Monitoring True NO2Monitoring True NO2Experience at Great Smoky Mountains Experience at Great Smoky Mountains with an LED Photolytic Converterwith an LED Photolytic Converter

John D. RayAir Resources Division, National Park Service, Denver, CO

Jim RenfroGreat Smoky Mountains NP, National Park Service, TN

Roger Tanner Tennessee Valley Authority, Muscle Shoals, AL

Martin BuhrAir Quality Design, Golden, CO

Experience Your AmericaExperience Your AmericaNational Park ServiceAir Resources Division

Discussion TopicsDiscussion Topics

•• Site and station informationSite and station information

•• Instrument design and layoutInstrument design and layout

•• Some data and comparisonsSome data and comparisons

•• Instrument assessmentsInstrument assessments

Experience Your AmericaExperience Your AmericaNational Park ServiceAir Resources Division

View NW of Look RockGreat Smoky Mountains NP

Great Smoky MountainsNational Park

Look Rock

TN

NC

Monitoring StationMonitoring Station

SoutheasternUnited States

Look Rock Monitoring StationLook Rock Monitoring StationGreat Smoky MountainsNational Park

•• NCORE: NCORE: O3, NOy, NO, NO2,O3, NOy, NO, NO2,

SO2, CO, PM2.5, SO4, BCSO2, CO, PM2.5, SO4, BC

•• CASTNet: CASTNet: filter pack, metfilter pack, met

•• IMPROVE: IMPROVE: fine, course PMfine, course PM

filter samples for visibilityfilter samples for visibility

•• Web camera; nephelometerWeb camera; nephelometer

View to northeast

IMPROVE

CASTNet

NCORE

Understanding NOUnderstanding NO22: Definitions: Definitions

NOy

= Σ

( NO + NO2

+ HNO3

+ organic nitrates + particulate nitrates + a few others )

NOy

is the sum of oxidized reactive nitrogen

NOx

= NO + NO2

(idealized)

NOz

= NOy

- NOx

Nitrogen Oxide Measurements at Look RockNitrogen Oxide Measurements at Look Rock

Mo converter

NO Chemiluminescence

analyzer

Photolytic converter

NO Chemiluminescence

analyzer

NO, NOx ’ by difference NO2 ’ NO, NO2 sum = NOx

DilutionCalibratorNO and NO2

TEI NOy Analyzer API NO2

Analyzer

External boxes

Measurement of NO2 using Photolysis

umbilical, up to 10 meters

Photolyticconverter

Temperaturecontrolledcritical orifice

Sample inlet

API Model 200EUNO instrument

Connect to theDilution calibrator

Weatherproof stainlesssteel inlet box

umbilical, up to 10 meters

Photolyticconverter

Temperaturecontrolledcritical orifice

Sample inlet

API Model 200EUNO instrument

Connect to theDilution calibrator

Weatherproof stainlesssteel inlet box

Measurement of NOMeasurement of NO2 2 using photolysisusing photolysis

High efficiency (~50-60% NO2 conversion)

Highly specific for NO2

Negligible radiant heating of the sample gas

Long light-source life (estimated >5,000 hours)

Power consumption: 30 W

Converter size: 5 cm (w) x 5 cm (h) x 15 cm (l)

LED Photolytic Converter

Particle filter

Temperature controlled flow orifice

Sample inlet

NO2

converter

Inside the External Converter BoxInside the External Converter Box

Implementation of NOImplementation of NO22 AnalyzerAnalyzer

Implementation works best with the converter located at the sample inlet.

Possible to locate the converter within the NO monitor, but must minimize the residence time of the ambient sample

Inlet box

NO Analyzer

10m tower

Nitrogen Oxides for Oct. to Dec. 2008Nitrogen Oxides for Oct. to Dec. 2008

••

Data generally as expected. NOData generally as expected. NOyy

> NO> NO22

> NO> NO••

Couple problem areas observed.Couple problem areas observed.

••

Difference between NODifference between NOyy

and NOand NO22

is variable.is variable.

Compare NOy and NOx for Oct. 2008Compare NOy and NOx for Oct. 2008

••

NONOxx

represents represents ““freshfresh””

emissions. emissions. PhotochemPhotochem active.active.

