# October 31, 2011

MEMORANDUM

SUBJECT: Data from the Evaluation of Instruments that Measure Nitrous Oxide (N 2 

# O)

FROM: Chris Laroo, Environmental Scientist

Assessment and Standards Division

TO: Docket EPA-HQ-OAR-2010-0799

This memorandum and attached file, “N 2 

# O Instrument Evaluation” shows the results of EPA’s

evaluation of 4 technologies for N 2 

# O measurement, conducted during the fall of 2011. These

technologies are the Gas Chromatograph Elect ron Capture Detector (GC-ECD), Fourier

Transform Infrared Spectrometer (FTIR), Non-Di spersive Infrared (NDIR) analyzer, and the

Quantum Cascade Laser (QCL) analyzer. These four technologies were evaluated for their

accuracy in measuring light-duty vehicle N 2 

# O emissions at the dilute exhaust gas levels expected

in meeting the 0.01 gram/mile N 2 

# O standard. This includes expected interference gas dilute

exhaust concentrations of H 2 

# O in the 0 to 2% range, CO in the 80 to 300 ppm range, and CO 2 

# in

the 0.7% to 2% range. The target range for N 2 

# O in dilute exhaust gas ranged from 400 to 800

ppb, which is within the range of dilute exhaust gas concentrations expected for a vehicle

complying with the light-duty vehicle N 2 

# O emission standard.

GC-ECD

The results indicate that the GC-ECD continues to be a robust, accurate measurement method for

low level N 2 

# O analysis.

FTIR

The results show that the FTIR can be prone to high bias due to interference from CO and CO 2 

# , however steps can be taken (like increasing the gas cell size and path length) to minimize the

interference contribution.

NDIR

While improvements have been made to the NDIR, the instrument evaluated was prone to

interference when the interference gas concentrations strayed from the concentration at which

the interference correction coefficient was generated. Thus interference could be controlled

within a given range of CO, CO 2 

# , and N 2 

# O concentrations; but care must be taken ensure

accurate measurement.

QCL

The QCL is the most recently developed instrument. Evaluation of the instrument shows that it

is not susceptible to interference from CO, CO 2 

# , or water. The instrument has excellent low

level accuracy and results from measurement with this instrument should be considered

comparable to that from a GC-ECD. The quad gas version of this bench that measures NO, NO 2 

# ,

# N 2 

# O, and NH 3 

# is currently available for purchase. The single gas (N 2 

# O only) versions of the

instruments that we evaluated from two different manufactures have just been brought to market.

One manufacturer’s instrument is available for purchase while the other manufacturer’s

instrument should be commercially available in Spring of 2012. In both cases the single gas N 2 

# O

bench is currently available for evaluation from each of the manufacturers.

Overall, the results indicate that methodologies are currently available to perform accurate low

level (sub 1 ppm) measurement of N 2 

# O and that new instrumentation has been developed in

response to EPA rulemakings to facilitate low level accurate measurement of N 2 

# O with no

contribution from interference gasses. We expect this new instrumentation to fully penetrate the

