28/1/08dr. j.j. remedios, erca space 2 1 observations of tropospheric chemistry from space i j.j....
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28/1/08 Dr. J.J. Remedios, ERCA Space 2 1
Observations of tropospheric chemistry from space IJ.J. Remedios
EOS-SRC, Physics and Astronomy, University of Leicester, U.K.
http://www.leos.le.ac.uk/home/
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Themes of Lecture
Part I: Introduction to observing tropospheric chemistry Important parameters for tropospheric chemistry Spectroscopy: scattered sunlight and thermal infra-red
emission Observing the Earth: nadir vs limb Current instruments
Part II: Examples of instruments and observations GOME/SCIAMACHY/OMI: NO2, HCHO, Glyoxal, BrO MOPITT: CO MIPAS AND ACE: Organic compounds such as PAN,
acetone, formic acid, methanol, hydrocarbons
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SOME KEY QUESTIONS BEING ADDRESSED
BY SPACE OBSERVATIONS OF
TROPOSPHERIC COMPOSITION AND CHEMISTRY
PART I
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SCIENCE IMPERATIVES:
CH4: CLIMATE AND OH (SCIAMACHY)
Images courtesy of MOPITT team
Frankenburg et al. Heidelburg, KNMI Science paper
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SCIENCE AND POLICY IMPERATIVES: AIR QUALITY NO2 (SCIAMACHY)
SCIAMACHY tropospheric NO2 columns, annual average: Heidelburg
Richter et al., Nature, 2005: NO2 over China
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MODIS Fire Map
MODIS Fire Map: 9th - 19th July, 2004
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MOPITT CO July 2001 “Surface” Level
Monthly mean CO observed from daytime retrievals of CO (“surface” retrieved level) – figure from N. Richards, PhD thesis, Leicester, 2004.
We get similar result for July 2004, showing that African biomass burning is a “climatological” feature
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OMI NO2: JULY 18 2006
AATSR LST: July 18 2006
PUBLIC IMPACT AND PUBLIC KNOWLEDGE
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Some major Atmospheric Composition Instruments
• ERS-1/2 (1990s)
GOME (T)
ATSR-1/2 (T)
MWR (T H2O)
• ENVISAT (2002)
MIPAS (UT)
SCIAMACHY (T)
GOMOS
AATSR (T)
MERIS (T H2O)
MWR (T H2O)
• NASA MISSIONS (1999, 2004)
MOPITT (T) ON EOS-TERRA
AIRS (T) ON EOS-AQUA
TES (T), OMI (T), MLS (UT) ON EOS-AURA
• METOP (2007)
IASI (T), GOME-2 (T)
T=Troposphere
UT = Upper troposphere
ATSR series only produces aerosols currently as do many of the others
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Parameters for tropospheric chemistry
Essentially we want to observe:• gases which are direct pollutants,• gases which control the lifetimes of pollutant and greenhouse
gases, • gases which are important in climate-chemistry interactions• Aerosols and clouds (not covered in these lectures)
Hence: Ozone and its precursors
Hydroxyl radical: OH and its sources and sinks
NOx (NO,NO2) and NOy (HNO3, PAN, organic nitrates)
VOCs (formaldehyde, glyoxal, hydrocarbons such as ethane, ethyne, PAN, acetone, methanol…)
Halogens
Sulphur compounds
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Influences on tropospheric chemistry
Natural sources and sinks Vegetation Oceans Volcanoes Snow
Sunlight and photochemistry
Clouds
Anthropogenic emissions Industry Transport Agricultural practices especially burning and intensive cultivation.
Implication: we wish to observe a large number of species on a regional basis throughout the globe
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Parameters for tropospheric chemistry
HOW DO WE OBSERVE THESE GASES IN THE TROPOSPHERE?
Ultra-violet/visible radiation/near infra-red – O3 and reactive gases
[UV/VIS/NIR]
Shortwave infra-red radiation (SWIR) – CO and climate gases
Thermal infra-red radiation (TIR OR MIR) – O3, CO, climate and reactive gases
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SOURCES OF SIGNALS FOR PASSIVE INSTRUMENTS:
SOLAR RADIATION
AND
TERRESTRIAL RADIATION
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SOLAR UV-VIS-SWIR AND TERRESTRIAL THERMAL I/R RADIATION
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THE PLANCK FUNCTION IS AT THE HEART OF
OBSERVATIONS FROM SPACE!
