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Improving OMI NO 2 retrievals over biomass burning: towards a measurement-based AMF

Improving OMI NO 2 retrievals over biomass burning: towards a measurement-based AMF. N. Bousserez, R. V. Martin, L. N. Lamsal, J. Mao, R. Cohen, and B. R. Anderson. NO 2 retrieval. Ω v = Ω s /AMF. Ω v = Vertical Column. Ω s = Slant Column. Spectral fitting. AMF = Air Mass Factor.

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Improving OMI NO 2 retrievals over biomass burning: towards a measurement-based AMF

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  1. Improving OMI NO2 retrievals over biomass burning: towards a measurement-based AMF N. Bousserez, R. V. Martin, L. N. Lamsal, J. Mao, R. Cohen, and B. R. Anderson

  2. NO2 retrieval Ωv = Ωs /AMF Ωv = Vertical Column Ωs = Slant Column Spectral fitting AMF = Air Mass Factor 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)

  3. Questions • Fires are random events that cannot be easily simulated in real-time in models. • Fires emit important quantities of NOxand aerosols. Impact of fire emissions on AMF calculation?

  4. ARCTAS 2008 experiment • Summer phase (June, 18 - July, 13) • Boreal forest fires over central Canada • DC-8 measurements: • NOx concentrations • Aerosol optical properties Total number of fires NASA DC-8 DC-8 flight tracks

  5. DABEX 2006 experiment (AMMA SOP-0) • Dry season (Jan., 13 – Feb., 2) • Savannah fires • FAAM BAe 146 aircraft: • NO2 measurements • Aerosol optical properties • AERONET stations: • Aerosols optical properties Total number of fires FAAM BAe 146 FAAM BAe 146 flight tracks

  6. Modeling 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

  7. GC vs. aircraft measurements (measurements impacted by biomass burning only) DABEX ARCTAS aircraft meas. GC Shape factor Shape factor Extinction(km-1) Extinction(km-1)

  8. Aerosol sensitivity analysis ARCTAS DABEX Mean: 3% AMF Aerosol cor = Mean: -18% AMF w/o aero Aerosol correction factor Aerosol correction factor shielding effect GC extinction GC extinction aerosols CALIPSO CALIPSO

  9. Local measurement-based correction for aerosols? Cloud impact on aerosol correction African savanna aerosol correction Aerosol correction Aerosol correction R = 0.81 Y = 0.91 X Cloud fraction 1 – 0.18 AOD + AOD*Cloud fraction Aerosol correction = 1-α.AOD + Cld frac.AOD Aerosol artefact: Aerosol layer increases cloud fraction Increases aerosol correction Needs for OMI AOD at 440 nm Combine with AI to detect elevated aerosol layer?

  10. Shape factor errors Shape factors: over fire GC pixel • Representativeness errors GC pixel • Space & time variability of emissions • Standard simulations use climatology • We use a daily biomass burning inventory (MODAPS)

  11. Shape factor correction dominates BB correction AMF Shape factor cor = shape factor bb correction (shape factor + aerosol) bb correction AMF w/obb DABEX -62% Mean AMF correction: -69% ARCTAS -38% -32% Mean AMF correction: Shape factor correction only ~ total BB correction

  12. Development of a measurement-based shape factor correction shape factor retrieved profile true profile reference column “perfect” retrieval C B A profile w/o bb C NO2 Correction = A A - B ΔNO2 = B GC-derived relationship

  13. Proof of concept Orig =OMI DP_GC New = OMI w/ measurement-based AMF New – Orig ΔNO2 = Orig 06/30-07/10 average DABEX MODIS AOD Orig ΔNO2

  14. Indirect validation: OMI-derived vs. ground-based surface concentrations Temporal correlation Orig (OMI DP_GC) New (measurement-based AMF)

  15. Conclusion • 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.

  16. THANK YOU

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