CN115656058A - NO based on DOAS 2 Concentration measuring method - Google Patents
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- 238000000034 method Methods 0.000 title claims abstract description 48
- 238000001658 differential optical absorption spectrophotometry Methods 0.000 title claims abstract description 30
- 238000001228 spectrum Methods 0.000 claims abstract description 65
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- 238000010521 absorption reaction Methods 0.000 claims abstract description 50
- 238000002835 absorbance Methods 0.000 claims abstract description 42
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- 238000007781 pre-processing Methods 0.000 claims abstract description 10
- 229910052724 xenon Inorganic materials 0.000 claims abstract description 10
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 claims abstract description 10
- 239000007789 gas Substances 0.000 claims description 30
- 230000009466 transformation Effects 0.000 claims description 20
- 238000000691 measurement method Methods 0.000 claims description 12
- 238000000354 decomposition reaction Methods 0.000 claims description 9
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 8
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- 239000000126 substance Substances 0.000 claims description 5
- 238000005516 engineering process Methods 0.000 claims description 4
- 238000011156 evaluation Methods 0.000 claims description 4
- 229910052757 nitrogen Inorganic materials 0.000 claims description 4
- 238000004611 spectroscopical analysis Methods 0.000 claims description 4
- 238000012935 Averaging Methods 0.000 claims description 3
- 230000008033 biological extinction Effects 0.000 claims description 3
- 238000012546 transfer Methods 0.000 claims description 3
- KZSNJWFQEVHDMF-UHFFFAOYSA-M valinate Chemical compound CC(C)C(N)C([O-])=O KZSNJWFQEVHDMF-UHFFFAOYSA-M 0.000 claims 1
- 238000005259 measurement Methods 0.000 abstract description 6
- 230000007547 defect Effects 0.000 abstract description 4
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 description 4
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 3
- 238000004847 absorption spectroscopy Methods 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
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- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
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Abstract
The invention discloses NO based on DOAS 2 A method of measuring concentration, the method comprising the steps of: s1, acquiring original spectrum data with different power intensities for preprocessing; s2, calculating a spectrum correction coefficient and verifying; s3, collecting NO with different concentrations 2 Is processed to obtain NO 2 (ii) spectral data; s4, calculating an optimal differential absorbance position data set and an optimal differential absorption cross section by calculating the relation between each spectrum point and the concentration; s5, establishing an equation through actually measured differential absorbance, optimal differential absorbance position data set and optimal differential absorption cross section of the gas to obtain NO 2 A concentration value; s6, performing least square method on NO 2 And correcting the concentration value. The spectral data are corrected by an exponential spectrum correction method, so that the defects of poor stability and poor repeatability of a xenon lamp light source are overcome, and the accuracy of the spectral data is greatly improved; increase of NO 2 The measurement precision meets the requirements of practical application.
Description
Technical Field
The invention relates to the technical field of gas concentration measurement, in particular to NO based on DOAS 2 And (3) a concentration measuring method.
Background
Differential Optical Absorption Spectroscopy (DOAS) -based energy to SO spectroscopy 2 、NO x Multi-component gasThe method is used for detecting the low concentration and high sensitivity, is slightly influenced by cross interference of moisture and other gases, is widely researched at home and abroad in recent years, and is successfully applied to places with concentrated emission of pollution sources, such as coal-fired power plants, paper mills, cement industry and the like.
With the increasingly strict national requirements on environmental protection, the emission concentrations of particulate matters, sulfur dioxide and nitrogen oxides in the emission standard of flue gas of a power plant need to stably reach 10 mg/cubic meter, 35 mg/cubic meter and below 50 mg/cubic meter, SO how to effectively solve the problem of SO 2 And NO x The problem of measuring the accuracy of the gas emission concentration is urgently needed in the industrial field at present.
In the DOAS-based analyzer, a pulse xenon lamp light source is mostly adopted, and the DOAS-based analyzer has the characteristics of long service life, high power and no need of preheating, but has the defects of poor stability and poor repeatability of a xenon lamp, and is always a difficult problem to be overcome in the DOAS technology. In addition, NO 2 The absorption cross section in the ultraviolet band is far smaller than that of NO and SO 2 This also results in nearly half of the analyzers currently on the market using NO x A converter to convert NO 2 Conversion to NO for measurement, using NO x The converter, on the one hand, results in a complex instrument structure and high costs, and, on the other hand, in the conversion process, results in NO 2 Loss of, actual NO cannot be accurately measured 2 The concentration of the emission.
