Global Monitoring of Tropospheric Pollution from Geostationary Orbit

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Global Monitoring of Tropospheric Pollution from
Geostationary Orbit
Kelly Chance Harvard-Smithsonian Center for
Astrophysics
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Collaborators
Thomas Kurosu Harvard-Smithsonian Center for
Astrophysics Xiong Liu NASA/UMBC/CfA The
GeoTRACE Team Jack Fishman, Doreen Neil, James
Crawford (NASA) David Edwards (NCAR) Kelly
Chance, Thomas Kurosu (Harvard-Smithsonian Center
for Astrophysics) Xiong Liu (NASA/UMBC) R.
Bradley Pierce (NOAA) Gary Foley, Rich Scheffe
(EPA)

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Outline

• Introduction and motivation
• Descriptions of current satellite instruments
• Determination of measurement requirements
• UV/visible gas concentrations
• Geophysical, spatial, and temporal requirements
• Scalable strawman
• Orbital considerations (not part of the strawman)
• Future work The two outstanding requirements

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Introduction and Motivation

• Target tropospheric gases are O3, NO2, SO2, HCHO,
• CHO-CHO in UV/visible, CO and O3 in IR, plus
  aerosols.
• The aims are
• To retrieve tropospheric gases from geostationary
  orbit at high spatial and temporal resolution.
• To integrate the results into air quality
  prediction, monitoring, and modeling, and
  climatological studies.
• This follows our successful developments (since
  1985, with SAO as U.S. investigator) of
  SCIAMACHY, GOME-1, and GOME-2, plus participation
  in OMI and OMPS.
• Successful retrievals have involved development
  of algorithm physics coupled with chemistry and
  transport modeling, and multiple-scattering
  radiative transfer calculations. With several
  minor exceptions (below) this development has
  been done and, in most cases, made operational.
  
  

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GOME/SCIAMACHY/OMI/GOME-2
Instrument Detectors Spectral Coverage nm Spectral Resolution nm Ground Pixel Size km2 Global Coverage
GOME (1995) Linear Arrays 240-790 0.2-0.4 40?320 (40?80 zoom) 3 days
SCIAMACHY (2002) Linear Arrays 240-2380 0.2-1.5 30?30 30?60 30?90 30?120 30?240 (depending on product) 6 days
OMI (2004) 2-D CCDs 270-500 0.42-0.63 15?30 42?162 (depending on swath position) daily
GOME-2a (2006) Linear Arrays 240-790 0.24-0.53 40?40 (40?80 wide-swath, 40?10 zoom) 1.5 to 3 days
Previous experience Scientific and operational
measurements of pollutants O3, NO2, SO2, HCHO,
and CHOCHO (and BrO, OClO, IO, H2O).
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Best fitting 2.0?10-4 FS radiance
Instrument vs. algorithm ? telescope optics size
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Fitting UV/visible trace species

• Requires precise (dynamic) wavelength (and often
  slit function) calibration, Ring effect
  correction, undersampling correction, and proper
  choices of reference spectra (HITRAN!)
• Best trace gas column fitting results (NO2, HCHO,
  CHOCHO) come from directly fitting L1b radiances
• Best tropospheric O3 and SO2 from direct profile
  retrievals using optimal estimation
• Remaining developments
• Tuning PBL O3 from UV/IR combination
  (demonstrated for the OMI/TES combination by SAO
  JPL)
• Tuning direct PBL SO2 from optimal estimation

