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SATELLITE OBSERVATIONS OF ATMOSPHERIC CHEMISTRY Daniel J. Jacob OBSERVATION BY SOLAR OCCULTATION “satellite sunrise” Tangent point; retrieve vertical profile of concentrations EARTH Recent extensions to lunar and stellar occultation OBSERVATION BY THERMAL EMISSION (IR, mwave) NADIR VIEW LIMB VIEW Absorbing gas or aerosol elIl(T1) T1 Il(To) To EARTH SURFACE OBSERVATION BY SOLAR BACKSCATTER (UV-IR) ATMOSPHERE Absorption/ scattering by Earth surface and atmosphere EARTH SURFACE TOMS OBSERVATION OF ANTARCTIC OZONE HOLE Example of observation by solar backscatter MOST OBSERVATIONS OF ATMOSPHERIC COMPOSITION FROM SPACE HAVE BEEN FOR THE STRATOSPHERE Mesosphere Stratopause Ozone layer Stratosphere Tropopause Troposphere Observation of troposphere is far more difficult because of • clouds • particles (dust) • water vapor continuum • strat ozone layer PRESENT AND FUTURE SATELLITE MEASUREMENTS FOR TROPOSPHERIC CHEMISTRY 2002 2002 2004 2004 2004 2004 2004 ATMOSPHERIC CHEMISTRY MODELS AND SATELLITE OBSERVATIONS: THE ODD COUPLE SATELLITE SPECTRA “L1 DATA” CLIMATOLOGICAL IN SITU OBSERVATIONS A PRIORI INFORMATION vertical gradient, concentration range, correlations… ATMOSPHERIC CHEMISTRY MODELS RETRIEVAL ATMOSPHERIC CONCENTRATIONS “L2 DATA” INCEST? EVALUATION ASSIMILATION INCREASED KNOWELDGE SCIENTIFIC ANALYSIS “L4 DATA” GEOS-CHEM global model of tropospheric chemistry (www-as.harvard.edu/chemistry/trop/geos) • Driven by NASA GEOS assimilated meteorological data, 1988-2001 • 1ox1o- 4ox5o horizontal resolution, 20-48 layers in vertical • Simulation of tropospheric ozone-NOx-hydrocarbon chemistry includes ~80 interacting species THE GOME SATELLITE INSTRUMENT • Nadir-viewing solar backscatter instrument (237-794 nm) • Low-elevation polar sunsynchronous orbit, 10:30 a.m. observation time • Field of view 320x40 km2, three cross-track scenes • Complete global coverage in 3 days USE GOME MEASUREMENTS OF NO2 AND HCHO COLUMNS TO MAP NOxAND VOC EMISSIONS GOME Tropospheric NO2 column ~ ENOx Tropospheric HCHO column ~ EVOC ~ 2 km BOUNDARY LAYER hn (420 nm) NO2 NO O3, RO2 hn (340 nm) HCHO OH CO hours hours 1 day VOC HNO3 Emission Deposition NITROGEN OXIDES (NOx) Emission VOLATILE ORGANIC CARBON (VOC) COLUMN MEASUREMENT OF AN ABSORBING GAS USING SOLAR BACKSCATTER absorption Backscattered intensity IB Slant optical depth ATMOSPHERE Scattering by Earth surface and by atmosphere “Slant column” l1 l2 wavelength I B ( l2 ) S ln[ ] I B ( l1 ) S eff S EARTH SURFACE SLANT COLUMNS OF HCHO FROM GOME High values over southeast U.S. are due to biogenic isoprene emission Palmer et al. [2002] SLANT COLUMNS OF NO2 FROM GOME Dominant stratospheric contribution (NO2 produced from N2O oxidation) Also see tropospheric hot spots (fossil fuel and biomass burning) Remove stratospheric column and instrument artifacts using data over Pacific Martin et al. [2002] SLANT COLUMNS OF TROPOSPHERIC NO2 FROM GOME 1996 Martin et al. [2002] AIR MASS FACTOR (AMF) CONVERTS SLANT COLUMN S TO VERTICAL COLUMN S AMF “Geometric AMF” (AMFG) for non-scattering atmosphere: 1 cos q AMF G cos q q EARTH SURFACE IN SCATTERING ATMOSPHERE, AMF DEPENDS ON SHAPE OF VERTICAL PROFILE (FOR WHICH GOME PROVIDES NO INFORMATION) ILLUSTRATIVE