Disclosure of Invention
Aiming at the problems in the related art, the invention provides a NO based on DOAS 2 A concentration measuring method, which overcomes the technical problems existing in the prior related art.
Therefore, the invention adopts the following specific technical scheme:
NO based on DOAS 2 A method of measuring concentration, the method comprising the steps of:
s1, acquiring original spectrum data with different power intensities for preprocessing;
s2, calculating a spectrum correction coefficient and verifying;
s3, collecting NO with different concentrations 2 Is processed to obtain NO 2 (ii) spectral data;
s4, calculating an optimal differential absorbance position data set and an optimal differential absorption cross section by calculating the relation between each spectrum point and the concentration;
s5, establishing an equation through actually measured differential absorbance, optimal differential absorbance position data set and optimal differential absorption cross section of the gas to obtain NO 2 A concentration value;
s6, using a least square method to carry out treatment on NO 2 And correcting the concentration value.
Further, the acquiring of raw spectral data of different power intensities for preprocessing includes the following steps:
s11, selecting a wavelet basis function and the number N of decomposition layers, and performing N-layer multi-scale decomposition on the signal;
s12, reconstructing a low-frequency coefficient of the Nth layer to obtain a reconstructed spectrum;
s13, adjusting the power of a xenon lamp light source, introducing pure nitrogen into the gas chamber, and collecting multiple groups of original spectral data with different power intensities;
s14, filtering each piece of original spectrum data by utilizing wavelet transformation;
s15, averaging the filtered spectrum data with different intensities to obtain the preprocessed spectrum data.
Further, the wavelet transformation is to the signal f (t) epsilon L 2 Integral transformation of (R), and the operation process and the expression comprise:
wherein a and b represent the expansion and translation factors of Ψ (t), respectively;
t represents the signal time, T ∈ (— infinity, + ∞);
the expression of the inverse transformation process is as follows:
wherein the content of the first and second substances,
the conditions were allowed.
Further, the calculating the spectrum correction coefficient and the verifying the spectrum correction coefficient includes the following steps:
s21 at SO 2 NO and NO 2 Selecting at least one waveband from the wavebands which are not absorbed;
s22, recording that the spectrum data after the corresponding preprocessing of the light source powers 800, 775 and 750 are respectively Lamp _800, lamp _775 and Lamp _750, and calculating a correction coefficient by taking the Lamp _750 as a reference spectrum, wherein the expression is as follows:
R1＝log(Lamp_750/Lamp_775)
wherein, R1 is the logarithm of the ratio of two kinds of power spectrum data, and represents the change of other power spectrum data relative to the spectrum data with fixed power;
k represents a correction coefficient;
lamp _775 represents the spectral data when the power of the light source is 775;
lamp _750 represents spectral data at a source power of 750;
253.6 to 256 represent SO 2 NO and NO 2 All of which are non-absorbing;
s23, calibrating the spectrum data by using the correction coefficient, wherein the expression is as follows:
R2＝log(Lamp_750/Lamp_800)
NEW_Lamp_800＝exp(K*mean(R2(253.6～256)))*Lamp_800
wherein R2 represents the change of other power spectral data relative to the spectral data of fixed power;
lamp — 800 represents spectral data when the light source power is 800;
new _ Lamp _800 represents the spectrum data after Lamp _800 correction.
Further, the collection of different concentrations of NO 2 Is processed to obtain NO 2 Spectroscopic data, comprising the steps of:
s31, keeping the power of a light source unchanged, and respectively collecting multiple groups of NO with different concentrations 2 (ii) spectral data;
s32, filtering the spectral data of each concentration by utilizing wavelet transform;
s33, calculating an average value of the filtered multiple groups of spectral data;
s34, calibrating the average value by utilizing the correction coefficient to obtain the calibrated NO 2 Spectral data.