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Some GOME, SCIAMACHY, and OMI examples
Kilauea activity, source of the VOG event in
Honolulu on 9 November 2004
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Required Concentrations
Molecule Vertical column (cm-2) Sensitivity Driver
O3 2.4?1016 10 ppbv in PBL reality (profiling) more complicated
NO2 3.0?1015 Distinguish clean from moderately polluted scenes
SO2 1.0?1016 Distinguish structures for anthropogenic sources
HCHO 1.0?1016 Distinguish clean from moderately polluted scenes
CHOCHO 1.0?1015 Tracking of most urban diurnal variation
In PBL. One of two issues needing the most
work (traceability from AQ requirements and
modeling)
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OMI Tropospheric NO2 (July 2005)
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GOME-1 HCHO
Fu et al., 2007 Monthly mean HCHO columns over
Asia as observed by GOME from 1996 to 2001 (left
panels) and as simulated by GEOS-Chem for 2001
(right panels). The GEOS-Chem simulation uses
the bottom-up emission inventories described in
the paper. Model results are sampled between
0900 and 1200 local time. GOME observations are
at about 1030 local time. The color scale is
capped at 2.5?1016 molecule cm-2 to emphasize
features. Peak GOME observations over Southeast
Asia in March and over North China Plain in June
are as high as 3.0?1016 molecule cm-2.
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European Requirements
Molecule Vertical column (cm-2) Sensitivity Driver
O3 10-25 10 of PBL 20 of FT 25 of troposphere
NO2 1.3?1015 10 of PBL 20 of FT 1.3?1015 background
SO2 1.3?1015 20 of PBL 20 of FT 1.3?1015 background
HCHO 1.3?1015 20 of PBL 20 of FT 1.3?1015 background
AQ requirements from CAPACITY study and Mission
Requirements for Sentinel 45 They are generic
at present and need further consideration of
actual AQ requirements and flowdown to
measurement requirements.
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Geostationary Minimal CaseScalable Strawman - 1
15o - 50o N, 60o - 130o W (parked at 0o N, 95o
W) Measure solar zenith angles from 0o
70o Effective solar zenith angles (ESZAs) 17.6o
76.0o
North American version!
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OMI Tropospheric NO2 (July 2005)
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An alternative (not in baseline) Inclined 24
hour orbits! Better viewing zenith angles at
high latitudes Possibility to measure same
location at different VZAs ? profile
information (Thanx, RVM!)
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Radiative Transfer Modeling and Fitting Studies
Note cloud windows Use of Raman scattering and
of the oxygen collision complex.
O2 A band
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Measurement Requirements
Molecule Fitting window (nm) Vertical column (cm-2) Slant column (cm-2)
O3 315-335 2.4?1016 5.0?1015
NO2 423-451 3.0?1015 1.1?1015
SO2 315-325 1.0?1016 1.5?1015
HCHO 325-357 1.0?1016 2.3?1015
CHOCHO 423-451 1.0?1015 3.7?1014
The slant column measurement requirements come
from full multiple scattering calculations,
including gas loading, aerosols, and the
GOME-derived (Koelemeijer et al., 2003) albedo
database, and assume a 1 km boundary layer height.
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Scalable Strawman - 2

• Lat/lon limits are 3892 km N/S and 7815-5003 km
  E/W (6565 average), or about 390?657 10?10 km2
  footprints.
• Measure 400 spectra N/S in two 200-spectrum
  integrations (each on two 10242 detector arrays
  1 UV and 1 visible).
• 2.5 seconds per longitude (2?1 s integration, 0.5
  s step and flyback) ? total sampling every lt ½
  hour (27 min).
• Detectors Rockwell HyViSi TCM8050A CMOS/Si PIN
• 3?106 e- well depth will need several rows (or
  readouts) per spectrum to reach the necessary
  statistical noise levels.
• Complicated by brightness issues cant always
  have full wells.
• Conclusions from OCO characterization
• of these detectors must be understood.

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Scalable Strawman - 3

• 200 spectra on each of two 10242 arrays each
  spectrum uses 4 detector rows (800 total out of
  1024).
• Channel 1 280-370 nm _at_ 0.09 nm sample, 0.36 nm
  resolution (FWHM).
• Channel 2 390-490 nm _at_ 0.1 nm sample, 0.4 nm
  resolution (FWHM) includes O2-O2 _at_ 477 nm.
• 4 samples per FWHM virtually eliminates
  undersampling for a symmetric instrument transfer
  (slit) function Chance et al., 2005.
• Pointing to 1 km 1/35,800 6 arcsecond.
• Size optics to fill sufficiently in 1 second (? 1
  cm2 (GOME size) ? v1.5 (GOME integration time) ?
  35,800 km / 800 km 55 cm telescope optics).
  More realistically .

