CN106644986B - High NO 2 Online measuring device and measuring method for NO concentration in low-NO atmosphere - Google Patents
High NO 2 Online measuring device and measuring method for NO concentration in low-NO atmosphere Download PDFInfo
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- CN106644986B CN106644986B CN201611261453.5A CN201611261453A CN106644986B CN 106644986 B CN106644986 B CN 106644986B CN 201611261453 A CN201611261453 A CN 201611261453A CN 106644986 B CN106644986 B CN 106644986B
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Abstract
The invention discloses a high NO 2 An on-line measuring device and method for NO concentration in low NO atmosphere comprises an ozone generating unit, a connecting pipe cleaning unit, a sampling pipe, a reaction bin and NO sequentially connected with each other 2 The measuring instrument, the second mass flowmeter and the first air pump; the connecting pipe cleaning unit comprises an electromagnetic three-way valve, an activated carbon pipe, a limiting hole and a second air pump. The invention adopts the cavity enhanced absorption spectrum technology, and a sampling mode (the actual atmosphere added with ozone) or a zero mode (the actual atmosphere) is set through an electromagnetic three-way valve; through a NO 2 Measuring the absorption spectrum intensity signals of the two modes respectively by a measuring instrument, taking the absorption spectrum intensity signals as a sampling spectrum and a reference spectrum, and obtaining NO conversion in the atmosphere through spectrum fitting to generate NO 2 The concentration value of the NO in the atmosphere is obtained by measurement; has NO free from NO 2 Concentration interference, low detection limit, high sensitivity, high space-time resolution, high stability and low cost.
Description
Technical Field
The invention belongs to the technical field of atmospheric quality measurement, relates to online measurement of NO in the atmosphere, and in particular relates to a method for measuring NO in the atmosphere at high NO content 2 An on-line measuring device and an on-line measuring method for accurately measuring the concentration of NO in the atmosphere under the condition of low NO atmosphere.
Background
Atmospheric NO is an important primary pollutant in the troposphere atmosphere, mainly derived from high-temperature combustion of nitrogen-containing fuels, including automobile exhaust, artificial process emission of industrial production and coal-fired power plants, and partly derived from natural process emission such as lightning and microbial release. NO in atmosphere, NO 2 ，O 3 The photochemical cycles between (ozone) form the basis of the photochemical reactions of the atmosphere, and are therefore of great significance for the accurate measurement of NO in the atmosphere.
The concentration level of the tropospheric atmosphere NO is between a few ppt and a few hundred ppb, with a wide range of concentration variations. In the field of atmospheric free radical chemistry research, accurate online measurement of low concentration NO (below 100 ppt) in the atmosphere on OH free radicals and NO 3 The radical balance analysis is of great importance, especially in the case of the typicalSuburban area, NO in atmosphere 2 The concentration of NO is relatively high (several tens ppb) and the concentration of NO is relatively low (as low as several tens ppt), under which conditions accurate measurement of NO is difficult to achieve.
Existing atmospheric NO measurement mainly includes direct measurement and indirect measurement methods. The direct measurement technique is mainly chemiluminescence method, and the principle is that NO and high-concentration O in the atmosphere 3 Reacting to form excited NO 2 * NO in excited state 2 * Infrared light is released during the decay back to the ground state, the intensity of the infrared light and NO 2 Has better linear relation with the concentration of NO obtained by measuring the photon number 2 The concentration of NO in the atmosphere is obtained based on the conversion, but the method is limited by the detection capability of the photon counter, so that the detection capability of the chemiluminescent method is limited. The indirect measurement method is mainly implemented by converting atmospheric NO into NO 2 Post measurement of total NO 2 Concentration (NO) X ) Reuse of NO X Subtracting NO in environment 2 The concentration of NO obtained includes techniques such as Neediamine hydrochloride spectrophotometry (luminol method), tunable Diode Laser Absorption (TDLAS), cavity ring-down absorption Spectroscopy (CRDs), and Laser Induced Fluorescence (LIF).
However, when higher NO is present in the atmosphere 2 And lower NO, such as some typical suburban atmospheres, NO measured by indirect methods X And NO 2 The values of (2) are large, and the measured NO is obtained by subtracting the difference between the two, even if the instrument measures NO 2 And less uncertainty in NOx, also results in a very large absolute error in the concentration of NO resulting from the subtraction, and therefore at high NO 2 Under the low NO environment condition, the NO measurement result obtained by the existing NO measurement technology has larger uncertainty, and accurate measurement is difficult to realize.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides an on-line measuring device and a method for the concentration of NO in the atmosphere, which are not affected by NO 2 Concentration interference, low detection limit, high sensitivity, high space-time resolution, high stability and low cost. The invention can aim at high NO 2 Low NO atmosphereIn-line accurate measurement of NO in the atmosphere, e.g. in a typical suburban atmosphere 2 Higher concentration of NO and lower concentration of NO. The invention is suitable for accurately measuring the concentration of NO in the atmosphere of a typical suburban area on line.
