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.

j.j.remedios@le.ac.uk

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.