Retrieval of SO 2 Vertical Columns from SCIAMACHY and OMI: Air Mass Factor Algorithm Development Chulkyu Lee, Aaron van Dokelaar, Gray O’Byrne: Dalhousie Univ. Randall V. Martin: Dalhousie Univ. and Harvard-Smithsonian Nickolay Krotkov: NASA Goddard and UMBC Andreas Richter: Univ. of Bremen Greg Huey: Georgia Tech John S. Holloway: NOAA April 07, th GEOS-Chem Users’ Meeting Harvard University

Scattering weight Local AMF Calculation dt(η) IoIo IBIB Earth Surface Radiative Transfer Model Scattering weight  (η) is temperature-dependent cross-section Calculate ω(η) as function of: solar and viewing zenith angle (θ s, θ v ) surface reflectivity, pressure cloud pressure, aerosol O 3 column: Atmospheric Chemistry Model: GEOS-Chem (Bey et al. 2001) For individual scenes Shape factor SO 2 mixing ratio, C SO2 (η) eta ( η ) * Based on Palmer et al., JGR, 2001; Martin et al., JGR, 2002 Geometric AMF:

GEOS-Chem Simulation  GEOS-Chem v GEOS-4, 30 η vertical levels, 2º latitude by 2.5º longitude - Based on EDGAR inventory - Regional inventories: NEI99, BRAVO, CAC, Streets, EMEP  Update of the eruptive volcanic inventory for 2006 using the database of Global Volcanism Program (GVP:  Recalculation of optical properties for mineral dust using refractive indices of Sinyuk et al., GRL, SSA at 300 nm increases by ~0.1 to the range of

Shape Factor: GEOS-Chem vs In-situ Differences would change AMF by <10% In-situ platform DC-8 & C-130

OMI SO 2 AMF for 2006  Calculated at nm; Cloud Radiance Fraction < 0.2; SZA < 70  SCIAMACHY AMF at nm within 25%

Local AMF Increases Agreement with Aircraft ▲ INTEX-A ■ INTEX-B

SO 2 Vertical Columns for 2006 Cloud Radiance Fraction < 0.2; SZA < 70 Correlation with GEOS-Chem (GC) : Globally r ~0.78 : ~0.84 over US : ~0.83 over China GC with OMI AMF within 10% GC with SCIAMACHY AMF

Sensitivity of Retrieved SO 2 to ΔEmissions GEOS-Chem SO 2 changes by ×2 OMI SO 2 AMF changes < 30%

Summary  Validation of GEOS-Chem SO 2 shape factors with airborne in-situ measurements for INTEX-A and B : <10% change in AMF  Validation of SO 2 vertical columns from SCIAMACHY and OMI with airborne in-situ measurements for INTEX-A and B : r = 0.9  Large sensitivity of retrieved SO 2 to emissions

GEOS-Chem Simulation  GEOS-Chem v GEOS-4, 30 η vertical levels, 2° latitude by 2.5° longitude - Based on EDGAR inventory - Regional inventories: NEI99, BRAVO, CAC, Streets, EMEP  Update of the eruptive volcanic inventory for 2006 Volcanic Explosivity Index (VEI) a 0123 SO 2 Emission b, Mg/day 2.5× × × ×10 2 Cloud Column Height c 50 m above crater 550 m above crater 3000 m above sea level 9000 m above sea level a Obtained from Global Volcanism Program (GVP: ); b Chin et al. [1996]; c Newhall et al. [1982]

Error Analysis c: cloud radiance fraction AMF error from surface reflectivity, shape factor, aerosol, cloud (Wenig et al., 2008) Cloud Radiance Fraction < 0.2; SZA < 70 Polluted: SO 2 > molec/cm 2