N2O Instrument Evaluation O Instrument Evaluation

3/22/12

U.S. Environmental Protection Agency
GC-ECD Comparison to FTIR

Evaluation Results

U.S. Environmental Protection Agency 
Overview

• GC-ECD and FTIR analyzed bags over 

phases of the FTP and HWFET for N2O

– Ambient measurement performed.

• Blended bag analysis of N2O using NDI

FTIR.

– Testing repeated, once on 5/9/11 and once 

5/31/11.

– Ambient analysis included.

U.S. Environmental Protection Agency 
ARB Comparison of GC-ECD to F

• ARB analyzed bags over three phases o

FTP and HWFET for N

2O.

– Bag analysis on GC-ECD and FTIR meetin

SOP No. MDL 136.

– Testing was done on 3 vehicles no repeats Testing was done on

3 vehicles, no repeats

– Tests were performed at ATDC under EPA 

contract.

– FTIR compared very well to GC-ECD, whic

considered the gold standard.

U.S. Environmental Protection Agency
U.S. Environmental Protection Agency
U.S. Environmental Protection Agency
U.S. Environmental Protection Agency
U.S. Environmental Protection Agency
U.S. Environmental Protection Agency
U.S. Environmental Protection Agency 
U.S. Environmental Protection Agency 
U.S. Environmental Protection Agency 
U.S. Environmental Protection Agency 
U.S. Environmental Protection Agency 
NDIR Comparison to FTIR

Evaluation Results

U.S. Environmental Protection Agency 
Comparison of NDIR and FTIR

• Horiba loaned us one of their only AIA-721(LE

analyzers for evaluation.

• AVL new generation FTIR was also made ava

AVL new generation FTIR was also made ava

to EPA for evaluation.

• We just recently evaluated the analyzers on ba

consi ti f bl d f CO CO isting o

f blen

ds o

f CO, CO

2, wat N er, 

N

2O 

, a

• The purpose was to validate the analyzers’ ab

compensate for CO, CO

2, and water interferen

• Both the NDIR and FTIR analyzers performed 

however some questions regarding performanremain.

U.S. Environmental Protection Agency 
U.S. Environmental Protection Agency 
U.S. Environmental Protection Agency 
U.S. Environmental Protection Agency 
U.S. Environmental Protection Agency 
U.S. Environmental Protection Agency 
U.S. Environmental Protection Agency 
U.S. Environmental Protection Agency 
U.S. Environmental Protection Agency 
U.S. Environmental Protection Agency 
Conclusion

• Current NDIR and FTIR technologies can have 

tendency to bias the measurement high due to interference contributions. interference contributions.

– Horiba NDIR can minimize interference effects by ta

representative CO2 concentration for factor generati

– Precision of NDIR CO correction remains an open is

(other possible contributing factors?).

– ARB FTIR data shows no bias, while AVL does (typ

0.75 ppm on average).

– Overall, interference contributions are well below the 

limit in 1065.375.

• GC-ECD does not have any measurement iss

U.S. Environmental Protection Agency 
Horiba MEXA-1100QL Evaluatio

Results

U.S. Environmental Protection Agency 
Evaluation of Horiba MEXA-1100

• Horiba loan EPA a MEXA-1100QL quantum ca

laser based N

2O measurement instrument for 

evaluation.

• EPA GC-ECD is not yet operational, therefore 

1100QL performance was evaluated against bblends of CO CO blends of CO, CO

2, water N water, 

N

2O and N O, and

N

2.

• The evaluation was identical to pervious evalu

of NDIR and FTIR N

2O analyzers performed b

• The purpose was to validate the analyzers’ ab

compensate for CO, CO

2, and water interferen

U.S. Environmental Protection Agency 
Evaluation of Horiba MEXA-1100

• The MEXA-1100QL performed with effe

no span drift over days of operation and 

minimal zero drift.

• The instrument consistently read ambie

b k dN ac

kgroun

d

N

2O 312 as

± 1 b pp

b.