N 2 

# O measurement market in the next 6 months.

Attachment: “N 2 

# O Instrument Evaluation”N2O Instrument EvaluationOInstrumentEvaluation10/31/1110/31/20111U.S. Environmental Protection AgencyGC-ECD Comparison to FTIREvaluation Results10/31/2011 U.S. Environmental Protection Agency 2Overview• GC-ECD and FTIR analyzed bags over threephases of the FTP and HWFET for N2O.– Ambient measurement performed.• Blended bag analysis of N2O using NDIR andFTIR.– Testing repeated, once on 5/9/11 and once on5/31/11.– Ambient analysis included.10/31/20113U.S. Environmental Protection AgencyARB Comparison of GC-ECD to FTIR• ARB analyzed bags over three phases of theFTP and HWFET for N2O.– Bag analysis on GC-ECD and FTIR meeting ARBSOP No. MDL 136.Testing was done on 3 vehicles no repeats–Testingwasdoneon3vehicles,norepeats.– Tests were performed at ATDC under EPAcontract.– FTIR compared very well to GC-ECD, which isconsidered the gold standard.10/31/20114U.S. Environmental Protection Agency10/31/20115U.S. Environmental Protection Agency10/31/20116U.S. Environmental Protection Agency10/31/20117U.S. Environmental Protection Agency10/31/20118U.S. Environmental Protection Agency10/31/20119U.S. Environmental Protection Agency10/31/201110U.S. Environmental Protection Agency10/31/201111U.S. Environmental Protection Agency10/31/201112U.S. Environmental Protection Agency10/31/201113U.S. Environmental Protection Agency10/31/201114U.S. Environmental Protection AgencyNDIR Comparison to FTIREvaluation Results10/31/2011 U.S. Environmental Protection Agency 15Comparison of NDIR and FTIR• Horiba loaned us one of their only AIA-721(LE) N2Oanalyzers for evaluation.•AVL new generation FTIR was also made availableAVLnewgenerationFTIRwasalsomadeavailableto EPA for evaluation.• We just recently evaluated the analyzers on bagsi ti f bl d f CO COt NO dNconsisting ofblends ofCO,CO2, waer,N2, andN2.• The purpose was to validate the analyzers’ ability tocompensate for CO, CO2, and water interference.• Both the NDIR and FTIR analyzers performed well,however some questions regarding performanceremain.10/31/201116U.S. Environmental Protection Agency10/31/201117U.S. Environmental Protection Agency10/31/201118U.S. Environmental Protection Agency10/31/201119U.S. Environmental Protection Agency10/31/201120U.S. Environmental Protection Agency10/31/201121U.S. Environmental Protection Agency10/31/201122U.S. Environmental Protection Agency10/31/201123U.S. Environmental Protection Agency10/31/201124U.S. Environmental Protection Agency10/31/201125U.S. Environmental Protection AgencyConclusion• Current NDIR and FTIR technologies can have atendency to bias the measurement high due tointerference contributions.interferencecontributions.– Horiba NDIR can minimize interference effects by targetingrepresentative CO2concentration for factor generation.–Precision of NDIR CO correction remains an open issue(other possible contributing factors?).– ARB FTIR data shows no bias, while AVL does (typically0.75 ppm on average).–Overall, interference contributions are well below the 1 ppmlimit in 1065.375.• GC-ECD does not have any measurement issues.10/31/201126U.S. Environmental Protection AgencyHoriba MEXA-1100QL EvaluationResults10/31/2011 U.S. Environmental Protection Agency 27Evaluation of Horiba MEXA-1100QL• Horiba loan EPA a MEXA-1100QL quantum cascadelaser based N2O measurement instrument forevaluation.• EPA GC-ECD is not yet operational, therefore MEXA1100QL performance was evaluated against bagblends of CO COwater NO and NblendsofCO,CO2,water,N2O,andN2.• The evaluation was identical to pervious evaluationsof NDIR and FTIR N2O analyzers performed by EPA.• The purpose was to validate the analyzers’ ability tocompensate for CO, CO2, and water interference.10/31/201128U.S. Environmental Protection AgencyEvaluation of Horiba MEXA-1100QL• The MEXA-1100QL performed with effectivelyno span drift over days of operation andminimal zero drift.• The instrument consistently read ambientb k dNO 3121 backgroundN2as±ppb.• Interference check results:–-9 ppb response on 15.19% CO2– 2 ppb response on 485 ppm CO10/31/201129U.S. Environmental Protection Agency0.6Comparison of N2O Concentrations Across Different Bag Blends of CO2and CO0.51.461%CO2194 8ppmCO1.948%CO2292 2ppmCOTargetN2OConcentration=0.391 ppmH2OConcentration=2.2%0.30.4