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Sizing for 10?10 km2 Footprint,1 Second
Integration Time
Mol ?Rad? ? cm-2 px-1 RMS ? px-1 a?Eff
O3 3.57?1012 2.51?104 1.40?10-3 1.28?105 5.088
NO2 6.25?1012 4.87?104 8.99?10-3 3.09?103 0.063
SO2 2.94?1012 2.06?104 7.25?10-3 4.76?103 0.230
HCHO 5.65?1012 3.97?104 5.51?10-4 8.23?105 20.76
CHOCHO 6.22?1012 4.85?104 8.90?10-3 3.16?105 6.503

• ?Rad? Minimum clear-sky radiance, cross-section
  weighted (photons
• s-1 nm-1 sr-1 cm-2)
• ? cm-2 px-1 photons cm-2 pixel-1 _at_ instrument
  in 1 second
• 10?10 km2 ?7.80 ?10-8 sr solid angle
• RMS Fitting RMS required for the minimum
  detectable amount
• 1 / required S/N
• ? px-1 photons pixel-1 needed in 1 second to
  meet RMS-S/N requirements includes factor of 4
  for 4 detectors rows per spectrum
• a?Eff Telescope collecting area (cm2) ? overall
  optical efficiency

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Sizing for 10?10 km2 Footprint,1 Second
Integration Time
Mol ?Rad? ? cm-2 px-1 RMS n?/4 a?Eff
O3 3.57?1012 2.51?104 1.40?10-3 1.28?105 5.088
NO2 6.25?1012 4.87?104 8.99?10-3 3.09?103 0.063
SO2 2.94?1012 2.06?104 7.25?10-3 4.76?103 0.230
HCHO 5.65?1012 3.97?104 5.51?10-4 8.23?105 20.76
CHOCHO 6.22?1012 4.85?104 8.90?10-3 3.16?105 6.503
Formaldehyde (HCHO) is the driver for almost any
conceivable choice of requirements! (Unless VOCs
are considered unimportant, in which case O3
would be the driver, with the above as a low
estimate). 20.76 cm2 is a16-cm diameter telescope
_at_ 10 optical efficiency (GOME, a much simpler
instrument, is 15 20 efficient in this
wavelength range). Also, IR needs (CO, maybe O3)
must be addressed.
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Major Tradeoffs and Questions

• Tradeoffs samples (footprint) vs. sensitivity
  (S/N) vs. integration time vs. geographical
  coverage vs. max SZA
• 5?5 km2 footprints in 1/2 hour with a 32 cm
  diameter telescope, if the instrument is 10
  efficient.
• Spatial Nyquist sampling must be carefully
  addressed.
• Questions Are lat and lon sampling necessarily
  the same? Is constant sampling necessary?
• IR Priorities are 2.4 ?m CO gt 9.6 ?m O3 gt 4.7 ?m
  CO.
• Scanning Fabry-Perot instruments may provide a
  compact IR solution (SAO and NASA LaRC have
  developments here).
• Option MODIS channels for aerosols? (TOMS
  absorbing aerosol index is automatic, but little
  else operationally.)
• OMI aerosol products should be reviewed.
• Should include polarization-resolved
  measurements
• Several such UV channels will improve PBL O3
  Hasekamp and Landgraf, 2002a,b Jiang et al.,
  2003.
• Everything is debatable this is why it is a
  strawman, but we must show why alternatives are
  better.

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Outstanding Needs

• Science Requirements (S/N, geophysical, spatial,
  temporal) from sensitivity and modeling studies
  (OSSEs), providing traceability for AQ forecast
  improvement and other uses.
• Unless things change a lot, HCHO will be the
  driver for instrument requirements. Then address
  trade space.
• Instrument Design. Reducing smile, enabling
  multiple readouts, increasing efficiency,
  optimizing ITF shape .
• GEO instrument is not just a super-OMI with
  CMOS/Si detectors instead of CCDs. Minimal
  geostationary requirements imply scanning instead
  of a pushbroom and they imply getting many more
  spectra onto a rectangular detector than OMI has
  obtained.
• Instrument optical and spectrograph design is the
  single most important outstanding issue in
  demon-strating the feasibility of geostationary
  pollution measurements.

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The End!