PROFILE OVER TENNESSEE AMFG = 2.08 actual AMF = 0.71 what GOME sees GOME sensitivity HCHO mixing ratio profile (GEOS-CHEM) CALCULATE AMF FOR EVERY GOME SCENE USING LOCAL SHAPE FACTORS FROM GEOS-CHEM AMF AMFG w( z ) S ( z )dz 0 Geometric AMF GOME efficiency Vertical = f (sun angle, concentration albedo, cloud…) profile shape factor RADIATIVE ATMOSPHERIC TRANSFER CHEMISTRY MODEL MODEL (GEOS-CHEM) From GOME Vertical column = Slant column AMF From model COMPARE MODEL VERTICAL PROFILES OF HCHO TO (THE FEW!) AVAILABLE AIRCRAFT OBSERVATIONS SOS (southeast U.S., Jul 1995) NARE (N. Atlantic, Sept 1997) Observations Model Palmer et al. [2001] DIAGNOSE MODEL CONTAMINATION OF RETRIEVAL BY CORRELATING AMF WITH VERTICAL COLUMN r = -0.65 r = -0.14 Negative correlation implies that AMF conversion to vertical columns will modify the slant column patterns to better fit the model Martin et al. [2002] PROPAGATION OF ERRORS IN NO2 RETRIEVAL (errors e in 1015 molecules cm-2) GOME SPECTRUM (423-451 nm) Fit spectrum e1 0.8 SLANT NO2 COLUMN Remove stratospheric contribution, diffuser plate artifact e2 0.4 Use Central Pacific GOME data with: •HALOE to test strat zonal invariance •PEM-Tropics, GEOS-CHEM 3-D model to treat tropospheric residual TROPOSPHERIC SLANT NO2 COLUMN Apply AMF to convert slant column to vertical column e3 0.5-3.2 Martin et al. [2002] Use radiative transfer model with: • local vertical shape factors from GEOS-CHEM • local cloud information from CRAG TROPOSPHERIC NO2 COLUMN CAN WE USE GOME TO ESTIMATE NOx EMISSIONS? TEST IN U.S. WHERE GOOD A PRIORI EXISTS Comparison of GOME retrieval (July 1996) to GEOS-CHEM model fields using EPA emission inventory for NOx GOME GEOS-CHEM (EPA emissions) R = 0.78 Bias = +18% Martin et al. [2002] BIAS = +3% R = 0.79 GOME RETRIEVAL OF TROPOSPHERIC NO2 vs. GEOS-CHEM SIMULATION (July 1996) Martin et al. [2002] GEIA emissions scaled to 1996 FORMALDEHYDE COLUMNS FROM GOME: July 1996 means Palmer et al. [2001] BIOGENIC ISOPRENE IS THE MAIN SOURCE OF HCHO IN U.S. IN SUMMER GEIA isoprene emissions R = 0.83 Bias 14% Precision: 4x1015 cm-2 MODEL AS INTERMEDIARY FOR GOME VALIDATION: EVALUATE AGAINST IN SITU SURFACE OBSERVATIONS Mean daytime HCHO surface observations Jun-Aug 1988-1998 Model (1996) vs. observations Palmer et al. [2002] GOME DETECTS THE ISOPRENE “VOLCANO” IN THE OZARKS Palmer et al. [2002] DEPENDENCE OF GOME HCHO COLUMNS OVER THE OZARKS ON SURFACE AIR TEMPERATURE Temperature dependence of isoprene emission (GEIA) Palmer et al. [2002] YIELD OF HCHO FROM ISOPRENE OXIDATION isoprene OH O2 ~1 hour OO . OH NO NO2 days GEOS-CHEM mechanism + HCHO + HO2 O methylvinylketone Palmer et al. [2002] GEOS-CHEM RELATIONSHIP BETWEEN HCHO COLUMNS AND ISOPRENE EMISSIONS IN N AMERICA Model HCHO column [1016 molec cm-2] Use relationship to map isoprene emissions from GOME observations NW NE GEOS-CHEM July 1996 SW SE model without isoprene Isoprene emission [1013 atomC cm-2 s-1] Palmer et al. [2002] MAPPING OF ISOPRENE EMISSIONS FOR JULY 1996 BY SCALING OF GOME FORMALDEHYDE COLUMNS [Palmer et al., 2002] GOME COMPARE TO… GEIA (IGAC inventory) BEIS2 (official EPA inventory) NEXT STEP: GLOBAL MAPPING OF VOC EMISSIONS FROM SPACE! T. Kurosu (SAO) and P. Palmer (Harvard) T. Kurosu (SAO) and P.I. Palmer (Harvard)