conversion relationship between particle number and mass concentration, comprising the following steps:

[0007] S1, for non-spherical particulate matter, introducing a voltage correction coefficient using the concept of equivalent diameter obtaining the calculation formula (1) of the mass concentration of non-spherical particulate matter;

[0008] ;

[0009] in, The average voltage of the particle pulse peak during the sampling time. This represents the number of effective pulses sampled by the optical sensor. This is the proportionality coefficient. This is the voltage correction factor;

[0010] S2. Under the test environment, collect the number of voltage pulses from the particulate matter sensor over a period of time. ,beg Average peak voltage of each pulse At the same time, PM2.5 mass concentration was collected using standard instruments. ;

[0011] S3, Assumption The range of values ​​is within Divide it into 100 equal parts and record the mass concentrations collected by the standard instrument. Divided into An interval, denoted as The number of voltage pulses at the corresponding time. and average voltage Also classified as Each interval, for each quality interval Calculate using formula (1) When, find set ;

[0012] S4, Utilization and Substitute into formula (1) to calculate the mass concentration of all samples within the total sampling time. Using formula (2):

[0013] ;

[0014] Calculate the relative error between the calculated and actual values, and identify those with a relative error within ±10%. The range of values, denoted as ;

[0015] S5, Get All The intersection of the values ​​and the average value are obtained. , will be obtained Substitute into formula (3):

[0016] ;

[0017] Find each mass range of values, and then their average value is obtained , and is the final value of the calibration parameter, and then the corresponding concentration is calculated according to formula (1).

[0018] Preferably, in the step S2, it is necessary to ensure that the collected voltage pulse information and the collected standard concentration are in the same time axis.

[0019] Preferably, in the step S2, the conditions of the test environment are temperature 25±2℃ and relative humidity RH 50±5%.

[0020] Preferably, in the step S5, after the corresponding concentration is calculated, the trend consistency between the calculated concentration and the standard concentration and the error size are observed, corresponding to the standard concentration of PM2.5 in the air, so as to verify the rationality of the calibration parameter.

[0021] Preferably, by performing multiple calibrations, multiple sets of calibration parameters are obtained and and the average value is taken to improve the calculation accuracy of the mass concentration.

[0022] Compared with the prior art, the beneficial effects of the present application are: combining the mass concentration measured by the standard instrument and the number concentration detected by the particulate matter sensor, after the calibration coefficient and the proportion coefficient are calculated and obtained, the number concentration detected by the particulate matter sensor is calculated to obtain the corresponding mass concentration, and at the same time, the measurement accuracy of the particulate matter sensor is ensured when the particulate matter concentration suddenly changes. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is the calibration flowchart of the present application;

[0024] Figure 2 is the result schematic diagram after single calibration fitting of the present application;

[0025] Figure 3 is the result schematic diagram after multiple calibration fitting of the present application. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described clearly and completely below by combining the drawings in the embodiments of the present application.

[0027] Please refer to Figures 1-3The application provides a technical solution: the calibration method is suitable for calibrating the mass concentration of particles of various particle sizes in theory, and the mass concentration of PM2.5 (particle size 0.3-2.5 μm) is taken as an example in the application. Since the optical sensor is sensitive to changes in environmental conditions (such as temperature, humidity, etc.), all tests of the application are carried out under the condition of 25±2℃, RH50±5%.

[0028] Assuming that the number of spherical particles in a unit volume of gas is , according to the mass calculation formula of a sphere and based on the relationship between the scattering light flux of a spherical particle and the particle diameter in the Mie scattering theory, the mass concentration calculation formula of particles in a unit volume is obtained:

[0029]

[0030] wherein, is the average voltage of the particle pulse peak in the sampling time, N is the number of particles in the sampling time (i.e. the number of effective pulses sampled by the optical sensor), is a proportional coefficient.

[0031] For non-spherical particles, the concept of equivalent diameter is used to introduce a voltage correction coefficient to obtain the mass concentration calculation formula (1) of non-spherical particles:

[0032]

[0033] The focus of the calibration method is to calibrate and in formula (1). In the test environment, the number of voltage pulses of the particle sensor in a period of time (such as 1000 seconds in Figure 2 ) is collected , the average value of the peak voltage of pulses is calculated , and the mass concentration of PM2.5 in the same time axis is collected by using a standard instrument , so as to ensure that the collected voltage pulse information is coaxial with the standard concentration.

[0034] Assuming that the value range of is , it is divided into 100 equal parts, and the mass concentration collected by the standard instrument is divided into intervals: , the number of voltage pulses at the corresponding time and the average voltage are also divided into intervals. For each mass interval ​​, the total sampling time is calculated by formula (1) , the set of is obtained .

