Folkert Boersma
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Transcript of Folkert Boersma
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Folkert BoersmaCollaborators: Daniel J. Jacob, Miri Trainic, Yinon Rudich, Ruud Dirksen, and Ronald van der A
Comparison of NOComparison of NO22 air pollution in Israeli cities air pollution in Israeli cities
measured from the ground and from measured from the ground and from SCIAMACHY and OMISCIAMACHY and OMI
Dutch OMI NO2 product
DOMINO (www.temis.nl)
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Motivation
Trends in emissions• Can we use satellite measurements of NO2 to obtain better estimates of NOx emissions?
Monitoring of a target polluter• Is tropospheric NO2 a proxy for near-surface NO2?
Boersma et al., Atmos. Environ., 2008
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Comparison of surface and satellite NO2
Different quantities and error budgets:• near-surface concentrations vs. trop. columns• point measurements vs. spatial average• interference from NOz vs. AMF errors
BUT: • Validation still sparse, especially on larger spatial and longer temporal scales• Allows for validation of diurnal cycle
Interference
• Ground-based instruments with molybdenum converter overestimate NO2 • Interference from HNO3, PAN, alkyl nitrates• Effect largest in summer (photochemistry) for regions downwind of sources
Schaub et al., ACP, 2006
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• 8 urban stations in Israel8 urban stations in Israel
• Half-hourly NOHalf-hourly NO22 & O & O33 concentrations concentrations
• Molybdenum convertersMolybdenum converters
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Known issues with in situ NO2Summarize Dunlea et al.Dunlea et al.,
(ACP, 2007)
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• Very little interference at 10:00 (fresh emissions, little photochemical processing yet)
• Interference modest at 13:30
• Interference correlates with ambient O3 concentration, but O3 itself does not represent an interference
What does this mean for urban, in situ NO2 ?
slope = 0.1
Israeli cities: no specific NO2 measurements available, but we have in-situ observed O3
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O3 = O3[13:30] – O3[10:00]
• Dunlea et al.: interference = 0.1 O3
• Two limiting cases: – no correction at all
– correcting NO2 at 13:45 as follows:
Interference correction based on in situ O3
slope = 0.09 slope = 0.24
slope = 0.10
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Δlat,lon < 0.1°
OMI VZA < 35°
fclrad < 50%
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No correction
Δlat,lon < 0.1°
OMI VZA < 35°
fclrad < 50%
r = 0.61 (n=396)RMA: y = -1.28 + 0.90x
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No correction
Δlat,lon < 0.1°
OMI VZA < 35°
fclrad < 50%
r = 0.54 (n=396)RMA: y = -0.68 + 0.92x
Uniform correction (-8%)
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• Assume well-mixed boundary-layer
• Extrapolate surface NO2 throughout the BL depth
• Seasonal variation in noontime BL depths over Israel from Dayan et al. [1988, 2002]
Boundary-layer columns from surface NO2
1091
790
608
DJF
MAM, SON
JJA
NO2 (ppb)
z (m)
Summertime subtropical high is associated with subsidence of FT air, “capping” the BL.
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Boundary-layer columns from surface NO2
Column-column comparison
No interference correction: y = -0.86 + 0.90 x
Interference correction: y = -0.35 + 0.94 x
Surface – OMI vs. BL column - OMI
No correction No correction
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Seasonal variation in surface and OMI NO2 columns
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Weekly cycle in surface and OMI NO2 columns
Beirle et al. (ACP, 2004)
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Diurnal cycle in NO2 columns?
NO2
NO2 : NOx
E
k
NO2+OH+M HNO3+M
Boersma et al., JGR, 2008
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Diurnal cycle in surface-based and satellite NO2
n = 26
Δlat,lon < 0.1°
fclrad < 50%
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Diurnal cycle in surface-based and satellite NO2
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MAM
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Diurnal cycle in surface-based and satellite NO2
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END
Dutch OMI NO2 productDOMINO (www.temis.nl)
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NOx emission inventories in need of verification
New set of emission inventories
• EDGAR (global)
• Streets et al. 2006
• EMEP (Europe)
Lin Zhang et al. (2008)
Konovalov et al., ACPD, 2008
GOME, SCIAMACHY (1996-2005)
EMEP (1996-2005)
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Trend 1996-2006 from GOME, SCIAMACHY
• Figure
NOx emissions show trends in the Middle East
Cairo + 1.3%/yrTehran + 6.1%/yrCalcutta + 2.2%/yrDelhi + 7.4%/yr
1996-2006
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NOx emissions show trends in the Middle East
1996-2002 1996-2006
Richter et al., 2005 van der A et al., 2008
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Effect of averaging kernel
),(
)(
bx
b
TM4M
aA ll
a: scattering weights
xTM4: TM4 NO2 profile
b: forward model parameters
MIGEOS-Chem with AK
GEOS-Chem direct
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GEOS-Chem direct
Effect of averaging kernel
NGC = ∑xGC,l
GEOS-Chem with AK
NGC,AK = ∑Al·xGC,l
NOMI = ∑Al·xtrue,l
OMI
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Effect of averaging kernel
OMI
GEOS-Chem with AK
GEOS-Chem direct
r (gc,omi) = 0.71
r (gc_ak,omi) = 0.75
Ngc = 0.87
Ngc_ak = 0.93 (+7%)
Nomi = 1.09
GEOS-Chem direct
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GCl
lGCl
NM
xa
)(
,
TM4x
GCTMTM
llGCl
NNS
xa
4
4
,
44 TM
GC
TM
GC
N
N
S
S
4
4)(TM
TM
N
SM TM4x
Write NGC,AK > NGC differently:
Definition of tropospheric air mass factor:
Substitute tropospheric air mass factor:
Or ( SGC = scatt. weights · GEOS-Chem NO2 profile ):
What does NGC,AK > NGC mean?
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What does NGC,AK > NGC mean?
44 TM
GC
TM
GC
N
N
S
S
Mean NO2 profiles over Middle East for 1-7 February 2006 from TM4 and GEOS-Chem
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Correcting for background NO2
Can we simply subtract UT NO2 at mid-latitudes?
Lin Zhang et al., 2008Rynda Hudman et al., JGR, 2007
Randall Martin, 2006
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Checking GEOS-Chem background NO2 with OMI
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• Qinbin paper
• Duncan paper
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Comparison of ground-based to GOME NO2
Ordonez et al. (ACP, 2006)
• Compares 7 years of data over Po Valley to GOME NO2• Regional comparison (~10.000 km2)• Struggles with interference for ground-based stations
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Comparison of ground-based to SCIAMACHY NO2
Blond et al. (2006)
• Compares 1 year of data over northwestern Europe to SCIAMACHY NO2
• Regional comparison (1.800 km2)• No interference correction for ground-based stations• Best agreement for rural stations
All stations
Rural stations
Differences attributed to (lack of) spatial representativity of stations
Annual mean 2003
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Boundary-layer columns from surface NO2
y = -0.35 + 0.70 x
If Δlat,lon < 0.1° as for OMI:
r = 0.65, n = 32
y = -0.47 + 0.93x
Surface – SCIAMACHY vs. BL column - SCIAMACHY
No correction No correction
y = -0.32 + 0.82 x
n = 135 Δlat,lon < 0.25°