The core of the invention is: the invention converts NO in the atmosphere by adopting a cavity enhanced absorption spectrum technology 2 And (3) performing measurement to indirectly obtain NO in the atmosphere. The invention is completely different from the traditional indirect measurement means in that: the invention does not need to quantify NO in the atmosphere 2 Concentration level of NO converted NO alone 2 Is measured. Although the direct measurement object of the present invention is NO 2 However, the definition of the reference spectrum and the sampling spectrum of the present invention is quite different from the conventional cavity enhanced absorption spectrum, which measures NO 2 The technical method respectively measures zero air (or pure nitrogen) and actual atmosphere as a reference spectrum and a sampling spectrum; while the invention respectively measures the actual atmosphere and adds O 3 The actual atmosphere in the atmosphere is used as a reference spectrum and a sampling spectrum, and then NO in the atmosphere is obtained through spectrum fitting to be converted into NO 2 Concentration values of (2). In particular, the invention is useful for measuring NO in the atmosphere 2 In the concentration process, in the zero mode, acquiring a spectrum obtained by the actual atmosphere as a reference spectrum; in the sampling mode, high-concentration O is injected in the sampling process 3 Chemical conversion of NO to NO 2 And then measuring the conversion to NO 2 The post spectrum is taken as a sampling spectrum; NO converted only from NO due to the difference in spectral intensity between the reference spectrum and the sampled spectrum 2 The difference between the sampled spectrum and the reference spectrum is caused to be related only to the absorption of NO2 by the NO conversion, and to the NO in the actual atmosphere 2 Is independent of the concentration and other spectral absorption. Thus, the concentration of NO in the atmosphere can be calculated by using the two spectra. The method does not need NO in the actual atmosphere 2 Quantification is performed, but the NO produced by the conversion is directly measured 2 Thus, the measurement of NO in the atmosphere is not subject to NO in the atmosphere 2 Concentration interference, thereby fundamentally avoiding high concentration NO in the actual atmosphere in the traditional NO measurement method 2 Is used for the interference of (a) and (b),the method has the characteristics of low detection limit, high sensitivity, high space-time resolution, high stability and low cost, and can realize the online accurate measurement of the concentration of NO in the low-NO atmosphere.
The technical scheme provided by the invention is as follows:
high NO 2 The on-line measuring device for NO concentration in low NO atmosphere comprises an ozone generating unit, a connecting pipe cleaning unit, a sampling pipe, a reaction bin, a second mass flowmeter, a first air pump and NO based on cavity enhanced absorption spectrum technology 2 A measuring instrument; wherein the ozone generating unit comprises pure oxygen gas, a first mass flowmeter and an ozone generator, and the pure oxygen gas is connected with the ozone generator through the first mass flowmeter to generate O 3 A gas; the connecting pipe cleaning unit comprises an electromagnetic three-way valve, an active carbon pipe, a limiting hole and a second air pump which are connected in sequence; generated O 3 The gas is divided into two paths after passing through a tee joint, and the first path is connected with a connecting pipe cleaning unit; the second path is connected with the rear end of the sampling tube; the rear end of the sampling tube is connected with the reaction bin and NO in sequence 2 A measuring instrument, a second mass flowmeter and a first air pump; setting a sampling mode or a zero mode through an electromagnetic three-way valve; only one NO is needed for the on-line measuring device 2 The measuring instrument (namely a measuring reaction cavity) respectively measures signals (respectively called a sampling spectrum and a reference spectrum) of absorption spectrum intensities of a sampling mode and a zero mode, and the concentration value of NO2 generated by converting NO in the atmosphere can be obtained through spectrum fitting, so that the measurement of NO in the atmosphere environment can be realized.
To above-mentioned atmosphere NO concentration on-line measuring device, its characterized in that: NO employed in the device 2 The light source adopted by the measuring instrument is a high-power LED monochromatic light source, the central wavelength of the emitted light spectrum is 460nm, and the energy of the light source is mainly concentrated at 440-480nm; the high-reflection mirror reflectivity in the measuring reaction cavity of the measuring instrument is more than 99.99 percent.
