1. OBSERVATION OF ATMOSPHERIC COMPOSITION FROM SPACE With material from: Daniel J. Jacob (Harvard), Andreas Richter (Bremen), Cathy Clerbaux (Service d’Aéronomie) Colette L. Heald ATS 737, October 15, 2008

2. Absorption and emission spectra provide a means of identifying and measuring the composition of the atmosphere. Radiation interacts with gases via: (1) Ionization-dissociation (UV-visible) (2) Electronic transitions (UV-visible) (3) Vibrational transitions (IR) (4) Rotational transitions (far IR and microwave)  IR spectra of many molecules is a combination of (3) and (4) WHAT IS THE EFFECT OF ATMOSPHERIC COMPOSITION ON RADIATION? Instead of discrete lines, transitions are observed in a whole wavelength region. natural line broadening (upper stratosphere, mesosphere) Doppler broadening (upper atmosphere: > 40 km) pressure broadening (lower atmosphere: < 40 km) E + hν E hνhνhνhν OBSERVED RADIATION includes : Reflection (solar, UV-visible) Emission (Earth/atmosphere, IR) Absorption (by gases and particles) Scattering (by gases and particles) Convolution: Voigt lines

3. - 3 - EXAMPLES OF ABSORPTION SPECTRA Chappuis band Huggins band Hartley band

4. ALL TOGETHER NOW…

5. STRATOSPHERIC OZONE HAS BEEN MEASURED FROM SPACE SINCE 1979 Method: UV solar backscatter Scattering by Earth surface and atmosphere   Ozone layer Ozone absorption spectrum  

6. SATELLITE OBSERVATIONS REVEAL THE MECHANISM FOR POLAR OZONE LOSS AND HELP US TRACK OZONE RECOVERY DU Southern hemisphere ozone column seen from TOMS, October 1 Dobson Unit (DU) = 0.01 mm O 3 STP = 2.69x10 16 molecules cm -2 MLS ClOTOMS O 3 Polar ozone depletion driven by halocarbon break- down (source of ClO)

7. ATMOSPHERIC COMPOSITION RESEARCH IS NOW MORE DIRECTED TOWARD THE TROPOSPHERE …but tropospheric composition measurements from space are difficult: optical interferences from water vapor, clouds, aerosols, surface, ozone layer Tropopause Stratopause Stratosphere Troposphere Ozone layer Mesosphere …but tropospheric composition measurements from space are difficult: optical interferences from water vapor, clouds, aerosols, surface, ozone layer Air quality, climate change, ecosystem issues

8. OBSERVING TROPOSPHERIC COMPOSITION SATELLITESAIRCRAFT CAMPAIGNSSURFACE SITES Long-term monitoring at the surface Chemical characterization throughout the troposphere Continuous, global measurements Observing system is presently very sparse; satellites will change this

9. WHY OBSERVE TROPOSPHERIC COMPOSITION FROM SPACE? Monitoring and forecasting of air quality: ozone, aerosols Long-range transport of pollution Monitoring of sources: pollution and greenhouse gases solar backscatter thermal emission solar occultation lidar FOUR OBSERVATION METHODS: Global/continuous measurement capability important for range of issues: Radiative forcing

10. SOLAR BACKSCATTER MEASUREMENTS (UV to near-IR) absorption wavelength   Scattering by Earth surface and by atmosphere Examples: TOMS, GOME, SCIAMACHY, MODIS, MISR, OMI, OCO Pros: sensitivity to lower troposphere small field of view (nadir) Cons: Daytime only Column only Interference from stratosphere concentration Retrieved column in scattering atmosphere depends on vertical profile; need chemical transport and radiative transfer models   z

11. THERMAL EMISSION MEASUREMENTS (IR,  wave) EARTH SURFACE I (T o ) Absorbing gas ToTo T1T1  I (T 1 ) LIMB VIEW NADIR VIEW Examples: MLS, IMG, MOPITT, MIPAS, TES, HIRDLS, IASI Pros: versatility (many species) small field of view (nadir) vertical profiling Cons: low S/N in lower troposphere water vapor interferences cannot see through clouds