• Interference check results:

– -9 ppb response on 15.19% CO

2

– 2 ppb response on 485 ppm CO

U.S. Environmental Protection Agency 
0.6

Comparison of N2O Concentrations Across Different Bag Blends of CO2 a

0.5

1.461 % CO2194 8 ppmCO

1.948 % CO2292 2 ppmCO

TargetN2OConcentration = 0.391 ppm

H2OConcentration = 2.2%

0.30.4

ntraiton (ppm)

292.2 ppmCO 194.8 ppmCO

0.2

N O Conce 2n

0.00.1

Bag 5 Bag 6

U.S. Environmental Protection Agency 

Calculated Blend Horiba MEXA-1100QL
0.8

Comparison of N2O Concentrations Across Different Bag Blends of CO2 an

TargetN OConcentration 0 587 ppm

0.60.7

0.97 % CO287.3 ppm CO

1.457 % CO2

116.5 ppmCO

0.777 % CO2

68.0 ppm CO

0 % CO2

193.9 ppmCO

1.457 % CO2

0 ppmCO

1.457 % CO2

193.6 ppmCO

1.457 % CO2

291.3 ppmCO

1.942 % CO

194.2 ppm

TargetN2OConcentration = 0.587 ppmH2OConcentration = 2.2%

0.40.5

entraiton (ppm)

0.20.3

N O Conc 2e

0.00.1

Bag 8 Bag 4 Bag 1 Bag 9 Bag 2 Bag 7 Bag 12 Bag 11 

U.S. Environmental Protection Agency 

Bag 8 Bag 4 Bag 1 Bag 9 Bag 2 Bag 7 Bag 12 Bag 11 

Calculated Blend Horiba MEXA-1100QL
350

Comparison of CO Concentrations Across Different Bag Blends of N2O, CO

and CO

300350200250

iton (ppm)

100150

CO Concentra

0

50

B 1 B 2 B 3 B 4 B 5 B 6 B 7 B 8 B 9 B 10 B 

U.S. Environmental Protection Agency 

Bag 1 Bag 2 Bag 3 Bag 4 Bag 5 Bag 6 Bag 7 Bag 8 Bag 9 Bag 10 Bag 

Calculated Blend Horiba AIA-721 NDIR Analyzer
2 5

Comparison of CO2 Concentrations Across Different Bag Blends of N2O, CO

and CO

2.02.51.5

traiton (%)

1.0

CO

2 Concen

0.00.5

B 1 B 2 B 3 B 4 B 5 B 6 B 7 B 8 B 9 B 10 B 

U.S. Environmental Protection Agency 

Bag 1 Bag 2 Bag 3 Bag 4 Bag 5 Bag 6 Bag 7 Bag 8 Bag 9 Bag 10 Bag 

Calculated Blend Horiba AIA-722 NDIR Analyzer
MEXA-1100QL Measurement Error vs. 

Divider Generated Concentrations

Target Generated Concentration Measured Concentration Error

Divider Generated Concentrations

5.056 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%

U.S. Environmental Protection Agency 
Conclusion

• The MEXA-1100QL performed very well and d

not appear to show any susceptibility to CO, C

water interference.

• Based on CO and CO

2 measurement error, we believe that the bulk of the associated N

2O measurement error is due to bag blending erro

( i f 5% f ll i ) (maximum error o

f 5%

for all species

).

• MEXA-1100QL out performs FTIR and NDIR 

previously tested by EPA.

• All i di ti th t th MEXA All indications are th

a

t the MEXA

-1100QL i 

1100QL is a 

accurate instrument for measurement of N

2O a

concentrations expected during light-duty chas

testing

U.S. Environmental Protection Agency 

.
MAHA QCL Evaluation Results

U.S. Environmental Protection Agency 
Evaluation of MAHA QCL Analyz

• Maschinenbau Haldenwang (MAHA) loaned E

MAHA QCL quantum cascade laser based N

2O 

measurement instrument for evaluation. measurement instrument for evaluation.

• EPA GC-ECD is not yet operational, therefore 

QCL performance was evaluated against bag of CO CO of CO, CO

2, water N water, 

N

2O and N O, and

N

2.

• The evaluation was identical to previous evalu

of QCL, NDIR, and FTIR N

2O analyzers perfor

EPA.