To above-mentioned atmosphere NO concentration on-line measuring device, its characterized in that: o (O) 3 In the generating unit, pure oxygen precisely controls the flow rate through a mass flowmeter, enters an ozone generator at a small flow rate, and is subjected to ultraviolet light irradiation and photolysis in the ozone generator to generate O with stable concentration 3 Gas, O 3 The concentration level of (a) is required to be such that NO is fully oxidized to NO within a short period of time (e.g., within 1 s) 2 。
To above-mentioned atmosphere NO concentration on-line measuring device, its characterized in that: in the connecting pipe cleaning unit, the electromagnetic three-way valve is two-in and one-out, a first air inlet of the electromagnetic three-way valve is connected with the ozone generator, and a second air inlet of the electromagnetic three-way valve is communicated with the ambient atmosphere; an outlet of the electromagnetic three-way valve is connected with an activated carbon tube of the connecting tube cleaning unit and is used for removing high-concentration O 3 The second air pump is always opened and controls the flow rate through the flow limiting hole.
To above-mentioned atmosphere NO concentration on-line measuring device, its characterized in that: the connecting pipe cleaning unit ensures that O in the connecting pipe can be rapidly removed in the switching process of the electromagnetic three-way valve 3 The fast switching of the two measurement modes of the sampling mode and the zero mode is realized.
To above-mentioned atmosphere NO concentration on-line measuring device, its characterized in that: o (O) 3 The flow rate of the supplied gas of the generating unit is far smaller than the flow rate of the sampled gas, namely, the set flow rate of the first mass flowmeter is far smaller than the flow rate of the second mass flowmeter, so that the influence caused by the flow change between the two modes is negligible. In the implementation of the invention, the air extraction speed of the second air pump matched with the flow limiting hole is stabilized at 50-100ml/min, and the flow speed of the second mass flowmeter is 2.0L/min; o (O) 3 The generating unit and the connecting pipe cleaning unit are connected by a tetrafluoro pipe with the outer diameter of 1/8 inch.
To above-mentioned atmosphere NO concentration on-line measuring device, its characterized in that: by accurate reaction kinetics calculation, the volume of the reaction chamber should be equal to the sampling flow rate and O 3 The concentration of (2) is matched, and the reaction time is shortened as much as possible while ensuring that the NO titration is just completed, so as to reduce NO 2 And O 3 Further causing interference. In the embodiment of the invention, the volume of the reaction bin is 30ml, so that the efficiency of NO titration is more than 99%.
To above-mentioned atmosphere NO concentration on-line measuring device, its characterized in that: two kinds of electromagnetic three-way valves are realized by automatically opening or closing the electromagnetic three-way valves through programmed settingMeasurement mode switching, ensuring NO in the atmosphere in the reference spectrum and the sampled spectrum by high frequency switching 2 And the absorption of other gases.
The atmospheric NO concentration online measuring device adopts a cavity enhanced absorption spectrum technology to carry out NO concentration online measurement 2 Measurements are taken but the definition of the reference spectrum and the sampled spectrum is quite different from the traditional cavity enhanced absorption spectrum; the device is in operation, in particular: in the zero mode, acquiring a spectrum obtained by the actual atmosphere as a reference spectrum; in the sampling mode, high-concentration O is injected in the sampling process 3 Chemical conversion of NO to NO 2 And then measuring the conversion to NO 2 The post spectrum is taken as a sampling spectrum; thus, the difference in spectral intensity between the reference spectrum and the sampled spectrum is NO converted only by NO 2 Causing NO in the actual atmosphere 2 Is independent of the concentration of (c).
When the online measuring device for the concentration of the NO in the atmosphere works, in the connecting pipe cleaning unit, when the electromagnetic three-way valve is communicated with the second air inlet and the first air inlet is closed, the online measuring device is in a sampling mode, and O 3 Through the connecting pipe and the sampling gas, the mixture enters a reaction chamber, and in the reaction chamber, the high-concentration ozone completely oxidizes NO into NO 2 And enter NO 2 The measuring instrument measures, the pumping power and the sampling flow rate are controlled by the first air pump and the second mass flowmeter respectively, the spectrum measured at the moment is the sampling spectrum, and the spectrum signal contains NO converted from atmospheric NO completely 2 Absorbing signals and NO in the atmosphere 2 Absorption signals, absorption and scattering due to other factors. At this time, the connecting pipe cleaning unit continuously pumps in the ambient atmosphere through the second air inlet hole, for keeping the state of the unit stably running and protecting the second air pump. When the electromagnetic three-way valve is communicated with the first air inlet and the second air inlet is closed, the electromagnetic three-way valve is in a zero mode, and the air suction flow speed of the connecting pipe cleaning unit is larger than O 3 Flow rate of gas supplied by generator, O generated 3 The gas does not enter the reaction bin, is completely pumped out and removed by the connecting pipe cleaning unit, and part of sampling gas is also pumped out and removed by the connecting pipe cleaning unit, and the gas of the connecting pipe forms backflow and cleans residual O in the connecting pipe 3 . At this time NO 2 The spectrum measured by the measuring instrument is used as a reference spectrum, and the spectrum signal comprises NO of the measuring instrument in the atmosphere 2 Absorption signals, absorption and scattering due to other factors. The absorption spectrum of the absorption and scattering portions caused by other factors is slowly varying with wavelength, and can be differentiated by the reference spectrum and the sample spectrum.