12. OCCULTATION MEASUREMENTS (UV to near-IR) “satellite sunrise” Tangent point; retrieve vertical profile of concentrations Examples: SAGE, POAM, GOMOS Pros: large signal/noise vertical profiling Cons: sparse data, limited coverage upper troposphere only low horizontal resolution EARTH

13. LIDAR MEASUREMENTS (UV to near-IR) EARTH SURFACE backscatter by atmosphere Laser pulse Examples: LITE, GLAS, CALIPSO Intensity of return vs. time lag measures vertical profile Pros: High vertical resolution Cons: Aerosols only (so far) Limited coverage

14. ALL ATMOSPHERIC COMPOSITION DATA SO FAR HAVE BEEN FROM LOW-ELEVATION, SUN-SYNCHRONOUS POLAR ORBITERS Altitude ~ 1,000 km Observation at same time of day everywhere Period ~ 90 min. Coverage is global but sparse

15. TROPOSPHERIC COMPOSITION FROM SPACE: platforms, instruments, species Platform multipleERS- 2 ADEOSTerraEnvisatAquaSpace station AuraMetOp -A Sensor TOMSAVHRR/ SeaWIFS GOMEIMGMOPITTMODIS/ MISR SCIAMA CHY MIPASAIRSSAGE-3TESOMIMLSHIRDLSCALIPSOIASIOCO Launch 1979199519961999 2002 2004 20072009 O3O3 XXXXXXXXX COXXXXXXX CO 2 XXX NOX NO 2 XXXX HNO 3 XXX CH 4 XXX HCHOXXX SO 2 XXXX BrOXXX CH 3 CNX aerosolXXXXXXX

16. OBSERVING TROPOSPHERIC OZONE AND ITS SOURCES FROM SPACE Nitrogen oxide radicals; NO x = NO + NO 2 Sources: combustion, soils, lightning Methane Sources: wetlands, livestock, natural gas Nonmethane VOCs (volatile organic compounds) Sources: vegetation, combustion CO (carbon monoxide) Sources: combustion, VOC oxidation Tropospheric ozone precursors

17. A NEEDLE IN A HAYSTACK: DERIVING TROPOSPHERIC OZONE Fishman and Larson, 1987; Fishman et al., 2008 Issues: high uncertainty seasonal averages only does not extend to high latitudes

18. FIRST REMOTE MEASUREMENTS OF CO: MAPS ABOARD THE SPACE SHUTTLE Gas-correlation radiometer (IR: 4.7  m): flew 4 times between 1981 and 1994 Connors et al., 1999; Reichle et al., 1999 APR 1994 OCT 1994

19. RETRIEVALS IN THE IR: THE STANDARD INVERSE PROBLEM Typical MOPITT Averaging Kernel Averaging kernel (A): describes the relative weighting of the ‘true’ mixing ratio (x) at each level to the retrieved value ( ) INVERSE PROBLEM: solution is not unique! SOLUTION: maximum a posteriori Characteristic absorption features in the IR. Use a known T profile to estimate the constituents

20. MOPITT: FIRST SATELLITE INSTRUMENT TARGETTING TROPOSPHERIC POLLUTION Comparison indicates that emission inventories may be inaccurate MOPITT CO Column MOPITT – Model Heald et al., 2004 MOPITT: solid Model: dotted Observations used to track transpacific transport of pollution CO Column over the NE Pacific in Spring 2001 Spring 2001

21. AIRSGEOS-Chem Model POLLUTION AND BIOMASS BURNING OUTFLOW DURING ICARTT AIRCRAFT MISSION (Jul-Aug 2004) Asian pollution U.S. pollution Alaskan fires Wallace McMillan (UMBC)Turquety et al., 2006 NEAR-REAL-TIME DATA FOR CO COLUMNS ON JULY 18

