1 Aerosol information from the UV-visible spectrometer GOME-2 Piet Stammes, KNMI, De Bilt, The Netherlands 7 November 2012

2 Contents Importance of aerosols Aerosol microphysics Spectral absorption by aerosols GOME-2 Absorbing Aerosol Index First results on Aerosol Height Acknowledgements to: Martin de Graaf, Gijs Tilstra, Ping Wang, Olaf Tuinder (KNMI) Eyk Boesche (FUB) Marloes Penning de Vries (MPIC)

3 weak events strong events Smoke and Dust Amazonian rainforest biomass burning Sahel biomass burning and desert dust storms Desert dust Sahara Bodélé Libian desert Saudi Arabian lowlands Thar desert Taklamakan desert Indonesian forest fires Siberian forest fires in July 2006 Californian forest fires Canadian and Alaskan forest fires June-July 2004 biomass burning smoke Smoke from forest fires Rice straw burning biomass burning smoke more data and information can be found at Absorbing Aerosol Index map from SCIAMACHY

4 Why are aerosols important? ©IPCC 2007 ClimateAir quality / Health Air traffic safety Visibility

5 Many aerosol types: chemical compositions, sizes and shapes

6 Dust aerosols ©nasa earthobservatory Sahara dust event Size distribution - Fine mode aerosols: around 0.1 micron - Coarse mode aerosols: around 1 micron Absorbing aerosols: Desert dust Smoke Volcanic ash

7 Absorption by smoke above clouds De Graaf et al., JGR, 2012 Observation by SCIAMACHY of absorption spectrum of smoke aerosols. This absorption leads to heating of the troposphere up to 125 W/m2.

8 GOME-2 on Metop since 2006 UV-visible-near-IR spectrometer 4 spectral channels, covering nm nm resolution Polarization Monitoring Devices (PMDs) at 15 bands Main products: ozone, NO2, SO2, minor gases Additional products: aerosols, clouds, surface albedo

9 Pixel size of GOME-2 w.r.t. other sensors GOME(-1) ERS-2 GOME-2 Metop-A+B SCIAMACHY Envisat OMI EOS-Aura 40 km 320 km 30 km 60 km 40 km 80 km 13 km 24 km Along track 40 km 10 km GOME-2 PMD

10 Absorbing Aerosol Index (AAI) Definition: where the surface albedo A for the Rayleigh atmosphere simulations is such that: A is assumed to be wavelength independent: A 340 = A 380 The residue represents the observed 340/380 nm colour as compared to the pure Rayleigh colour (OMI: 354/388 nm) residue AAI is the positive part of the residue

11 Reflectance at TOA with absorbing aerosols Doubling-Adding KNMI Radiative Transfer Model Solar zenith angle = 30° Viewing zenith angle = 0° Surface albedo = 5% Absorbing aerosols: altitude = 3-4 km optical thickness  = 2 single scattering albedo  0 = 0.75

12 To match the reflectance in the absorbing aerosol atmosphere at 380 nm, the surface albedo is decreased in the Rayleigh atmosphere: Rayleigh atmosphere Surface albedo = 0.6% Reflectance at TOA with absorbing aerosols and matched Rayleigh reflectance As Match at reference wavelength

13 Reflectance at TOA with absorbing aerosols and matched Rayleigh reflectance The curves don’t match at 340 nm: Absorbing aerosols create a positive residue. Residue As

14 Generally: no clouds, no aerosols: r = 0 clouds, no absorbing aerosols: r < 0 absorbing aerosols : r > 0 AAI: r > 0 Pros and Cons: + AAI can detect UV absorbing aerosols: volcanic ash, desert dust and smoke. + AAI works in cloudy scenes. + AAI works over ocean and land. - AAI is an index: it depends on AOT (  ), SSA (  ) and altitude (  ). - AAI is very sensitive to absolute calibration.

15 Simulations of AAI for biomass burning aerosols Clear-sky caseCloudy case AAI increases with AOT AAI decreases with SZA Nadir view Aerosols at 4-5 km Clouds at 1-2 km DAK RTM simulations Wang et al., ACP, 2012

16 Daily AAI map of GOME-2 spectral channels

17 Daily AAI map from GOME-2 PMDs PMDs have 8x higher spatial resolution than the spectral channels

18 Information for the VAAC (volcanic ash advisory centre) Eyjafjoll- eruption of April-May 2010

19 Smoke over Borneo from AAI, /1998 El Niño: drought caused many forest fires; km 2 forest burned. Satellite data sources: GOME, SCIAMACHY, GOME-2 Figure: L.G. Tilstra, KNMI

20 UV residue has two parts: Absorbing Index & Scattering Index GOME-2 Aerosol Indices for July, 2011, cloud fraction < 0.2. Work of Marloes Penning de Vries (MPIC, Mainz). Penning de Vries et al., ACP, 2012 Penning de Vries, Visiting Scientist report of O3MSAF, 2012 Scattering aerosols and cloudsAbsorbing aerosols

21 Effect of instrument degradation on the AAI GOME-2 (for individual scan mirror positions) The global mean residue, the mean of all residues on a day between 60°N and 60°S, is about constant, showing only a very mild seasonal variation. Instrument degradation has a very large impact on the residue/AAI: 2.3 % reflectance change ~ 1 AAI point. Tilstra et al. (JGR, 2012) developed an in-flight degradation correction method.