Further, the calculating of the optimal differential absorbance position data set and the optimal differential absorption cross section by calculating the relationship between each spectral point and the concentration includes the steps of:
s41, collecting spectral range and SO according to used spectrometer 2 NO and NO 2 Absorption cross section, selecting the spectrum in the range of 390 nm-415 nm as NO calculation 2 The band of concentration;
s42, calculating [0,20,40,60,80,100] according to the differential absorption spectrum technology]NO at ppm concentration 2 The differential absorbance and the differential absorption cross section of (a);
s43, calculating a correlation coefficient between the differential absorbance of each wavelength point in the range of concentration value [0,20,40,60,80,100] ppm and 390 nm-415 nm, and selecting the wavelength point corresponding to the correlation coefficient larger than 0.99 to form an optimal differential absorbance position data set;
and S44, selecting the position of the differential absorption cross section corresponding to the optimal differential absorbance position data set to form an optimal differential absorption cross section.
Further, the operational expression of the differential absorption spectrum technique includes:
σ i (λ)＝σ i,slow (λ)+σ i,rapid (λ)
wherein, I 0 (λ) represents the source intensity of the incident light at wavelength λ;
i (λ) represents the source intensity of the outgoing light at wavelength λ;
l represents an optical length;
a (λ) represents the transfer function of the system;
c i represents the concentration of the ith gas;
σ i (λ) represents an absorption cross section of the i-th gas;
ε R (lambda) and epsilon M (λ) extinction coefficients representing rayleigh scattering and mie scattering, respectively;
d (λ) represents the optical thickness of the substance;
σ i,slow (λ) represents a slowly varying fraction with wavelength;
σ i,rapid (λ) represents a portion that changes rapidly with wavelength, i.e., a differential absorption cross section of gas.
Further, an equation is established by actually measuring the differential absorbance, the optimal differential absorbance position data set and the optimal differential absorption cross section of the gas, and the expression is as follows:
C＝(P′·P) -1 ·P′·D
wherein C represents NO 2 A concentration value;
d represents the gas differential absorbance after selection using the optimal differential absorbance position dataset;
p denotes an optimum differential absorption cross section, and P' denotes a transposition of P.
Further, said applying least squares to said NO 2 The method for correcting the concentration value comprises the following steps:
s61, solving NO by fitting cubic polynomial by using least square method 2 Obtaining a cubic polynomial relation formula according to the relation between the concentration value and the actual concentration value;
s62, converting the NO 2 And substituting the concentration value into the cubic polynomial equation to obtain a corrected concentration value.
Further, the expression of the cubic polynomial is:
Fit_c＝polyfit(C,y,3)
con＝polyval(Fit_c,C)
wherein, the polyfit () is a polynomial fitting function in Matlab;
c represents NO 2 A concentration value;
y represents the corresponding actual concentration value;
3 is the polynomial fit degree;
fit _ c represents a cubic polynomial coefficient obtained by fitting;
the polyfal () represents a polynomial evaluation function;
con represents the corrected concentration value.
The invention has the beneficial effects that: the spectral data are corrected by an exponential spectrum correction method, so that the defects of poor stability and poor repeatability of a xenon lamp light source are overcome, and the accuracy of the spectral data is greatly improved; and then, a correlation coefficient method is utilized to obtain a correlation coefficient between the concentration and the differential absorbance, so that an optimal differential absorbance position data set and an optimal differential absorption section are constructed, the NO2 measurement precision is improved, and the actual application requirements are met.
In addition, in order to meet the practical application, the calculation amount of a chip is reduced, the reaction time is prolonged, wavelet transformation is adopted for removing high-frequency noise of the spectral data and solving the slow change part, and only the corresponding low-frequency part is reconstructed according to the spectral absorption frequency range.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required in the embodiments will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a DOAS-based NO in accordance with an embodiment of the present invention 2 A flow chart of a concentration measurement method;
FIG. 2 is a DOAS-based NO in accordance with an embodiment of the present invention 2 A graph of spectrum preprocessing data in a concentration measurement method;
FIG. 3 is a DOAS-based NO in accordance with an embodiment of the present invention 2 Two different spectrum calibration method comparison graphs in the concentration measurement method;
FIG. 4 is a DOAS-based NO in accordance with an embodiment of the present invention 2 Calculating a change curve graph of a differential absorption cross section in the concentration measurement method;
FIG. 5 is a DOAS-based NO in accordance with an embodiment of the present invention 2 Graph of correlation coefficient between differential absorbance and concentration in a concentration measurement method.
Detailed Description
According to an embodiment of the present invention, there is provided a DOAS-based NO 2 And (3) a concentration measuring method.
