Improving OMI NOImproving OMI NO22 retrievals retrievals over biomass burning: over biomass burning:

towards a measurement-towards a measurement-based AMFbased AMF

N. Bousserez, R. V. Martin, L. N. Lamsal, J. Mao, R. Cohen, and B. R. Anderson

NONO22 retrieval retrieval

Ωv = Ωs

/AMF

Ωs = Slant ColumnΩv = Vertical Column

AMF = Air Mass FactorSpectral fitting

Radiative transfer calculation

Scattering weights(Radiative transfer model + model output)

Shape factor: normalized NO2 profile(model output)

Geometric correction

Uncertainties dominated by errors in AMF ~30-55 % over polluted area (Boersma et al. 2004)

QuestionsQuestions

Fires are random events that cannot be easily simulated in real-time in models.

Fires emit important quantities of NOx and aerosols.

Impact of fire emissions on AMF calculation?

ARCTAS 2008 experimentARCTAS 2008 experiment

Summer phase (June, 18 - July, 13) Boreal forest fires over central Canada DC-8 measurements:

NOx concentrations

Aerosol optical properties

NASA DC-8

DC-8 flight tracks

Total number of fires

DABEX 2006 experiment DABEX 2006 experiment (AMMA SOP-0)(AMMA SOP-0)

• Dry season (Jan., 13 – Feb., 2)• Savannah fires• FAAM BAe 146 aircraft:

NO2 measurementsAerosol optical properties

• AERONET stations:Aerosols optical properties

FAAM BAe 146

FAAM BAe 146 flight tracks

Total number of fires

Modeling toolsModeling tools

LIDORT radiative transfer model Multilayer atmosphere with multiple scattering (discrete ordinate

method) 0.5 km vertical resolution INPUTS: viewing geometry, cloud fraction, cloud pressure, surface

albedo, aerosol optical properties, NO2 shape profile

GEOS-Chem near-real time simulation: GEOS-Chem v8-01-01 Modifications:

◦ David Streets 2006 emissions over SE Asia & China◦ FLAMBE daily biomass burning emissions

GEOS-5 Metfields Horizontal Grid: 2º lat x 2.5º lon Vertical Grid: Reduced 47 layers

Provide NO2 shape profiles + aerosol optical properties profiles

GC vs. aircraft measurementsGC vs. aircraft measurements

aircraft meas.GC

Shape factor Shape factor

Extinction(km-1) Extinction(km-1)

ARCTAS DABEX

(measurements impacted by biomass burning only)

Aerosol sensitivity analysisAerosol sensitivity analysis

ARCTAS DABEX

Aerosol correction factor

GC extinction GC extinction

Aerosol correction factor

CALIPSOCALIPSO

aerosols

Aerosol cor =AMF

AMF w/o aero

Mean: 3%Mean: -18%

shielding effect

Aerosol correction = 1-α.AOD + Cld frac.AOD

Needs for OMI AOD at 440 nm

Combine with AI to detect elevated aerosol layer?

Local measurement-based correction for Local measurement-based correction for aerosols?aerosols?

Aerosol artefact: Aerosol layer increases cloud fractionIncreases aerosol correction

Cloud impact on aerosol correction African savanna aerosol correction

R = 0.81

Y = 0.91 X

Cloud fraction 1 – 0.18 AOD + AOD*Cloud fraction

Ae

roso

l co

rre

ctio

n

Ae

roso

l co

rre

ctio

n

Shape factor Shape factor errorserrors

• Space & time variability of emissions

Shape factors:

GC pixel

over fire

• Representativeness errors

Standard simulations use climatology We use a daily biomass burning inventory

GC pixel

(MODAPS)

Shape factor correction dominates BB Shape factor correction dominates BB correctioncorrection

-38% -32%

-62% -69%

DABEX

ARCTAS

Mean AMF correction:

Mean AMF correction:

shape factor bb correction (shape factor + aerosol) bb correction

Shape factor correction only ~ total BB correction

Shape factor cor =AMF w/o bb

AMF

Development of a measurement-based shape factor Development of a measurement-based shape factor

correctioncorrection

A B C

NO2 Correction = C

A

ΔNO2 = A - B

B

shape factor

retrieved profile

GC-derived relationship

true profile

profile w/o bb

“perfect” retrievalreference column

DABEX

Orig =OMI DP_GC

New = OMI w/ measurement-based AMF OrigΔNO2 =

New – Orig

Proof of conceptProof of concept

Orig MODIS AOD

ΔNO2

06/30-07/10 average

New (measurement-based AMF)

Temporal correlation

Indirect validation: OMI-derived vs. ground-based surface Indirect validation: OMI-derived vs. ground-based surface concentrationsconcentrations

€

r = 0.60

€

r = 0.51

Orig (OMI DP_GC)

ConclusionConclusion

Canadian boreal fires: aerosol correction increases AMF but negligible (mean ~ +3%)

Western Africa savanna fires: aerosol correction decreases AMF (mean ~ -18%) shielding effect due to an elevated aerosol layer.

Results show paths toward a measurement-based correction for aerosols over savanna fires.

Shape factor perturbation dominates the AMF correction associated with fire emissions.

Development of a measurement-based AMF.First evaluations show improvements

compared to the original product.

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