CN106092841A - The method being constraints inverting Aerosol Extinction moisture absorption growth factor Yu relative humidity functional relationship with PM2.5 mass concentration - Google Patents

Abstract

The invention discloses a kind of method being constraints inverting Aerosol Extinction moisture absorption growth factor Yu relative humidity functional relationship with PM2.5 mass concentration.Aerosol Extinction α during relative humidity≤40% that it will record_DryWith PM2.5 mass concentration C_PM2.5Substitute into formulaIn calculate Proportional coefficient K after, record Aerosol Extinction α under Arbitrary Relative humidity prior to same place_wetWith PM2.5 mass concentration C_PM2.5, and by PM2.5 mass concentration C under Proportional coefficient K and this Arbitrary Relative humidity_PM2.5Substitute into formula α=K C_PM2.5In calculate " doing " Aerosol Extinction α under this Arbitrary Relative humidity_dry, then the α that will record_wetWith the α calculated_drySubstitute into formula

Description

Method for inverting functional relation between aerosol extinction coefficient moisture absorption growth factor and relative humidity by taking PM2.5 mass concentration as constraint condition

Technical Field

The invention relates to a method for inverting a functional relation between an aerosol extinction coefficient moisture absorption growth factor and relative humidity, in particular to a method for inverting a functional relation between an aerosol extinction coefficient moisture absorption growth factor and relative humidity by taking PM2.5 mass concentration as a constraint condition.

Background

The atmospheric aerosol is a general term for solid and liquid particles with the particle diameter of 0.001-100 mu m suspended in the atmosphere, and PM2.5 is aerosol particles with the diameter of less than 2.5 mu m, which is an important component of the atmospheric aerosol. In recent years, air pollution has attracted more and more attention, and PM2.5, one of the main pollutants in the air, can be suspended in the air for a longer time, and the higher the content concentration in the air, the more serious the air pollution is represented. At present, the method for detecting PM2.5 in the atmosphere mainly uses equipment, namely a PM2.5 mass concentration monitor, for monitoring. Although the method can measure PM2.5 in the atmosphere, the method is limited by the height of a platform where a PM2.5 mass concentration monitor is located, only PM2.5 within the height range of less than or equal to 30m can be detected, if PM2.5 within a higher range needs to be detected, a high-altitude balloon platform or an airplane platform needs to be used, the PM2.5 is difficult to detect in real time at any time, the detection cost is greatly increased, and the method is extremely inconvenient and time-consuming. In addition, although the laser radar is also a powerful tool for detecting the atmospheric aerosol, the detection is only the atmospheric aerosol extinction coefficient or the backscattering coefficient, and the mass concentration of PM2.5 in the atmosphere cannot be directly detected.

Disclosure of Invention

The technical problem to be solved by the invention is to overcome the defects in the prior art, and provide a method for conveniently and quickly detecting the mass concentration of PM2.5 in the atmosphere in a larger height range on the near ground at any time and with low cost and inverting the functional relation between the aerosol extinction coefficient moisture absorption growth factor and the relative humidity by taking the mass concentration of PM2.5 as a constraint condition.

In order to solve the technical problem of the invention, the adopted technical scheme is as follows: the method for inverting the functional relation between the aerosol extinction coefficient moisture absorption growth factor and the relative humidity by taking the PM2.5 mass concentration as the constraint condition comprises the following steps of measuring the PM2.5 mass concentration, and particularly comprises the following main steps:

step 1, measuring the extinction coefficient α of aerosol when the relative humidity is less than or equal to 40%_{Dry matter}And PM2.5 Mass concentration C_PM2.5Substitution formulaIn the process, a proportionality coefficient K is calculated,

wherein α represents the extinction coefficient of aerosol,Is the average extinction efficiency factor of aerosol, C ═ C_Total/C_PM2.5、C_TotalIs the total concentration of particulate matter in the atmosphere, r_effIs the effective radius of the aerosol particles,Is the average mass density of the aerosol;

step 2, firstly measuring the extinction coefficient α of aerosol under any relative humidity at the same place_wetAnd PM2.5 Mass concentration C_PM2.5Then, the proportionality coefficient K and the PM2.5 mass concentration C at any relative humidity are compared_PM2.5Substituting formula α ═ K · C_PM2.5The "dry" aerosol extinction coefficient α at this arbitrary relative humidity was calculated_dryThen the measured extinction coefficient α of aerosol under any relative humidity_wetAnd the calculated dry aerosol extinction coefficient α at any relative humidity_drySubstitution formulaCalculating to obtain an aerosol extinction coefficient moisture absorption growth factor f;

