Measurement of NOy During SCOS97-NARSTO

Dennis R. Fitz

University of California, RiversideCollege of Engineering

Center for Environmental Research and Technology

ORGANIZATION

• NOy BACKGROUND

• CONVERTER-BASED INTERFERENCES

• NITRIC ACID

• TYPICAL DATA

• CONCLUSIONS

NOy IMPORTANCE

• Mass Balance– Quality control– Missing species

• Estimate Nitric Acid by Difference– Sum of other species– Scrub nitric acid and use a second converter

and analyzer channel

DEFINITIONS

• NOy = Reactive Oxidized Nitrogen (N2O not included)

• NOy = NO + NO2 +HNO3 + PAcN + HONO+ 2N2O5 + HO2NO2 + Organic Nitrates + NO3 + NO3

-

• (NOy)i = Catalytically Reduced NOy

• NOx = NO + NO2

• NOz = NOy - NOx

(NOy)i MEASUREMENT

• Chemiluminescent NO Analyzer

• (NOy)i Converter to NO Located Outside Without an Inlet Filter (to reduce HNO3 losses)– Heated Molybdenum (300°-350°C)

– Heated Gold (400°C) + CO (or H2)

– Heated Vitreous Carbon (350°C)– Ferrous Sulfate

INTERFERENCES

• Chemiluminescent Analyzer

• Converter

• Both have become more noticeable with commercial analyzers as they have become more sensitive

INTERFERENCES - ANALYZER

• Water Vapor- Quenching– Zero (sub ppb)– Span (can be 10 %)

• Methods to Minimize– Zero and/or Calibrate with Ambient Air

Scrubbed of NOy

– Method of Standard Addition

INTERFERENCES - HEATED CONVERTERS

• Variable Efficiency for Nitrogenous Species

• Conversion of Ammonia and Amines

• Conversion of Cyanides

MOLYBDENUM CONVERTER CHARACTERISTICS

• Ammonia Conversion

• “Memory Effect” (High NOy or Hydrocarbon Concentrations)– Long stabilization period– Elevated “zero” response

• Compound Selective Degradation

• Lowered Efficiencies at Atmospheric Pressure

INTERFERENCE TEST SYSTEM

NO-NOxANALYZER

ZEROAIR

0.05 LPM

HUMIDIFIERTRAP

VENT

VACUUMPUMP

PERMTUBEOVEN

CONVERTERNOx

MASS FLOWMETER

AMMONIA COVERTER EFFICIENCY FOR THERMOENVIRONMENTAL MOLY CONVERTER

56 ppb Ammonia - Dry

% NH3 Conversion Converter Temperature, C14.8% 31526.8% 3135.2% 3604.5% 376

26.6% 3145.2% 3709.5% 3652.5% 30111.9% Average

NITRIC ACID MEASUREMENT

• Use dual converters and scrub nitric acid (NA) using a denuder from the inlet of one to obtain NA by difference

• Problems– Difference between large numbers– Converter efficiencies must be exactly the same

for all NOy species and interferences

– NOy memory effect greater than NOy -NA

NITRIC ACID MEASUREMENT

NOy Converter

NOy Converter

NaCl Coated Filter

NO Analyzer

3- Way Solenoid Valve

NO Detector

External Converter Housing

0

1

2

3

4

5

6

7

950 1000 1050 1100 1150

Time, PST

An

aly

zer

Re

sp

on

se

, p

pb

NOy

NOy-NA

TYPICAL RESPONSE LAG DUE TO MEMORY EFFECT

To Zero Air 1005

Typical Measurements-AzusaSite: Azusa

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

7/13/97 18:00 7/14/97 0:00 7/14/97 6:00 7/14/97 12:00 7/14/97 18:00 7/15/97 0:00 7/15/97 6:00

NO

y an

d N

Oy-

(pp

b)

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

HN

O3

(ppb

)

NOy

NOy-

HNO3

Typical Results-AzusaSite: Azusa

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

9/3/97 12:00 9/4/97 0:00 9/4/97 12:00 9/5/97 0:00 9/5/97 12:00 9/6/97 0:00 9/6/97 12:00 9/7/97 0:00 9/7/97 12:00

NO

y an

d N

Oy-

(pp

b)

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

HN

O3

(ppb

)

NOy

NOy-

HNO3

HNO3 Comparison vs TDLASValid Data at Azusa

y = 0.295x + 1.7257

R2 = 0.4436

-5.0

0.0

5.0

10.0

15.0

0 5 10 15 20 25 30

TDLAS HNO3 (ppb)

NO

Y A

nal

yzer

NA

(p

pb

)

Typical Results- Simi ValleySite: Simi Valley

0

20

40

60

80

100

120

140

160

180

200

9/3/97 12:00 9/4/97 0:00 9/4/97 12:00 9/5/97 0:00 9/5/97 12:00 9/6/97 0:00 9/6/97 12:00 9/7/97 0:00 9/7/97 12:00

NO

y an

d N

Oy-

(pp

b)

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

HN

O3

(ppb

)

NOy

NOy-

HNO3

SMOG CHAMBER NOy -NA4/7/98

-50.0

0.0

50.0

100.0

150.0

200.0

250.0

4/7/988:00

4/7/989:00

4/7/9810:00

4/7/9811:00

4/7/9812:00

4/7/9813:00

4/7/9814:00

4/7/9815:00

4/7/9816:00

4/7/9817:00

4/7/9818:00

No

x, N

Oy,

NO

2, N

O (

pp

b)

TDLAS, NO2,Cal1

LANM, NOx,Cal1

STI_2, NOy,Cal1

STI_1, NOy,Cal1

BANN, NOy,Cal1

BARSTOW, NOy,Cal1

SVAL, NOy,Cal1

SOLM, NOy,Cal1

UCDC, NOy,Cal1

AZSA, NOy,Cal1

LANM, NO,Cal1

Irridiation started

NOy RESPONSE TO FILTERED AIR WITH NITRIC ACID REMOVED

-15.0

-10.0

-5.0

0.0

5.0

10.0

7/3/9800:00

7/4/9800:00

7/5/9800:00

7/6/9800:00

7/7/9800:00

7/8/9800:00

NA_1

NA_2

CONCLUSIONS

• Present converters have significant biases and interferences

• Frequent (hourly?) zero checks are needed to assess memory effect

• Routine converter efficiency checks for major NOy species and ammonia are needed

• Acid coated denuders should be tried to remove ammonia (but let all NA pass)