n traiton (ppm)194.8ppmCO292.2ppmCO0.2

N 2 O Conce n0.00.1Bag 5 Bag 610/31/201130U.S. Environmental Protection AgencyCalculated BlendHoriba MEXA-1100QL0.8Comparison of N2O Concentrations Across Different Bag Blends of CO2and COTargetNOConcentration0 587ppm0.60.70.97%CO287.3ppmCO1.457%CO2116.5ppmCO0.777%CO268.0ppmCO0%CO2193.9ppmCO1.457%CO20ppmCO1.457%CO2193.6ppmCO1.457%CO2291.3ppmCO1.942%CO2194.2ppmCO1.942%CO2291.3ppmCOTargetN2OConcentration=0.587ppmH2OConcentration=2.2%0.40.5

e ntraiton (ppm)0.20.3

N 2 O Conc e0.00.1Bag 8Bag 4Bag 1Bag 9Bag 2Bag 7Bag 12Bag 11Bag 1010/31/201131U.S. Environmental Protection AgencyBag8Bag4Bag1Bag9Bag2Bag7Bag12Bag11Bag10Calculated BlendHoriba MEXA-1100QL350Comparison of CO Concentrations Across Different Bag Blends of N2O, CO2,and CO300350200250

i ton (ppm)100150

CO Concentra050B 1B 2B 3B 4B 5B 6B 7B 8B 9B 10B 11B 1210/31/201132U.S. Environmental Protection AgencyBag1Bag2Bag3Bag4Bag5Bag6Bag7Bag8Bag9Bag10Bag11Bag12Calculated BlendHoriba AIA-721 NDIR Analyzer2 5Comparison of CO2Concentrations Across Different Bag Blends of N2O, CO2,and CO2.02.51.5

traiton (%)1.0

CO 2 Concen0.00.5B 1B 2B 3B 4B 5B 6B 7B 8B 9B 10B 11B 1210/31/201133U.S. Environmental Protection AgencyBag1Bag2Bag3Bag4Bag5Bag6Bag7Bag8Bag9Bag10Bag11Bag12Calculated BlendHoriba AIA-722 NDIR AnalyzerMEXA-1100QL Measurement Error vs. GasDivider Generated ConcentrationsTarget Generated Concentration Measured Concentration ErrorDividerGeneratedConcentrations5.056 5.077 0.41%3.0336 3.0415 0.26%1.0112 0.9971 -1.41%0.9101 0.9023 -0.86%0.809 0.8035 -0.68%0.7078 0.7035 -0.61%0.6067 0.6081 0.23%0.5056 0.5093 0.73%0.4045 0.4075 0.74%0.3034 0.3088 1.75%0.2022 0.2054 1.56%0.1011 0.0983 -2.85%0 0.0086 0.17%10/31/201134U.S. Environmental Protection AgencyConclusion• The MEXA-1100QL performed very well and doesnot appear to show any susceptibility to CO, CO2, orwater interference.• Based on CO and CO2measurement error, webelieve that the bulk of the associated N2Omeasurement error is due to bag blending error( i f 5% f ll i )(maximum error of5%for allspecies).• MEXA-1100QL out performs FTIR and NDIRpreviously tested by EPA.All i di ti th t th MEXA1100QL i i bl•Allindications arethattheMEXA-1100QLis a viable,accurate instrument for measurement of N2O at theconcentrations expected during light-duty chassistesting10/31/201135U.S. Environmental Protection Agency.MAHA QCL Evaluation Results10/31/2011 U.S. Environmental Protection Agency 36Evaluation of MAHA QCL Analyzer• Maschinenbau Haldenwang (MAHA) loaned EPA aMAHA QCL quantum cascade laser based N2Omeasurement instrument for evaluation.measurementinstrumentforevaluation.• EPA GC-ECD is not yet operational, therefore MAHAQCL performance was evaluated against bag blendsof CO COwater NO and NofCO,CO2,water,N2O,andN2.• The evaluation was identical to previous evaluationsof QCL, NDIR, and FTIR N2O analyzers performed byEPA.• The purpose was to validate the analyzers’ ability tocompensate for CO, CO2, and water interference.10/31/201137U.S. Environmental Protection AgencyEvaluation of MAHA QCL• The instrument had issues with the computer thatcontrolled the zero and span functions (a complication ofconverting the instrument from 220 VAC to 110 VAC).S h d t b t d ll–Spanhadtobe enteredmanually.– During the evaluation we lost the ability to rezero theinstrument.–Zero/span drift issues and the inabilityto calibrate out this driftycould be the cause of the negative bias seen throughout thetesting.• The instrument read ambient background N2O as 320ppb drifting down to 305 ppb over the course of the dayppb,driftingdownto305ppboverthecourseoftheday.• Interference check results:– 4 ppb response on 15.19% CO2–-2ppb response on 485ppm CO10/31/201138U.S. Environmental Protection Agencypp p pp0.9Comparison of N2O Concentrations Across Different Bag Blends of CO2and COT tNOC t ti0 5870.70.80.976%CO287 8ppmCO1.457%CO2116 5ppmCO0%CO2195 4ppmCO1.467%CO20ppmCO1.467%CO2293 4ppmCO1.956%CO2195 6ppmCO1.956%CO2293 4ppmCOTargetN2OConcentration=0.587ppmH2OConcentration=2.2%0.50.6