and 3, repeating the step 2 for at least 5 times, and then obtaining a function relation of the aerosol extinction coefficient moisture absorption increase factor and the atmospheric relative humidity by inverting the aerosol extinction coefficient moisture absorption increase factor by taking the PM2.5 mass concentration as a constraint condition through a fitting method for two groups of data of the atmospheric relative humidity RH and the aerosol extinction coefficient moisture absorption increase factor f which are respectively measured at the same place.

As a further improvement of a method for inverting the functional relationship between the aerosol extinction coefficient moisture absorption growth factor and the relative humidity by taking PM2.5 mass concentration as a constraint condition:

preferably, the number of times of repeating the step 2 is 5-20 times.

Preferably, C_TotalBy the formulaObtaining the radius of the aerosol particles, and n (r) is the ratio of the number dN of the aerosol particles to dr in the interval of the radius r → r + dr in the unit volume.

Preferably, r_effBy the formulaAnd (4) obtaining.

Compared with the prior art, the beneficial effects are that:

by adopting the method, the PM2.5 mass concentration in the atmosphere within a larger height range can be conveniently detected on the near ground at any time with low cost through the obtained functional relation between the aerosol extinction coefficient moisture absorption growth factor and the relative humidity of the atmosphere, the detected height range is as wide as 0-30 km, namely the height range of the aerosol extinction coefficient detected by the laser radar, so that the method is extremely easy to be widely and commercially applied to monitoring the PM2.5 mass concentration in the atmosphere.

The specific inference process of the method is as follows:

1. based on a large number of experiments, a certain relation exists between the PM2.5 mass concentration and the aerosol extinction coefficient, wherein the atmospheric relative humidity has a large influence on the relation between the mass concentration and the aerosol extinction coefficient, namely the relative humidity can influence the extinction coefficient by influencing the particle size of aerosol particles, but does not influence the PM2.5 mass concentration. Therefore, the relative humidity correction can be carried out on the aerosol extinction coefficient by determining the function of the moisture absorption increase factor of the aerosol extinction coefficient, so that the relative humidity correction is converted into the PM2.5 mass concentration.

Let the aerosol size spectrum distribution function be n (r), which is defined as the ratio of the number of aerosol particles dN to dr in the interval of radius r → r + dr in unit volume, i.e. the ratio

$n\left(r\right)=\frac{dN}{dr}.---\left(1\right)$

Total concentration of particulate matter in the atmosphere C_TotalCan be defined as

$C_{Total}={\∫}_0^{100um}\stackrel{\‾}{\mathrm{\ρ}}\left(\frac{4}{3}{\mathrm{\πr}}^3\right)n\left(r\right)dr,---\left(2\right)$

Wherein,is the average mass density of the aerosol.

Mass concentration C of PM2.5_PM2.5Can be defined as

$C_{PM2.5}={\∫}_0^{2.5um}\stackrel{\‾}{\mathrm{\ρ}}\left(\frac{4}{3}{\mathrm{\πr}}^3\right)n\left(r\right)dr.---\left(3\right)$

The aerosol extinction coefficient α can be defined as the approximate condition of neglecting multiple scattering

$\mathrm{\α}={\∫}_0^{\mathrm{\∞}}{\mathrm{\πr}}^2{\stackrel{\‾}{Q}}_{ext}n\left(r\right)dr,---\left(4\right)$

Wherein,is the average extinction efficiency factor of the aerosol.

Introduction of effective radius of aerosol particlesThen, the relation between the extinction coefficient of the aerosol and the concentration of the particulate matters can be obtained

$\mathrm{\α}=\frac{3{\stackrel{\‾}{Q}}_{ext}}{4r_{eff}\stackrel{\‾}{\mathrm{\ρ}}}{C}_{Total}.---\left(5\right)$

Let C_Total/C_PM2.5From this, a relation between the extinction coefficient of the aerosol and the mass concentration of PM2.5 can be obtained

$\mathrm{\α}=\frac{3{\stackrel{\‾}{Q}}_{ext}C}{4r_{eff}\stackrel{\‾}{\mathrm{\ρ}}}{C}_{PM2.5}=K\·C_{PM2.5},---\left(6\right)$

WhereinIs a scaling factor that is a function of the aerosol micro-physical parameter and the relative humidity.