• The purpose was to validate the analyzers’ ab

compensate for CO, CO

2, and water interferen

U.S. Environmental Protection Agency 
Evaluation of MAHA QCL

• The instrument had issues with the computer that 

controlled the zero and span functions (a complicaconverting the instrument from 220 VAC to 110 VA

– S h d t b t d ll Span 

h

a

d

to 

be en

tere

d manually.

– During the evaluation we lost the ability to rezero the 

instrument.

– Zero/s

p y an drift issues and the inabilit

y to calibrate out t

could be the cause of the negative bias seen throughotesting.

• The instrument read ambient background N

2O as 3

ppb drifting down to 305 ppb over the course of thppb, drifting down to 305 ppb over the course of th

• Interference check results:

– 4 ppb response on 15.19% CO

2

– -2 ppb res

ponse on 485 ppm CO

U.S. Environmental Protection Agency 

pp p pp
0.9

Comparison of N2O Concentrations Across Different Bag Blends of CO2 a

T tN OC t ti 0 587

0.70.8

0.976 % CO287 8 ppm CO

1.457 % CO2116 5 ppmCO

0 % CO2195 4 ppmCO

1.467 % CO20 ppmCO

1.467 % CO2293 4 ppmCO

1.956 % CO2195 6 ppmCO

TargetN2OConcentration = 0.587 ppm

H2OConcentration = 2.2%

0.50.6

ntraiton (ppm)

87.8 ppm CON2ODiff ‐0.035

116.5 ppmCON2ODiff ‐0.010

195.4 ppmCON2ODiff ‐0.024

0 ppmCON2ODiff ‐0.032

293.4 ppmCON2ODiff ‐0.038

195.6 ppmCON2ODiff ‐0.017

0 20.30.4

N O Conce 2n

0.00.10.2

B 8 B 1 B 9 B 7 B 12 B 11 

U.S. Environmental Protection Agency 

Bag 8 Bag 1 Bag 9 Bag 7 Bag 12 Bag 11 

Calculated Blend MAHA QCL
350

Comparison of CO Concentrations Across Different Bag Blends of N2O, C

and CO

300200250

iton (ppm)

100150

CO Concentra

0

50

U.S. Environmental Protection Agency 

Bag 1 Bag 7 Bag 8 Bag 9 Bag 10 Bag 11 

Calculated Blend Horiba AIA-721 NDIR Analyzer
2.5

Comparison of CO2 Concentrations Across Different Bag Blends of N2O, C

and CO

2.01.5

ntraiton (%)

1.0

CO

2 Conce

n

0.00.5

Bag 1 Bag 7 Bag 8 Bag 9 Bag 10 Bag 11 

U.S. Environmental Protection Agency 

Bag 1 Bag 7 Bag 8 Bag 9 Bag 10 Bag 11 

Calculated Blend Horiba AIA-722 NDIR Analyzer
Conclusion

• Th MAHA QCL f d ll d d The MAHA QCL performed well and does not appe

show any susceptibility to CO, CO2, or water interf

• Based on CO and CO2 measurement error (maxim

3%) we believe that some of the associated N 3%), we believe that some of the associated N2O measurement error is due to bag blending error.

• It should also be noted that the average 5% negati

on N2O measurement is influenced by the inability 

2 y y properly zero/span the instrument after the initial 

zero/span at the start of the testing.

– The negative drift is evident when looking at the increa

negative bias in the order the bags were read: negative bias in the order the bags were read: 7 8 9 

7, 8, 9, 

12, and 1.

– It is also noted in the decrease in ambient concentratio

the course of the testing: 320, 310, 305 ppb.

U.S. Environmental Protection Agency 
Conclusion cont.

• Th MAHA QCL f FTIR d NDIR The MAHA QCL out performs FTIR and NDIR

previously tested by EPA.

• All indications are that if the instrument zero/sp

f ti ki l th MAHA QCL functions are working properly, the MAHA QCL

should be a viable, accurate instrument for measurement of N2O at the concentrations exp

during light during light-duty chassis testing duty chassis testing.

• EPA intends to re-evaluate this instrument afte

manufacturer has resolved issues regarding th

power configuration for use in North America power configuration for use in North America.