The present invention will now be further described with reference to the accompanying drawings and detailed description, wherein, as shown in FIG. 1, a DOAS based NO is provided according to an embodiment of the present invention 2 A method of concentration measurement, the method comprising the steps of:
s1, acquiring original spectrum data with different power intensities for preprocessing, and comprising the following steps:
s11, selecting a wavelet basis function and a decomposition layer number N, and performing N-layer multi-scale decomposition on the signal (in the invention, the basis function is selected to be 'bior 2.8' through testing, and the decomposition layer number is 2);
s12, reconstructing a low-frequency coefficient of the Nth layer (the high-frequency part does not contain useful information basically after being verified, so that the high-frequency coefficient is not subjected to threshold quantization processing in order to reduce the calculation amount), and obtaining a reconstructed spectrum;
s13, adjusting the power of a xenon lamp light source, introducing pure nitrogen into the gas chamber, and collecting multiple groups of original spectral data with different power intensities;
in the invention, the power of a xenon lamp light source is adjusted to be 800, 775 and 750 respectively, under the conditions that pure nitrogen is introduced into a gas chamber, the temperature, the pressure and the like are the same, 10 pieces of spectrum data are collected for each power, the average value of 10 pieces of spectrum is obtained after wavelet transformation processing is carried out on each spectrum in the steps (a) and (b), and the preprocessed spectrum data are obtained as shown in figure 2;
s14, filtering each original spectrum data by utilizing wavelet transformation;
s15, averaging the filtered spectrum data with different intensities to obtain the preprocessed spectrum data.
At present, the common spectral data denoising method mainly comprises principal component analysis, a low-pass filtering method, a Kalman filtering method, fourier transformation and the like, but the principal component analysis and calculation amount is too large, the Fourier transformation lacks the analysis capability on local signals, the absorption wave band in the spectral data is a partial wave band in the whole acquisition range, and finally the spectral data are denoised by selecting wavelet transformation through evaluation and are simulated by Matlab.
Wherein the wavelet transformation is to the signal f (t) epsilon L 2 Integral transformation of (R), and the operation process and the expression comprise:
wherein a and b represent the scale and translation factors of Ψ (t), respectively;
t represents the signal time, t ∈ (— infinity, + ∞);
the expression of the inverse transformation process is as follows:
wherein the content of the first and second substances,
the conditions were allowed.
In practical application, will Ψ ab Taking continuous variables a and b in (t) as integer discrete forms, and making psi ab (t) is expressed as:
the corresponding wavelet transform is represented as a discrete wavelet transform:
W f (j,k)＝(f(t),Ψ j,k (t))
s2, calculating a spectrum correction coefficient and verifying, wherein the method comprises the following steps:
s21 in SO2, NO and NO 2 Selecting at least one waveband (the waveband of 253.3-256 nm is selected in the invention) from the wavebands which are not absorbed;
s22, recording that the spectrum data after the corresponding preprocessing of the light source powers 800, 775 and 750 are respectively Lamp _800, lamp _775 and Lamp _750, and calculating a correction coefficient by taking the Lamp _750 as a reference spectrum, wherein the expression is as follows:
R1＝log(Lamp_750/Lamp_775)
wherein, R1 is a logarithm of a ratio of two kinds of power spectrum data, and represents a change of other power spectrum data relative to the spectrum data of a fixed power (spectrum data of other power may also be selected);
k represents a correction coefficient;
lamp _775 represents spectral data when the power of the light source is 775;
lamp _750 represents spectral data at a source power of 750;
253.6 to 256 represent SO 2 NO and NO 2 (ii) none absorbing band;
s23, calibrating the spectrum data by using the correction coefficient, wherein the expression is as follows:
R2＝log(Lamp_750/Lamp_800)
NEW_Lamp_800＝exp(K*mean(R2(253.6～256)))*Lamp_800
wherein R2 represents the change of other power spectral data relative to the spectral data of fixed power;
lamp — 800 represents spectral data when the light source power is 800;
new _ Lamp _800 represents the spectrum data corrected by Lamp _800, i.e. represents the spectrum data to be calibrated.
As shown in fig. 3, the left graph is obtained by using the conventional method, i.e. using the non-absorption band to obtain a proportionality coefficient, and then directly multiplying the proportionality coefficient by the spectrum to be calibrated, and the right graph is the exponential calibration method proposed in the present invention.
