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Ground-level nitrogen dioxide concentrations Ground-level nitrogen dioxide concentrations
inferred from the satellite-borne Ozone inferred from the satellite-borne Ozone
Monitoring InstrumentMonitoring Instrument
Lok Lamsal and Randall Martin with contributions from Martin Steinbacher, Empa Edward Celarier, SGT Inc. Eric Bucsela, NASA GSFC Edward Dunlea, CIRES Joseph Pinto, U.S. EPA
13.08.2007
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Nitrogen dioxide
Is a reddish-brown gas and has a sharp biting odor
Is a prominant toxic air pollutant
Current WHO guideline: 200 µg/m3 (hourly average), 40 µg/m3 (annual average)
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NOx sources
aircraft1.05%
stratosphere0.21%
fossil fuel55.25%
biomass burning13.65%
lightning12.60%
soil12.60%
biofuel4.62%
Surface sources: 85%
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NOx: Impacts on public health and the environment
Acid deposition
Toxic products
Visibility impairment Eutrophication
Health effects
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Ambient NO2 as indicator of toxic air pollution
Strong association between between NO2 and mortality.
NO2 strongly
correlated with other air pollutants
NO2 can serve as an
indicator of level of toxicity in air
VOC
PAH
Brook et al., 2007
Correlation of NO2 and PM2.5 with certain
PAH and VOC
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Ground-based NO2 measurements
NO2 measuring instruments:CLNOx
(molybdenum, photolytic), DOAS, LIF, TILDAS
Sparse fixed sites
Surface NO2 shows a large gradient
Don‘t reflect personal exposure to NO2
Satellite-derived NO2 would be very
useful
Not possible to retrieve surface NO2
from satellite
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Tropospheric column as a proxy for surface NO2
Tropospheric column retrieval from satellite
Strong relation between tropospheric columns and surface NOx
emissions
NO2 in the lower mixed
layer makes 70-90% contribution to tropospheric column
Aim: derive ground-level NO2 from OMI
San Francisco
Los Angeles Phoenix
Houston
Dallas
Chicago
Toronto
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NO2 from OMI
Launch 15th July 2004 onboard EOS-Aura
OMI instrument is from the contribution from NIVR and FMI
Spectral coverage: 270-500 nm
Ozone, NO2, SO2, HCHO, BrO, OClO,
cloud and aerosol properties Horizontal resolution ≥ 13 x 24 km2
Daily global coverage
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GEOS-Chem
GEOS-CHEM
In situ
Need of information on NO2
profile from a 3D model GEOS-Chem at 2x2.5,
version 7-03-06, 12:00-14:00 local time
GEOS-Chem NO2 profile
shape consistent with in situ measurements
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Approach to derive surface NO2
2
2
2 2NO
NNO N
O GEOS-CHEMO
OMI OMIS T X S
T
GEOS-CHEMIn situ
GEOS-Chem NO2 [ppbv]
2 2
tropopause
NO
surface
T NO dh
2
2
2 2NO
NNO N
O GEOS-CHEMO
OMI OMIS T X S
T
SATSAT
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Sensitivity studies: Effect of model profileOMI grids
GEOS-Chem grids
Error < 10%
in polluted
areaspolluted
unpolluted
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In situ NO2 measurements: Chemiluminescent NOx analyzer
Chemiluminescent NOx analyzer does not provide true NO2
NO + O3 → NO2* + O2
NO2* → NO2 + h
NO mode
NOx mode
NO2 → NO
NO2 = NOx - NO
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Comparison with DOAS measurements
OMI over pass time (12.00 to 14:00 local time)
Interference~50%
HNO3~60%
∑AN~10-30%
Mexico City
Apr 2003
Dunlea et al. 2007
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Comparison with photolytic analyzers
Taenikon/Switzerland
Jan-Dec 2000
Steinbacher et al. 2007
Interference:20-60%
PAN:30-50%
HNO3, particulate
nitrates
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Interference in chemiluminescent analyzers with molybdenum converter
Compounds Conversion
efficiency
Experiments
NO, NO2, ethyl nitrate ~ 100% Winer et al.,
1974
PAN 92% Winer et al.,
1974
HNO3, PAN, n-propyl
nitrate, n-butyl nitrate
≥98% Grosjean and
Harrison, 1985
Ammonia, gas phase
olefins, particulate
nitrate
No significant
interference
Dunlea et al.,
2007
Difficult issue: Loss of HNO3 on stainless steel of inlet
Difficult to quantify the conversion efficiency
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Correction of interference
Bias = 40%
Bias = 8%
Taenikon, Switzerland
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2 3
NOCF=
NO + AN+0.95×PAN+0.35×HNO
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Correction for interference for USA and Canada
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Comparison between OMI and in situ measurements
Selected 214 stations201 US and 13 Canada
Collocation criteriaRadius 10 km, time = 12:00 to
14:00 local time
► Mean correlation 0.51, maximum 0.86
► Stronger correlation in polluted areas
Correlation map
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Comparison between OMI and in situ measurements
►Uncorrected >
corrected by
up to a factor of 3
►OMI and corrected
in situ measurements
consistent
►summer minima
►OMI<corrected in
situ measurements
DJF MAM JJA SON
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Comparison between OMI and in situ measurements
J F M A M J J A S O N D
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Comparison between OMI and in situ measurements according to land type
Urban, suburban, rural
Mean bias -21 to -48%
Underestimation of tropospheric column by OMI
Seasonal bias in OMI retrievalsOMI-Chemiluminescent
bias=chemiluminescient
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Seasonal bias in OMI retrievals
33% -20% -58% -15%
DJF MAM JJA SON
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Conclusions
We derived ground-level NO2 from OMI using information from
the GEOS-Chem model.
OMI-derived surface NO2 is robust to model profile in polluted
areas. In situ measurements have significant interference from PAN,
alkyl nitrates, and HNO3
Following laboratory studies and field measurements, we developed a correction algorithm to the in situ measurements.
We compared OMI-derived surface NO2 with the corrected in
situ measurements from US and Canadian stations to validate our approach
OMI derived surface NO2 agrees to 21 to 48% with the corrected
in situ measurements. The remaining discrepancy is associated with the OMI retrievals. Submitted to JGR atmospheres
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