22. USING MODIS TO MAP FIRES AND MOPITT CO TO OBSERVE EMISSIONS MOPITT CO Summer 2004 GEOS-Chem CO x MOPITT AK Bottom-up emission inventory (Tg CO) for North American fires in Jul-Aug 2004 without peat burning with peat burning MOPITT data support large peat burning source, pyro-convective injection to upper troposphere Turquety et al., 2006 18 Tg CO 9 Tg CO From above-ground vegetation From peat

23. USING ADJOINTS OF CHEMICAL TRANSPORT MODELS TO INVERT FOR EMISSIONS WITH HIGH RESOLUTION MOPITT daily CO columns (Mar-Apr 2001) A priori emissions from Streets et al. [2003] and Heald et al. [2003] Kopacz et al., 2008 Inverse of atmospheric model Correction to model sources of CO

24. CONSTRAINING NO x AND REACTIVE VOC EMISSIONS USING SOLAR BACKSCATTER MEASUREMENTS OF TROPOSPHERIC NO 2 AND FORMALDEHYDE (HCHO) Emission NO h (420 nm) O 3, RO 2 NO 2 HNO 3 1 day NITROGEN OXIDES (NO x ) VOLATILE ORGANIC COMPOUNDS (VOC) Emission VOC OH HCHO h (340 nm) hours CO hours BOUNDARY LAYER ~ 2 km Tropospheric NO 2 column ~ E NOx Tropospheric HCHO column ~ E VOC Deposition GOME: 320x40 km 2 SCIAMACHY: 60x30 km 2 OMI: 24x13 km 2

25. DIFFERENTIAL OPTICAL ABSORPTION SPECTROSCOPY Use multiple wavelengths to characterize optical absorption of a species.  determine the amount of absorber along the light path (slant column,  s ) Pioneered for stratospheric ozone, used for detection in UV-visible Scattering by Earth surface and by atmosphere Vertical column: Air mass factor (AMF) depends on the viewing geometry, the scattering properties of the atmosphere, and the vertical distribution of the absorber Requires an RT model and a CTM Or alternate of DOAS: direct fit of GOME backscattered spectrum in 338- 356 nm HCHO band Chance et al. [2000]

26. GOME sensitivity w(z) HCHO mixing ratio profile S(z) (GEOS-Chem) what GOME sees AMF G = 2.08 actual AMF = 0.71 AMF FORMULATION FOR A SCATTERING ATMOSPHERE Palmer et al., 2001 w(z): GOME sensitivity (“scattering weight”), determined from LIDORT radiative transfer model including clouds and aerosols S(z): normalized mixing ratio (“shape factor”) from GEOS-Chem CTM AMF G : geometric air mass factor (no scatter)

27. GOME CONSTRAINTS ON NO x EMISSIONS 10 15 molecules cm -2 r = 0.75 bias=5% JJA 1997 Tropospheric NO 2 Columns GOME GEOS-CHEM model (GEIA) Error weighting A priori emissions (GEIA)A posteriori emissions Difference Martin et al. [2003]

28. HIGHER SPATIAL RESOLUTION FROM SCIAMACHY Launched in March 2002 aboard Envisat Potential for finer resolution of sources, but need to account for transport will complicate the inversion 320x40 km 2 60x30 km 2

29. K. Folkert Boersma (KNMI) TROPOSPHERIC NO 2 FROM OMI: CONSTRAINT ON NO x SOURCES October 2004

30. NO X MEASUREMENTS REVEAL TRENDS IN DOMESTIC EMISSIONS East-Central China NO 2 emissions in US, EU and Japan decline … while emissions growing in China Importance of long- term record! Richter et al., 2005; Fishman et al., 2008

31. FORMALDEHYDE COLUMNS MEASURED BY GOME (JULY 1996) High HCHO regions reflect VOC emissions from fires, biosphere, human activity -0.5 0 0.5 1 1.5 2 2.5x10 16 molecules cm -2 South Atlantic Anomaly (disregard) detection limit

32. RELATING HCHO COLUMNS TO VOC EMISSION VOC i HCHO h (340 nm), OH oxn. k ~ 0.5 h -1 Emission E i smearing, displacement In absence of horizontal wind, mass balance for HCHO column  HCHO : yield y i … but wind smears this local relationship between  HCHO and E i depending on the lifetime of the parent VOC with respect to HCHO production: Local linear relationship between HCHO and E VOC source Distance downwind  HCHO Isoprene  -pinene propane 100 km detection limit