• We will update our results with this instrument 

our re-evaluation.

U.S. Environmental Protection Agency 
Sensors LASAR Evaluation Resu

U.S. Environmental Protection Agency 
Evaluation of Sensors LASAR

• Sensors loaned EPA a LASAR scanning laser 

N

2O measurement instrument for evaluation.

• EPA GC-ECD is not 

yp , et o

perational, therefore 

LASAR’s performance was evaluated against blends of CO, CO

2, water, N

2O, CH

4, and N

2.

• The evaluation was identical to 

previous evalu

of NDIR, FTIR, and QCL N

2O analyzers perfor

EPA.

• The purpose was to validate the analyzers’ ab

compensat f CH e 

for CH CO CO d t

4, CO, CO

2, an

d wa

ter 

interference.

• The LASAR is advertized as not being suscep

it f f h t i

U.S. Environmental Protection Agency 

any in

ter

ference 

from ex

haus

t gas species.
Evaluation of Sensors LASAR

• The analyzer was set up for the followin

ranges:

– N

2O calibrated for 0 – 50 ppm

– CH

4 calibrated for 0 – 100 ppm

– NH

3 calib t d f 0 libra

t

e

d

for 

0

– 100 ppm

– CO

2 calibrated for 0 – 30 %

–

H

2O calibrated for 0 O calibrated for

0

– 30 %

U.S. Environmental Protection Agency 
Evaluation of Sensors LASAR

• CO and CO

2 bag concentrations were mea

with Horiba MEXA 700 series NDIR analyz

• CH

4 measurement was performed using th

LASAR system.

• The LASAR performed ith effecti el no s

The LASAR performed with effecti

vely no s

drift over days of operation and minimal zedrift.

• The instrument consistently read ambient 

background N

2O as 338 

± 1 ppb.

U.S. Environmental Protection Agency 
Evaluation of Sensors LASAR

• Interference check results:

– 21 ppb response on 15.42% CO

2

– 25 ppb response on 475 ppm CO 25 ppb response on 475 ppm CO– 37 ppb response on 24 ppm CH

4

– 25 ppb response on pure N

2

• Instrument was not zero calibrated at EPA

– Response from CO

2 and CO is the same as N

2

• Indicates no interference Indicates no interference.

• Response could be zero offset or N

2O contaminatio

balance gas.

• CH

4 response 12 ppb higher than N

2

U.S. Environmental Protection Agency 

CH

4 response 12 ppb higher than

N

2.
0.6

Comparison of N2O Concentrations Across Different Bag Blends of CO2 

TargetN2OConcentration = 0.391 ppm

0.5

1.465 % CO2195.3 ppmCO

N2ODiff 0.011 ppm

1.952 % CO2

292.9 ppmCON2ODiff 0.008 ppm

g 2 pp

H2OConcentration = 2.3%

0.30.4

entraiton (ppm)

2 pp

0 10.2

N O Conc 2e

0.00.1

Bag 5 Bag 6

U.S. Environmental Protection Agency 

Calculated Blend LASAR
0.9

Comparison of N2O Concentrations Across Different Bag Blends of CO2, C

and CH4

TargetN2OConcentration = 0.586 ppmH OC t ti 2 3%

0.70.8

0.977 % CO287.9 ppm CO

N2ODiff 0.027

1.466 % CO2

117.3 ppmCON ODiff 0 011

0.782 % CO268.5 ppm CON ODiff 0 001

19.9 N2O

H2OConcentration = 2.3%

0 40.50.6

centraiton (ppm)

N2ODiff ‐0.001 N2ODiff 0.011

0.20.30.4

N O Con 2

0.00.1

Bag 4 Bag 1 Bag 2 Ba

U.S. Environmental Protection Agency 

Calculated Blend LASAR
350

Comparison of CO Concentrations Across Different Bag Blends of N2O, CO

and CO

250300200

raiton (ppm)

100150

CO Concent

0

50

Bag 1 Bag 2 Bag 3 Bag 4 Bag 5 

U.S. Environmental Protection Agency 

Calculated Blend MEXA
2 5

Comparison of CO2 Concentrations Across Different Bag Blends of N2O, C

and CO

2.02.51.5

traiton (%)

1.0

CO

2 Concen

t

0.00.5

B 1 B 2 B 3 B 4 B 

U.S. Environmental Protection Agency 

Bag 1 Bag 2 Bag 3 Bag 4 Bag 5 

Calculated Blend MEXA
Conclusion – Part 1

• The Sensors LASAR performed very well and does 

appear to show any susceptibility to CO, CO

2, CH

4

water interference.

