GB/T 33672-2017 Cavity Ring-Down Spectroscopy Observation System for Atmospheric Methane GB/T33672-2017 |tt||Standard compression package decompression password: www.bzxz.net
This standard specifies the working principle, composition and function, technical index requirements and installation environment requirements of the cavity ring-down spectroscopy observation system for observing atmospheric methane concentration. ? This standard is applicable to the cavity ring-down spectroscopy observation of atmospheric methane, and also to the design and processing of the observation system.

ICS_07.060
National Standard of the People's Republic of China
GB/T33672—2017
Cavity Ring-Down Spectroscopy System for Measurement of Atmospheric Methane Issued on 2017-05-12
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China Standardization Administration of China
Implementation on 2017-12-01
This standard was drafted in accordance with the rules given in GB/T1.1-2009. This standard was proposed by the China Meteorological Administration.
GB/T33672—2017
This standard is under the jurisdiction of the Sub-Technical Committee on Atmospheric Composition Observation, Forecast and Warning Service of the National Technical Committee for Climate and Climate Change Standardization (SAC/TC540/SC1).
Drafting units of this standard: Meteorological Observation Center of China Meteorological Administration, Chinese Academy of Meteorological Sciences. The main drafters of this standard are Fang Shuangxi, Liang Miao, Liu Lixin, Yao Bo, Xia Lingjun, Wang Hongyang, Pan Jingjing, Li Geng, Xu Lina, Chen Liqu. I
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1 Scope
Atmospheric methane cavity ring-down spectroscopy observation system GB/T33672—2017
This standard specifies the working principle, composition and function, technical index requirements and installation environment requirements of the cavity ring-down spectroscopy observation system for observing atmospheric methane concentration
This standard applies to the cavity ring-down spectroscopy observation of atmospheric methane, and also to the design and processing of the observation system. 2 Terms and definitions
The following terms and definitions apply to this document. 2.1
Cavity Ring-Down Spectroscopy method; CRDS Cavity Ring-Down Spectroscopy method
After a single-wavelength laser beam enters the optical cavity, the beam reflects back and forth between the cavity mirrors. When the light source is cut off, its energy will decay over time, and the decay rate is related to the loss of the optical cavity itself (including transmission and scattering) and the absorption of the medium in the cavity. A method for quantifying the content of the measured component based on the decay rate of light energy.
Standard gas
A mixed gas with a known concentration of the standard substance, based on clean air. Note: Adapted from QX/T1252011, definition 10.2. 2.3
Working standard gas is a standard gas used for quantitative measurement of the concentration of the target substance in the sample. Note: Rewritten from QX/T125—2011, definition 10.82.4bzxZ.net
target standard gas
Self-standard standard gas
Standard gas used to check and evaluate the operating status of the measurement system and used as a sample for regular and repeated measurements. Note: Rewritten from QX/T1252011, definition 10.9.2.5
Sample gassamplegas
Gas measured by the measurement system.
3 Working principle
The sample acquisition and processing unit draws air from the sampling pipeline, and after temperature balance, pressure control, drying and other treatments, the air/standard gas selection unit selects the sample gas or standard gas to enter the optical cavity ring-down host unit for measurement, and the relevant data is stored in the data acquisition and processing unit. According to the different responses of the system to air/standard gas, the concentration of the target substance in the sample can be quantified. The target substance content is determined according to formula (1): D
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GB/T33672—2017
Wherein:
methane content, in mol/mol; D
density of the measured molecule, which is proportional to the content, in cubic meter (m-3); total density of gas molecules, in cubic meter (m-\); Avogadro constant, 6.0221367×10 23mol-1 Pressure in the optical cavity pool, in Pascals (Pa); volume of the optical cavity pool, in cubic meters (m\); gas constant, 8.314510Pa?m/(mol·K); temperature in the optical cell, in Kelvin (K): speed of light, in meters per second (m/s);
absorption cross section of the molecule at the laser frequency, in square meters (m2); t(u) - decay time with absorption medium (methane), in seconds (s); tempty - decay time without absorption medium, in seconds (s). 4 System
4.1 System Composition
It mainly includes sample collection and processing unit, air/standard gas selection unit, optical cavity ring-down host unit, standard gas unit and data collection and processing unit. The typical system structure is shown in Appendix A. The main components of each unit are as follows: Sample collection and processing unit: including air intake filter, sampling pipeline, sampling pump, pressure controller, temperature balance equipment, sample gas dehumidification equipment, etc.;
Air/standard gas selection unit: including flow controller, air/standard gas selection module (solenoid valve, multi-port sample selection valve, etc.): - Optical cavity ring-down host unit: including optical cavity, laser generator, signal receiving and processing module, temperature and pressure control module, etc.! - Standard gas unit: including working standard gas, target standard gas, standard gas pressure reducing valve, etc.; - Data collection and processing unit: including terminals with control and data recording functions such as computers and data collectors. 4.2 Unit Functions
The unit functions are as follows:
Sample collection and processing unit: collect ambient atmospheric samples, and perform temperature balance, pressure control and sample dehydration, etc.: 一Air/standard gas selection unit: used to set and control the standard gas or air sample to enter the host for measurement; 一Optical cavity ring-down host unit: measure the methane concentration of the gas: 一Standard gas unit: provide standard gas close to the ambient concentration, as a reference factor to quantify the sample concentration or test the system accuracy; 一Data acquisition and processing unit: collect system output signals and instrument parameters and other related information, and store and convert operations, etc. 5
Technical index requirements
5.1 Overall technical index
The atmospheric methane concentration range is (1200～4000)×10-(mole fraction), and the 5min average methane measurement accuracy should be better than 2×10-(mole fraction). All pipelines and connectors of the system should not adsorb or contaminate methane. 5.2 Technical requirements of each unit
5.2.1 Sample collection and processing unit
5.2.1.1 The residence time of the sample gas from the outdoor sample inlet to the optical cavity ring-down main unit shall not exceed 5min. 2
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GB/T33672—2017
5.2.1.2 The air inlet filter shall be able to remove particles with a particle size greater than 7μm, and stainless steel or polytetrafluoroethylene filter membranes shall be preferably used. 5.2.1.3 The sample gas shall be temperature balanced and pressure controlled before entering the air/standard gas selection unit. The air/standard gas temperature entering the optical cavity ring-down main unit shall be roughly the same, and the pressure shall be close to the ambient pressure. The dehumidification device shall have no obvious adsorption or contamination of methane, and shall be made of stainless steel or hard glass. The water content in the sample gas after dehydration shall be less than 5X10- (volume fraction), and it is recommended to dehydrate in an environment below -50℃. 5.2.1.4 The sampling pump should be an oil-free pump, and the internal material should preferably be polytetrafluoroethylene. 5.2.2 Air/standard gas selection unit
5.2.2.1 When switching between different pipelines, the sealing should be good, no air leakage and no cross contamination, and programmable control should be available. 5.2.2.2 The sample gas inlet flow rate should not exceed 300mL·min-. 5.2.3 Optical cavity ring-down host unit
5.2.3.1 The 5min average methane measurement accuracy should be better than ±2×10-* (mole fraction). 5.2.3.2 The 24h drift methane should be less than 2×10- (mole fraction). 5.2.4 Standard gas unit
5.2.4.1 One or more working standard gas should be used, and the concentration should be close to or the span basically covers the range of atmospheric methane concentration changes at the observation site. 5.2.4.2 One or more target standard gas should be used, and the concentration should be close to the atmospheric methane concentration at the observation site. 5.2.4.3 The uncertainty of the methane value in the calibration gas should be better than one thousandth. 5.2.4.4 When the pressure of the calibration gas (or target calibration gas) is lower than 2MPa, the calibration gas (or target calibration gas) should be stopped and recalibrated. 5.2.5 Data acquisition unit
The signal acquisition device should save the various parameter information output by the instrument, including date, time, methane response signal, air/calibration gas identification, sample gas moisture content, optical cavity temperature and pressure, etc. The acquisition frequency of the signal acquisition device should not be lower than the instrument signal output frequency. 6 Installation environment requirements
6.1 Inlet requirements
It should be located at least 10m above the top of the ground vegetation canopy, less directly affected by human activities, and have certain dust, water and insect prevention measures.
6.2 Site surrounding environment requirements
The surrounding area of ​​50m or more is relatively open and the air flow is smooth. 6.3 Laboratory temperature requirements
To avoid the influence of ambient temperature fluctuations on observation, the installation environment temperature of the cavity ring-down spectroscopy host unit should be kept relatively stable, preferably at 25℃±3℃.
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See Figure A.1 for the typical system structure.
Sample collection and processing unit
Air inlet
Temperature balancing equipment
Air inlet filter
Sampling pump
Appendix A
(Informative Appendix)
Typical system structure
Standard gas unit
Pressure gauge
Working standard gas
Target standard gas
Pressure controller
Removal equipment
Flow meter
: Sample selection module
Typical system structure diagram
Air/standard gas
Selection unit
Pressure controller
Flow controller
Cavity ring-down
Host unit
CRDS host
Data collection
and processing unit
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References
GB/T33672—2017
GB/T5832.3—2011 Determination of trace moisture in gases Part 3: Cavity ring-down spectroscopy[
QX/T125—2011 Terminology for greenhouse gas background observations[2]
China Meteorological Administration. Atmospheric composition observation business specifications (trial). Beijing: Meteorological Press, 2012[4General Observation Department of China Meteorological Administration. Atmospheric composition observation business technical manual (Volume 1: Greenhouse gases and related trace components). Beijing: Meteorological Press, 2014.
[5]GAW Report No.213.17th WMO/IAEA Meeting on Carbon Dioxide,Other GreenhouseGases and Related Tracers Measurement Techniques (GGMT-2013), 2014.5
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GB/T33672-2017
People's Republic of China
National Standard
Atmospheric Methane Cavity Ring-Down Spectroscopy Observation System GB/T33672—2017
Published and distributed by China Standards Press
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