When the PM2.5 mass concentration detector detects, the sucked atmosphere is dried first and then measured. It therefore measures the PM2.5 mass concentration of a "dry" atmosphere, independent of the relative humidity of the atmosphere. The extinction coefficient of the atmosphere is a direct measure of the ambient atmosphere, that is, it measures the extinction coefficient of a wet atmosphere, relative to the relative humidity of the atmosphere.

If the effect of the relative humidity in the atmosphere can be eliminated and the extinction coefficient of the "dry" aerosol is obtained, the proportionality coefficient K in this case is only a function of the micro-physical parameters. It is further assumed that the microphysical parameters of the aerosol are considered to be unchanged during the detection time, and the proportionality coefficient K is constant, so that the extinction coefficient of the "dry" aerosol can be converted into PM2.5 mass concentration.

2. Method for inverting functional relation between ambient atmospheric aerosol extinction coefficient moisture absorption growth factor and relative humidity

The aerosol extinction coefficient of the actual ambient atmosphere is related to the relative humidity of the atmosphere besides the concentration, the scale spectrum and the refractive index of the particulate matters. When the relative humidity of the atmosphere becomes higher, the hydrophilic particles contained in the aerosol absorb moisture and grow due to the increase of the relative humidity, so that the total extinction efficiency of the aerosol is enhanced, and the extinction coefficient is increased. On the other hand, due to the decrease in relative humidity, the aerosol particles are weathered to cause a decrease in extinction efficiency, resulting in a decrease in extinction coefficient.

The hygroscopic growth factor of an aerosol is described by f, which is defined as

$f=\frac{{\mathrm{\α}}_{wet}}{{\mathrm{\α}}_{dry}},---\left(7\right)$

Wherein, α_wetAnd α_dryRespectively, the extinction coefficient of the aerosol at relative humidity and the extinction coefficient of the "dry" aerosol at the time of measurement.

In practice, a common instrument for measuring the moisture absorption factor is a series connection electric mobility particle moisture absorption particle size analyzer (H-TDMA), and the working principle of the instrument is that ambient atmosphere is dried after being sucked from a port, and then the dry particle size and the scale spectrum of the ambient atmosphere are measured; then creating the relative humidity of the atmospheric environment at that time, increasing the particle size, measuring the wet particle size and the scale spectrum, calculating the extinction coefficients under dry and wet conditions respectively by using the formula (4), and finally calculating the extinction coefficient moisture absorption factor by using the formula (7). This is the current method of use.

In a measurement process of an ambient atmosphere (for example, 3 hours), if the source of the aerosol is the same, the micro physical parameters such as the scale spectrum and the refractive index can be considered to be unchanged, and only the total concentration of the particle number and the relative humidity are changed. From the above analysis, it can be seen that the proportional relationship K between the "dry" aerosol extinction coefficient and the mass concentration of PM2.5 is considered to be a constant. Measurement in ambient atmosphereIn the process, the aerosol extinction coefficient α and the PM2.5 mass concentration C are continuously measured at the same place_PM2.5And the relative humidity RH of the atmosphere, under the assumed conditions, the mass concentration of PM2.5 is taken as the constraint condition, and the relationship between the extinction coefficient hygroscopic growth factor and the relative humidity in the inversion environment atmosphere is obtained.

Detailed Description

In this example, the extinction coefficient of aerosol and the mass concentration C of PM2.5 were continuously measured at the same place_PM2.5And the atmosphere relative humidity RH instruments are respectively an aerosol extinction coefficient detection device, a PM2.5 mass concentration monitor and a relative hygrometer; wherein, the aerosol extinction coefficient detection device is a laser radar.

The method for inverting the functional relationship between the aerosol extinction coefficient moisture absorption growth factor and the relative humidity by taking the PM2.5 mass concentration as the constraint condition comprises the following steps:

step 1, measuring the extinction coefficient α of aerosol when the relative humidity is less than or equal to 40%_{Dry matter}And PM2.5 Mass concentration C_PM2.5Substitution formulaIn the process, a proportionality coefficient K is calculated,

wherein α represents the extinction coefficient of aerosol,Is the average extinction efficiency factor of aerosol, C ═ C_Total/C_PM2.5、C_TotalIs the total concentration of particulate matter in the atmosphere, r_effIs the effective radius of the aerosol particles,Is the average mass density of the aerosol; wherein,

C_Totalby the formulaObtaining the radius of the aerosol particles, n (r) is the ratio of the number dN of the aerosol particles to dr in the interval of r → r + dr in unit volume,

r_effby the formulaAnd (4) obtaining.