By using the online measuring device for the low-NO atmospheric NO concentration, the online accurate measurement of the atmospheric NO concentration can be realized.
The invention also provides a method for online measurement of the concentration of the NO in the atmosphere, which is characterized in that a sampling mode or a zero mode is set through an electromagnetic three-way valve, and O is generated in the sampling mode 3 The gas converts all atmospheric NO into NO 2 Then the signals of absorption spectrum intensities of the sampling mode and the zero mode are respectively measured, and the NO in the atmosphere is converted into NO through spectrum fitting 2 Thereby obtaining the concentration of NO in the atmosphere; the method specifically comprises the following steps:
1) Set O 3 The generation unit is used for generating O 3 A gas; at O 3 The generation unit is divided into two paths after passing through a tee joint, the first path is connected with the connecting pipe cleaning unit, and the connecting pipe cleaning unit is formed by sequentially connecting an electromagnetic tee valve, an active carbon pipe, a limiting hole and a second air pump; the second path is connected with the rear end of the sampling tube, and the rear end of the sampling tube is sequentially connected with the reaction bin and NO 2 A measuring instrument, a second mass flowmeter and a first air pump; NO (NO) 2 The light source adopted by the measuring instrument is a high-power LED monochromatic light source, the central wavelength of the emitted light spectrum is 460nm, and the reflectivity of the high-reflectivity lens in the measuring reaction cavity is more than 99.99 percent;
O 3 the generating unit comprises a first mass flowmeter and an ozone generator, and pure oxygen is connected to the ozone generator through the first mass flowmeter to generate O 3 And (3) gas. In the practice of the invention, the flow rate of the first mass flow meter is 10ml/min.
O 3 The generating unit and the connecting pipe cleaning unit are connected by a tetrafluoro pipe with the outer diameter of 1/8 inch.
The electromagnetic three-way valve is two-inlet and one-outlet, a first air inlet of the electromagnetic three-way valve is connected with the ozone generator, and a second air inlet of the electromagnetic three-way valve is communicated with the ambient atmosphere; the outlet of the electromagnetic three-way valve is connected with an activated carbon tube of the connecting tube cleaning unit.
2) Setting a sampling mode or a zero mode through an electromagnetic three-way valve; collecting a spectrum obtained by the actual atmosphere in a zero mode as a reference spectrum; in the sampling mode, high-concentration O is injected in the sampling process 3 Chemical conversion of NO to NO 2 And then measuring the conversion to NO 2 The post spectrum is taken as a sampling spectrum;
21 The electromagnetic three-way valve is communicated with the first air inlet, the second air inlet is closed, the electromagnetic three-way valve enters a zero mode, and the air suction flow rate of the connecting pipe cleaning unit is larger than O at the moment 3 Flow rate of gas supplied by generator, O generated 3 The gas does not enter the reaction bin, is completely pumped out and removed by the connecting pipe cleaning unit, and part of sampling gas is also pumped out and removed by the connecting pipe cleaning unit, and the gas of the connecting pipe forms backflow and cleans residual O in the connecting pipe 3 The method comprises the steps of carrying out a first treatment on the surface of the NO at this time 2 The spectrum measured by the measuring instrument is used as a reference spectrum, and the reference spectrum signal comprises NO of the measuring instrument in the atmosphere 2 Absorption signals, absorption and scattering due to other factors;
22 When the electromagnetic three-way valve is communicated with the second air inlet and the first air inlet is closed, the sampling mode is adopted, and at the moment, O 3 O generated by a generator 3 Through the connecting pipe, the gas is mixed with the sampling gas in the reaction bin; in the reaction bin, high-concentration ozone completely oxidizes NO into NO 2 Enter NO 2 The measuring instrument measures, the pumping power and the sampling flow rate are respectively controlled by the first air pump and the second mass flowmeter, the spectrum obtained by measurement at the moment is a sampling spectrum, and the sampling spectrum signal contains NO converted from atmospheric NO completely 2 Absorbing signals and NO in the atmosphere 2 Absorption signals, absorption and scattering due to other factors; at this time, the connecting pipe cleaning unit continuously pumps in the ambient atmosphere through the second air inlet hole, for keeping the state of the unit stably running and protecting the second air pump.
