NO 2 Measurements with Different Converters Molybdenum Converters
NO 2 Measurements with Different Converters Molybdenum Converters vs. Specific NO 2 Converters Robert Gehrig; Christoph Hüglin, Beat Schwarzenbach EMPA Dübendorf Switzerland Air Pollution / Environmental Technology
Outline EMEP vs. EU Directive n NO 2 automatic measurement techniques n Results of parallel measurements n Conclusions n R. Gehrig; EMEP TFMM 2011
NO 2 : EMEP vs. EU Directive EMEP: • Specific NO 2 measurements required. • Na. I manual method as standard technique. • Automatic specific monitoring with photolytic converters. EU Directive (compliance measurements): • Measurement with chemiluminescence after conversion of NO 2 to NO as standard technique according to EN 14’ 211. • Not specific. R. Gehrig; EMEP TFMM 2011
NO 2 : Molybdenum converter Standard technique: Measurement of NO with chemiluminescence • NO 2 is reduced to NO by a converter Heated metal converters, mostly molybdenum (Mo) + Efficient, long lifetime, reliable not specific • NOx = NO + a·NO 2 + b·HNO 3+ c·NO 3 -+ d·PAN + e·NH 3 + … R. Gehrig; EMEP TFMM 2011
NO 2 : Photolytic converter n Principle: NO 2 is reduced photolytically to NO NO 2 + hν NO + O 2 O 3 NO + O 3 NO 2 + O 2 hν: < 410 nm NO 2 + hν NO + O 3 n Light source: Xe vapour lamp, metal halid lampe of Array of UV LED n Specific, but low converter efficiency n Converter efficiency needs to be calibrated at regular intervals R. Gehrig; EMEP TFMM 2011
„Blue Light Converter“ BLC Cell volume: 17 ml Cell purge time at 1 l/min: 1 s Array von UV LED‘s ca. 380 410 nm 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
Set-up of NOx-monitor with BLC n Molybdenum converter replaced or bypassed, flow controll capillary after converter Example: Thermo Electron Model 42 C TL NO Mo-Konverter 2 -Konverter Sample BLC NOx Filter NO R. C. Trockner Ozonator PMT Vorkammer Pumpe R. Gehrig; EMEP TFMM 2011
BLC integrated in NOx monitor Thermo Electron Model 42 i TL Thermo Electron Model 42 C TL R. Gehrig; EMEP TFMM 2011
Specific NO 2 measurements in NABEL (NABEL = Swiss National Monitoring Network) Sites with NO 2 measurements with photolytic converters: System Cranox 1) BLC 1) Cranox: Site type Altitude Measurement periods Jungfraujoch (JUN) high alpine 3580 m from Sep 1991 Rigi Seebodenalp (RIG) rural 1030 m Oct 2001 to Feb 2006 Rigi Seebodenalp (RIG) rural 1030 m from Nov 2004 Payerne (PAY) rural 490 m from Feb 2006 Zürich (ZUE) urban 410 m from Jan 2010 Chemiluminescence monitor (CLD 770 AL ppt resp. CLD 89 p) with photolytic converter (PLC 760 with Xe vapour lamp or PLC 762 mit metal halid lamp), Eco Physics. R. Gehrig; EMEP TFMM 2011
Comparison Cranox – BLC n n NO 2 Daily means at Rigi Seebodenalp NO Daily means at Rigi Seebodenalp R. Gehrig; EMEP TFMM 2011
NO 2 (photolytic) at different sites R. Gehrig; EMEP TFMM 2011
NO 2 comparison Payerne R. Gehrig; EMEP TFMM 2011 Rigi
NO 2 at different sites daily means R. Gehrig; EMEP TFMM 2011
Mean values (Jan – Oct 2010) NO 2 photolytic NO 2 (Mo) NO 2 in % of NO 2 (Mo) Rigi-Seebodenalp 2. 2 ppb 4. 1 ppb 1. 9 ppb 45 % Payerne 5. 5 ppb 7. 4 ppb 1. 8 ppb 25 % 14. 7 ppb 16. 4 ppb 1. 7 ppb 10 % 0. 61 ppb 1) 73 % Site Zürich Jungfraujoch 1) 0. 23 ppb 0. 84 ppb 1) Jungfaujoch: NO 2 (Mo) is NOy – NO; NO 2 is NOy NO NO 2; means 2005 2009 R. Gehrig; EMEP TFMM 2011
New spectroscopic laser techniques Cavity Enhanced Absorption Spectroscopy n Cavity Ring Down Spectroscopy n Quantum Cascade Laser Spectroscopy n R. Gehrig; EMEP TFMM 2011
Conclusions NO 2 measurements with molybdenum converters overestimate NO 2 by 10 70%. n Photolytic converters and new spectroscopic methods allow for automatic specific NO 2 measurements. n Choice of method depends on the aim of the measurements. n Clear specification of methods is needed for NO 2 data series. n R. Gehrig; EMEP TFMM 2011
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