Air Monitoring Instrumentation Nitrogen Oxides (NOy) · Air Monitoring Instrumentation -Nitrogen Oxides (NOy) November 6, 2006 Technique Measurement using Nitric Oxide-Ozone Chemilumescence

Air Monitoring InstrumentationNitrogen Oxides (NOy)

David A. Neuschuler

Director of Engineering

Teledyne – API

November 6, 2006

November 6, 2006Air Monitoring Instrumentation - Nitrogen Oxides (NOy)

What is NOy

� Total Reactive Nitrogen

� Precursors in the formation of Ozone

� Definitions

NOy = NOz + NOx

NOx = NO + NO2

NOz = HNO3 + HONO + 2N2O5 + HO2NO2

+ PAN + NO3 + Organic Nitrates – but not NH3

� Some NOz compounds have short lifetimes

� NO2 specific analyzer required to measure NOz

“Collective name for oxidized forms of nitrogen in the atmospheresuch as nitric oxide (NO), nitrogen dioxide (NO2), nitric acid(HNO3), and organic nitrates; usually designated by NOy.” - AMS


Technique

� Measurement using Nitric Oxide-Ozone Chemilumescence analyzer

� Conversion of NOy species to NO

� Molybdenum ~325°C

� Gold with CO or H2 injection ~ 400°C

� Vitreous Carbon ~ 350°C

� Ferrous Sulfate

� Converter as near inlet as possible with no sample filter

� Requires trace level analyzer for useful measurement

� Minimizing residence time essential to good measurement


Simple Pneumatic Block Diagram

BYPASS PUMP PACK

REMOTE CONVERTER

PUMP

CAL GAS

INPUT

NO

NOY

MOLY

CONVERTER

UMBILICAL

TRACE LEVEL

CHEMILUMINESCENCE

ANALYZER

CALIBRATOR

PUMP


Analyzer Differences

Specification

or Characteristic

Standard

NOx Analyzer

Premium

NOx

Analyzer Purpose

LDL <400 ppt <50 ppt

zero drift 24 hours <500 ppt <100 ppt

zero drift 7 days <1000 ppt <200 ppt

Propylene reject. Ratio >20,000:1

Ethylene reject. Ratio >40,000:1

PMT Anode Sensitivity 2500 A/lm 3000 A/lm More sensitivity, higher SNR

Reaction Cell Non-plated Gold Plated Increased signal out

Flow Rate 500 ccm 1000 ccm Increased signal out

Nominal Cell Pressure 5" HgA 2.5" HgA Increased sensitivity

Autoref scheme

Autozero stop

sample flow

Autozero with

prereactor Improved hydrocarbon rejection


Inlet Materials(or how can we keep “It” from sticking)

� “It” = gasses that readily stick to surfaces especially nitric acid and ammonia

� Causes memory effect leading to excessive rise and fall times:

� Operation – over or under actual value, smear features

� Calibration – Elevated zeros, reduced spans

� Exacerbated by long tubing, low temperatures


Inlet Materials

Standard: ¼” stainless tubing, adapters and fittings

Field Testing:

� SilcoSteel® (hydrogenated amorphous silicon) coated, stainless for inlet and other NOy wetted surfaces, including body and inlet tubing of converter

� PFA bulkhead, cross and tubing to within ½” of converter inlet; converter inlet and body SilcoSteel® coated


Calibration

� Gases: Nitric, iPan, nPan, NO2, NO/GPT

� No SRM

� Nitric: very difficult to use

� N-propyl nitrate: difficult to obtain & questionable analog for nitric

� Iso-propyl nitrate: readily available

� Errors in verifying conversion efficiency using bottles

� Big cal gas flows required

� Can not run from common manifold

� Losses due to conditioning

� Must be VERY, VERY patient


Conditioning with 500 ppb NO2

0

200

400

600

800

1000

1200

8:24 9:36 10:48 12:00 13:12 14:24 15:36

Time

NO2 Concentration (ppb)

