NO2 Measurements with Different Converters
Transcript of NO2 Measurements with Different Converters
NO2 Measurements with Different ConvertersMolybdenum Converters vs. Specific NO2 Converters
Robert Gehrig; Christoph Hüglin, Beat SchwarzenbachEMPA Dübendorf SwitzerlandAir Pollution / Environmental Technology
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Outline
NO2 measurement techniquesRequirements of EN 14‘211Results of parallel measurementsConclusions
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NO2 Measurement TechniquesStandard technique: Measurement of NO with chemiluminescence
NO2 is reduced to NO by a converter
Heated metal converters, mostly molybdenum (Mo)+ efficient+ long lifetime+ reliable- not specific
NOx = NO + a·NO2 + b·HNO3+ c·NO3-+ d·PAN + e·NH3 + …
Alternative: photolytic converters
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Principle: NO2 is reduced photolytically to NONO2 + 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-LEDSpecific, but low converter efficiencyConverter efficiency needs to be calibrated at regular intervals
Photolytic converter
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„Blue Light Converter“ BLC
Cell volume: 17mlCell purge time at 1 l/min: 1sArray von UV-LED‘s λ ca. 380 - 410nmAir Quality Design, Inc., Wheatridge, CO, (USA)(formerly: Droplet Measurement Technologies, Inc., Boulder)Sale in Europa: meteorologie consult gmbh, D-Königstein (www.metcon.de)
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NOx
Set-up of NOx-monitor with BLCMolybdenum converter replaced or bypassed, flow-controllcapillary after converter
Example: Thermo Electron Model 42C TL
R.C. PMT
Vor-kammer
Mo-Konverter
Ozonator
Pumpe
Sample
Filter
Trockner
NO2-Konverter
BLC
NO
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BLC integrated in NOx monitor
Thermo Electron Model 42C TL
Thermo Electron Model 42i TL
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EN 14‘211; NOx measurements
ChemiluminescenceNo converter type specifiedConverter efficiency > 95%Interferences to other N-compounds: Only specified for NH3 (≤ 5,0 nmol/mol)
How to deal with specific measurements?
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Sites with NO2 measurements with photolytic converters:
Specific NO2 measurements in NABEL
System Site Site type Altitude Measurement periods
Jungfraujoch (JUN) high alpine 3580 m from Sep 1991
Rigi-Seebodenalp (RIG) rural 1030 m Oct 2001 to Feb 2006Cranox1)
Rigi-Seebodenalp (RIG) rural 1030 m from Nov 2004
Payerne (PAY) rural 490 m from Feb 2006BLC
Zürich (ZUE) urban 410 m from Jan 2010
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.
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Comparison Cranox – BLCNO2
NO
Daily means at Rigi-Seebodenalp
Daily means at Rigi-Seebodenalp
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NO2 (photolytic) at different sites
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NO2 comparison
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NO
2 (pp
b)
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NO2 (MC)NO2 (PC)Diff NO2
Payerne Rigi
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ppb
ZUEPAYRIG
ΔNO2 at different sites
daily means
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ppb ZUE
PAYRIG
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Mean values (Jan – Oct 2010)
SiteNO2
photolyticNO2
(Mo)ΔNO2
ΔNO2 in% of NO2 (Mo)
Rigi-Seebodenalp 2.2 ppb 4.1 ppb 1.9 ppb 45 %
Payerne 5.5 ppb 7.4 ppb 1.8 ppb 25 %
Zürich 14.7 ppb 16.4 ppb 1.7 ppb 10 %
Jungfraujoch 0.23 ppb 0.84 ppb 1) 0.61 ppb 1) 73 %1) Jungfaujoch: NO2 (Mo) is NOy – NO; ΔNO2 is NOy-NO-NO2; means 2005-2009
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ΔNO2 vs. Nitrate + HNO3Rigi- Seebodenalp
Payerne
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Conclusions
NO2 measurements with molybdenumconverters overestimate NO2 by 10-70%.ΔNO2 consists mostly of HNO3 and NO3
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Photolytic converters and new spectroscopicmethods allow for specific NO2 measurements.Choice of method depends on the aim of themeasurements.Clear specification of methods is needed for NO2data series.