••

NONOyy

––

NONOxx

(called (called NONOzz) is ) is ““agedaged””

oxidized oxidized speciesspecies

0

5

10

15

Nitr

ogen

Oxi

des

(ppb

)

10/08/2008 10/15/2008 10/22/2008 10/29/2008DATE_TIME

Y NOx_ph NOy

Over period Oct. 2008 to Jan. 2009: Mean component % of NOyNOx 34%HNO3 12% NOy of other 49%p-NO3 5%

Component Fractions of NOyComponent Fractions of NOy

0

1

2

3

4

5

6

7

8

9

10

41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 1 2 3 4

Week of Year

Nitr

ogen

Oxi

des

(ppb

)

p-NO3 HNO3 NOx NOy

CASTNetHNO3 + P-NO3data

Aged Nitrogen Oxides for Oct. 2008Aged Nitrogen Oxides for Oct. 2008

••

At Look Rock, most of the NOy is agedAt Look Rock, most of the NOy is aged••

NOzNOz

is episodic; events lasting several days.is episodic; events lasting several days.

••

Negative Negative NOzNOz

a problem. Instrument balance?a problem. Instrument balance?

-5

0

5

10

15

NO

z (a

ged)

(p

pb)

10/08/2008 10/15/2008 10/22/2008 10/29/2008DATE_TIME

Ozone and Ozone and NOzNOz for Oct. 2008for Oct. 2008

••

Ozone and Ozone and NOzNOz

follow synoptic weatherfollow synoptic weather

0

10

20

30

40

50

60

70

80

Y

10/01/2008 10/08/2008 10/15/2008 10/22/2008 10/29/2008DATE_TIME

Y O3_PPB NOz_(NOy-NOx)

Weather Data for Oct. 2008Weather Data for Oct. 2008

••

Incorrect Incorrect NOzNOz

happens during rapid changes ofhappens during rapid changes ofsynoptic weathersynoptic weather

0

10

20

Y

10/08/2008 10/15/2008 10/22/2008 10/29/2008DATE_TIME

Y TMP_DEGC SWS_M_SNOz_(NOy-NOx)

Ozone to Ozone to NOzNOz Relationship for Oct. 2008Relationship for Oct. 2008

••

Weak ozone production from aged Weak ozone production from aged NOzNOz

air air massesmasses

••

Incorrect Incorrect NOzNOz

< 0 only when ozone low< 0 only when ozone low

Sample Data for Oct.2008 to Aug. 2009Sample Data for Oct.2008 to Aug. 2009

••

Agreement in NO is not perfect between Agreement in NO is not perfect between analyzersanalyzers

••

Instrument balance, calibrations, validation Instrument balance, calibrations, validation importantimportant

API

NO

-TE

I N

O

API NO high

TEI NO high

Frequency Distributions of NO and NOyFrequency Distributions of NO and NOy

••

NO and NONO and NOxx are nearly lognormalare nearly lognormal••

NONOyy

somewhere between normal and lognormalsomewhere between normal and lognormal

NO NOy

Diurnal Patterns for Oct. 2008Diurnal Patterns for Oct. 2008

•• Ozone and NO peak at different timesOzone and NO peak at different times

•• NONO22 and ozone peak in eveningand ozone peak in evening

NO Diurnal NO2 Diurnal

Ozone Diurnal

• Winter NO2 /NO ratio shows a daytime minimum of about 5• Summer NO2 /NO ratio shows a daytime minimum of about 2,

consistent with greater solar insolation and photochem.

PhotochemPhotochem NONO22/NO Diurnal Patterns/NO Diurnal Patterns

• Winter ratio shows a daytime minimum of about 30%• Summer ratio shows a daytime minimum of about 10%• In both seasons, the daytime air masses are photochemically

aged, with very aged air masses observed in the summer

Diurnal NOx Fraction of NOyDiurnal NOx Fraction of NOy

Winter 2008Winter 2008--2009 Diurnal Patterns2009 Diurnal Patterns

•• Variation probably dominated by dynamic effects; Variation probably dominated by dynamic effects; some photochemistry.some photochemistry.

•

Local ozone photochem production observed near solar noon, superimposed on a stronger transported ozone signal

Summer 2009 Diurnal PatternsSummer 2009 Diurnal Patterns

Seasonal Variation in NOSeasonal Variation in NO22

•• NONO22 concentrations are seasonalconcentrations are seasonal

•• Dependent on solar radiationDependent on solar radiation

NO

2_ph

NO

2_ph

• Photolytic NO2 measurements greatly enhancethe diagnostic strength of the data set.

• Observed NO2 /NO ratios are consistent with ourunderstanding of photochemistry; should serveas a good diagnostic for modeling efforts.

• Summertime observations suggest that at least a portion of the observed ozone is produced locally.

• Attention required to balance the independent systems.

SummarySummary