0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1

NO2 Norm

alized (peak for segment)

NXCNC1 (PPB)

NO2 Norm


Checking Converter Efficiency

� Gas Phase Titration (GPT) golden standard

� Auto-referencing - independent of NO or Ozone concentration

� Independent of MFC calibrations and matching

� NO/NO2, nPan or i-Pan bottles

� Limited by accuracy of bottles

� Limited by accuracy and linearity of MFCs

� Best to maintain MFC flows use ratio of bottles

� Check for contaminants in NO and other bottle


GPT vs. NO/NO2 gas Efficiency

Efficiency by GPT (100 ppbv)

-20

0

20

40

60

80

100

120

1 3 5 7 9

11

13

15

17

19

21

23

25

27

29

31

33

35

37

39

41

43

45

47

Time (min)

Concentration (ppbv)

NXCNC1 (PPB)

NOCNC1 (PPB)

N2CNC1 (PPB)

````NOx NO Efficiency

NO 100.15 99.19

NO + O3 99.58 43.26

delta 0.57 55.93 99.0%

Efficiency with NO & NO2 Bottles

80

90

100

110

120

130

140

1

12

23

34

45

56

67

78

89

100

111

122

133

144

155

166

177

188

199

210

221

232

243

254

265

276

287

298

309

320

Time (min)


NXCNC1 (PPB)

NOCNC1 (PPB)

N2CNC1 (PPB)

NO2 NO Ratio

Converter

Efficiency

Bottle Concentration (ppm) 49.50 50.90 0.97

Measured Concentration (ppb) 111.08 113.55

Corrected concentration (ppb) 114.22

Converter efficiency (%) 101%

101%Gas Bottles

99%GPT

EfficiencyMethod


iPan/nPan Efficiency

-100

0

100

200

300

400

500

600

1 7

13

19

25

31

37

43

49

55

61

67

73

79

85

91

97

103

109

115

121

127

133

139

145

Time (min)


NXCNC1 (PPB)

NOCNC1 (PPB)

N2CNC1 (PPB)

span at 500

ppb

nPAN bottle: 4.85 ppm (5%)

computed conv eff: 103%

iPAN bottle: 5.02ppm(5%)

computed conv eff: 102%


Interferences

� Water: no effect at zero, ~ 3% quench at span

� NH3: 1 – 5 %

� Ammines ??

� Hydrocarbons


Siting

� Be aware of nearby sources of:

� Hydrocarbons – roofing materials

� Ammonia – sewer vents

NSF UV Spectroradiometer – Barrow, AK Courtesy of Biospherical Instruments Pinnacle State Park, NY


Pinnacle State Park NOy ComparisonCourtesy of Atmospheric Sciences Research Center

University at Albany - State University of NY

-1.00

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

8/26 8/31 9/5 9/10 9/15 9/20 9/25 9/30 10/5 10/10

Date/Time

NOy

(ppb)

TECO

T-API


Acknowledgements & Bibliography

� Jim SchwabAtmospheric Sciences Research CenterUniversity at Albany - State University of NY

� Dirk FeltonDivision of Air Resources, NYS Department of Environmental Conservation,

� Measurement of NOy During SCOS97-NARSTO Dennis R. Fitz, University of California, Riverside, College of Engineering, Center for Environmental Research and Technology

� Review of M200AU: NOY Converter Design Theory and PracticeMartin Buhr, Regional Air Quality Council, Denver, CO, 1997

� AMS Glossary of MeteorologyAmerican Meteorological Societyhttp://amsglossary.allenpress.com/glossary/acknowledge

Documents

Air Monitoring Instrumentation Nitrogen Oxides (NOy) · Air Monitoring Instrumentation -Nitrogen Oxides (NOy) November 6, 2006 Technique Measurement using Nitric Oxide-Ozone Chemilumescence