monitoring true no2 - us epacompare noy and nox for oct. 2008 • no x represents “fresh”...
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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