[0035] Using and , the total sampling time is calculated by formula (1) , using formula (2):

[0036] ;

[0037] The relative error between the calculated value and the actual value is obtained, and the value range of the relative error within ±10% is found, denoted as . Take the intersection of all and take the average value to obtain , and the obtained is brought into formula (3):

[0038] ;

[0039] The value of is obtained for each mass interval , and their average value , and is the final value of the calibration parameter.

[0040] According to formula (1), the corresponding concentration is calculated, which corresponds to the standard concentration of PM2.5 in the air. Whether the calculated concentration and the standard concentration are consistent in trend and the size of the error are observed to verify the rationality of the calibration parameter. As shown in Figure 2 , the calibration result is obtained . After calculating the mass concentration, the mass concentration measured by the standard instrument is fitted, where the red curve represents the mass concentration measured by the standard instrument, and the blue curve represents the mass concentration calculated using the calibration parameter. The fitting degree , and the calibration effect is good.

[0041] Generally, the calculation accuracy of the mass concentration can be improved by performing multiple calibrations to obtain multiple sets of calibration parameters and and taking the average value. As shown in Figure 3 , the mass concentration fitting is performed using the calibration parameters and obtained after ten calibrations, and the fitting degree , which proves that the mass concentration obtained using the calibration coefficient can still maintain a high fitting degree when the concentration changes dramatically.

[0042] ​The application provides a method for calibrating the conversion relationship between particle count and mass concentration. By particle count, the current air PM2.5 concentration is directly calculated according to the calibrated formula. By introducing the proportional coefficient , the complex shape of non-spherical particles is quantified as an equivalent diameter parameter, replacing the traditional fixed shape factor, making the algorithm more adaptable.

[0043] Based on dynamic segmentation calibration and equivalent particle diameter model, the conversion between particle number and mass concentration is realized through calibration coefficients and , and the measurement accuracy of the optical sensor in the concentration mutation scene is significantly improved (error < 10%). This method is not only suitable for PM2.5 (0.3-2.5 μm), but also can be adapted to other particle size ranges (such as PM10 or ultrafine particles) by adjusting the calibration parameters.

[0044] Although embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for calibrating the conversion relationship between particle number and mass concentration, characterized in that, Includes the following steps: S1. For non-spherical particles, a voltage correction coefficient is introduced using the concept of equivalent diameter. The formula for calculating the mass concentration of non-spherical particulate matter is (1); ； in, The average voltage of the particle pulse peak during the sampling time. This represents the number of effective pulses sampled by the optical sensor. This is the proportionality coefficient. This is the voltage correction factor; S2. Under the test environment, collect the number of voltage pulses from the particulate matter sensor over a period of time. ,beg Average peak voltage of each pulse At the same time, PM2.5 mass concentration was collected using standard instruments. ; S3, Assumption The range of values ​​is within Divide it into 100 equal parts and record the mass concentrations collected by the standard instrument. Divided into An interval, denoted as The number of voltage pulses at the corresponding time. and average voltage Also classified as Each interval, for each quality interval Calculate using formula (1) When, find set ; S4, Utilization and Substitute into formula (1) to calculate the mass concentration of all samples within the total sampling time. Using formula (2): ； Calculate the relative error between the calculated and actual values, and identify those with a relative error within ±10%. The range of values, denoted as ; S5, Get All The intersection of the values ​​and the average value are obtained. , will be obtained Substitute into formula (3): ； Find each mass range of The values ​​are then calculated, and their average is obtained. , and This is the final value of the calibration parameter, and then the corresponding concentration is calculated according to formula (1).

2. The calibration method for the conversion relationship between particle number and mass concentration according to claim 1, characterized in that: In step S2, it is necessary to ensure that the collected voltage pulse information and the collected standard concentration are on the same time axis.

3. The calibration method for the conversion relationship between particle number and mass concentration according to claim 1, characterized in that: In step S2, the test environment conditions are a temperature of 25±2℃ and a relative humidity of RH50±5%.

4. The calibration method for the conversion relationship between particle number and mass concentration according to claim 1, characterized in that: In step S5, after calculating the corresponding concentration, it is compared with the standard concentration of PM2.5 in the air. The calculated concentration and the standard concentration are observed to see if they are consistent in trend and the magnitude of error, so as to verify the rationality of the calibration parameters.

5. The calibration method for the conversion relationship between particle number and mass concentration according to claim 1, characterized in that: By performing multiple calibrations, multiple sets of calibration parameters are obtained. and The accuracy of mass concentration calculation is improved by taking the average value.

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