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
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
Objectives Air Quality Monitoring Network
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
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 1 1.805 392.64 9346.98 209473.65 780787.82 Ref 1 1.828 392.47 9448.62 208836.57 781338.37 Ref 1 2.122 398.25 9305.94 211382.44 778916.67 Ref 1 1.559 400.63 9564.23 210600.63 779571.15 Verification of 4 mixtures above with GC-FID (methanizer)
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
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
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 2005 4 th WMO Round robin intercomparison (CO 2, CH 4, CO) 2006 WCC-EMPA (O 3, CO and CH 4 ) 2006 WCC-AP (aerosols) 2009 5 th WMO Round robin intercomparison (CO 2, CH 4, CO) 2011 WCC-EMPA (O 3, CO, CO 2, CH 4 ) 2014 6 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
Round-Robins results CPT GAW Source: https://www.esrl.noaa.gov/gmd/ccgg/wmorr/wmorr_results.php?rr=rr 5¶m=co2 Courtesy of Cape Point team: Labuschagne et.al
Cape Point GAW Data http://gaw.kishou.go.jp/wdcgg/ http://www.saaqis.org.za/ Montreal Kyoto IPCC IFCCC http://www.esrl.noaa.gov/gmd/ccgg/carbontracker/ Courtesy of Cape Point team: Labuschagne et.al
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
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 S1 397.72 1.7863 397.67 1.7862 0.0125 0.0077 S2 398.38 1.7946 398.39 1.7936 0.0051 0.0528 S3 420.39 1.7959 420.63 1.7959 0.0566 0.0003 S4 376.18 1.7812 376.17 1.7824 0.0032 0.0232 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
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
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
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 M51 8085 i-pentane 20.4 76.5 0.29 3.75 n-pentane 20.8 74.7 0.28 3.59 Hexane 22.5 88.4 0.36 3.92 M51 8073 i-pentane 20.1 75.6 0.23 3.76 n-pentane 20.5 73.9 0.26 3.60 Hexane 22.3 87.7 0.20 3.94
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
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
The 7200 flow diagrams 21 stages
18.694 8.541 18.211 19.103 21.706 12.987 24.329 18.254 18.735 19.141 21.728 8.602 13.011 Results (BTEX) pa 60 50 FID2 B, Back Signal (30082017PPB\19062017-b 2017-08-30 10-41-51\F-001-1-M555700.D) Reference mixture at 100nmol.mol -1 Volume preconcentrated 500ml 40 30 20 10 Styrene additional component from the sample 0 5 10 15 20 25 FID2 B, Back Signal (30082017PPB\19062017-b 2017-08-30 17-36-51\F-003-1-APEX121.D) pa min 140 M xylene as impurity from one of the isomers 120 100 80 60 40 Sample from another Laboratory: Mole fraction between 100 and 70 nmol.mol -1 20 0 5 10 15 20 25 min
Results (BTEX) Method: reference A-sample B-reference A A Benzene Toluene Ethyl-benzene p-xylene m-xylene o-xylene 1 654.4 713.2 602.1 567.9 559 512.9 2 653.4 714.5 598.7 571.5 560.5 518.6 3 654.9 711 596.5 566.8 557 515.3 Average 654.23 712.90 599.10 568.73 558.83 515.60 Stdev 0.76 1.77 2.82 2.46 1.76 2.86 %rsd 0.12 0.25 0.47 0.43 0.31 0.56 B Benzene Toluene Ethyl-benzene p-xylene m-xylene o-xylene 1 467 520 545.6 31.7 530.2 544.8 2 466.7 517.3 544.5 27 529.6 544.1 3 461.3 519.2 540 23.2 524.1 537.4 Average 465.00 518.83 543.37 27.30 527.97 542.10 Stdev 3.21 1.39 2.97 4.26 3.36 4.09 %rsd 0.69 0.27 0.55 15.60 0.64 0.75 u = 2 2 2 u grav + u ver + u stab A Benzene Toluene Ethyl-benzene p-xylene m-xylene o-xylene 1 653.8 711.3 597.6 570.1 558.7 512.9 2 655.3 706 602.1 567.5 562 514.6 3 651.4 709.7 593.9 572.1 556 511.3 Average 653.50 709.00 597.87 569.90 558.90 512.93 Stdev 1.97 2.72 4.11 2.31 3.00 1.65 %rsd 0.30 0.38 0.69 0.40 0.54 0.32 Drift -0.11-0.55-0.21 0.21 0.01-0.52 u= 3% (k=1)
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
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
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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