Step 2, firstly measuring the extinction coefficient α of aerosol under any relative humidity at the same place_wetAnd PM2.5 Mass concentration C_PM2.5Then, the proportionality coefficient K and the PM2.5 mass concentration C at any relative humidity are compared_PM2.5Substituting formula α ═ K · C_PM2.5The "dry" aerosol extinction coefficient α at this arbitrary relative humidity was calculated_dryThe measured extinction coefficient α of aerosol at any relative humidity_wetAnd the calculated dry aerosol extinction coefficient α at any relative humidity_drySubstitution formulaAnd calculating to obtain the aerosol extinction coefficient moisture absorption growth factor f.

And 3, repeating the step 2 for 15 (5-20) times, and then obtaining a function relation between the aerosol extinction coefficient moisture absorption growth factor and the atmospheric relative humidity by using a fitting method according to two groups of data of the atmospheric relative humidity RH measured at the same place and the aerosol extinction coefficient moisture absorption growth factor f obtained by calculation and taking the PM2.5 mass concentration as a constraint condition.

It is apparent that those skilled in the art can make various changes and modifications to the method for inverting the relationship between the moisture absorption increase factor and the relative humidity of the aerosol extinction coefficient by taking the mass concentration of PM2.5 as the constraint condition, without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such modifications and variations.

Claims (4)

1. A method for inverting the functional relationship between aerosol extinction coefficient moisture absorption growth factor and relative humidity by taking PM2.5 mass concentration as a constraint condition comprises the measurement of PM2.5 mass concentration, and is characterized by mainly comprising the following steps:

step 1, measuring the extinction coefficient α of aerosol when the relative humidity is less than or equal to 40%_{Dry matter}And PM2.5 Mass concentration C_PM2.5Substitution formulaIn (1), calculating the proportionality coefficientK,

Wherein α represents the extinction coefficient of aerosol,Is the average extinction efficiency factor of aerosol, C ═ C_Total/C_PM25、C_TotalIs the total concentration of particulate matter in the atmosphere, r_effIs the effective radius of the aerosol particles,Is the average mass density of the aerosol;

step 2, firstly measuring the extinction coefficient α of aerosol under any relative humidity at the same place_wetAnd PM2.5 Mass concentration C_PM2.5Then, the proportionality coefficient K and the PM2.5 mass concentration C at any relative humidity are compared_PM2.5Substituting formula α ═ K · C_PM2.5The "dry" aerosol extinction coefficient α at this arbitrary relative humidity was calculated_dryThen the measured extinction coefficient α of aerosol under any relative humidity_wetAnd the calculated dry aerosol extinction coefficient α at any relative humidity_drySubstitution formulaCalculating to obtain an aerosol extinction coefficient moisture absorption growth factor f;

and 3, repeating the step 2 for at least 5 times, and then obtaining a function relation of the aerosol extinction coefficient moisture absorption increase factor and the atmospheric relative humidity by inverting the aerosol extinction coefficient moisture absorption increase factor by taking the PM2.5 mass concentration as a constraint condition through a fitting method for two groups of data of the atmospheric relative humidity RH and the aerosol extinction coefficient moisture absorption increase factor f which are respectively measured at the same place.

2. The method for inverting the functional relationship between the aerosol extinction coefficient moisture absorption growth factor and the relative humidity by taking the PM2.5 mass concentration as the constraint condition according to claim 1, wherein the number of times of repeating the step 2 is 5-20.

3. The method for inverting the functional relationship between the moisture absorption growth factor and the relative humidity of the aerosol extinction coefficient by using the mass concentration of PM2.5 as the constraint condition according to claim 1, wherein C is_TotalBy the formulaObtaining the radius of the aerosol particles, and n (r) is the ratio of the number dN of the aerosol particles to dr in the interval of the radius r → r + dr in the unit volume.

4. The method for inverting the functional relationship between the moisture absorption growth factor and the relative humidity of the aerosol extinction coefficient by using the mass concentration of PM2.5 as the constraint condition according to claim 3, wherein r is_effBy the formulaAnd (4) obtaining.