33. SEASONAL VARIATION OF GOME FORMALDEHYDE COLUMNS reflects seasonal variation of biogenic isoprene emissions SEP AUG JUL OCT MAR JUN MAY APR GOME GEOS-Chem (GEIA) GOME GEOS-Chem (GEIA) Abbot et al., 2003

34. AEROSOLS FROM SPACE To retrieve aerosol optical depth need aerosol properties (size distribution, index of refraction). Can use wavelength dependence to get idea of composition/size ISSUE: Need to characterize Rayleigh scattering and surface reflectance (including sun glint)  thus easier over oceans (dark surfaces) Depending on the ratio of the size of the scattering particle (r) to the wavelength ( ) of the light: Mie parameter  = 2  r /, different regimes of atmospheric scattering can be distinguished. MIE SCATTERING scattering on „large“ particles (aerosols, droplets, suspended matter in liquids) explained by coherent scattering from many individual particles for spherical particles, Mie scattering can be computed from the refractive index using the Maxwell equations wavelength of incoming radiation is not changed angular distribution is changed depending on , forward scattering is strongly favoured effectiveness of Mie scattering is proportional to  s Mie ( )  -1... -1.5 in general, Mie scattering is not polarising Extinction = Scattering + Absorption Usually in visible MODIS MULTI-SPECTRAL: 7 bands from 0.4 – 2.1 µm MISR MULTI-ANGLE: 9 cameras (visible)

35. TRANSPACIFIC TRANSPORT OF ASIAN AEROSOL POLLUTION AS SEEN BY MODIS Heald et al., 2006 Detectable sulfate pollution signal correlated with MOPITT CO

36. MAPPING SURFACE PM2.5 USING MISR (2001 data) MISR PM2.5 MISR AOD (annual mean) EPA (FRM+STN) PM2.5 Evaluate against EPA station data: R = 0.78, Slope = 0.91 Liu et al.,2004 Validation with AERONET: R 2 =0.80 Slope=0.88 Convert AOD to surface PM2.5 using GEOS-CHEM +GOCART scaling factors

37. NASA AURA SATELLITE (launched July 2004)Aura MLS TES nadir OMI HIRDLS Direction of motion TES limb Polar orbit; four passive instruments observing same air mass within 14 minutes OMI: UV/Vis solar backscatter NO 2, HCHO. ozone, BrO columns TES: high spectral resolution thermal IR emission nadir ozone, CO limb ozone, CO, HNO 3 MLS: microwave emission limb ozone, CO (upper troposphere) HIRDLS: high vertical resolution thermal IR emission ozone in upper troposphere/lower stratosphere Tropospheric measurement capabilities:

38. GOME JJA 1997 tropospheric columns (Dobson Units) TROPOSPHERIC OZONE OBSERVED FROM SPACE IR emission measurement from TESUV backscatter measurement from GOME Liu et al., 2006 Zhang et al., 2006 Coincident CO measurements from TES Coincidental observations of CO and O 3 with TES allows us to look at ozone production

39. (sensitivity) OBSERVING CO 2 FROM SPACE: Orbiting Carbon Observatory (OCO) to be launched in 2009 Averaging kernel Pressure (hPa) OCO will provide powerful constraints on regional carbon fluxes Polar-orbiting solar backscatter instrument, measures CO 2 absorption at 1.61 and 2.06  m, O 2 absorption (surface pressure) at 0.76  m: global mapping of CO 2 column mixing ratio with 0.3% precision

40. UV-IR sensors would provide continuous high-resolution mapping (~1 km) on continental scale: boon for air quality monitoring and forecasting LOOKING TOWARD THE FUTURE: GEOSTATIONARY ORBIT NRC Decadal Survey Recommendation: GEO-CAPE in 2013-2016, with Aura-like GACM in 2016-2020 (also ACE for aerosols 2013-2016) NRC, 2007