• B d CO d CO Base

d on CO an

d CO t b 

2 measuremen

t error, we 

b

e

that the bulk of the associated N

2O measurement e

due to bag blending error (maximum error of 6% fos

p ) ecies

).

• LASAR out performs FTIR and NDIR previously te

EPA.

• Results are com

parable to Horiba MEX

A-1100 QL 

previously tested by EPA.

• All indications are that the LASAR is a viable, accu

instrument for measurement of N

2O at the concent

expected during light duty chassis testing

U.S. Environmental Protection Agency 

expected during light

-duty chassis testing.
Exhaust Emissions Analysis - Over

• EPA used their RepTruck repeatable vehicle to perform several 505 c

evaluate analyzer performance

• Three “stabilized” tests were performed in addition to a “cold” and “ho

505’s.

• Th CVS eFl t owra e was nomi ll 550 inally 550 scfm

• The Sensors analyzer evaluated was able to measure N

2O, CH

4, CO

2

H

2O. 

• Horiba bench results were also recorded.

• The Sensors analyzer was mounted on a portable cart with a two The Sensors analyzer was mounted on

a portable cart with

a two-way 

way 

installed on the sample port to allow switching between ambient and tbag. 

• The unit was a 19” rack-mount (3U or 4U form) with a depth of approx

24”

• The sample bag line was installed with a quick disconnect to allow the 

to remove the line from the Horiba bench to connect to the Sensors s

• 10 Hz data was collected from the Sensors instrument

U.S. Environmental Protection Agency 
Exhaust Emissions Analysis – Purp

• N

2O measurement evaluation

– Measure actual exhaust data– Repeatability of stabilized cycles– Capture “Cold” & “Hot” start emissions– Evaluate response time and stabilization– Overall Analyzer Performance

U.S. Environmental Protection Agency 
Exhaust Emissions Analysis – Res

• The instrument experienced instability issues w

was moved to the test cell. Unfortunately we halready performed the first two stabilized tests d t ti t i t ld t t th due 

to time cons

train

ts could no

t repea

t them

• Data from the first two stabilized tests were ev

but upon further investigation by the instrumen

manuf t th i t bilit d th d t 

fac

turer the ins

t

ability ma

de the 

d

a

ta uns

for any meaningful analysis. This instability diprovide insight into the functioning of the instru

and would be useful as a diagnostic tool and would be useful as

a diagnostic tool.

• The “Cold” and “Hot” start tests provided us 

additional information on response time and 

stabilization

U.S. Environmental Protection Agency 
Instrument Instability

• Th f t fi d th t th f th i t bilit 

The manufacturer confirmed that the source of the instability w

spectrometer temperature not being stabilized after the instrumfirst moved to the test cell. The instrument had been off for aptwo hours prior to its installation in the test cell.

• This instability is evident from the Tau parameter (dynamic me

of the path-length and resonance quality at 10Hz) and the ValMparameter (dynamic measurement of the variation of light sour

at 10H ) Th t t bi d i t i l di 

t 10Hz). These two parameters are combined into a single di

Normalized which is plotted on the following graph.

5/24/2012 U.S. Environmental Protection Agency 
5/24/2012 U.S. Environmental Protection Agency

Graph supplied by Sensors Inc.
Determining Signal Stability

• Th f t i d d t f th thi d t bili d t t 

The manufacturer reviewe

d

d

ata for the thi

r

d stabilize

d test an

and “Hot” start 505’s and re-plotted the graphs. The instability occurred in the first two tests rendered that data unusable.