S3, collecting NO with different concentrations 2 Is processed to obtain NO 2 Spectroscopic data comprising the steps of:
s31, keeping the power of a light source unchanged, and respectively collecting multiple groups of NO with different concentrations 2 (ii) spectral data;
in the embodiment of the invention, the power of the xenon lamp light source is kept at 750, NO2 spectrum data with [0,20,40,60,80,100] ppm concentration are respectively collected,
s32, filtering the spectral data of each concentration by utilizing wavelet transformation;
s33, calculating an average value of the filtered multiple groups of spectral data;
s34, calibrating the average value by using the correction coefficient to obtain the calibrated NO 2 Spectral data.
S4, calculating an optimal differential absorbance position data set and an optimal differential absorption cross section by calculating the relation between each spectrum point and the concentration, and comprising the following steps of:
s41, collecting spectral range and SO according to used spectrometer 2 NO and NO 2 Absorption cross section (provided by HITRAN database), spectrum in 390 nm-415 nm range is selected as NO calculation 2 The band of concentration;
s42, calculating the differential absorbance and the differential absorption cross section of NO2 under the [0,20,40,60,80,100] ppm concentration according to the differential absorption spectroscopy (DOAS);
s43, calculating a correlation coefficient between the concentration value [0,20,40,60,80,100] and the differential absorbance of each wavelength point in the range of 390nm to 415nm, and selecting the wavelength point corresponding to the correlation coefficient larger than 0.99 to form an optimal differential absorbance position data set;
s44, selecting the position of the differential absorption cross section corresponding to the optimal differential absorption degree position data set to form an optimal differential absorption cross section.
Wherein, the differential absorption spectroscopy (DOAS) is based on the detection of the narrow-band absorption characteristics of trace gas molecules, the absorbed light intensity obeys Lambert Beer's law of absorption, and when Rayleigh scattering (Rayleigh), meter scattering (Mie) and other molecular absorption are considered, the operational expression includes:
spectroscopic detection techniques apply this law to measure the average concentration of trace gases along the optical path. General definitions
Expressed as D (λ), is the optical thickness of the material, expressed as:
in order to eliminate the effects of Rayleigh scattering, mie scattering and the like, a filtering technique is generally used mathematically to separate the spectral changes caused by molecular absorption contained in the atmospheric absorption spectrum, and the absorption cross section of a gas can be generally considered to be composed of two parts, the expression of which is:
σ i (λ)＝σ i,slow (λ)+σ i,rapid (λ)
wherein, I 0 (λ) represents the light intensity of the incident light at wavelength λ;
i (λ) represents the light intensity of the outgoing light at the wavelength λ;
l represents an optical length;
a (λ) represents a transfer function of the system;
c i represents the concentration of the ith gas;
σ i (λ) represents an absorption cross section of the ith gas;
ε R (lambda) and epsilon M (λ) represents extinction coefficients of rayleigh scattering and meter scattering, respectively;
d (λ) represents the optical thickness of the substance;
σ i,slow (λ) represents a slowly varying fraction with wavelength;
σ i,rapid (λ) represents a portion that changes rapidly with wavelength, i.e., a differential absorption cross section of gas.
Total absorption cross section σ i (lambda) subtracting the calculated slow variation sigma i,slow (lambda) is the differential absorption cross section σ of the gas i,rapid (λ) in which σ is varied slowly i,slow (λ) can be obtained by reconstructing the low frequency part of a wavelet multi-scale decomposition, e.g. SO 2 May be obtained by reconstructing the low frequency part after wavelet 5-layer decomposition, as shown in fig. 4.
S5, establishing an equation through actually measured differential absorbance, optimal differential absorbance position data set and optimal differential absorption cross section of the gas to obtain NO 2 A concentration value;
the equation is established by actually measuring the differential absorbance of the gas, the optimal gas differential absorbance position data set and the optimal differential absorption section, and the expression is as follows:
C＝(P′·P) -1 ·P′·D
wherein C represents NO 2 A concentration value;
d represents the gas differential absorbance after selection using the optimal differential absorbance position dataset;
p denotes the optimal differential absorption cross section, and P' is the transpose of P.
S6, using a least square method to carry out treatment on NO 2 Correcting the concentration value, comprising the following steps:
s61, determining NO by fitting cubic polynomial by least square method 2 Obtaining a cubic polynomial relation formula according to the relation between the concentration value and the actual concentration value;
s62, reacting the NO 2 And substituting the concentration value into the cubic polynomial equation to obtain a corrected concentration value.
