Traceability of greenhouse gases and volatile organic compounds for air monitoring in South Africa

Transcription

1 Traceability of greenhouse gases and volatile organic compounds for air monitoring in South Africa James Tshilongo *1, Silindile L. Lushozi 1,2, Napo Ntsasa 1, Mudalo Jozela 1,2 Luke Chimuka 2 and Goitsemang Lukoto 1,2 1 National Metrology Institute of South Africa (NMISA), Private Bag X34, Lynnwood Ridge, 0040, 2 University of Witwatersrand, Department of Chemistry, PO. Bag 3, Braamfontein, jtshilongo@nmisa.org European Geosciences Union General Assembly 2018 Vienna Austria 12 April 2018 Johannesburg, 2050, South Africa

2 James Tshilongo, Napo Ntsasa, Silindile L. Lushozi, Mudalo Jozela, Goitsemang Lekoto and Luke Chimuka. European Geosciences Union General Assembly 2018 Vienna Austria 12 April 2018 Title page 2 minutes presentation Objectives Preparation and sampling Cape Point Station Results greenhouse gases VOCs and results

3 Objectives Air Quality Monitoring Network

4 Objectives Traceability for greenhouse gases at ambient and emission levels Support Department of Environmental Affairs activities Traceability of Ozone measurement Reference gases Calibration Proficiency Testing Scheme Collaboration South African Weather Service (Cape Point Station) for greenhouse gases and VOC s Collaboration with academia and industry for specific gas measurement

5 Greenhouse gases preparation Preparation by gravimetric method Sequential weighing and filling of components into cylinders Several dilution steps depending on the mole fraction Gas Mixture composition (µmol.mol -1 ) CH 4 CO 2 Ar O 2 N 2 Ref Ref Ref Ref Verification of 4 mixtures above with GC-FID (methanizer)

6 Gas samples from Cape Point Location (position and elevation) : 34 21' S, 18 29' E, elevation 230 meters above mean sea-level. The height of the ambient air intake is 260 m above sea level from the top of a 30 m high mast. Two freezing units (-4 and -45 C respectively) are used in series to dry the ambient air prior to analysis at the station and into pressurised gas cylinders Sampling into cylinders by oil free compressor filling up to 150 bar (RIX industries) Samples transported to Pretoria Sample conditioning for a week prior to analysis by CRDS NMISA CRDS calibrated with gravimetric mixtures prepared in the laboratory Linear response for CO 2 and CH 4 of the four mixtures prepared

7 Cape Point Station Location (position and elevation) : 34 21' S, 18 29' E, elevation 230 meters above mean sea-level. Cape Point (CPT) = Global station (one of ~30 global stations world-wide ) o Strategic position of CPT ensures air mass footprint from south Atlantic ocean Courtesy of Cape Point team: Labuschagne et.al

8 Quality Control GAW Audits Audit History: 1997 WCC-EMPA (O 3 ) Round-Robing experiments 1998 WCC-EMPA (O 3 & CO) 2002 WCC-EMPA (O 3, CO & CH 4 ) 2003 WCC-N 2 O Audit th WMO Round robin intercomparison (CO 2, CH 4, CO) 2006 WCC-EMPA (O 3, CO and CH 4 ) 2006 WCC-AP (aerosols) th WMO Round robin intercomparison (CO 2, CH 4, CO) 2011 WCC-EMPA (O 3, CO, CO 2, CH 4 ) th WMO Round robin intercomparison (CO 2, CH 4, CO) 2015 WCC-EMPA (O 3, CO, CO 2, CH 4, N 2 O) Courtesy of Cape Point team: Labuschagne et.al

9 Round-Robins results CPT GAW Source: 5&param=co2 Courtesy of Cape Point team: Labuschagne et.al

10 Cape Point GAW Data Montreal Kyoto IPCC IFCCC Courtesy of Cape Point team: Labuschagne et.al

11 Regulator Analysis of GAW samples (CRDS) NMISA CRDS analytical system MFC Picarro G2401 Vent A = ℇlc CRDS principle ℇ: molar absorptivity l: pathlength C: mole fraction or concentration Standard gas Dried air sample Courtesy of Picarro