In the implementation of the invention, the air extraction speed of the second air pump matched with the flow limiting hole is stabilized at 50-100ml/min, and the flow speed of the second mass flowmeter is 2.0L/min; the volume of the reaction bin is 30ml, and the efficiency of NO titration is ensured to be more than 99%.
In the embodiment of the invention, the electromagnetic three-way valve is programmed to realize automatic switching between a sampling mode and a zero mode, and the sampling mode and the zero mode are one-time circulation, so that the alternating acquisition of spectrum signals of the sampling mode and the zero mode can be realized. NO (NO) 2 The resolution of the measuring instrument is 1s, the cycle time is set to be 1min, and the first 10s is in a zero point mode (reference spectrum is acquired); the back 50s is a sampling mode (sampling spectrum is acquired), and the reference spectrum and NO in the sampling spectrum are ensured through high-frequency switching 2 And other absorption and scattering are unchanged.
3) Obtaining converted NO based on a standard cavity enhancement data processing method by utilizing measured reference spectrum and sampling spectrum data 2 Concentration (i.e., concentration of NO in the atmosphere), thereby achieving on-line measurement of atmospheric NO concentration.
In the embodiment of the invention, specifically, the reference spectrum (averaged) and the sampling spectrum in each cycle are paired as a unit for data processing, and the difference between the signals of the reference spectrum and the sampling spectrum is only NO generated by NO conversion 2 Absorption causes NO in the atmosphere 2 The concentration is irrelevant, and NO in the atmosphere can be generated 2 Is carried into the measurement of NO. Finally, obtaining NO by calculating absorption coefficient and adopting least square fitting 2 I.e. the concentration of NO in the atmosphere.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides an on-line measuring device and a measuring method for the concentration of NO in the atmosphere, and particularly realizes accurate measurement of NO in a typical suburban area. Comprises at least pure oxygen gas, a first mass flowmeter, an ozone generator, a connecting pipe, a sampling pipe, a reaction bin and NO 2 The device comprises a measuring instrument, a second mass flowmeter, a first air pump, an electromagnetic three-way valve, an active carbon tube, a flow limiting hole and a second air pump. The invention adopts a chemical conversion method to convert NO into NO 2 NO generated by converting NO in atmosphere by adopting broadband cavity enhanced absorption spectrum technology 2 And (3) quantifying to realize the online accurate measurement of the concentration of the atmospheric NO. The scheme of the invention has the characteristics of low detection limit, high sensitivity, high space-time resolution, high stability and low cost.
Advantages of the invention include the following:
the invention adopts the cavity enhanced absorption spectrum technology as the part of NO generated by NO conversion 2 Quantifying to contain atmospheric environment NO 2 Instead of using the conventional pure nitrogen spectrum as the reference spectrum to include conversion to NO 2 The obtained measurement result is used as a sampling spectrum to realize NO of the NO conversion part 2 Accurate quantification without measuring NO in the atmosphere 2 Nor does it need to perform NOx to NO concentration 2 Difference and subtraction, avoiding error transfer, avoiding NO in the atmosphere during measurement 2 Interference of concentration with NO.
(II) the invention adopts the connecting pipe cleaning unit to clean O in the connecting pipe when the zero mode is converted into the sampling mode 3 And the quick pumping and removing are carried out, so that the quick switching of the two measurement modes is realized, the transition time is short, and the data integrity is ensured as much as possible.
(III) the invention only adopts a set of cavity enhanced absorption spectrum equipment as NO 2 Measuring instrument for high concentration NO 2 The absolute measurement of low NO in the background has very high resolution and detection sensitivity. And the detection accuracy of NO is improved.
The invention is a single-point sampling technology, and has high stability, low cost and simple operation and maintenance.
Drawings
FIG. 1 is a block diagram of an on-line measuring device for NO concentration in a typical suburban atmosphere according to an embodiment of the present invention;
wherein, 1-pure oxygen; 2-a first mass flowmeter; 3-an ozone generator; 4-connecting pipes; 5-sampling tube; 6, a reaction bin; 7-NO 2 A measuring instrument; 8-a second mass flowmeter; 9-a first air pump; 10-an electromagnetic three-way valve; 11-a first air inlet; 12-a second air inlet hole; 13-an activated carbon tube; 14-a flow limiting hole; 15-thTwo air pumps.
Fig. 2 is a flow chart of an on-line measuring method for the concentration of atmospheric NO according to an embodiment of the present invention.
Detailed Description
The invention is further described by way of examples in the following with reference to the accompanying drawings, but in no way limit the scope of the invention.