Wherein, the expression of the cubic polynomial is:
Fit_c＝polyfit(C,y,3)
con＝polyval(Fit_c,C)
wherein, the polyfit () is a polynomial fitting function in Matlab;
c represents the concentration value of NO 2;
y represents the corresponding actual concentration value;
3 is the polynomial fit degree;
fit _ c represents a cubic polynomial coefficient obtained by fitting;
the polyfal () represents a polynomial evaluation function;
con represents the corrected concentration value.
In conclusion, by means of the technical scheme, the spectrum data are corrected by an exponential spectrum correction method, and the defects of poor stability and poor repeatability of a xenon lamp light source are overcome, so that the accuracy of the spectrum data is greatly improved; and then, a correlation coefficient method is utilized to obtain a correlation coefficient between the concentration and the differential absorbance, so that an optimal differential absorbance position data set and an optimal differential absorption section are constructed, the NO2 measurement precision is improved, and the actual application requirements are met.
In addition, in order to meet the practical application, the calculation amount of a chip is reduced, the reaction time is prolonged, wavelet transformation is adopted for removing high-frequency noise of the spectral data and solving the slow change part, and only the corresponding low-frequency part is reconstructed according to the spectral absorption frequency range.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (10)
1. NO based on DOAS 2 A concentration measuring method, characterized in that the method comprises the steps of:
s1, acquiring original spectrum data with different power intensities for preprocessing;
s2, calculating a spectrum correction coefficient and verifying;
s3, collecting NO with different concentrations 2 Is processed to obtain NO 2 (ii) spectral data;
s4, calculating an optimal differential absorbance position data set and an optimal differential absorption cross section by calculating the relation between each spectrum point and the concentration;
s5, establishing an equation through actually measured differential absorbance, optimal differential absorbance position data set and optimal differential absorption cross section of the gas to obtain NO 2 A concentration value;
s6, performing least square method on NO 2 The density value is corrected.
2. A DOAS-based NO as claimed in claim 1 2 The concentration measurement method is characterized in that the method for acquiring raw spectral data with different power intensities for preprocessing comprises the following steps:
s11, selecting a wavelet basis function and the number N of decomposition layers, and performing N-layer multi-scale decomposition on the signal;
s12, reconstructing a low-frequency coefficient of the Nth layer to obtain a reconstructed spectrum;
s13, adjusting the power of a xenon lamp light source, introducing pure nitrogen into the gas chamber, and collecting multiple groups of original spectral data with different power intensities;
s14, filtering each original spectrum data by utilizing wavelet transformation;
s15, averaging the filtered spectrum data with different intensities to obtain the preprocessed spectrum data.
3. A DOAS-based NO as claimed in claim 2 2 The concentration measurement method is characterized in that the wavelet transformation is carried out on signals f (t) epsilon L 2 Integral transformation of (R), and the operation process and the expression comprise:
wherein a and b represent the scale and translation factors of Ψ (t), respectively;
t represents the signal time, t ∈ (— infinity, + ∞);
the expression of the inverse transformation process is as follows:
wherein, the first and the second end of the pipe are connected with each other,
the conditions were allowed.
4. A DOAS-based NO as claimed in claim 1 2 The concentration measurement method is characterized in that the method for calculating the spectral correction coefficient and verifying the spectral correction coefficient comprises the following steps:
s21 at SO 2 NO and NO 2 Selecting at least one waveband from the wavebands which are not absorbed;
s22, recording that the spectrum data after the corresponding preprocessing of the light source powers 800, 775 and 750 are respectively Lamp _800, lamp _775 and Lamp _750, and calculating a correction coefficient by taking the Lamp _750 as a reference spectrum, wherein the expression is as follows:
R1＝log(Lamp_750/Lamp_775)
wherein, R1 is the logarithm of the ratio of two kinds of power spectrum data, and represents the change of other power spectrum data relative to the spectrum data with fixed power;
k represents a correction coefficient;
lamp _775 represents spectral data when the power of the light source is 775;
lamp _750 represents spectral data at a source power of 750;
253.6 to 256 represent SO 2 NO and NO 2 All of which are non-absorbing;
s23, calibrating the spectrum data by using the correction coefficient, wherein the expression is as follows:
R2＝log(Lamp_750/Lamp_800)
NEW_Lamp_800＝exp(K*mean(R2(253.6～256)))*Lamp_800
wherein R2 represents the variation of other power spectral data relative to the spectral data of a fixed power;
lamp — 800 represents spectral data when the light source power is 800;
new _ Lamp _800 represents the spectrum data after Lamp _800 correction.