22 Aerosol Height retrieval Approach: use cloud algorithm FRESCO for aerosol height - FRESCO algorithm: fit of O 2 A-band at 760 nm using a Lambertian reflector as cloud model. - FRESCO v6 has two retrieval modes for 2 retrieved quantities: Normal: Effective cloud fraction (cloud albedo  0.8) and Cloud height Alternative: Scene albedo (cloud fraction  1) and Scene height Wang et al., ACP, 2008

23 FRESCO retrievals using simulated O 2 A band spectra for dust aerosols Clear-sky Cloudy Cloud layer Aerosol layer Wang et al., ACP, 2012

24 Puyehue volcano (Chile), , Westerly Box Wang et al., ACP, 2012

25 Puyehue volcano (Chile), , Easterly Box Wang et al., ACP, 2012

26 Conclusions Absorbing aerosols, like desert dust, smoke, and volcanic ash can be detected by GOME-2 GOME-2 provides near-real-time monitoring information on these aerosols, with the products: -AAI for absorbing aerosols -SCI for scattering aerosols (if cloud mask is used) -FRESCO for aerosol height.

27 Links O3MSAF GOME-2 data products: TEMIS GOME-2 data products: GOME-2 and Metop: GOME-2 L0 data quality information:

28 References on GOME(-2) aerosol retrievals M. de Graaf, P. Stammes, O. Torres, and R.B.A. Koelemeijer, Absorbing Aerosol Index: Sensitivity analysis, application to GOME and comparison with TOMS, J. Geophys. Res. 110, D010201, doi: /2004JD005178, 2005.doi: /2004JD M. de Graaf, L.G. Tilstra, P. Wang and P. Stammes, Retrieval of the aerosol direct radiative effect over clouds from space-borne spectrometry, J. Geophys. Res., 117, D07207, doi: /2011JD017160, 2012doi: /2011JD M. de Graaf and P. Stammes and E.A.A. Aben, Analysis of reflectance spectra of UV-absorbing aerosol scenes measured by SCIAMACHY, J. Geophys. Res. 112, D02206, doi: /2006JD007249, 2007.doi: /2006JD M. Penning de Vries, Beirle, S., and Wagner, T.: UV Aerosol Indices from SCIAMACHY: introducing the SCattering Index (SCI), Atmos. Chem. Phys., 9, , doi: /acp , 2009 M. Penning de Vries, and Wagner, T.: Modelled and measured effects of clouds on UV Aerosol Indices on a local, regional, and global scale, Atmos. Chem. Phys., 11, , doi: /acp , L.G. Tilstra, M. de Graaf, I. Aben and P. Stammes, In-flight degradation correction of SCIAMACHY UV reflectances and Absorbing Aerosol Index, J. Geophys. Res., 117, D06209, doi: /2011JD016957, 2012.doi: /2011JD L.G. Tilstra, M. de Graaf, O.N.E. Tuinder, R.J. van der A, and P. Stammes, Studying trends in aerosol presence using the Absorbing Aerosol Index derived from GOME-1, SCIAMACHY, and GOME-2, Proceedings of the 2011 EUMETSAT Meteorological Satellite Conference, EUMETSAT P.59, ISBN , 2011.Studying trends in aerosol presence using the Absorbing Aerosol Index derived from GOME-1, SCIAMACHY, and GOME-2 L.G. Tilstra, O.N.E. Tuinder, and P. Stammes, A new method for in-flight degradation correction of GOME-2 Earth reflectance measurements, with application to the Absorbing Aerosol Index, Proceedings of the 2012 EUMETSAT Meteorological Satellite Conference, EUMETSAT P.??, ISBN ??????????, 2012.A new method for in-flight degradation correction of GOME-2 Earth reflectance measurements, with application to the Absorbing Aerosol Index P. Wang, P. Stammes, R. van der A, G. Pinardi, M. van Roozendael, FRESCO+: an improved O2 A-band cloud retrieval algorithm for tropospheric trace gas retrievals, Atmospheric Chemistry and Physics, 8, , 2008 P. Wang, O.N.E. Tuinder, L.G. Tilstra, M. de Graaf, and P. Stammes, Interpretation of FRESCO cloud retrievals in case of absorbing aerosol events, Atm. Chem. Phys., 12, doi: /acp , 2012.doi: /acp

29 Back-up slides

30 Wavelength pair (nm) Equator crossing time Pixel size (km) Days needed for global coverage Platform / Operation period GOME–1 340 / : 30 LT320 × 403 ERS-2 (1995 – 2003*) SCIAMACHY 340 / : 00 LT60 × 306 Envisat (2002 – 2012) GOME–2 340 / : 30 LT80 × MetOp-A (2006 – present) OMI 354 / : 30 LT13 × 241 Aura (2004 – present) AAI products from GOME, SCIAMACHY, GOME-2, and OMI * GOME-1: loss of global coverage on 22 June 2003 ; instrument retired on 4 July 2011

31 FRESCO retrievals using simulated O 2 A band spectra for biomass burning aerosols Clear-sky Cloudy Aerosol layer Cloud layer Wang et al., ACP, 2012

Australian Wildfires Feb 7 th – Feb 12 th 2009 Figure: O. Tuinder, KNMI