The invention provides an atmospheric NO concentration online measurement device and a measurement method, at least comprising pure oxygen gas, a first mass flowmeter, an ozone generator, a connecting pipe, a sampling pipe, a reaction bin and NO 2 The device comprises a measuring instrument, a second mass flowmeter, a first air pump, an electromagnetic three-way valve, an active carbon tube, a limiting hole and a second air pump. The invention adopts a chemical conversion method to convert NO into NO 2 NO generated by converting NO in atmosphere by adopting broadband cavity enhanced absorption spectrum technology 2 And (3) quantifying so as to realize the online accurate measurement of the concentration of the atmospheric NO.
The embodiment of the invention aims at the typical suburban atmosphere, adopts an atmosphere NO concentration on-line measuring device as shown in figure 1, and comprises the following steps: pure oxygen 1, a first mass flowmeter 2, an ozone generator 3, a connecting pipe 4, a sampling pipe 5, a reaction bin 6 and NO 2 The device comprises a measuring instrument 7, a second mass flowmeter 8, a first air pump 9, an electromagnetic three-way valve 10, a first air inlet hole 11, a second air inlet hole 12, an active carbon tube 13, a limiting hole 14 and a second air pump 15. Wherein pure oxygen 1 is connected with an ozone generator 3 through a first mass flowmeter 2 to form O 3 And a generating unit. Generated O 3 The gas is divided into two paths after passing through a tee joint, and the connecting pipe cleaning unit connected with one path is formed by connecting an electromagnetic tee valve 10, an active carbon pipe 13, a limiting hole 14 and a second air pump 15; the other path is connected with the rear end of the sampling tube 1, and the rear end of the sampling tube 1 is respectively connected with a reaction bin 6 and NO 2 A meter 7, a second mass flow meter 8 and a first air pump 9.
The workflow and data collection process of the present invention is described below by way of a specific example.
The invention adopts the cavity enhanced absorption spectrum technology as a measuring instrument to measure NO 2 To make measurements and only one NO needs to be used 2 Meter (i.e. a measuring reaction chamber), NO 2 The light source adopted by the measuring instrument is a high-power LED monochromatic light source, the central wavelength of the emitted light spectrum is 460nm, and the energy of the light source is mainly concentrated at 440-480nm. The high reflectance of the mirror within the cavity is greater than 99.99%. In the implementation of the invention, the flow rate of the first mass flowmeter is 10ml/min, the air suction speed of the second air pump matched with the flow limiting hole is stabilized at 100ml/min, and the flow rate of the second mass flowmeter is 2.0L/min; o (O) 3 The generating unit and the connecting pipe cleaning unit are connected by a tetrafluoro pipe with the outer diameter of 1/8 inch; the sampling tube adopts a tetrafluoro tube with the outer diameter of 1/4 inch, and is connected with a connecting pipe by a reducing tee joint, the volume of the reaction bin is 30ml, and the NO titration efficiency is ensured to be more than 99 percent.
When the online measuring device for the concentration of the NO in the atmosphere works, the O is debugged 3 A generating unit for ensuring continuous output of O with a concentration of about 200ppm after mixing 3 The method comprises the steps of carrying out a first treatment on the surface of the Debugging NO 2 And the measuring instrument ensures the temperature stability of the light source and calibrates the emissivity. The electromagnetic three-way valve is programmed to realize automatic switching between a sampling mode and a zero mode, and the primary sampling mode and the primary zero mode are one-time circulation, so that the alternating collection of spectrum signals of the sampling mode and the zero mode is realized. The resolution of the instrument is 1s, the cycle time is set to be 1min, and the first 10s is in a zero point mode (reference spectrum is acquired); the back 50s is a sampling mode (sampling spectrum is collected), and NO in the atmosphere environment is ensured through high-frequency switching 2 And other absorption and scattering. In sampling mode, O 3 The high-concentration ozone in the reaction bin completely oxidizes NO into NO 2 And enter NO 2 The measuring instrument performs measurement to obtain a sampling spectrum, and the spectrum signal contains NO converted from atmospheric NO 2 Absorbing signals, NO in the atmosphere 2 Absorption signals, other absorption and scattering. In the zero mode, the pumping flow speed of the connecting pipe cleaning unit is greater than O 3 The generator has a gas supply flow rate of 10ml/min O 3 Is pumped by the connecting pipe cleaning unit, and simultaneously 90ml/min of sampling gas forms backflow and cleans the connecting pipe. NO at this time 2 Spectrum measured by measuring instrument as reference spectrumThe spectral signal contains NO from itself in the atmosphere 2 Absorption signals, other absorption and scattering.