12 Results Dried air sample NMISA CRDS ( mol/mol) WMO/GAW CAPE POINT STATION CRDS ( mol/mol) %DIFFERENCE CO 2 CH 4 CO 2 CH 4 CO 2 CH 4 S S S S a CRDS %DIFF = [(WMO-GAW CAPE POINT STATION NMISA)/ NMISA]*100 Cape point results generated online by CRDS during sampling Sampling performed on different days Value extrapolated, sampled during inland air stream

13 Volatile Organic Compounds List of VOCs Hazardous air Pollutants Chloroform 1,2 Butadiene Methylene Chloride 1,1,2,2-Tetrachloroethane Trichloroethylene Ethylene dichloride Vinyl chloride Ethylene oxide Benzene Toluene Ethyl benzene Xylenes Non-Methane hydrocarbons ethane propane butane N-Pentane Iso-pentane hexane heptane octane nonane Decane

14 Preparation VOC Mixing of similar vapour pressure compounds Weighing in syringe on semi-micro balance (0.1 mg) readability Transfer into pre-evacuated cylinder in nitrogen stream Mass of single component subtracted from total solution transfer Cylinder weighing with mass comparator balance (1mg) readability

15 NMHC three component Detector (FID); 175 o C Temperature program: 80 o C for 5 min, 180 o C for 2 min at 20 o C/min Carrier gas : Hydrogen Sample loop: 1 ml Column: HP-PLOT Al 2 O 3 S Carrier gas flow: 2 ml/min Run time: 12 minutes Cylinder number Component Mole fraction µmol/mol Means %RSD Sensitivity M i-pentane n-pentane Hexane M i-pentane n-pentane Hexane

16 GC parameters for selected VOC GC-2xFID (Front and back) Inlets-2 Front with H 2 carrier gas directly to column to detector (µmol.mol -1 analysis) Back with N 2 (BIP) through pre-concentrator to column to FID (nmol.mol -1 analysis) Detector (FID); 350 o C Temperature program: 40 C hold for 5 min, ramp at 2 C/min to 60 C hold for 2 min, ramp at 4 C/min to 75 C hold for 1 min, ramp at 20 4 C/min to 120 C hold for 2 min. Carrier gas : Nitrogen Split mode: Split-less mode through the cryogenic pre-concentrator Column: HP-INNOWax, (60 m x 320 μm x 0.5 μm) Carrier gas flow: 3.4 ml/min Run time: 20 minutes

17 Preconcentration of VOC at nmol.mol -1 Microscale P&T Extended Cold Trap Dehydration Trap 1:-40 C Trap 2:-40 to -60 C Focusing trap: -150 C

18 The 7200 flow diagrams 21 stages

19 Results (BTEX) pa FID2 B, Back Signal ( PPB\ b \F M D) Reference mixture at 100nmol.mol -1 Volume preconcentrated 500ml Styrene additional component from the sample FID2 B, Back Signal ( PPB\ b \F APEX121.D) pa min 140 M xylene as impurity from one of the isomers Sample from another Laboratory: Mole fraction between 100 and 70 nmol.mol min

20 Results (BTEX) Method: reference A-sample B-reference A A Benzene Toluene Ethyl-benzene p-xylene m-xylene o-xylene Average Stdev %rsd B Benzene Toluene Ethyl-benzene p-xylene m-xylene o-xylene Average Stdev %rsd u = u grav + u ver + u stab A Benzene Toluene Ethyl-benzene p-xylene m-xylene o-xylene Average Stdev %rsd Drift u= 3% (k=1)

21 Conclusion Analysis of CO 2 and CH 4 at ambient level by CRDS CRDS calibrated by CO 2 and CH 4 prepared at NMISA Results within the values from Cape GAW Three component mixture of NMHC at 20 µmol.mol -1 BTEX mixture containing 6 components at 100 nmol.mol -1

22 Future work Preparation of gas mixtures will all greenhouse gases at background level of Southern Hemisphere mole fraction Addition of more components of NMHC Method optimization of nmol.mol -1 VOC components Dilute to 3 nmol.mol -1 minimum Analysis of field samples from selected monitoring stations from South Africa Benchmarking through international key comparisons

23 Acknowledgements For funding of projects For Student funding Authors: Dr. James Tshilongo Mr. Napo Ntsasa Ms. Silindile L. Lushozi Ms. Mudalo Jozela 1,2 Ms. Goitsemang Lekoto 1,2 and Prof. Luke Chimuka. Collaborators: C. Labuschagne, W. Joubert, L. Martin, T. Mkololo, E. Mbambalala, and D. vd Spuy, G. Coetzee

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