spectroscopy (IRIS) for δ 13 C of CO 2 monitoring

Transcription

1 Yale NUIST Center on Atmospheric Environment: Center Weekly Video Conference Calibration strategy of isotope ratio infrared spectroscopy (IRIS) for δ 13 C of CO 2 monitoring Xuefa Wen 1*, Yao Meng 1, Xinyu Zhang 1, Xiaomin Sun 1, Xuhui Lee 2,3* 1 Key Lb Laboratory of Ecosystem Network Nt kobservation and Modeling, Institute t of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing , China 2 Key Laboratory of Meteorological Disaster of Ministry of Education & Yale NUIST Center on Atmospheric Environment, Nanjing University of Information Science & Technology, Nanjing , China 3 School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut 06511, USA Nov. 29, 2012 New Haven

2 Outlines 1. Introduction 2. Materials and methods 3. Results and Discussion i 4. Conclusions

3 1. Introduction [1] Important tracer, and traditional methods (IRMS), alternative method of IRIS 同位素组成 δ(isotopic composition) δ sample =(R sample /R standard -1)*10 3 R= 13 CO 2 / 12 CO 2 同位素判别 (isotopic p discriminationδ) Δ= (δ R - δ P ) /(1+ δ P ) Characteristics of isotopes 同位素特性 物理性质 同位素分馏作用平衡分馏效应 Equilibrium isotope fractionation 动力学分馏效应 kinetic isotope fractionation 扩散效应 diffusive effects 影响同位素分馏的主要因素化学组成晶体结构特殊效应

4 生态系统尺度

5 区域 / 全球尺度 生态系统尺度 Walker Branch, TN R A A R A R Isotope ratio mass spectrometry (IRMS), anaccurate butexpensive and Isotope ratio mass spectrometry (IRMS), an accurate but expensive and high maintenance analytical method; Alternative method of IRIS, continuously

6 [2] State of the art of IRIS, and necessity of frequent calibration: stability and concentration dependence Model TGA100/100A/200, Campbell Scientific Inc. Models G1101i/2101i Model DLT 100 Because of instrumental drift and sensibility to changing environmental parameters, frequent calibration is necessary to ensure accurate measurements.

7 [3] State of the art of calibration methods 同位素组成 δ(isotopic composition) δ sample =(R sample /R standard -1)*10 3 Methods 3 (delta gain and offset) and 4 (delta offset) R= 13 CO 2 / 12 CO 2 Methods 1 (mixing ratio gain and offset) Methods 2, isotopic mixing ratio gain and offset [4] Objectives of our study Inter comparison of different calibration methods for Los Gaots and Picarro measurement

8 2. Material and Methods 2.1. Analyzers, sampling and calibration systems In brief, the analyzer was configured with two three way solenoid, with three air sample or calibration gas intakes. Model DLT 100 Models dlg1101i

9 2.2. Calibration procedure Method 1: A two point mixing ratio gain and offset calibration procedure (by Bowling et al.) x x x2, t x [ CO 1, t ] [ CO2] [ CO2] f [CO2] a, t x, 1, a m x t x1, t x2, m x1, m Ra [ C]/[ C] [ CO2]/[ CO2] RVPDB x x x x x , t 1, t a, t a, m 1, t 1, t x2, m x1, m 12 [ CO2] [CO2](1 f )]/(1 RVPDB(1 a /1000)) [ CO2] [CO2](1 f ) [ CO2] (1 /1000) Method 2: A two point isotopic mole mixing ratio calibration procedure (by Lee et al.) a,1 x 13 a ( R x1 a 12 x 1 1 1) 1000 x R VPDB x 1 a x2 a, 2 ( R2 1) x x R a 2 a VPDB a,2 a, x x a 1 a, 1 x x 2 1 Method 3: A delta gain and offset calibration procedure a Method 4: A delta offset calibration procedure a a, m ( r, t r, m )

10 2.3.3 Calibration crosschecks and atmospheric measurement 1. Precision and stability Compressed air tank: 9.8 ; 420ppm, 24hr 2. Calibration crosschecks Compressed air tank A: ; ppm Compressed air tank B: ; ppm Compressed air tank C: ; ppm 3. Atmospheric measurement, and keeling plot Dayof year: 103~

11 3. Results and Discussions 3.1. Allan variance 1 Tank: 9.8, 420ppm 24hr24hr 12 CO 2 Los Gaots Picarro δ 13 C Los Gaots Picarro Allan deviation (square root of the Allan variance) expresses the measurement precision as a function of the averaging time. Figure 1 Allan deviation as a function of averaging time, for both 12CO 2 concentration and δ13c

12 3.2. Comparison among different calibration methods Table 1 Crosschecks of different calibration methods Concen Delta Measured Mthd1 Method Mthd2 Method Mthd3 Method Mthd4 Method tration values PIC ± ± ± ± ±0.39 LG R ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.23

13 Concentration error sensitivity of method 1 (neglected, only in the text) Concentra tion Delta Bowling error +1%(436.41) Bowling error Bowling 1%(436.41) 41) error +1%(361.25) Bowling error +1%(361.25) PIC ± ±0 020±0 0.20± ± ± ± ± ± ±0.58 LGR ± ± ± ± ± ± ± ±0.22

14 3.3. Atmospheric measurement -8 (a) Los Gatos_Bowling Picarro_Bowling (b) Method 1: 0.01±0.18 (mean+std) Method 2: 0.07±0.20 (mean+std) Figure 2 Daily variation of (a) δ13c and by method 1 and (b) residual error between Los Gatos and Picarro measurement

15 Los Gatos Picarro Picarro-Los Gaots y = x x R²= The diluted and dry gas mole fractions are related by the following expression: The presence of water vapour in the sample generates an underestimation of the CO2 and CH4 concentrations due to dilution and spectral line broadening effects ±1.1ppm (mean+std) Figure3(a) Daily variation of co2 concentration for Los Gaots and Picarromeasurement and (b) Dependence of co2 difference between Los gatos and picarro on the h2o concentration

16 Los Gatos_Lee Los Gatos_Bowling Geometric Mean Regression (Reduced Major Axis Regression), 95% confident level) y = x R² = y = x R² = Picarro_ Lee -9 Picarro_Bowling -10 y = x R² = 0.81 y = x R²= Figure 4 keeling plot of δ13c by method 1 (Bowling) and 2 (Lee, neglected) vs 1/co2 for (a) Los Gaots and (b) Picarro measurement

17 Los Gatos_Lee-Los Gatos_Bolwing Picarro_Lee-Picarro_Bolwing y = x R² = y = -8E-06x R² = 9E Figure 5 Dependence of delta difference between method 1 (Bowling) and 2 g p ( g) (Lee) on the co2 concentration for Los gatos and picarro measurement

18 (a) Picarro_Lee-Los Gatos_Lee Picarro_Bowling-Los Gatos_Bolwing Concentration dependence y = x y = x R² = R² = (b) Picarro_Lee-Los Gatos_Lee Picarro_Bowling-Los Gatos_Bolwing y = x y = x R² = R² = Figure 6 Dependence of delta difference between Los gatos and picarro Figure 6. Dependence of delta difference between Los gatos and picarro measurement on the(a) Los Gatos co2 concentration and (b) Picarro co2 concentration for method 1 (Bowling) and 2 (Lee, neglected)

19 4. Conclusion Method 1 and 2 were appropriate p calibration methods Concentrationdependence affect theintercept ofkeeling plot significantly Moisture correction should be taken care on the measurement of concentration and isotopic ratio of co2