• In addition to the raw 10 Hz data a 10 In addition to the raw 10 Hz data

a 10-second moving average 

second moving average 

plotted on the graph. This averaged signal is constructed from boxcar average filter where the dynamic portion consists of tesconsecutive observations (1 second of data) against a +/- 2 sig

with i b i 1 t d d d i ti i f th N ith sigma 

b

eing 

1 stan

dar

d

deviation noise of the 

N O i l 

2

O signal 

7.5ppb). If 5 consecutive observations deviate from the boxcacalculated for N

2O by more than +/- 2 sigma the boxcar averag

z

e or

o.

• Once the 10-second signal is stabilized the 30-second average 

second signal is calculated along with the 1 sigma standard dethe averaged signal. These results are presented at the bottom graph.

5/24/2012 U.S. Environmental Protection Agency 
5/24/2012 U.S. Environmental Protection Agency

Graph supplied by Sensors Inc.
5/24/2012 U.S. Environmental Protection Agency

Graph supplied by Sensors Inc.
5/24/2012 U.S. Environmental Protection Agency

Graph supplied by Sensors Inc.
Exhaust Emissions Analysis Summary Table

Test #1* Test #2* Test #3 Test #4 

Analyzer

N2O

(ppm)

CH4

(ppm)

CO2

(%)

CO

(ppm)

N2O

(ppm)

CH4

(ppm)

CO2

(%)

CO

(ppm)

N2O

(ppm)

CH4

(ppm)

CO2

(%)

CO

(ppm)

N2O

(ppm)

CH4

(ppm)

CO2

(%)

CO

(ppm)

N2O

(ppm)

LASAR 0.024 0.210 0.737 NA 0.021 0.197 0.684 NA 0.014 0.183 0.741 NA 0.583 1.476 0.801 NA 0.203 MEXA NA 0.373 0.725 7.498 NA 0.328 0.727 9.004 NA 0.276 0.722 4.355 NA 1.579 0.776 125.603 NA 

CH4

Intfrn

(ppb)

CH4

Intfrn (%

of Meas)

Test #1 0.2 0.94%Test #2 0.2 0.83%Test #3 0.1 0.69%Test #4 0.8 0.14%

Test #5 0 4 0 22%

• The calculated interference from CH

4 for all cycles was less than 1% of measure

Test #5 0.4 0.22%

*LASARAnalyzerUnstable

U.S. Environmental Protection Agency 
Analyzer Performance

• The analyzer was able to discriminate nearly a 10 ppb differen

between the bag and ambient measurements for Test #3

• Standard deviations were approximately 1ppb for processed re

(not including Test #4 second measurement cycle) (not including Test #4 second measurement cycle)

• Test #4 & #5 response times (t10 – t90) were within 4 seconds o

second and third measurement cycles

• Test #4 & #5 signal response was within +/- 2% of final reading 

seconds on second and third measurement cycles seconds on second and third measurement cycles

• Cycle times for sample and ambient measurements averaged 

minutes

• The calculated interference from CH

4 for all cycles was less th

measurement

• Bag sample valve opening contamination is being investigated 

by manufacturer

U.S. Environmental Protection Agency 
Conclusion – Part 2

• Temperature stability is critical to the proper functioning 

LASAR

• The RD diagnostic is an effective tool of determining an

stability

• Averaged readings eliminate noise from the signal witho

seriously degrading analyzer performance for response 

• Once stabilized the Sensors LASAR analyzer performed 

exceptionally well.

• Response time and reading stabilization period were we

what is generally required in a light-duty test environme

• Calculated interference from CH Calculated interference from CH was less than 1% of 4 was less than 1% of measurement for all cycles.

• The physical dimensions of the LASAR would facilitate 

installation into most if not all analytical benches used in 

U.S. Environmental Protection Agency 
Addendum – FFT of LASAR N2O Data at Ambient

0.4

0 25

0.3

0.35

A

Dominant frequency occurs at f = 0Hz

Amplitude = 338.9 ppb

0.15

0.2

m

0.25

p

li

t

u

N2O 

0

0.05

0.1

0 1 2

3

4

5

6

d

e

• FFT performed on 10 Hz data • RMS of Signal = 338.3 ppb

-0.05

0 1 2

3

4

5

6 Frequency (Hz)

U.S. Environmental Protection Agency 

• Mean of Signal = 338.2 ppb