The reference spectrum (averaged) and the sampled spectrum in each cycle are data processed as a unit pair based on the reference spectrum and the sampled spectrum data, the difference in the reference spectrum and the sampled spectrum signals being only the NO generated by the NO conversion 2 Absorption results in a calculated absorption coefficient that can be fitted by least squares to obtain NO 2 I.e. the concentration of NO in the atmosphere. When the reflectance R (λ) and the effective cavity length d of the high reflectance mirror are known, the absorption coefficient α (λ) is calculated by equation 1:
wherein I (lambda) samples the spectrum, I 0 (lambda) reference spectrum, other Rayleigh scattering, mie scattering (fitting by third order polynomial) and NO at wavelength of 440-480nm by least squares fitting 2 Is passed through NO 2 Fitting to the absorption coefficient, resulting in the concentration of NO in the atmosphere.
It should be noted that the purpose of the disclosed embodiments is to aid further understanding of the present invention, but those skilled in the art will appreciate that: various alternatives and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the disclosed embodiments, but rather the scope of the invention is defined by the appended claims.
Claims (8)
1. An on-line measuring device for NO concentration in atmosphere comprises an ozone generating unit, a connecting pipe cleaning unit, a sampling pipe, a reaction bin, a second mass flowmeter, a first air pump and a NO based on cavity enhanced absorption spectrum technology 2 A measuring instrument; the ozone generating unit comprises pure oxygen gas, a first mass flowmeter and an ozone generator, wherein the pure oxygen gas is connected with the ozone generator through the first mass flowmeter to generate ozone gas; the ozoneIn the generating unit, pure oxygen enters an ozone generator through a first mass flowmeter at a small flow rate by accurately controlling the flow rate, and is subjected to ultraviolet light photolysis in the ozone generator to generate ozone gas with stable concentration, wherein the concentration level of the ozone gas is used for oxidizing NO into NO completely in a short time 2 The method comprises the steps of carrying out a first treatment on the surface of the The connecting pipe cleaning unit comprises an electromagnetic three-way valve, an active carbon pipe, a limiting hole and a second air pump which are connected in sequence; in the connecting pipe cleaning unit, the electromagnetic three-way valve is a two-in one-out electromagnetic three-way valve; the first air inlet of the electromagnetic three-way valve is connected with the ozone generator; the second air inlet hole is communicated with the ambient atmosphere; an outlet of the electromagnetic three-way valve is connected with an activated carbon tube of the connecting tube cleaning unit; the second air pump is always opened and controls the flow rate through the flow limiting hole; the generated ozone gas is divided into two paths through a tee joint, and the first path is connected with a connecting pipe cleaning unit; the second path is connected with the rear end of the sampling tube; the rear end of the sampling tube is connected with the reaction bin and NO in sequence 2 The measuring instrument, the second mass flowmeter and the first air pump; the NO 2 The light source adopted by the measuring instrument is a high-power LED monochromatic light source; the NO 2 The reflectivity of the high-reflectivity lens in the measuring reaction cavity of the measuring instrument is more than 99.99 percent; the on-line measuring device sets a sampling mode or a zero mode through the electromagnetic three-way valve, and passes through the NO 2 Measuring the absorption spectrum intensity signals of the sampling mode and the zero mode respectively by a measuring instrument to serve as a sampling spectrum and a reference spectrum, and obtaining NO conversion in the atmosphere through spectrum fitting to generate NO 2 And (3) the concentration value of the NO in the atmosphere environment is obtained by measurement.
2. The on-line measuring device of claim 1, wherein: the NO 2 The spectrum center wavelength of the light emitted by the high-power LED monochromatic light source adopted by the measuring instrument is 460nm.
3. The on-line measuring device of claim 1, wherein: the set flow rate of the first mass flowmeter is far smaller than the flow rate of the second mass flowmeter, so that the air supply flow rate of the ozone generating unit is far smaller than the flow rate of the sampling gas; the air extraction speed of the second air pump matched with the flow limiting hole is stabilized at 50-100ml/min, and the flow speed of the second mass flowmeter is 2.0L/min.
4. The on-line measuring device of claim 1, wherein: the ozone generating unit and the connecting pipe cleaning unit are connected by a tetrafluoro pipe with the outer diameter of 1/8 inch.
5. The on-line measuring device of claim 1, wherein: the volume of the reaction bin is matched with the sampling flow rate and the concentration of ozone gas generated by the ozone generating unit; the volume of the reaction bin is 30ml, so that the efficiency of NO titration is more than 99%.
6. The on-line measuring device of claim 1, wherein: automatically opening or closing the electromagnetic three-way valve by programming to realize high-frequency switching of a sampling mode and a zero mode so that NO in the atmosphere environment in a reference spectrum and a sampling spectrum 2 And the absorption of other gases.
