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)

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

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

• 8 urban stations in Israel8 urban stations in Israel

• Half-hourly NOHalf-hourly NO22 & O & O33 concentrations concentrations

• Molybdenum convertersMolybdenum converters

Known issues with in situ NO2Summarize Dunlea et al.Dunlea et al.,

(ACP, 2007)

• 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

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

Δlat,lon < 0.1°

OMI VZA < 35°

fclrad < 50%

No correction

Δlat,lon < 0.1°

OMI VZA < 35°

fclrad < 50%

r = 0.61 (n=396)RMA: y = -1.28 + 0.90x

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%)

• 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.

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

Seasonal variation in surface and OMI NO2 columns

Weekly cycle in surface and OMI NO2 columns

Beirle et al. (ACP, 2004)

Diurnal cycle in NO2 columns?

NO2

NO2 : NOx

E

k

NO2+OH+M HNO3+M

Boersma et al., JGR, 2008

Diurnal cycle in surface-based and satellite NO2

n = 26

Δlat,lon < 0.1°

fclrad < 50%

Diurnal cycle in surface-based and satellite NO2

MAM

Diurnal cycle in surface-based and satellite NO2

END

Dutch OMI NO2 productDOMINO (www.temis.nl)

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)

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

NOx emissions show trends in the Middle East

1996-2002 1996-2006

Richter et al., 2005 van der A et al., 2008

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

GEOS-Chem direct

Effect of averaging kernel

NGC = ∑xGC,l

GEOS-Chem with AK

NGC,AK = ∑Al·xGC,l

NOMI = ∑Al·xtrue,l

OMI

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

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?

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

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

Checking GEOS-Chem background NO2 with OMI

• Qinbin paper

• Duncan paper

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

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

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°