SO ALSO IS SPECTROSCOPY!!
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Planck’s Radiation Law – Earth and Sun
SUN EARTH
U/V VIS SWIR TIR FIR MICROWAVE
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SCIAMACHY SPECTRA – SIMULATIONS I
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SCIAMACHY SPECTRA – SIMULATIONS II
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EXAMPLE FIT TO WEAK SPECTRAL FEATURES: SCIAMACHY CO
Can fit to very weak absorbers!!
[Frankenberg et al, 2005]
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Infra-red emission spectrum to space[Nadir signal for an i/r instrument]
10 m 4 m20 m 5 m
12 m window
8 m window
CO2O3
N2O, CH4
H2O
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NADIR INFRA-RED TRANSMISSION TO SPACEClerbaux et al., ACP, 2003
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INFRA-RED LIMB SPECTRUMLONGER PATHLENGTH SO MORE SENSITIVE
The total spectral region (4.15 – 14.6μm) of MIPAS as measured at 18.7 km tangent altitude, this region is divided in 5 spectral intervals (A, AB, B, C, D); the large number of spectral emission lines demonstrates the enormous amount of information in the measurements; a considerable number of trace constituents can be detected as indicated.
Fischer et al, ACPD, 2007
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INFRA-RED LIMB SPECTRUM EXAMPLE MIPAS SPECTRA I
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Example MIPAS SPECTRA II: CO2
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Example MIPAS spectra III
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Instruments for tropospheric chemistry
WHAT SORTS OF INSTRUMENT DO WE CURRENTLY USE?
Nadir sounders – sensing throughout the troposphere at high spatial but low vertical (mostly) resolution
Limb sounders – mid- to upper troposphere at high vertical resolution but low spatial resolution
Low Earth Orbit (LEO) instruments – overwhelming configuration
Geostationary (GEO) instruments – only just starting to be used for trace gases other than water vapour.
Spectrometers – the majority
“High” resolution radiometers – e.g. MOPITT
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Spectroscopy
Major gases dominate the spectrum
Chemistry demands detection and analysis of very weak spectral features:
Instrument noise performance Instrument stability and calibration Spectral resolution
It is incredible what modern spectroscopic systems can achieve!
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Nadir and Limb measurements[Illustrated for SCIAMACHY]
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CURRENT IMPORTANT NADIR SOUNDERS FOR TROPOSPHERIC CHEMISTRY
INSTRUMENT SATELLITE ORBIT TYPE REGION
MOPITT EOS-TERRA LEO GAS CORRELATION RADIOMETRY
I/R
TES EOS-AURA LEO FTS1 I/R
IASI METOP LEO FTS1 I/R
GOME, GOME-2
ERS-2, METOP
LEO GRATING2 UV/VISIBLE
SCIAMACHY ENVISAT LEO GRATING2 UV/VISIBLE/NIR3
OMI EOS-AURA LEO GRATING2 UV/VISIBLE
1. Fourier Transform Spectrometer.
2. Grating Spectrometer.
3. Near infra-red.
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CURRENT IMPORTANT LIMB SOUNDERS FOR TROPOSPHERIC CHEMISTRY
INSTRUMENT SATELLITE ORBIT TYPE REGION
ACE SCISAT LEO FTS1 I/R
MIPAS ENVISAT LEO FTS1 I/R
MLS EOS-AURA LEO SPECTRO-RADIOMETER
MICROWAVE
1. Fourier Transform Spectrometer.
2. Grating Spectrometer.
3. Near infra-red.
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Summary part I
• Tropospheric chemistry has some big impacts and space measurements are increasingly being used to investigate and monitor it.
• Spaceborne observations are currently passive instruments, i.e. using natural sources of radiation. Both Sun and Earth radiation (sources) are driven by the Planck function
• Chief technique is nadir sounding but limb sounding provides vertical resolution of the mid-to upper troposphere.
• Instruments are usually spectrometers or of equivalent “high” spectral resolution enabling measurements of many chemical species.