1 inferring ground-level nitrogen dioxide concentrations from omi 14.12.2007 martin steinbacher,...
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Inferring Ground-level Nitrogen Dioxide
Concentrations from OMI
14.12.2007
Martin Steinbacher, Empa
Edward Celarier, SGT Inc.
Eric Bucsela, NASA GSFC
Edward Dunlea, CIRES
Joseph Pinto, U.S. EPA
Lok Lamsal, Randall Martin,
Aaron van Donkelaar
AGU Fall Meeting, 10-14 Dec 2007, San Francisco, CA
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Large regions lack sufficient in-situ data for air quality
NO2 associated with mortality
Limitations of current NO2
networks
Insufficient NO2 measurements
for air quality
NO2 measurements
contaminated by reactive
nitrogen species
Satellite-derived surface NO2
complement the existing ground-based
networks
NO2 monitoring networks
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Tropospheric column as a proxy for surface NO2
No profile information in
satellite measurements
70-90% of tropospheric
column in polluted boundary
layer
San Francisco
Los Angeles
Phoenix
Houston
Dallas
ChicagoToronto
OMI tropospheric NO2 column (standard product)
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Approach to derive surface NO2 from OMI
S Surface NO2
Tropospheric NO2 column
GO O
G
SS Ω
Ω
Information of NO2 profile shape
from GEOS-Chem
GEOS-CHEM
In situ
Texas AQS (Martin et al, 2004) O
FGG
GO Ω
1)Ω(λλΩ
λSS
GEOS-Chem
(2x2.5o)
OMI
(2x2.5o)
OMI
(0.2x0.2o)
G OO
O
O
Ω
Ωλ F free tropospheric NO2
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OMI-derived surface NO2 over North America
ppb
Seasonal average (SON)
Seasonal
mean
<0.1 ppbv in
rural areas
>10 ppbv in
urban areas
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Validation data sources for OMI-derived surface NO2
2NO
232231PSS2
J
][ROk][HOk][Ok[NO]][NO
DOAS, LIF, TILDAS
Chemiluminescent
NOx analyzer
Molybdenum
converter
Photolytic
converter
Research grade instruments
Photochemical steady
state NO2 (PSS-NO2)
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1 3
NO
k [O ][NO]
J
Typical air quality
monitor
JNO2 from Fast-J radiative transfer model
(Cloud filtered)
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Interference in molybdenum converter measurements
See Dunlea et al, 2007; Steinbacher et al., 2007 for
interference
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2 3
NOCF=
NO +alkyl nitrates+(0.95×PAN)+(0.35×HNO )
Compounds Conversion
efficiency
Experiments
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
Inlet loss of HNO3
35% for HNO3 inferred comparing with photolytic
converter
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Corrected molybdenum best reproduces photolytic NO2
Taenikon, Switzerland
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2 3
NOCF=
NO +alkyl nitrates+(0.95×PAN)+(0.35×HNO )
molybdenum
Photolytic
Photolytic
Molybdenum (>60%, R2=0.96)
Molybdenum cor. (< 4%, R2=0.95)
PSS-NO2 (6-20%, R2=0.86)
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Correlation between in-situ and OMI-derived surface NO2
296 stationsCorrelation 0.3 to 0.85Stronger correlation in polluted
areas
53 stations
Stations with PSS-NO2
> molybdenum not selected
OMI versus corrected in-situ OMI versus PSS-NO2
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General overall agreement
DJF MAM JJA SON
OMI
Cor.
in-situ
PSS-
NO2
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Comparison between in-situ and OMI-derived surface NO2
corrected in-situ
OMI-derived PSS-NO2
uncorrected in-situ
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Comparison between OMI and in-situ measurements according to land use type
OMI-derived surface NO2
is biased low by 6 to 40%Seasonal bias in OMI-
derived surface NO2
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Conclusions
Promising approach for inferring ground-level NO2 from
satellite
Surface measurements provide indirect validation of OMI
tropospheric NO2 column
Acknowledgement
This work is supported by NSERC and NASA
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Approach to derive surface NO2 from OMI
OFGG
GO Ω
1)Ω(λλΩ
λSS
GEOS-Chem
(2x2.5o)
OMI
(2x2.5o)
OMI
(0.2x0.2o)
Dallas, TX
G
O
O
S → Surface NO2
→ Tropospheric NO2 column
F→ free tropospheric NO2 column
O
O
Ω
Ωλ
SO
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Approach to derive surface NO2 from OMI
O
O
Ω
Ωλ
F→ free tropospheric NO2 column
GO O
G
SS Ω
Ω
OFGG
GO Ω
1)Ω(λλΩ
λSS
( a )
( b )
percent difference (b – a)
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Interference in molybdenum converter measurements
Molybdenum Conv.
DOAS
OMI
GOME-2
SCIA
GOME
Results from Mexico City Metropolitan Area (MCMA) field campaign, 2003
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Interference for US and Canadian sites during OMI overpass time
Larger interference in summer
Larger interference in clean areas
Interference during OMI overpass time
can be up to a factor of 3 over land
CF=