5. A DOAS-based NO as claimed in claim 1 2 Method for measuring concentration, characterized in that, the NO with different concentration is collected 2 Is processed to obtain NO 2 Spectroscopic data comprising the steps of:
s31, keeping the power of a light source unchanged, and respectively collecting multiple groups of NO with different concentrations 2 (ii) spectral data;
s32, filtering the spectral data of each concentration by utilizing wavelet transformation;
s33, calculating an average value of the filtered multiple groups of spectral data;
s34, calibrating the average value by utilizing the correction coefficient to obtain the calibrated NO 2 Spectral data.
6. A DOAS-based NO as claimed in claim 1 2 The concentration measurement method is characterized in that the calculation of the optimal differential absorbance position data set and the optimal differential absorption cross section by calculating the relationship between each spectral point and the concentration comprises the following steps:
s41, collecting spectral range and SO according to used spectrometer 2 NO and NO 2 Absorption cross section, selecting the spectrum in the range of 390 nm-415 nm as the calculation of NO 2 The band of concentration;
s42, calculating [0,20,40,60,80,100] according to the differential absorption spectrum technology]NO in ppm concentration 2 Differential absorbance and differential absorption cross section of (a);
s43, calculating a correlation coefficient between the differential absorbance of each wavelength point in the concentration value [0,20,40,60,80,100] ppm and the range of 390 nm-415 nm, and selecting the wavelength point corresponding to the correlation coefficient larger than 0.99 to form an optimal differential absorbance position data set;
and S44, selecting the position of the differential absorption cross section corresponding to the optimal differential absorbance position data set to form an optimal differential absorption cross section.
7. A DOAS-based NO as claimed in claim 6 2 The concentration measurement method is characterized in that the operational expression of the differential absorption spectrum technology comprises the following steps:
σ i (λ)＝σ i,slow (λ)+σ i,rapid (λ)
wherein, I 0 (λ) represents the light intensity of the incident light at the wavelength λ;
i (λ) represents the light intensity of the transmitted light at wavelength λ;
l represents an optical length;
a (λ) represents the transfer function of the system;
c i represents the concentration of the ith gas;
σ i (λ) represents an absorption cross section of the i-th gas;
ε R (lambda) and epsilon M (λ) extinction coefficients representing rayleigh scattering and mie scattering, respectively;
d (λ) represents the optical thickness of the substance;
σ i,slow (λ) represents a portion that changes slowly with wavelength;
σ i,rapid (λ) represents a portion that changes rapidly with wavelength, i.e., a differential absorption cross section of gas.
8. A DOAS-based NO as claimed in claim 1 2 The concentration measurement method is characterized in that an equation is established by actually measuring the differential absorbance, the optimal differential absorbance position data set and the optimal differential absorption section of the gas, and the expression is as follows:
C＝(P′·P) -1 ·P′·D
wherein C represents NO 2 A concentration value;
d represents the gas differential absorbance after selection using the optimal differential absorbance position dataset;
p denotes an optimal differential absorption section, and P' denotes a transpose of P.
9. A DOAS-based NO as claimed in claim 1 2 A concentration measuring method characterized in that said NO is measured by the least square method 2 The method for correcting the concentration value comprises the following steps:
s61, solving NO by fitting cubic polynomial by using least square method 2 Obtaining a cubic polynomial relation formula according to the relation between the concentration value and the actual concentration value;
s62, reacting the NO 2 And substituting the concentration value into the cubic polynomial equation to obtain a corrected concentration value.
10. A DOAS-based NO as claimed in claim 1 2 The concentration measurement method is characterized in that the expression of the cubic polynomial is as follows:
Fit_c＝polyfit(C,y,3)
con＝polyval(Fit_c,C)
wherein, the polyfit () is a polynomial fitting function in Matlab;
c represents NO 2 A concentration value;
y represents the corresponding actual concentration value;
3 is the polynomial fit degree;
fit _ c represents a cubic polynomial coefficient obtained by fitting;
poly val () represents a polynomial evaluation function;
con denotes the corrected density value.
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| Title |
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| 郝利君等: "汽车排气污染物遥感检测", vol. 1, 30 April 2021, 北京理工大学出版社, pages: 124 - 127 * |
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