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Aerosol information from the UV-visible spectrometer GOME-2
Piet Stammes, KNMI, De Bilt, The Netherlands
7 November 2012
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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)
3weakevents
strongevents
Smoke and Dust
Amazonian rainforestbiomass burning
Sahel biomass burningand desert dust storms
Desert dustSahara
Bodélé
Libian desert
Saudi Arabian lowlands
Thar desert
Taklamakan desert
Indonesian forest fires
Siberian forest firesin July 2006
Californian forest fires
Canadian and Alaskan forest fires June-July 2004
biomass burningsmoke
Smoke from forest fires
Rice straw burning
biomass burning smoke
more data and information can be found at www.temis.nl
Absorbing Aerosol Index map from SCIAMACHY
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Why are aerosols important?©
IPC
C 2007
ClimateAir quality / Health
Air traffic safety Visibility
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Many aerosol types: chemical compositions,
sizes and shapes
http://alg.umbc.edu/
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Dust aerosols
©nasa earthobservatory
Sahara dust event Size distribution
- Fine mode aerosols: around 0.1 micron
- Coarse mode aerosols: around 1 micronAbsorbing aerosols:• Desert dust• Smoke• Volcanic ash
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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.
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GOME-2 on Metop
since 2006
• UV-visible-near-IR spectrometer • 4 spectral channels, covering 240 - 790 nm • 0.2-0.4 nm resolution• Polarization Monitoring Devices (PMDs) at 15 bands
• Main products: ozone, NO2, SO2, minor gases• Additional products: aerosols, clouds, surface albedo
http://www.esa.int/esaLP/SEMTTEG23IE_LPmetop_0.html
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Pixel size of GOME-2 w.r.t. other sensors
• GOME(-1) ERS-2
• GOME-2Metop-A+B
• SCIAMACHYEnvisat
• 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
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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:
A340 = A380
Rayleigh
380
34010
meas
380
34010 loglog100R
R
R
Rr
)(Rayleigh380
meas380 ARR
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
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Reflectance at TOA with absorbing aerosols
Doubling-Adding KNMIRadiative Transfer Model
Solar zenith angle = 30°Viewing zenith angle = 0°Surface albedo = 5%
Absorbing aerosols:altitude = 3-4 kmoptical thickness = 2single scattering albedo0= 0.75
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To match the reflectance in the absorbing aerosol atmosphere at 380 nm , the surface albedo is decreased in the Rayleigh atmosphere:
Rayleigh atmosphereSurface albedo = 0.6%
Reflectance at TOA with absorbing aerosolsand matched Rayleigh reflectance
As
Match at reference wavelength
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Reflectance at TOA with absorbing aerosolsand matched Rayleigh reflectance
The curves don’t match at 340 nm:
Absorbing aerosols create a positive residue.
Residue
As
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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.
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Simulations of AAI for biomass burning aerosols
Clear-sky case Cloudy case
AAI increases with AOTAAI decreases with SZA
Nadir view
Aerosols at 4-5 km
Clouds at 1-2 km
DAK RTM simulationsWang et al., ACP, 2012
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Daily AAI map of GOME-2 spectral channels
http://www.temis.nl/airpollution/absaai/
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Daily AAI map from GOME-2 PMDs
http://www.temis.nl/o3msaf/vaac_pmd/
PMDs have 8x higher spatial resolution thanthe spectral channels
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Information for the VAAC (volcanic ash advisory centre)
http://www.temis.nl/o3msaf/vaac_pmd/
Eyjafjoll-eruptionof April-May 2010
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Smoke over Borneo from AAI, 1995 -2010
1997/1998 El Niño: drought caused many forest fires; 120.000 km2 forest burned.
Satellite data sources: GOME, SCIAMACHY, GOME-2
Figure: L.G. Tilstra, KNMI
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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, 2012Penning de Vries, Visiting Scientist report of O3MSAF, 2012
Scattering aerosols and clouds Absorbing aerosols
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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.
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Aerosol Height retrieval
Approach: use cloud algorithm FRESCO for aerosol height
- FRESCO algorithm: fit of O2 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
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FRESCO retrievals using simulated O2 A band spectra for dust aerosols
Clear-skyCloudy
Cloud layer
Aerosol layer
Wang et al., ACP, 2012
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Puyehue volcano (Chile), 20110606, Westerly Box
Wang et al., ACP, 2012
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Puyehue volcano (Chile), 20110606, Easterly Box
Wang et al., ACP, 2012
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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.
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Links
• O3MSAF GOME-2 data products: http://o3msaf.fmi.fi
• TEMIS GOME-2 data products: http://www.temis.nl
• GOME-2 and Metop: http://www.eumetsat.int
• GOME-2 L0 data quality information: http://gome.eumetsat.int
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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:10.1029/2004JD005178, 2005.
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: 10.1029/2011JD017160, 2012
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: 10.1029/2006JD007249, 2007.
M. Penning de Vries, Beirle, S., and Wagner, T.: UV Aerosol Indices from SCIAMACHY: introducing the SCattering Index (SCI), Atmos. Chem. Phys., 9, 9555-9567, doi:10.5194/acp-9-9555-2009, 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, 12715-12735, doi:10.5194/acp-11-12715-2011, 2011.
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: 10.1029/2011JD016957, 2012.
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 978-92-9110-093-4, 2011.
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.
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, 6565-6576, 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: 10.5194/acp-12-9057-2012, 2012.
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Back-up slides
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Wavelength pair (nm)
Equator crossing time
Pixel size (km)
Days needed for global coverage
Platform / Operation period
GOME–1 340 / 380 10 : 30 LT 320 × 40 3ERS-2
(1995 – 2003*)
SCIAMACHY 340 / 380 10 : 00 LT 60 × 30 6Envisat
(2002 – 2012)
GOME–2 340 / 380 09 : 30 LT 80 × 40 1.5MetOp-A
(2006 – present)
OMI 354 / 388 13 : 30 LT 13 × 24 1Aura
(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
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FRESCO retrievals using simulated O2 A band spectra for biomass burning aerosols
Clear-skyCloudy
Aerosol layer
Cloud layer
Wang et al., ACP, 2012
Australian WildfiresFeb 7th – Feb 12th 2009
Figure: O. Tuinder, KNMI