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NO 2 Measurements with Different Converters

This study compares NO2 measurements using Molybdenum Converters and Specific NO2 Converters, evaluating accuracy and efficiency. It discusses techniques such as photolytic conversion and spectroscopic laser methods, highlighting advantages and considerations. Results indicate potential overestimation with Molybdenum Converters, emphasizing the importance of method selection based on measurement goals. Clear methodology specifications are crucial for NO2 data integrity in environmental research.

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NO 2 Measurements with Different Converters

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  1. NO2 Measurements with Different Converters Molybdenum Converters vs. Specific NO2 Converters Robert Gehrig; Christoph Hüglin, Beat Schwarzenbach EMPA Dübendorf Switzerland Air Pollution / Environmental Technology

  2. Outline • EMEP vs. EU Directive • NO2 automatic measurement techniques • Results of parallel measurements • Conclusions R. Gehrig; EMEP TFMM 2011

  3. NO2 : EMEP vs. EU Directive • EMEP: • Specific NO2measurementsrequired. • NaImanualmethodasstandardtechnique. • Automaticspecificmonitoringwithphotolyticconverters. • EU Directive (compliancemeasurements): • Measurement withchemiluminescence after conversionof NO2to NO asstandardtechniqueaccordingto EN 14’211. • Not specific. R. Gehrig; EMEP TFMM 2011

  4. NO2 : Molybdenum converter • Standard technique: Measurement of NO withchemiluminescence • NO2isreducedto NO by a converterHeatedmetalconverters, mostlymolybdenum (Mo) • Efficient, longlifetime, reliable • not specificNOx = NO + a·NO2 + b·HNO3+ c·NO3-+ d·PAN + e·NH3 + … R. Gehrig; EMEP TFMM 2011

  5. NO2 : Photolytic converter • Principle: NO2 is reduced photolytically to NO NO2 + hν NO + O hν: < 410nm O + O2 O3 NO + O3 NO2 + O2 NO2 + O2 + hν NO + O3 • Light source: Xe-vapour lamp, metal halid lampe of Array of UV-LED • Specific, but low converter efficiency • Converter efficiency needs to be calibrated at regular intervals R. Gehrig; EMEP TFMM 2011

  6. „Blue Light Converter“ BLC Cell volume: 17ml Cell purge time at 1 l/min: 1s Array von UV-LED‘s  ca. 380 - 410nm Air Quality Design, Inc., Wheatridge, CO, (USA)(formerly: Droplet Measurement Technologies, Inc., Boulder) Sale in Europa: meteorologie consult gmbh, D-Königstein (www.metcon.de) R. Gehrig; EMEP TFMM 2011

  7. Set-up of NOx-monitor with BLC Molybdenum converter replaced or bypassed, flow-controll capillary after converter Example: Thermo Electron Model 42C TL Mo-Konverter NO2-Konverter NOx BLC Sample Filter NO R.C. PMT Trockner Vor-kammer Ozonator Pumpe R. Gehrig; EMEP TFMM 2011

  8. BLC integrated in NOx monitor Thermo Electron Model 42i TL Thermo Electron Model 42C TL R. Gehrig; EMEP TFMM 2011

  9. Specific NO2 measurements in NABEL(NABEL = Swiss National Monitoring Network) 1) Cranox: Chemiluminescence monitor (CLD770AL ppt resp. CLD 89p) with photolytic converter (PLC 760 with Xe-vapour lamp or PLC 762 mit metal halid lamp), Eco Physics. Sites with NO2 measurements with photolytic converters: R. Gehrig; EMEP TFMM 2011

  10. Comparison Cranox – BLC Daily means at Rigi-Seebodenalp • NO Daily means at Rigi-Seebodenalp NO2 R. Gehrig; EMEP TFMM 2011

  11. NO2 (photolytic) at different sites R. Gehrig; EMEP TFMM 2011

  12. NO2 comparison Payerne Rigi R. Gehrig; EMEP TFMM 2011

  13. NO2 at different sites daily means R. Gehrig; EMEP TFMM 2011

  14. Mean values (Jan – Oct 2010) Jungfraujoch 0.23 ppb 0.84 ppb 1) 0.61 ppb 1) 73 % 1) Jungfaujoch: NO2 (Mo) is NOy – NO; NO2 is NOy-NO-NO2; means 2005-2009 R. Gehrig; EMEP TFMM 2011

  15. New spectroscopic laser techniques • Cavity-Enhanced-Absorption-Spectroscopy • Cavity-Ring-Down-Spectroscopy • Quantum Cascade Laser Spectroscopy R. Gehrig; EMEP TFMM 2011

  16. Conclusions • NO2 measurements with molybdenum converters overestimate NO2 by 10-70%. • Photolytic converters and new spectroscopic methods allow for automatic specific NO2 measurements. • Choice of method depends on the aim of the measurements. • Clear specification of methods is needed for NO2 data series. R. Gehrig; EMEP TFMM 2011

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