7. An on-line measuring method for NO concentration in atmosphere includes setting sampling mode or zero mode by electromagnetic three-way valve, and converting all atmospheric NO into NO by generating ozone gas in sampling mode 2 Then pass through a NO 2 Measuring the signals of absorption spectrum intensities of a sampling mode and a zero mode respectively by a measuring instrument, and obtaining NO conversion in the atmosphere to generate NO through spectrum fitting 2 Thereby obtaining the concentration of NO in the atmosphere; the method specifically comprises the following steps:
1) An ozone generating unit is provided for generating a high concentration ozone gas; the ozone generating unit is divided into two paths after passing through a tee joint, the first path is connected with a connecting pipe cleaning unit, and the connecting pipe cleaning unit comprises an electromagnetic tee joint valve, an activated carbon pipe, a limiting hole and a second air pump which are sequentially connected; the second path is connected with the rear end of the sampling tube, and the rear end of the sampling tube is sequentially connected with the reaction bin and the NO 2 The measuring instrument, the second mass flowmeter and the first air pump;
2) Through an electromagnetic tee jointThe valve is set to a sampling mode or a zero mode; collecting a spectrum obtained by the actual atmosphere in a zero mode as a reference spectrum; in the sampling mode, injecting the high-concentration ozone gas in the step 1) in the sampling process to chemically convert NO into NO 2 And then measuring the conversion to NO 2 The post spectrum is taken as a sampling spectrum; comprising the following steps:
21 When the electromagnetic three-way valve enters a zero mode, the air suction flow rate of the connecting pipe cleaning unit is larger than the air supply flow rate of the ozone generating unit, the connecting pipe cleaning unit completely pumps away and removes generated ozone gas, part of sampling gas is also pumped away and removed through the connecting pipe cleaning unit, and the gas of the connecting pipe forms backflow and cleans residual ozone in the connecting pipe; at this point will pass through NO 2 The spectrum measured by the measuring instrument is used as a reference spectrum, and the reference spectrum signal comprises NO in the atmosphere 2 Absorption signals, absorption and scattering due to other factors;
22 When the electromagnetic three-way valve is in a sampling mode, ozone generated by the ozone generating unit passes through the connecting pipe and is mixed with sampling gas passing through the sampling pipe into the reaction bin; in the reaction bin, high-concentration ozone completely oxidizes NO into NO 2 Enter NO 2 The measuring instrument measures, the pumping power and the sampling flow rate are respectively controlled by the first air pump and the second mass flowmeter, the spectrum obtained by measurement at the moment is a sampling spectrum, and the sampling spectrum signal contains NO converted from atmospheric NO completely 2 Absorption signals, self NO2 absorption signals in the atmosphere, absorption and scattering caused by other factors;
3) Processing the reference spectrum and the sampled spectrum data obtained by the step 2) by a cavity enhancement data processing method to obtain converted NO 2 The concentration is the concentration of NO in the atmosphere, so that the on-line measurement of the concentration of NO in the atmosphere is realized.
8. The online measurement method of claim 7, wherein the NO 2 The light source adopted by the measuring instrument is a high-power LED monochromatic light source, the central wavelength of the emitted light spectrum is 460nm, and the reflectivity of the high-reflectivity lens in the measuring reaction cavity is more than 99.99 percent; the odor isThe oxygen generation unit comprises a first mass flowmeter and an ozone generator, and pure oxygen is connected to the ozone generator through the first mass flowmeter, namely ozone gas is generated; the ozone generating unit and the connecting pipe cleaning unit are connected by a tetrafluoro pipe with the outer diameter of 1/8 inch; the electromagnetic three-way valve is two-in and one-out, a first air inlet of the electromagnetic three-way valve is connected with the ozone generator, a second air inlet is communicated with the ambient atmosphere, and an outlet is connected with an activated carbon tube of the connecting tube cleaning unit; when the electromagnetic three-way valve is in a sampling mode, the connecting pipe cleaning unit continuously pumps ambient atmosphere through the second air inlet hole, so as to keep the state of the unit to stably operate and protect the second air pump; the cavity enhancement data processing method specifically obtains NO by calculating absorption coefficient and adopting least square fitting 2 The concentration of NO in the atmosphere.
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| CN109100316A (en) * | 2018-09-04 | 2018-12-28 | 深圳市卡普瑞环境科技有限公司 | A kind of high reflection mirror screening technique applied to optical cavity structure |
| CN109001132A (en) * | 2018-09-04 | 2018-12-14 | 深圳市卡普瑞环境科技有限公司 | A kind of atmospheric molecule detection method |
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| CN113281311B (en) * | 2020-02-20 | 2021-11-19 | 北京大学 | Online detection device and method for organic peroxy radicals in atmosphere |
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