n traiton (ppm)87.8ppmCON2ODiff‐0.035116.5ppmCON2ODiff‐0.010195.4ppmCON2ODiff‐0.0240ppmCON2ODiff‐0.032293.4ppmCON2ODiff‐0.038195.6ppmCON2ODiff‐0.017293.4ppmCON2ODiff‐0.0360 20.30.4

N 2 O Conce n0.00.10.2B 8B 1B 9B 7B 12B 11B 1010/31/201139U.S. Environmental Protection AgencyBag8Bag1Bag9Bag7Bag12Bag11Bag10Calculated BlendMAHA QCL350Comparison of CO Concentrations Across Different Bag Blends of N2O, CO2,and CO300200250

i ton (ppm)100150

CO Concentra05010/31/201140U.S. Environmental Protection AgencyBag 1 Bag 7 Bag 8 Bag 9 Bag 10 Bag 11 Bag 12Calculated BlendHoriba AIA-721 NDIR Analyzer2.5Comparison of CO2Concentrations Across Different Bag Blends of N2O, CO2,and CO2.01.5

n traiton (%)1.0

CO 2 Conce n0.00.5Bag 1Bag 7Bag 8Bag 9Bag 10Bag 11Bag 1210/31/201141U.S. Environmental Protection AgencyBag1Bag7Bag8Bag9Bag10Bag11Bag12Calculated BlendHoriba AIA-722 NDIR AnalyzerConclusionTh MAHA QCL f d ll d d•TheMAHAQCLperformedwellanddoes not appear toshow any susceptibility to CO, CO2, or water interference.• Based on CO and CO2measurement error (maximum3%) we believe that some of the associated NO3%),webelievethatsomeoftheassociatedN2measurement error is due to bag blending error.• It should also be noted that the average 5% negative biason N2O measurement is influenced bythe inabilityto2y yproperly zero/span the instrument after the initialzero/span at the start of the testing.– The negative drift is evident when looking at the increase innegative bias in the order the bags were read:7 8 9 10 11negativebiasintheorderthebagswereread:7,8,9,10,11,12, and 1.– It is also noted in the decreasein ambient concentration overthe course of the testing: 320, 310, 305 ppb.10/31/201142U.S. Environmental Protection AgencyConclusion cont.Th MAHA QCL f FTIR d NDIR•TheMAHAQCLout performsFTIRandNDIRpreviously tested by EPA.• All indications are that if the instrument zero/spanf ti ki l th MAHA QCLfunctions are working properly,theMAHAQCLshould be a viable, accurate instrument formeasurement of N2O at the concentrations expectedduring light-duty chassis testingduringlightdutychassistesting.• EPA intends to re-evaluate this instrument after themanufacturer has resolved issues regarding thepower configuration for use in North AmericapowerconfigurationforuseinNorthAmerica.• We will update our results with this instrument afterour re-evaluation.10/31/201143U.S. Environmental Protection Agency